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2 Comments
Transport in Plants and Animals
Transport in plants
Internal structure of roots and root hairs
The main functions of roots are;
Internal structure of a root hair cell
The main functions of the stem are;
Collenchyma
The Stem
Absorption of Water and Mineral Salts Absorption of Water
Transpiration
Structure and function of Xylem
Tracheids
Forces involved in Transportation of Water and Mineral Salts
Transpiration pull
As water vaporises from spongy mesophyll cells into sub-stomatal air spaces, the cell sap of mesophyll cells develop a higher osmotic pressure than adjacent cells. Water is then drawn into mesophyll cells by osmosis from adjacent cells and finally from xylem vessels. A force is created in the leaves which pulls water from xylem vessels in the stem and root. This force is called transpiration pull. Cohesion and Adhesion: The attraction between water molecules is called cohesion. The attraction between water molecules and the walls of xylem vessels is called adhesion. The forces of cohesion and adhesion maintain a continuous flow of water in the xylem from the root to the leaves. Capillarity: This is the ability of water to rise in fine capillary tubes due to surface tension. Xylem vessels are narrow, so water moves through them by capillarity. Root Pressure: If the stem of a plant is cut above the ground level, it is observed that cell sap continues to come out of the cut surface. This shows that there is a force in the roots that pushes water up to the stem. This force is known as root pressure.
Importance of Transpiration
Transpiration leads to excessive loss of water if unchecked. Some beneficial effects are:
The factors that affect transpiration are grouped into two. i.e. environmental and structural. Environmental factors Temperature High temperature increases the internal temperature of the leaf. Which in turn increases kinetic energy of water molecules which increases evaporation. High temperatures dry the air around the leaf surface maintaining a high concentration gradient. More water vapour is therefore lost from the leaf to the air.
Humidity
The higher the humidity of the air around the leaf, the lower the rate of transpiration. The humidity difference between the inside of the leaf and the outside is called the saturation deficit. In dry atmosphere, the saturation deficit is high. At such times, transpiration rate is high. Wind Wind carries away water vapour as fast as it diffuses out of the leaves. This prevents the air around the leaves from becoming saturated with vapour. On a windy day, the rate of transpiration is high. Light Intensity When light intensity is high; more stomata open hence high rate of transpiration. Atmospheric Pressure The lower the atmospheric pressure the higher the kinetic energy of water molecules hence more evaporation. Most of the plants at higher altitudes where atmospheric pressure is very low have adaptations to prevent excessive water-loss. Availability of Water The more water there is in the soil, the more is absorbed by the plant and hence a lot of water is lost by transpiration.
Structural Factors
Cuticle Plants growing in arid or semi-arid areas have leaves covered with a thick waxy cuticle. Stomata The more the stomata, the higher the rate of transpiration. Xerophytes have few stomata which reduce water-loss. Some have sunken stomata which reduces the rate of transpiration as the water vapour accumulates in the pits. Others have stomata on the lower leaf surface hence reducing the rate of water-loss. Some plants have reversed stomatal rhythm whereby stomata close during the day and open at night. This helps to reduce water-loss. Leaf size and shape Plants in wet areas have large surface area for transpiration. Xerophytes have small narrow leaves to reduce water-loss. The photometer can be used to determine transpiration in different environmental conditions. Translocation of organic compounds Translocation of soluble organic products of photosynthesis within a plant is called translocation. It occurs in phloem in sieve tubes. Substances translocated include glucose, amino acids, and vitamins. These are translocated to the growing regions like stem, root apex, storage organs e.g. corms, bulbs and secretory organs such as nectar glands. Phloem
Phloem is made up of;
TRANSPORT IN PLANTS.
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TYPES OF GERMINATION
- The nature of germination varies in different seeds.
- During germination the cotyledons may be brought above the soil surface.
- This type of germination is called epigeal germination.
- If during germination the cotyledons remain underground the type of germination is known as hypogeal.
GERMINATION
Epigeal Germination
- During the germination of a bean seed, the radicle grows out through the micropyle.
- It grows downwards into the soil as a primary root from which other roots arise.
- The part of the embryo between the cotyledon and the radicle is called the hypocotyl.
- This part curves and pushes upwards through the soil protecting the delicate shoot tip.
- The hypocotyls then straightens and elongates carrying with it the two cotyledons which turn green and leafy.
- They start manufacturing food for the growing seedling.
- The plumule which is lying between two cotyledons, begins to grow into first foliage leaves which start manufacturing food.
Hyopgeal Germination
- In maize, the endosperm provides food to the embryo which begins to grow.
- The radicle along with a protective covering grows out of the seed.
- The epicotyl is the part of the embryo between the cotyledon and the plumule.
- The epicotyl elongates and the plumule grows out of the coleoptile and forms the first foliage leaves.
- The seedling now begins to produce its own food and the endosperm soon shrivels.
- This type of germination in which the cotyledon remains below the ground is known as hypogeal germination.
Practical Activity - To investigate epigeal and hypogeal germination
Requirements
- Tin or box,
- soil,
- water,
- maize grains
- bean seeds.
- Place equal amounts of soil into two containers labelled A and B.
- In A, plant a few maize grains. In B, plant a few bean seeds.
- Water the seeds and continue watering daily until they germinate.
- Place your set-ups on the laboratory bench.
- Observe daily for germination.
- On the first day the seedlings emerge from the soil, observe them carefully with regard to the soil level.
- Carefully uproot one or two seedlings from each set.
- Observe and draw the seedlings from each set Label the parts and indicate the soil level on your diagram.
- On the fifth day since emergence, again uproot another seedling.
- Observe and draw.
- Indicate the soil level on your diagram..
- Tabulate the differences between the two types of germination studied.
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GROWTH AND DEVELOPMENT IN PLANTS
The main growth and development phase in plants begins with the germination of the mature seed. Seeds are of two kinds depending on the number of cotyledons or embryo leaves.
Practical Activity:
Requirements
Practical Activity:
Requirements
- Bean seeds and maize grains which have been soaked overnight.
- Scalpel or razor blades,
- iodine solution,
- Petri-dish and
- hand lens.
- Using a scalpel or razor blade make longitudinal sections (LS) of both the bean seed and the maize grain.
- Observe the LS of the specimens using a hand lens.
- Note any structural difference between the specimens.
- Draw the LS of each specimen and label.
- Put a drop of iodine solution on the cut surfaces of both specimens.
- Note any differences in colouration with iodine on the surfaces of the two specimens.
- On your diagrams indicate the distribution of the stain.
- Account for the difference in distribution of the colouration with iodine in the two specimens.
STRUCTURE OF THE SEED
- A typical seed consists of a seed coat enclosing an embryo.
- The seed coat is the outer covering which, in most seeds, is made up of the two layers, an outer testa and inner one, the tegmen.
Structure of dicotyledon seed (bean grain)
- The testa is thick; the tegmen is a transparent membrane tissue.
- The two layers protect the seed bacteria, fungi and other organisms which may damage it.
- There is a scar called hilum on one part of the seed.
- This is point where the seed had been attached the seed stalk or funicle.
- Near one end of hilum is a tiny pore, the micropyle.
- This allows water and air into the embryo, embryo is made up of cotyledons, a plumule (embryonic (and a radicle (the embryonic root).
- In some seeds the cotyledons swollen as they contain stored food for growing plumule and radicle. Such seeds, called non-endospermic seeds.
- In other cases, the seeds have their food stored in endosperm.
- Such seeds are called endospermic seeds. Seeds with one cotyledon are referred to as monocotyledonous while those with two are referred to dicotyledonous.
- This is the major basis in differentiation between the two large categories of plants, the monocotyledonae and dicotyledonae.
Dormancy in Seeds
- The embryo of a dry, fully developed seed usually passes through a period of rest after ripening period.
- During this time the seed performs all its life (physiological) processes very slowly and uses up little food. This is a period of dormancy.
- Even if all the favorable environmental conditions for germination are provided to the seed during this period of dormancy, the seed will not germinate.
- This is due to the fact that the seed embryo may need to undergo further development before germination.
- Some seeds can germinate immediately after being shed from the parent plant (e.g. most tropical plants) while others must pass through dormancy period, lasting for weeks, months or even years before the seed can germinate.
- Dormancy provides the seeds with enough time for dispersal so that they can germinate in a suitable environment.
- It also enables seeds to survive during adverse environmental conditions without depleting their food reserves.
- The embryo has time to develop until favorable conditions are available e.g. availability of water
Factors that Cause Dormancy
- Embryo may not yet be fully developed.
- Presence of chemical inhibitors that inhibit germination in seeds e.g. Abscisic acid.
- Very low concentrations of hormones e.g. gibberellins and enzymes reduces the ability of seeds to germinate.
- Hard and impermeable seed coats prevent entry of air and water in some seeds e.g. wattle.
- In some seeds the absence of certain wavelengths of light make them remain dormant e.g. in some lettuce plants.
- Freezing of seeds during winter lowers their enzymatic activities rendering them dormant.
Ways of Breaking Dormancy
- When the seed embryos are mature then the seed embryos can break dormancy and germinate.
- Increase in concentration of hormones e.g. cytokinins and gibberellins stimulate germination.
- Favourable environmental factors such as water, oxygen and suitable temperature.
- Some wavelengths of light trigger the production of hormones like gibberellins leading to breaking of dormancy.
- Scarification i.e. weakening of the testa is needed before seeds with hard impermeable seed coats can germinate.
- This is achieved naturally by saprophytic bacteria and fungi or by passing through the gut of animals.
- In agriculture the seeds of some plants are weakened by boiling, roasting and cracking e.g. wattle.
Seed Germination
- The process by which the seed develops into a seedling is known as germination.
- It refers to all the changes that take place when a seed becomes a seedling.
- At the beginning of germination water is absorbed into the seed through the micropyle in a process known as imbibition and causes the seed to swell.
- The cells of the cotyledons become turgid and active.
- They begin to make use of the water to dissolve and break down the food substances stored in the cotyledons.
- The soluble food is transported to the growing plumule and radicle.
- The plumule grows into a shoot while the radicle grows into a root.
- The radical emerges from the seed through micropyle, bursting the seed coat as it does so.
Conditions Necessary for Germination
- Seeds can easily be destroyed by unfavourable conditions such as excessive heat, cold or animals.
- Seeds need certain conditions to germinate and grow.
- Some of these conditions are external, for example water, oxygen and suitable temperature while others are internal such as enzymes, hormones and viability of the seeds themselves.
1. Water
- A non-germinating seed contains very little water.
- Without water a seed cannot germinate.
- Water activates the enzymes and provides the medium for enzymes to act and break down the stored food into soluble form.
- Water hydrolyses and dissolves the food materials and is also the medium of transport of dissolved food substances through the various cells to the growing region of the radical and plumule.
- Besides, water softens the seed coat which can subsequently burst and facilitate the emergence of the radicle.
- Germinating seeds require energy for cell division and growth.
- This energy is obtained from the oxidation of food substances stored in the seed through respiration thus making oxygen an important factor in seed germination.
- Seed in water logged soil or seed buried deep into the soil will not germinate due to lack of oxygen.
- Several hormones play a vital role in germination since they act as growth stimulators.
- These include gibberellins and cytokinins.
- These hormones also counteract the effect of germination inhibitors.
- Only seeds whose embryos are alive and healthy will be able to germinate and grow.
- Seeds stored for long periods usually lose their viability due to depletion of their food reserves and destruction of their embryo by pests and diseases.
- Most seeds require suitable temperature before they can germinate.
- Seeds will not germinate below 0°C or above 47° C.
- The optimum temperature for seeds to germinate is 30°C.
- At higher temperature the protoplasm is killed and the enzymes in the seed are denatured.
- At very low temperatures the enzymes become inactive.
- Therefore, the protoplasm and the enzymes work best within the optimum temperature range.
- The rate of germination increases with temperature until it reaches an optimum.
- This varies from plant to plant.
- Enzymes play a vital role during germination in the breakdown and subsequent oxidation of food.
- Food is stored in seeds in form of carbohydrates, fats and proteins which are in insoluble form.
- The insoluble food is converted into a soluble form by the enzymes.
- Carbohydrates are broken down into glucose by the diastase enzyme, fats into fatty acids and glycerol by lipase, and proteins into amino acids by protease.
- Enzymes are also necessary for the conversion of hydrolysed products to new plant tissues.
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ROLE OF PLACENTA
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TABLE OF CONTENTS
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Protection
Maternal blood and foetal blood do not mix. This ensures that the pathogens and toxins from maternal blood do not reach the foetus. The placenta allows maternal antibodies to pass into the foetus, providing the foetus with immunity. |
Nutrition
The placenta facilitates the transfer of nutrients from maternal blood to foetus.
Excretion
Placenta facilitates the removal of nitrogenous wastes from the foetus' blood to maternal blood.
Gaseous exchange
Oxygen from the maternal blood diffuses into the foetal blood while carbon (IV) oxide from foetal blood diffuse into maternal blood.
Production of hormones
Placenta produces progesterone and oestrogen.
The placenta facilitates the transfer of nutrients from maternal blood to foetus.
Excretion
Placenta facilitates the removal of nitrogenous wastes from the foetus' blood to maternal blood.
Gaseous exchange
Oxygen from the maternal blood diffuses into the foetal blood while carbon (IV) oxide from foetal blood diffuse into maternal blood.
Production of hormones
Placenta produces progesterone and oestrogen.
Gestation period
The period between conception and birth is called gestation.
In humans gestation takes nine months (40 weeks).
The embryo differentiates into tissues and organs during this period.
Week 1 to 3:
Zygote divides to form blastocyst.
Implantation takes place.
The three germ layers form endoderm, mesoderm and ectoderm.
Nervous system starts to form.
Week 4 to 7:
Development of circulating and digestive systems.
Further development of nervous system, formation of sensory organs,
All major internal organs are developed.
At week 5, heartbeat starts.
Week 8 to 24:
All organs well developed including sex organs.
Hair, finger and toe nails grow.
Foetus move and eyelids open.
Week 25- 30:
The fully developed foetus responds to touch and noises and moves vigorously.
The head turns and faces downwards ready for birth.
Week 31-40:
Foetus increases in size.
Birth occurs.
In humans gestation takes nine months (40 weeks).
The embryo differentiates into tissues and organs during this period.
Week 1 to 3:
Zygote divides to form blastocyst.
Implantation takes place.
The three germ layers form endoderm, mesoderm and ectoderm.
Nervous system starts to form.
Week 4 to 7:
Development of circulating and digestive systems.
Further development of nervous system, formation of sensory organs,
All major internal organs are developed.
At week 5, heartbeat starts.
Week 8 to 24:
All organs well developed including sex organs.
Hair, finger and toe nails grow.
Foetus move and eyelids open.
Week 25- 30:
The fully developed foetus responds to touch and noises and moves vigorously.
The head turns and faces downwards ready for birth.
Week 31-40:
Foetus increases in size.
Birth occurs.
Reproductive Hormones
Examining the stages of mitosis
- About 2 mm of a root tip of onion bulb is cut off and placed on a microscope slide.
- A stain e.g. aceto-orcein is added and the root tip macerated using a scapel.
- A cover slip is added and observations made.
- Different stages of mitosis can be observed.
- An unopened bud of Tradescantia is obtained
- The anther is removed and placed on a microscope slide.
- A few drops of hydrochloric acid and acetic-orcein stain are added.
- A cover slip is placed on the anther.
- Pressing the cover slip gives a thin squash, which is observed under the microscope.
- Different stages of meiosis are observed.
- Rhizopus grow on moist bread left under suitable temperature
- A piece of moist bread is placed on a petri-dish or enclosed in a plastic bag and observe daily for four days.
- Under a low power microscope the sporangia and stolons can be observed.
- Obtain the fern plant.
- Detach a frond from the plant and observe the under-side using a hand lens to see the raised brown patches - the sori.
- Open up the sorus to observe the sporangia.
To examine spores on sori of ferns
Dispersal of fruits and seeds
- Obtain the fern plant.
- Detach a frond from the plant and observe the under-side using a hand lens to see the raised brown patches - the sori.
- Open up the sorus to observe the sporangia.
- Obtain insect pollinated flowers e.g. crotalaria, hibiscus/Ipomea, Solanum, incunum.
- Note the scent, colour and nectar guides.
- A description of the calyx, corolla, androecium and gynoecium is made.
- Obtain a wmd pollinated flower e.g.,' maize, star-grass, sugar-cane, Kikuyu grass.
- Observe the glumes, spikes and spikelet.
- Examine a single floret, and identify the androecium and gynoecium.
- Obtain different fruits - oranges, mangoes, maize, castor oil, bean pod, black jack .
- Observe the fruits, classify them into succulent, dry-dehiscent or indehiscent.
- Obtain an orange and a mango fruit.
- Make a transverse section.
- Observe the cut surface and draw and label the parts.
- Note that the fruit is differentiated into epicarp, mesocarp and endocarp.
- Obtain a pod of a legume.
- Open up the pod and observe the exposed surface.
- Draw and label the parts.
Dispersal of fruits and seeds
- Obtain animal dispersal fruits, like oranges, tomatoes, black jack, sodom apple.
- Identify the way by which each is adapted to dispersal by animals.
- Obtain wind dispersed fruit/seed e.g. Nandi flame, Jacaranda Sonchus, cotton seed, Tecoma.
What is Measurement of Growth?
Growth can be estimated by measuring some aspect of the organism such as height, weight, volume and length over a specified period of time. The measurements so obtained if plotted against time result into a growth curve.
Study Question
The following results were obtained from a study of germination and early growth of maize.
The grains were sown in soil in a greenhouse and.at two-day intervals. Samples were taken, oven dried and weighed. See table.
The grains were sown in soil in a greenhouse and.at two-day intervals. Samples were taken, oven dried and weighed. See table.
Plot a graph of dry mass of embryo against time after sowing.
Describe the shape of the graph.
For most organisms when the measurements are plotted they give an S-shaped graph called a sigmoid curve such as in figure. This pattern is due to the fact that growth tends to be slow at first and then speeds up and finally slows down as adult size is reached. A sigmoid curve may therefore be divided into four parts.
For most organisms when the measurements are plotted they give an S-shaped graph called a sigmoid curve such as in figure. This pattern is due to the fact that growth tends to be slow at first and then speeds up and finally slows down as adult size is reached. A sigmoid curve may therefore be divided into four parts.
Lag phase (slow growth)
This is the initial phase during which little growth occurs. The growth rate is slow due to various factors namely:
- The number of cells dividing are few.
- The cells have not yet adjusted to the surrounding environmental factors.
Exponential phase (log phase)
This is the second phase during which growth is rapid or proceeds exponentially. During this phase the rate of growth is at its maximum and at any point, the rate of growth is proportional to the amount of material or numbers of cells of the organism already present.
This rapid growth is due to:
This rapid growth is due to:
- An increase in number of cells dividing, 2-4-8-16-32-64 following a geometric progression,
- Cells having adjusted to the new environment,
- Food and other factors are not limiting hence cells are not competing for resources,
- The rate of cell increase being higher than the rate of cell death.
Decelerating Phase
This is the third phase during which time growth becomes limited as a result of the effect of some internal or external factors, or the interaction of both.
The slow growth is due to:
The slow growth is due to:
- The fact that most cells are fully differentiated.
- Fewer cells still dividing,
- Environmental factors (external and internal) such as:
- shortage of oxygen and nutrients due to high demand by the increased number of cells.
- space is limited due to high number of cells.
- accumulation of metabolic waste products inhibits growth.
- limited acquisition of carbon (IV) oxide as in the case of plants.
Plateau (stationary) phase
This is the phase which marks the period where overall growth has ceased and the parameters under consideration remain constant.
This is due to the fact that:
This is due to the fact that:
- The rate of cell division equals the rate of cell death.
- Nearly all cells and tissues are fully differentiated, therefore there is no further increase in the number of cells.
- The nature of the curve during this phase may vary depending on the nature of the parameter, the species and the internal factors.
- In some cases, the curve continue to increase slightly until organism dies as is the case monocotyledonous plants, man invertebrates, fish and certain reptiles. indicates positive growth.
- In some other cases the curve flattens out indicating change in growth while other growth curves may tail off indicating a period of negative growth rate.
- This negative pattern characteristic of many mammals including humans and is a sign of physical senses associated with increasing age.
PRACTICAL ACTIVITY I: PROJECT
To measure the growth of a plant
Requirements
Small plots/boxes, meter rule and seeds of beans (or green grams, peas, maize),
Procedure
Requirements
Small plots/boxes, meter rule and seeds of beans (or green grams, peas, maize),
Procedure
- Place some soil in the box or prepare a small plot outside the laboratory.
- Plant some seeds in the box and place it in a suitable place outside the laboratory (or plant the seeds in your plot).
- Water the seeds daily.
- Observe the box/plot daily and note the day the seedlings emerge out of the soil.
- Measure the height of the shoot from the soil level up to the tip of the shoot. Repeat this with four other seedlings. Work out the average height of the shoots for this day.
- Repeat procedure 5 every three days for at least three weeks.
- Record the results in a table form.
- On the same seedlings measure the length of one leaf from each of the five seedlings (from leaf apex to its attachment on the stem
- Calculate the average length of the leaves and record in the table.
- Plot a graph of the height of the shoot against time. On the same axes plot length of leaf against time.
- Compare the two graphs drawn.
Reproduction in Animals
- Sexual reproduction involves the fusion of gametes.
- In animals two individuals are involved, a male and a female.
- Special organs known as gonads produce gametes.
- In males testes produce sperms while in females ovaries produce ova.
- The fusion of male gamete and female gamete to form a zygote is called fertilisation.
External fertilization
- Example in amphibians takes place in water.
- The male mounts the female and shed sperms on the eggs as they are laid.
- Eggs are covered by slippery jelly-like substance which provides protection.
- Many eggs are released to increase the chances of survival.
- This occurs in reptiles, birds and mammals.
- Fertilisation occurs within the body of the female.
- Fewer eggs are produced because there are higher chances of fertilisation since sperms are released into the female body.
Reproduction in Humans
Structure of female reproduction system,
The female reproduction system consist of the following: Ovaries
The female reproduction system consist of the following: Ovaries
- Are two oval cream coloured structures found in lower abdomen below the kidneys.
- They produce the ova.
- Are tubes which conduct the ova produced by the ovaries to the uterus.
- Fertilisation occurs in the upper part of the oviduct.
- The uterus is a hollow muscular organ found in the lower abdomen.
- The embryo develops inside the uterus.
- The inner lining endometrium supplies nutrients to embryo.
- The embryo is implanted into the inner uterine wall- the endometrium which nourishes the embryo.
- The thick muscles of the uterus assist in parturition.
- Has a ring of muscles that separates the uterus from the vagina.
- It forms the opening to the uterus
- Is a tube that opens to the outside and it acts as the copulatory and birth canal through the vulva.
Structure of male reproductive system
The male reproductive system consists of the following:
Testis:
The male reproductive system consists of the following:
Testis:
- Each testis is a mass of numerous coiled tubes called semniferous tubules.
- Each is enclosed within a scrotal sac that suspends them between the thighs.
- This ensures that sperms are maintained at a temperature lower than that of the main body.
- The lining of seminiferous tubules consists of actively dividing cells which give rise to sperms.
- Between the seminiferous tubules are interstitial cells which produce the male hormones called androgens e.g. testosterone.
- The seminiferous tubules unite to form the epididymis, which is a coiled tube where sperms are stored temporarily .
- Vas deferens (sperm duct) is the tube through which sperms are carried from testis to urethra.
- Seminal vesicle produces an alkaline secretion which nourishes the spermatozoa.
- Produces an alkaline secretion to neutralise vaginal fluids.
- Secretes an alkaline fluid.
- All these fluids together with spermatozoa form semen.
- Is a long tube through which the semen is conducted during copulation.
- It also removes urine from the bladder.
- Is an intro-mittent organ which is inserted into the vagina during copulation.
Fertilisation in Animals
- Fertilisation is preceded by copulation in which the erect penis is inserted into the vagina.
- This leads to ejaculation of semen.
- The sperms swim through the female's genital tract to the upper part of the oviduct.
- The head of the sperm penetrates the egg after the acrosome_ releases lytic enzymes t dissolve the egg membrane.
- The tail is left behind.
- Sperm nucleus fuses with that of the ovum and a zygote is formed.
- A fertilisation membrane forms around the zygote which prevents other sperms from penetrating the zygote.
- After fertilisation the zygote begins to divide mitoticaly as it moves towards the uterus.
- It becomes embedded in the wall of the uterus a process called implantation.
- By this time the zygote is a hollow ball of cells called blastocyst or embryo.
- In the uterus the embryo develops villi which project into uterus for nourishment later the villi and endometrium develop into placenta.
- Embryonic membranes develop around the embryo.
- The outermost membrane is the chorion which forms the finger-like projections (chorionic villi) which supply nutrients to the embryo.
- The amnion surrounds the embryo forming a fluid filled cavity within which the embryo lies.
- Amniotic cavity is filled with amniotic fluid.
- This fluid acts as a shock absorber and protects the foetus against mechanical injury.
- It also regutates temperature.
- The chorionic villi, allantois together with the endometrium from the placenta.
- The embryo is attached to the placenta by a tube called umbilical cord which has umbilical vein and artery.
- The maternal blood in the placenta flows in the spaces lacuna and surrounds capillaries from umbilical vein and artery.
- The umbilical cord increase in length as the embryo develops.
Growth is a characteristic feature of all living organisms.
Most multi cellular organisms start life as a single cell and gradually grow into complex organisms with many cells. This involves multiplication of cells through the process of cell division.
This quantitative permanent increase in size of an organism is referred to as growth.
Most multi cellular organisms start life as a single cell and gradually grow into complex organisms with many cells. This involves multiplication of cells through the process of cell division.
This quantitative permanent increase in size of an organism is referred to as growth.
For growth to take place the following aspects occur
- Cells of organisms assimilate nutrients hence increase in mass.
- Cell division (mitosis) that lead to increase in the number of cells.
- Cell expansion that leads to enlargement an increase in the volume and size of the organism. It is therefore possible to measure growth using such parameters as mass, volume, length, height, surface area.
- On the other hand development is the qualitative aspect of growth which involves differentiation of cells and formation of various tissues in the body of the organism in order for tissues to be able to perform special functions.
- It is not possible to measure all aspects of development quantitative.
- Therefore development can be assessed in terms of increase in complexity of organism e.g. development of leaves, flowers and roots.
- A mature human being has millions of cells in the body yet he or she started from; single cell, that is, a fertilised egg.
- During sexual reproduction mammals an ovum fuses with a sperm to form a zygote.
- The zygote divides rapidly without increasing in size, first into 2, 4, 8, 16,32, 64 and so on, till it forms a mass cells called morula.
- These first cell division is called cleavages.
- The morula develops a hollow part, resulting into a structure known as a blastula (blastocyst).
- Later, blastocyst cells differentiate into an inner layer (endoderm) and the outer layer (ectoderm).
- The two-layered embryo implants into the uterine wall and, by obtaining nutrients from the maternal blood, starts to grow and develop.
EMBRYONIC DEVELOPMENT
- As the embryo grows and develops, changes occur in cell sizes and cell -types.
- Such changes are referred to as growth and development respectively.
- These processes lead to morphological and physiological changes in the developing young organism resulting into an adult that is more complex and efficient.
- In the early stages, all the cells of the embryo look alike, but as the development process continues the cells begin to differentiate and become specialized into different tissues to perform different functions.
- Growth involves the synthesis of new material and protoplasm.
- This requires a continuous supply of food, oxygen, water, warmth and means of removing waste products.
- In animals, growth takes place all over the body but the rates differ in the various parts of the body and at different times.
- In plants however, growth and cell division mostly take place at the root tip just behind the root cap and stem apex.
- This is referred to as apical growth which leads to the lengthening of the plant.
- However, plants do not only grow upwards and downwards but sideways as well.
- This growth leads to an increase in width (girth) by the activity of cambium cells.
- The increase in girth is termed as secondary growth.
Male
- Testerone is the main androgen that stimulates the development of secondary sexual characteristics.
- Broadening of the shoulders.
- Deepening of the voice due to enlargement of larynx.
- Hair at the pubic area, armpit and chin regions.
- Penis and testis enlarge and produce sperms.
- Body becomes more masculine.
Female
- Enlargement of mammary glands.
- Hair grows around pubic and armpit regions.
- Widening of the hips.
- Ovaries mature and start producing ova.
- Menstruation starts.
- Oestrogen triggers the onset of secondary sexual characteristics.
Sexually transmitted infections (STl)
Menstrual Cycle
- This is characterized by discharge of blood and tissue debris (menses) from the uterus every 28 days.
- This is due to the breakdown of the endometrium which occurs when the level of progesterone falls and the girl starts to menstruate.
- The follicle stimulating hormone (FSH) causes the Graafian follicle to develop and also stimulate the ovary to release oestrogen.
- Oestrogen hormone triggers the onset of secondary sexual characteristics.
- Luteinising hormone (L.H) causes the mature ovum to be released from the Graafian follicle - a process called ovulation.
- After ovulation progesterone hormone is produced.
- After menstruation, the anterior lobe of the pituitary gland starts secreting the follicle stimulating hormone (FS.H) which causes the Graafian follicle to develop in the ovary.
- It also stimulates the ovary tissues to secrete oestrogen.
- Oestrogen brings about the repair and healing of the inner lining of the uterus (endometrium) which had been destroyed during menstruation.
- Oestrogen level stimulates the pituitary gland to produce (Luteinising Hormone (L.H).
- This hormone makes the mature Graafian follicle to release the ovum into the funnel of oviduct, a process called ovulation.
- After releasing the ovum, the Graafian follicle changes into a yellow body called corpus luteum.
- The luteinising hormone stimulates the corpus luteum to secrete a hormone called progesterone which stimulates the thickening and vascularisation of endometrium.
- This prepares the uterine wall for implantation of the blastocyst.
- If fertilisation takes place, the level of progesterone increases and thus inhibits FSH from stimulating the maturation of another Graafian follicle.
- If fertilisation does not occur, the corpus luteum disintegrates and the level of progesterone goes down.
- The endometrium, sloughs off and menstruation occurs.
Advantages of Reproduction Asexual
- Good qualities from parents are retained in the offspring without variation.
- New individuals produced asexually mature faster.
- Process does not depend on external factors which may fail such as pollination.
- New individuals obtain nourishment from parent and so are able to survive temporarily under unsuitable conditions.
- No indiscriminate spreading of individuals which can result in wastage of offspring.
- Takes a shorter time and leads to rapid colonization.
Disadvantages of asexual reproduction
- New offspring may carry undesirable qualities from parents.
- Offspring may be unable to withstand changing environmental conditions.
- Faster maturity can cause overcrowding and stiff competition.
- Reduced strength and vigour of successive generations.
Advantages of sexual reproduction
- Leads to variations.
- Variations which are desirable often show hybrid vigour.
- High adaptability of individuals to changing environmental conditions.
- Variations provide a basis for evolutionary changes.
Disadvantages of sexual reproduction
- Fusion is difficult if two individuals are isolated.
- Some variations may have undesirable qualities.
- Population growth is slow.
In flowering plants, the flower is the reproductive organ which is a specialised shoot consisting of a modified stem and leaves. The stem-like part is the pedicel and receptacle, while modified leaves form corolla and calyx.
Structure and functions of parts of named insect and wind pollinated flowers
Structure of a flower
A typical flower consists of the following parts:
A typical flower consists of the following parts:
Calyx
Made up of sepals.
They enclose and protect the flower when it is in a bud. Some flowers have an outer whorl made of sepal-like structures called epicalyx.
Corolla
Consists of petals. The petals are brightly coloured in insect - pollinated flowers.
Androecium
This is the male part of the flower, it consists of stamens. Each stamen consists of a filament whose end has an anther. Inside the anther are pollen sacs which contain pollen grains.
Gynoecium (pistil)
It is the female part of the flower, it consists of one or more carpels. Each carpel consists of an ovary, a sty le and a stigma. The ovary contains ovules which become seeds after fertilisation.
A monocarpous pistil has one carpel e.g. Beans, a polycarpous pistil has many carpels. If the carpes are free, it is called apocarpous as in rose and Bryophyllum, in carpels that are fused it is called syncarpous as in Hibiscus.
A complete flower has all the four floral parts, a regular flower can be divided into two halves by any vertical section passing through the centre. E.g. morning glory. Irregular flower can be divided into two halves in only one plane e.g. crotalaria.
Made up of sepals.
They enclose and protect the flower when it is in a bud. Some flowers have an outer whorl made of sepal-like structures called epicalyx.
Corolla
Consists of petals. The petals are brightly coloured in insect - pollinated flowers.
Androecium
This is the male part of the flower, it consists of stamens. Each stamen consists of a filament whose end has an anther. Inside the anther are pollen sacs which contain pollen grains.
Gynoecium (pistil)
It is the female part of the flower, it consists of one or more carpels. Each carpel consists of an ovary, a sty le and a stigma. The ovary contains ovules which become seeds after fertilisation.
A monocarpous pistil has one carpel e.g. Beans, a polycarpous pistil has many carpels. If the carpes are free, it is called apocarpous as in rose and Bryophyllum, in carpels that are fused it is called syncarpous as in Hibiscus.
A complete flower has all the four floral parts, a regular flower can be divided into two halves by any vertical section passing through the centre. E.g. morning glory. Irregular flower can be divided into two halves in only one plane e.g. crotalaria.
Pollination and agents of pollination
Pollination
This is the transfer of pollen grains from the anther to the stigma.
Types of pollination
Self-pollination is the transfer of pollen grains from the anther of one flower to the stigma of the same flower.
Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of a different flower, of the same species.
Agents of pollination
Agents of pollination include wind, insects, birds and mammals.
Insect pollinators include bees, butterflies and mosquitoes.
This is the transfer of pollen grains from the anther to the stigma.
Types of pollination
Self-pollination is the transfer of pollen grains from the anther of one flower to the stigma of the same flower.
Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of a different flower, of the same species.
Agents of pollination
Agents of pollination include wind, insects, birds and mammals.
Insect pollinators include bees, butterflies and mosquitoes.
Features and mechanisms that hinder self-pollination and self-fertilization
- Stamens ripen early and release their pollen grains before the stigma, mature. This is called protandry e.g. in sunflower.
- The stigma matures earlier and dries before the anthers release the pollen grains.
- This is called protogyny and is common in grasses.
- Self-sterility or incompatibility
- Pollen grains are sterile to the stigma of the same flower, e.g. in maize flower.
- Shorter stamens than pistils.
The process of fertilization
Fertilisation in Plants
The pollen grain contains the generative nucleus and a tube nucleus. When the pollen grain lands on the stigma, it absorbs nutrient and germinates forming a pollen tube. This pollen tube grows through the style pushing its way between the cells thus getting nourishment from these cells.
The tube nucleus occupies the position at the tip of the growing pollen tube. The generative nucleus follows behind the tube nucleus, and divides to form two male gamete nuclei. The pollen tube then enters the ovule through the micropyle.
When the pollen tube penetrates the ovule disintegrates and the pollen tube bursts open leaving a clear way for the male nuclei. One male nucleus fuses with the egg cell nucleus to form a diploid zygote which develops into an embryo. The other male gamete nucleus fuses with the polar nucleus to form a triploid nucleus which forms the primary endosperm. This is called double fertilisation.
After fertilisation the following changes take place in a flower:
The pollen grain contains the generative nucleus and a tube nucleus. When the pollen grain lands on the stigma, it absorbs nutrient and germinates forming a pollen tube. This pollen tube grows through the style pushing its way between the cells thus getting nourishment from these cells.
The tube nucleus occupies the position at the tip of the growing pollen tube. The generative nucleus follows behind the tube nucleus, and divides to form two male gamete nuclei. The pollen tube then enters the ovule through the micropyle.
When the pollen tube penetrates the ovule disintegrates and the pollen tube bursts open leaving a clear way for the male nuclei. One male nucleus fuses with the egg cell nucleus to form a diploid zygote which develops into an embryo. The other male gamete nucleus fuses with the polar nucleus to form a triploid nucleus which forms the primary endosperm. This is called double fertilisation.
After fertilisation the following changes take place in a flower:
- The integuments develops into seed coat (testa).
- The zygote develops into an embryo.
- The triploid nucleus develops into an endosperm.
- The ovules become seeds.
- The ovary develops into a fruit.
- The ovary wall develops into pericarp.
- The style, dries up and falls off leaving a scar.
- The corolla, calyx and stamens dry up and fall off.
- In some the calyx persists.
Fruit and seed formation and dispersal
Fruit development without fertilisation is called parthenocarpy e.g. as in pineapples and bananas.Such fruits do not have seeds.
Classification of fruits
Classification of fruits
- False fruits develops from other parts such as calyx, corolla and receptacle, e.g. apple and pineapple which develops from an inflorescence.
- True fruits develop from the ovary, e.g. bean fruit (pod), they can be divided into fleshy or succulent fruits e.g. berries and drupes and dry fruits.
- The dry ones can be divided into Dehiscent which split open to release seeds and indehiscent which do not open.
Placentation
This is the arrangement of the ovules in an ovary.
Marginal placentation:
The placenta appears as one ridge on the ovary wall e.g. bean.
Parietal placentation:
The placenta is on the ridges on ovary wall.
Ovules are in them e.g. pawpaw.
Axile placentation:
The placenta is in the centre.
Ovary is divided into a number of loculi. e.g. orange.
Basal placentation.
The placenta is formed at the base of the ovary e.g. sunflower.
Free Central placentation.
Placenta is in the centre of the ovary.
There are no loculi e.g. in primrose.
This is the arrangement of the ovules in an ovary.
Marginal placentation:
The placenta appears as one ridge on the ovary wall e.g. bean.
Parietal placentation:
The placenta is on the ridges on ovary wall.
Ovules are in them e.g. pawpaw.
Axile placentation:
The placenta is in the centre.
Ovary is divided into a number of loculi. e.g. orange.
Basal placentation.
The placenta is formed at the base of the ovary e.g. sunflower.
Free Central placentation.
Placenta is in the centre of the ovary.
There are no loculi e.g. in primrose.
Methods of fruit and seed dispersal.
Animal dispersal
Fleshy fruits are eaten by animals.
Animals are attracted to the fruits by the bright colour, scent or the fact that it is edible.
The seeds pass through the digestive tract undamaged and are passed out with faeces. E.g. tomatoes and guavas.
Such seeds have hard, resistant seed coats.
Others have fruits with hooks or spines that stick on animal fur or on clothes.
Later the seeds are brushed of or fall off on their own e.g. Bidens pilosa (Black jack).
Wind dispersal
Fruits and seeds are small and light in order to be carried by air currents.
A fruit that is a capsule e.g. tobacco split or has pores at the top e.g. Mexican poppy.
The capsule is attached to along stalk when swayed by wind the seeds are released and scattered.
Some seeds have hairy or feather-like structures which increase their surface area so that they can be blown off by the wind e.g. Sonchus.
Others have wing-like structures e.g. Jacaranda and Nandi Flame.
These extensions increase the surface area of fruits and seeds such that they are carried by the wind.
Water dispersal
Fruits like coconut have fibrous mescocarp which is spongy to trap air, the trapped air make the fruit light and buoyant to float on water.
Plants like water lily produce seeds whose seed coats trap air bubbles.
The air bubbles make the seeds float on water and are carried away.
The pericarp and seed coat are waterproof.
Self-dispersal (explosive) Mechanism
This is seen in pods like bean and pea.
Pressure inside the pod forces it to open along lines of weakness throwing seeds away from parent plant.
Fleshy fruits are eaten by animals.
Animals are attracted to the fruits by the bright colour, scent or the fact that it is edible.
The seeds pass through the digestive tract undamaged and are passed out with faeces. E.g. tomatoes and guavas.
Such seeds have hard, resistant seed coats.
Others have fruits with hooks or spines that stick on animal fur or on clothes.
Later the seeds are brushed of or fall off on their own e.g. Bidens pilosa (Black jack).
Wind dispersal
Fruits and seeds are small and light in order to be carried by air currents.
A fruit that is a capsule e.g. tobacco split or has pores at the top e.g. Mexican poppy.
The capsule is attached to along stalk when swayed by wind the seeds are released and scattered.
Some seeds have hairy or feather-like structures which increase their surface area so that they can be blown off by the wind e.g. Sonchus.
Others have wing-like structures e.g. Jacaranda and Nandi Flame.
These extensions increase the surface area of fruits and seeds such that they are carried by the wind.
Water dispersal
Fruits like coconut have fibrous mescocarp which is spongy to trap air, the trapped air make the fruit light and buoyant to float on water.
Plants like water lily produce seeds whose seed coats trap air bubbles.
The air bubbles make the seeds float on water and are carried away.
The pericarp and seed coat are waterproof.
Self-dispersal (explosive) Mechanism
This is seen in pods like bean and pea.
Pressure inside the pod forces it to open along lines of weakness throwing seeds away from parent plant.
Abiotic factors (environmental factors)
According to biology dictionary, abiotic factors are non-living factors in the ecosystem. These factors do affect the living things in it, but they are not living themselves. In this context, we will focus mainly on light, temperature, atmospheric pressure, salinity, humidity, pH and wind.
Beetle
Temperature
This is the hotness or coldness of an area or habitat. It directly affects the distribution and productivity (yield) of populations and communities.
Most organisms are found in areas where temperature is moderate. However, certain plants and animals have adaptations that enable them to live in areas where temperatures are in the extremes such as the hot deserts and the cold Polar Regions. Temperatures not only influence distribution of organisms but also determine the activities of animals. High temperatures usually accelerates the rates of photosynthesis, transpiration, evaporation and the decomposition and recycling of organic matter in the ecosystem.
Light
Light is required by green plants for photosynthesis. Light intensity, duration and quality affect organisms in one way or another.
Atmospheric Pressure
This is the force per unit area of atmospheric air that is exerted on organisms at different altitudes. Growth of plants and activity of animals is affected by atmospheric pressure e.g., rate of transpiration in plants and breathing in animals.
Salinity
This is the salt content of soil or water. Animals and plants living in saline conditions have special adaptations.
Humidity
Humidity describes the amount of moisture (water vapour) in the air. It affects the rate of transpiration in plants and evaporation in animals.
pH
pH Is the measure of acidity or alkalinity of soil solution or water, it is very important to organisms living in water and soil. Most organisms prefer a neutral pH.
Wind:
Wind is moving air currents and it influences the dispersion of certain plants by effecting the dispersal of spores, seeds and fruits.
Air currents also modify the temperature and humidity of the surroundings.
Topography:
These are surface features of a place. The topographical factors considered include altitudes, gradient (slope), depressions and hills, all these characteristics affect the distribution of organisms in an area e.g. the leeward and windward sides of a hill.
This is the hotness or coldness of an area or habitat. It directly affects the distribution and productivity (yield) of populations and communities.
Most organisms are found in areas where temperature is moderate. However, certain plants and animals have adaptations that enable them to live in areas where temperatures are in the extremes such as the hot deserts and the cold Polar Regions. Temperatures not only influence distribution of organisms but also determine the activities of animals. High temperatures usually accelerates the rates of photosynthesis, transpiration, evaporation and the decomposition and recycling of organic matter in the ecosystem.
Light
Light is required by green plants for photosynthesis. Light intensity, duration and quality affect organisms in one way or another.
Atmospheric Pressure
This is the force per unit area of atmospheric air that is exerted on organisms at different altitudes. Growth of plants and activity of animals is affected by atmospheric pressure e.g., rate of transpiration in plants and breathing in animals.
Salinity
This is the salt content of soil or water. Animals and plants living in saline conditions have special adaptations.
Humidity
Humidity describes the amount of moisture (water vapour) in the air. It affects the rate of transpiration in plants and evaporation in animals.
pH
pH Is the measure of acidity or alkalinity of soil solution or water, it is very important to organisms living in water and soil. Most organisms prefer a neutral pH.
Wind:
Wind is moving air currents and it influences the dispersion of certain plants by effecting the dispersal of spores, seeds and fruits.
Air currents also modify the temperature and humidity of the surroundings.
Topography:
These are surface features of a place. The topographical factors considered include altitudes, gradient (slope), depressions and hills, all these characteristics affect the distribution of organisms in an area e.g. the leeward and windward sides of a hill.
Biotic factors
These are living components of an ecosystem. These factors affect the ecosystem through enhancing
Inter-relationships between Organisms
The relationships between organisms in a given ecosystem is primarily a feeding one. Organisms in a particular habitat have different feeding levels referred to as trophic levels. There are two main trophic levels:
Producers:
These organisms that occupy the first trophic level, they manufacture their own food hence are autotrophic.
Consumers:
These are the organisms that feed on organic substances manufactured by green plants, they occupy different trophic levels as follows:
Primary consumers:
These are herbivores and feed on green plants.
Secondary consumers:
These are carnivores and feed on flesh. First order carnivores feed on herbivores while second order carnivores feed on other carnivores, i.e., tertiary consumers.
Omnivores:
These are animals that feed on both plant and animal material. They can be primary, secondary or tertiary consumers.
Competition between themselves for survival
this describes the situation where two or more organisms in the same habitat require or depend on the same resources. Organisms in an ecosystem compete for resources like food, space, light, water and mineral nutrients. Competition takes place when the environmental resource is not adequate for all.
Predation is a relationship whereby one animal (the predator) feeds on another (the prey).
Saprophytism
Inter-relationships between Organisms
The relationships between organisms in a given ecosystem is primarily a feeding one. Organisms in a particular habitat have different feeding levels referred to as trophic levels. There are two main trophic levels:
Producers:
These organisms that occupy the first trophic level, they manufacture their own food hence are autotrophic.
Consumers:
These are the organisms that feed on organic substances manufactured by green plants, they occupy different trophic levels as follows:
Primary consumers:
These are herbivores and feed on green plants.
Secondary consumers:
These are carnivores and feed on flesh. First order carnivores feed on herbivores while second order carnivores feed on other carnivores, i.e., tertiary consumers.
Omnivores:
These are animals that feed on both plant and animal material. They can be primary, secondary or tertiary consumers.
Competition between themselves for survival
this describes the situation where two or more organisms in the same habitat require or depend on the same resources. Organisms in an ecosystem compete for resources like food, space, light, water and mineral nutrients. Competition takes place when the environmental resource is not adequate for all.
- Intraspecific competition.
This is competition between organisms of the same species, For example, maize plants in a field compete for water and nutrients among themselves. - Interspecific competition.
This refers to competition between organisms of different species, e.g., different species of predators can compete for water and prey among themselves.
Predation is a relationship whereby one animal (the predator) feeds on another (the prey).
Saprophytism
- Saprophytism is the mode of nutrition common in certain species of fungi and bacteria, such organisms feed on dead organic material and release nutrients through the process of decomposition or decay.
- Saprophytes produce enzymes, which digest the substrates externally.
- The simpler substances are then absorbed.
- Saprophytes help in reducing the accumulation of dead bodies of plants and animals.
- Harmful saprophytes cause rapid decay of foods such as fruits, vegetables, milk and meat.
- Others damage buildings by causing wood rot.
- Some fungi produce poisonous substances called aflatoxins.
- These substances are associated with cereal crops which are stored under warm, moist conditions.
- If the infected grain is eaten, it may cause serious illness, and death.
- This is an association between members of different species.
- The parasite lives on or in the body of another organism, the host.
- The parasite derives benefits such as food and shelter from the host but the heist suffers harm as a result.
- Organisms of different species derive mutual benefit from one another.
- Some symbiotic associations are loose and the two partners gain very little from each other.
- Other symbiotic associations are more intimate and the organisms show a high degree of interdependence.
Nitrogen cycle
- Is the interdependence of organisms on one another and the physical environment as nitrogen is traced from and back into the atmosphere
- Although nitrogen is abundant in the atmosphere, most organisms are not able to utilize it directly.
- Some bacteria are capable of converting atmospheric nitrogen into forms which can be used by other living organisms.
- These bacteria are referred to as nitrogen fixing bacteria.
- Symbiotic nitrogen fixing bacteria live in the root nodules of leguminous plants such as beans and peas.
- Non-symbiotic nitrogen fixing bacteria live in the soil.
- Nitrifying' bacteria convert ammonia into nitrites and nitrates.
- Denitrifying bacteria convert nitrates into atmospheric nitrogen.
Questions on Topic
1. The flow chart below shows a food web in a terrestrial ecosystem.
- From the food web construct a food chain with the hawk as
- a tertiary consumer
- a quartenary consumer
- Name the trophic level occupied by the toads
- What would happen if leopards were introduced into the ecosystem
2. The food web represents a feeding relationship in an ecosystem.
- Name two organisms which are both secondary and tertiary consumers (2mks)
- State the short term effect of immigration of insects in the ecosystem. (2mks)
- Which organism has the least biomass in the food web? Give reasons (2mks)
- Explain the disadvantages of using synthetic pesticides over biological control in agriculture (2mk)
3. State four abiotic factors in an ecosystem.
4.
- The following organisms were found in a grassland ecosystem; caterpillars, aphids, praying mantis, spiders, grass, acacia trees, rabbits, wild dogs, hyenas, carnivorous beetles and gazelles.
- Name two organisms from the list that can be classified as:
- i.producers (1mk)
- ii.tertiary consumers (1mk)
- Construct a food chain ending with a secondary consumers (1mk)
- Name two organisms from the list that can be classified as:
Concept of reproduction
The process by which mature individuals produce offspring is called reproduction. Reproduction is a characteristic of all living organisms and prevents extinction of a species.
Monkeys Mating
There are two types of reproduction:
- Sexual
this reproduction involves the fusion of male and female gametes to form a zygote. -
Asexual reproduction.
This is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes, and almost never changes the number of chromosomes. [Source: Wikipedia.org]
Importance of reproduction
The main importance to reproduction is to give rise to young ones of same ensuring continuity of the group.
Chromosomes, mitosis and meiosis (mention gamete formation)
Cell Division
Cell division starts with division of nucleus. In the nucleus are a number of thread-like structures called chromosomes, which occur in pairs known as homologous chromosomes.
Each chromosome contains-genes that determine the characteristics of an organism. The cells in each organism contains a specific number of chromosomes.
There are two types of cell division:
a) Mitosis
This takes place in all body cells of an organism to bring about increase in number of cells, resulting in growth and repair. The number of chromosomes in daughter cells remain the same as that in the mother cell.
Mitosis is divided into five main stages:
Cell division starts with division of nucleus. In the nucleus are a number of thread-like structures called chromosomes, which occur in pairs known as homologous chromosomes.
Each chromosome contains-genes that determine the characteristics of an organism. The cells in each organism contains a specific number of chromosomes.
There are two types of cell division:
- Mitosis
- Meiosis
a) Mitosis
This takes place in all body cells of an organism to bring about increase in number of cells, resulting in growth and repair. The number of chromosomes in daughter cells remain the same as that in the mother cell.
Mitosis is divided into five main stages:
-
Interface
The term interphase is used to describe the state of the nucleus when the cell is just about to divide. During this time the following take place:- Replication of genetic material so that daughter cells will have the same number of chromosomes as the parent cell.
- Division of cell organelles such as mitochondria, ribosomes and centrioles.
- Energy for cell division is synthesised and stored in form of Adenosine Triphosphate (ATP) to drive the cell through the entire process.
During interphase, the following observations can be made:
- Chromosomes are seen as long, thin, coiled thread-like structures.
- Nuclear membrane and nucleolus are intact.
- Prophase
the chromosomes shorten and thicken. Each chromosome is seen to consist of a pair of chromatids joined at a point called centromere.
Centrioles (in animal cells) separate and move to opposite poles of the cell. The centre of the nucleus is referred to as the equator. Spindle fibres begin to form, and connect the centriole pairs to the opposite poles. The nucleolus and nuclear membrane disintegrate and disappear. - Metaphase
Spindle fibres lengthen, in animal cells they attach to the centrioles at both poles. Each chromosome moves to the equatorial plane and is attached to the spindle fibres by the centromeres. Chromatids begin to separate at the centromere. - Anaphase
Chromatids separate and migrate to the opposite poles due to the shortening of spindle fibres. Chromatids becomes a chromosome. In animal cell, the cell membrane starts to constrict. - Telophase.
The cell divides into two. In animal cells it occurs through cleavage of cell membrane. In plants cells, it is due to deposition of cellulose along the equator of the cell.(Cell plate formation). A nuclear membrane forms around each set of chromosome. Chromosomes later become less distinct.
- It brings about the growth of an organism.
- It brings about asexual reproduction.
- Ensures that the chromosome number is retained.
- Ensures that the chromosomal constitution of the offspring is the same as the parents.
b) Meiosis
This type of cell division takes place in reproductive organs (gonads) to produce gametes. The number of chromosomes in the gamete is half that in the mother cell.
Meiosis involves two divisions of the parental cell resulting into four daughter cells. The mother cell has the diploid number of chromosomes. The four cells (gametes) have half the number of chromosomes (haploid) that the mother cell had, in the first meiotic division there is a reduction in the chromosome number because homologous chromosomes and not chromatids separate.
Homologue pairs separate during a first round of cell division, called meiosis I. Sister chromatids separate during a second round, called meiosis II. Since cell division occurs twice during meiosis, one starting cell can produce four gametes (eggs or sperm). In each round of division, cells go through four stages: prophase, metaphase, anaphase, and telophase. [additional information by the Khan Academy]
Meiosis I (First Meiotic division)
Before entering meiosis I, a cell must first go through interphase. As in mitosis the cell prepares for division, this involves replication of chromosomes, organelles and buildup of energy to be used during the meiotic division.
Usually the two daughter cells go into a short resting stage (interphase) but sometimes the chromosomes remain condensed and the daughter cells go straight into metaphase of second meiotic division. The second meiotic division takes place just like mitosis.
This type of cell division takes place in reproductive organs (gonads) to produce gametes. The number of chromosomes in the gamete is half that in the mother cell.
Meiosis involves two divisions of the parental cell resulting into four daughter cells. The mother cell has the diploid number of chromosomes. The four cells (gametes) have half the number of chromosomes (haploid) that the mother cell had, in the first meiotic division there is a reduction in the chromosome number because homologous chromosomes and not chromatids separate.
Homologue pairs separate during a first round of cell division, called meiosis I. Sister chromatids separate during a second round, called meiosis II. Since cell division occurs twice during meiosis, one starting cell can produce four gametes (eggs or sperm). In each round of division, cells go through four stages: prophase, metaphase, anaphase, and telophase. [additional information by the Khan Academy]
Meiosis I (First Meiotic division)
Before entering meiosis I, a cell must first go through interphase. As in mitosis the cell prepares for division, this involves replication of chromosomes, organelles and buildup of energy to be used during the meiotic division.
- Prophase I
Homologous chromosomes lie side by side in the process of synapsis forming pairs called bivalents. Chromosomes shorten and thicken hence become more visible. Chromosomes may become coiled around each other and the chromatids may remain in contact at points called chiasmata (singular chiasma). Chromatids cross-over at the chiasmata exchanging chromatid portions. Important genetic changes usually result. - Metaphase I
Spindle fibres are fully formed and attached to the centromeres, the bivalents move to the equator of the spindles. - Anaphase I
Homologous chromosomes separate and migrate to opposite poles, this is brought about by shortening of spindle fibres hence pulling the chromosomes, the number of chromosomes at each pole is half the number in the mother cell. - Telophase I
Cytoplasm divides to separate the two daughter cells.
Usually the two daughter cells go into a short resting stage (interphase) but sometimes the chromosomes remain condensed and the daughter cells go straight into metaphase of second meiotic division. The second meiotic division takes place just like mitosis.
- Prophase II
each chromosome is seen as a pair of chromatids. - Metaphase II
Spindle forms and are attached to the chromatids at the centromeres, chromatids move to the equator. - Anaphase II
Sister Chromatids separate from each other, then move to opposite poles, pulled by the shortening of the spindle fibres. - Telophase II
The spindle apparatus disappears, the nucleolus reappears and nuclear membrane is formed around each set of chromatids. The chromatids become chromosomes, cytoplasm divides and four daughter cells are formed, each has a haploid number of chromosomes.
- Meiosis brings about formation of gametes that contain half the number of chromosomes as the parent cells.
- It helps to restore the diploid chromosomal constitution in a species at fertilisation.
- It brings about new gene combinations that lead to genetic variation in the offspring.
Asexual reproduction
Asexual reproduction is the formation of offspring from a single parent, the offspring are identical to the parent.
Types of asexual reproduction.
Types of asexual reproduction.
- Binary fission in amoeba.
- Spore formation in Rhizopus.
- Budding in yeast.
Binary fission in amoeba
This involves the division of the parent organism into two daughter cells, the nucleus first divides into two and then the cytoplasm separates into two portions. Binary fission also occurs in bacteria, Paramecium, Trypanosoma and Euglena.
Spore formation/reproduction in mucor / Rhizopus
Rhizopus is a saprophytic fungus which grows on various substrate such as bread, rotting fruits or other decaying organic matter. The vegetative body is called mycelium which has many branched threads called hyphae. Horizontal hyphae are called stolons, vertical hyphae are called sporangiophore.
The tips of sporangiophore become swollen to form sporangia, the spore bearing structure, each sporangium contains many spores, as it matures and ripens, it turns black in colour.
When fully mature the sporangium wall burst and release spores which are dispersed by wind or insects. When spores land on moist substratum, they germinate and grow into a new Rhizopus and start another generation.
Spore formation in ferns
The fern plant is called a sporophyte, on the lower side of the mature leaves are sari (Singular: sorus) which bear spores.
The tips of sporangiophore become swollen to form sporangia, the spore bearing structure, each sporangium contains many spores, as it matures and ripens, it turns black in colour.
When fully mature the sporangium wall burst and release spores which are dispersed by wind or insects. When spores land on moist substratum, they germinate and grow into a new Rhizopus and start another generation.
Spore formation in ferns
The fern plant is called a sporophyte, on the lower side of the mature leaves are sari (Singular: sorus) which bear spores.
Budding in yeast
Budding involves the formation of a protrusion called a bud from the body of the organism, the bud separates from the parent cell, in yeast budding goes on so fast and the first bud starts to form another bud before the separation. A short chain or mass of cells is formed.
WHAT IS ECOLOGY?
Introduction
Ecology, also called ‘bioecology’, ‘bionomics’, or ‘environmental biology’ is the scientific study of interactions among organisms and between organisms and their environment.
"The word ecology was coined by the German zoologist Ernst Haeckel, who applied the term oekologie to the “relation of the animal both to its organic as well as its inorganic environment.” The word comes from the Greek oikos, meaning “household,” “home,” or “place to live.”" Thus, ecology deals with the organism and its environment. [Source: britannica.com]
Ecology, also called ‘bioecology’, ‘bionomics’, or ‘environmental biology’ is the scientific study of interactions among organisms and between organisms and their environment.
"The word ecology was coined by the German zoologist Ernst Haeckel, who applied the term oekologie to the “relation of the animal both to its organic as well as its inorganic environment.” The word comes from the Greek oikos, meaning “household,” “home,” or “place to live.”" Thus, ecology deals with the organism and its environment. [Source: britannica.com]
Tree
Organisms are affected by their environment, and they in turn affect the environment. Green plants manufacture food by photosynthesis which other organisms obtain directly or indirectly.
Growth of plants is mainly affected by environmental factors such as soil and climatic factors, on the other hand, organisms modify the environment through various activities.
This interrelationship comprises the study of ecology, which is important in several fields of study such as agriculture and environmental studies.
Growth of plants is mainly affected by environmental factors such as soil and climatic factors, on the other hand, organisms modify the environment through various activities.
This interrelationship comprises the study of ecology, which is important in several fields of study such as agriculture and environmental studies.
Concepts of Ecology
Ecosystem
The community and the abiotic or non-living environment together make up an ecosystem or ecological system.
In this system energy flow is clearly defined from producers to consumers and nutrient cycling takes place in paths that links all the organisms and the non-living environment.
Habitat
This is the place or "home" that an organism lives or is found, e.g., forest or grassland.
Niche
A niche is the functional unit in the habitat which includes not only the specific place in which an organism lives but also how the organism functions. To avoid or reduce competition, organisms are separated or segregated by their niches, for example, different species of birds make their nest on one tree, some at tips of terminal branches, and others feed on leaves, some on flowers and yet others on fruits of the same tree, i.e., food niche.
Yet others feed on same food, e.g., worms in the same place but at different times - time niche.
Population
The term population refers to the total number of individuals of a species living in a given area at a particular time.
Density
Density is used in relation to population to refer to the number of individuals of a population found in a unit area.
Community
This is the term used to describe all the organisms living together in an area. During the development of an ecosystem, the species composition of a community changes progressively through stages.
Finally a steady state is reached and this is described as the climax community. This development of an ecosystem is termed succession. Each stage in development of an ecosystem is a sere.
(A seral community (or sere) is an intermediate stage found in ecological succession in an ecosystem advancing towards its climax community. In many cases more than one seral stage evolves until climax conditions are attained.)[Source: wikipedia.org].
Succession is primary when it starts with bare ground, and secondary when it starts in a previously inhabited area e.g. after clearing a forest.
Biomass
This is the mass of all the organisms in a given area, ideally, it is the dry mass that should be compared.
Dictionary.com defines biomass as; ‘the amount of living matter in a given habitat, expressed either as the weight of organisms per unit area or as the volume of organisms per unit volume of habitat.’
Carrying capacity
This is the maximum sustainable density in a given area e.g. the number of herbivores a given area can support without overgrazing.
Dispersion
This is the distribution of individuals in the available space.
Dispersion may be uniform as in maize plants in a plantation; random as in cactus plants in the savannah ecosystem or clumped together as in human population in cities.
The community and the abiotic or non-living environment together make up an ecosystem or ecological system.
In this system energy flow is clearly defined from producers to consumers and nutrient cycling takes place in paths that links all the organisms and the non-living environment.
Habitat
This is the place or "home" that an organism lives or is found, e.g., forest or grassland.
Niche
A niche is the functional unit in the habitat which includes not only the specific place in which an organism lives but also how the organism functions. To avoid or reduce competition, organisms are separated or segregated by their niches, for example, different species of birds make their nest on one tree, some at tips of terminal branches, and others feed on leaves, some on flowers and yet others on fruits of the same tree, i.e., food niche.
Yet others feed on same food, e.g., worms in the same place but at different times - time niche.
Population
The term population refers to the total number of individuals of a species living in a given area at a particular time.
Density
Density is used in relation to population to refer to the number of individuals of a population found in a unit area.
Community
This is the term used to describe all the organisms living together in an area. During the development of an ecosystem, the species composition of a community changes progressively through stages.
Finally a steady state is reached and this is described as the climax community. This development of an ecosystem is termed succession. Each stage in development of an ecosystem is a sere.
(A seral community (or sere) is an intermediate stage found in ecological succession in an ecosystem advancing towards its climax community. In many cases more than one seral stage evolves until climax conditions are attained.)[Source: wikipedia.org].
Succession is primary when it starts with bare ground, and secondary when it starts in a previously inhabited area e.g. after clearing a forest.
Biomass
This is the mass of all the organisms in a given area, ideally, it is the dry mass that should be compared.
Dictionary.com defines biomass as; ‘the amount of living matter in a given habitat, expressed either as the weight of organisms per unit area or as the volume of organisms per unit volume of habitat.’
Carrying capacity
This is the maximum sustainable density in a given area e.g. the number of herbivores a given area can support without overgrazing.
Dispersion
This is the distribution of individuals in the available space.
Dispersion may be uniform as in maize plants in a plantation; random as in cactus plants in the savannah ecosystem or clumped together as in human population in cities.
Ecology Practical Activities
- Ecology is best studied outdoors. Students identify a habitat within or near the school compound, e.g. a flower bed.
- The quadrat method is used.
- Observation and recording of the various animals as well as their feeding habits is done.
- Birds that feed on the plants or arthropods in the area studied are noted through observation of habitat at various times of the day.
- Food chains are constructed e.g. green plants ~ caterpillar ~ lizard and many others involving all organisms in the area.
- The numbers of animals in 1M squared is counted directly or estimated e.g. small arthropods like black ants.
- The number of plants is easily counted and recorded and ratio of consumers to producers calculated.
- It will be noted that in terms of numbers where invertebrates are involved, there are very many consumers of one plant.
- Several other quadrats are established and studied and averages calculated.
Adaptions to Habitat
Hydrophytes
- Specimen of hydrophytes e.g. water lily is observed.
- Students should note the poorly developed root systems and broad leaves.
- Stomata distribution on leaf surface is studied through microscopy or by immersing a leaf in hot water and counting number of bubbles evolved.
- Ordinary plants e.g bean hibiscus and zebrina can be studied.
- Size of leaves is noted and stomata distribution studied.
- Specimen include Euphorbia, cactus and sisal which are easily available.
- The root system e.g. in sisal is noted as shallow but extensive.
- It will be noted that sisal has fleshy leaves and stem while cactus and Euphorbia have fleshy stem but leaves are reduced to small hair-like structures.
Comparison of Root nodules from fertile and poor soils
Root nodules
- These are swellings on roots of leguminous plants.
- Soil fertility determines number of root nodules per plant.
- Bean plants are best used in this study.
- One plot can be manured while the other is not.
- Similar seeds are planted in the two plots.
- The plants are uprooted when fully mature (vegetatively) i.e. any time after flowering and before drying.
- The number of nodules per plant is counted.
- An average for each plot is calculated.
- It is noted that the beans from fertile soil have more and large nodules than those grown in poor soils.
Estimation of Population using Sampling Methods
- The number of organisms both producers and the various consumers is recorded in each area studied e.g. using a quadrat.
- The total area of the habitat studied is measured.
- The average number of organisms per quadrat (1 m2) is calculated after establishing as many quadrats as are necessary to cover the area adequately.
- Total population of organisms is calculated from the area.
- Abiotic environment is studied within the area sampled.
- Air temperature soil surface temperature are taken and recorded.
- This is best done at different times of day, i.e., morning afternoon and evening.
- Any variations are noted.
- pH of the soil is measured using pH distilled water to make a solution.
- Litmus papers can be used to indicate if soil is acidic or alkaline, but pH paper or meter gives more precise pH values.
- Humidity is measured using anhydrous blue cobalt chloride paper which gives a mere indication of level of humidity.
- A windsock is used to give an indication of direction of wind.
- As all the abiotic factors are recorded observations are made to find the relationships between behaviour of organism and the environmental factors for example:
- The temperature affects the behaviour of animals.
- The direction of wind will affect growth of plants.
- The level of humidity determines the type, number and distribution of organisms in an area.
Energy Flow in an Ecosystem
Most of the energy used in an ecosystem is derived from the sun. Solar energy is trapped by photosynthetic plants.
It flows through different trophic levels and at each level energy is lost as heat to space and also through respiration.
Besides animals lose energy through excretion and defecation, the amount of energy passed on as food from one trophic level to another decreases progressively.
The energy in the organisms is recycled back to plants through the various nutrient or material cycles.
It flows through different trophic levels and at each level energy is lost as heat to space and also through respiration.
Besides animals lose energy through excretion and defecation, the amount of energy passed on as food from one trophic level to another decreases progressively.
The energy in the organisms is recycled back to plants through the various nutrient or material cycles.
Food Chains
A food chain is a linear relationship between producers and consumers. It represents the transfer of food energy from green plants through repeated stages of eating and being eaten.
Types of Food Chain
Detritivores feed on organic wastes and dead matter derived from the grazing food chain. Many different types of organisms feed on detritus, they include fungi, protozoa, insects, mites annelids and nematodes.
Types of Food Chain
- Grazing food chain - starts with green plants.
- Detritus food chain - starts with dead organic material (debris or detritus).
Detritivores feed on organic wastes and dead matter derived from the grazing food chain. Many different types of organisms feed on detritus, they include fungi, protozoa, insects, mites annelids and nematodes.
Food Web
In a natural community, several food chains are interlinked to form a food web.
Several herbivores may feed on one plant, similarly, a given herbivore may feed on different plants and may in turn be eaten by different carnivores.
Decomposers
These are mainly bacteria and fungi. These organisms feed on dead organic matter thereby causing decomposition and decay and releasing nutrients for plants. They form a link between the biotic and the abiotic components.
Pyramid of Numbers
Refers to the number of organisms in each trophic level presented in a graphic form and a pyramid shape is obtained.
The length of each bar is drawn proportional to the number of organisms represented at that level.
This is because an herbivore feeds on many green plants. One carnivore also feeds on many herbivores.
In a forest the shape of the pyramid is not perfect, this is because very many small animals such as insects, rodents and birds feed on one tree.
Pyramid of Biomass
This is the mass of the producers and consumers at each trophic level drawn graphically.
In a natural community, several food chains are interlinked to form a food web.
Several herbivores may feed on one plant, similarly, a given herbivore may feed on different plants and may in turn be eaten by different carnivores.
Decomposers
These are mainly bacteria and fungi. These organisms feed on dead organic matter thereby causing decomposition and decay and releasing nutrients for plants. They form a link between the biotic and the abiotic components.
Pyramid of Numbers
Refers to the number of organisms in each trophic level presented in a graphic form and a pyramid shape is obtained.
The length of each bar is drawn proportional to the number of organisms represented at that level.
This is because an herbivore feeds on many green plants. One carnivore also feeds on many herbivores.
In a forest the shape of the pyramid is not perfect, this is because very many small animals such as insects, rodents and birds feed on one tree.
Pyramid of Biomass
This is the mass of the producers and consumers at each trophic level drawn graphically.
Population Estimation Methods
It is important to find or estimate the sizes of the different populations in a habitat. Direct counting or head count which involves the counting of every individual, is not always applicable for all organisms. e.g., it is impossible to count directly the numbers of grasshoppers in an area.
Different sampling methods are thus used; a sample acts as a representative of the whole population. .
Different sampling methods are thus used; a sample acts as a representative of the whole population. .
Sampling Methods
Quadrat Method
A Quadrat is a square, made of wood’s metal/hard plastic. It can also be established on the ground using pegs, rope/permanent coloured ink, using metre rule or measuring tape. The size is usually one square metre (1M2), in grassland.
In wooded or forest habitat it is usually larger, and can reach up to 20 m2 depending on particular species under investigation. The number of each species found within the quadrat is counted and recorded. Total number of organisms is then calculated by, finding the average quadrats and multiplying it with the total area of the whole habitat.
The number of quadrats and their positions is determined by the type of vegetation studied.
In a grassland, the quadrat frame can be thrown at random. In other habitats of forest, random numbers that determine the locus at which to establish a quadrat are used.
Line Transect
A line transect is a string or rope that is stretched along across the area in which all the plants that are touched are counted.
It is tied on to a pole or tent peg.
It is particularly useful where there is change of populations traversing through grassland, to woodland to forest land.
This method can also be used in studying the changes in growth patterns in plants over a period of time.
Belt Transect
Two line transects are set parallel to each other to enclose a strip through the habitat to be studied. The width is determined by the type of habitat, i.e., grass or forest and by the nature of investigation.
In grassland it can be 0.5 m or 1 m. Sometimes it can be 20 metres or more especially when counting large herbivores. The number of organisms within the belt is counted and recorded.
Capture-recapture method
This is used for animals such as fish, rodents, arthropods and birds.
The animals are caught, marked, counted and released. For example, grasshoppers can be caught with a net and marked using permanent ink. After sometime, the same area is sampled again, i.e., the grasshoppers are caught again. The total number caught during the second catch is recorded.
The number of marked ones is also recorded:
A Quadrat is a square, made of wood’s metal/hard plastic. It can also be established on the ground using pegs, rope/permanent coloured ink, using metre rule or measuring tape. The size is usually one square metre (1M2), in grassland.
In wooded or forest habitat it is usually larger, and can reach up to 20 m2 depending on particular species under investigation. The number of each species found within the quadrat is counted and recorded. Total number of organisms is then calculated by, finding the average quadrats and multiplying it with the total area of the whole habitat.
The number of quadrats and their positions is determined by the type of vegetation studied.
In a grassland, the quadrat frame can be thrown at random. In other habitats of forest, random numbers that determine the locus at which to establish a quadrat are used.
Line Transect
A line transect is a string or rope that is stretched along across the area in which all the plants that are touched are counted.
It is tied on to a pole or tent peg.
It is particularly useful where there is change of populations traversing through grassland, to woodland to forest land.
This method can also be used in studying the changes in growth patterns in plants over a period of time.
Belt Transect
Two line transects are set parallel to each other to enclose a strip through the habitat to be studied. The width is determined by the type of habitat, i.e., grass or forest and by the nature of investigation.
In grassland it can be 0.5 m or 1 m. Sometimes it can be 20 metres or more especially when counting large herbivores. The number of organisms within the belt is counted and recorded.
Capture-recapture method
This is used for animals such as fish, rodents, arthropods and birds.
The animals are caught, marked, counted and released. For example, grasshoppers can be caught with a net and marked using permanent ink. After sometime, the same area is sampled again, i.e., the grasshoppers are caught again. The total number caught during the second catch is recorded.
The number of marked ones is also recorded:
- Let the number caught and marked be a.
- The total number in the second catch be b.
- The number of marked ones in the second catch be c.
- The total number of grasshoppers in the area be T.
- The total number T can be estimated using the following formula:
The following assumptions are made:
Density is calculated by dividing the number of organisms by the size of the area studied.
Frequency:
Frequency is the number of times that a species occurs in the area being studied.
Percentage Cover:
This is the proportion of the area covered by a particular species. For example, a given plant species may cover the whole of a given area. In this case the plant is said to have 100% cover.
Dominance:
This is the term used to describe a species that exerts the most effect on others. The dominance may be in terms of high frequency or high density.
- No migration, i.e., no movement in and out of the study area.
- There is even distribution of the organisms in the study area.
- There is random distribution of the organisms after the first capture.
- No births or deaths during the activity.
- After the estimation, the results can be used to show anyone of the following population characteristics:
Density is calculated by dividing the number of organisms by the size of the area studied.
Frequency:
Frequency is the number of times that a species occurs in the area being studied.
Percentage Cover:
This is the proportion of the area covered by a particular species. For example, a given plant species may cover the whole of a given area. In this case the plant is said to have 100% cover.
Dominance:
This is the term used to describe a species that exerts the most effect on others. The dominance may be in terms of high frequency or high density.
Adaptations of Plants to Various Habitats
Organisms have developed structural features that enable them to live successfully in their particular habitats. Plants found beneath the canopies of trees are adapted to low light intensities by having broad leaves.
Xerophytes
These are plants that grow in dry habitats, i.e., in deserts and semi-deserts.
They have adaptations to reduce the rate of transpiration in order to save on water consumption. Others have water storage structures.
Adaptations include:
These are the ordinary land plants which grow in well-watered habitats and have no special adaptations.
Stomata are found on both upper and lower leaf surfaces for efficient gaseous exchange and transpiration.
However, those found in constantly wet places e.g. tropical rain forests, have features that increase transpiration.
These plants are called hygrophytes.
The leaves are broad to increase surface areas for transpiration and thin to ensure short distance for carbon (IV) oxide to reach photosynthetic cells and for light penetration. The stomata are raised above the epidermis to increase the rate of transpiration. They have grandular hairs or byhathodes that expel water into the saturated atmosphere. This phenomenon is called guttation.
Hydrophytes (Water plants)
Water plants are either submerged, emergent or floating.
Submerged Plants
The leaves have an epidermis with very thin walls and a delicate cuticle.
They have no stomata.
Water is excreted from special glands and pores at the tips.
Other adaptations include the following:
Their structure is similar to that of mesophytes.
The leaves are broad to increase the surface area for water loss.
They have more stomata on the upper surface than on the lower surface to increase rate of water loss. Examples are Pistia sp. (water lettuce), Salvinia and Nymphea.
Halophytes (Salt plants)
These are plants that grow in salt marshes and on coastlines, have root cells that concentrate salts and enable them to take in water by osmosis; they also have salt glands which excrete salts.
Fruits have large aerenchymatous tissues for air storage that makes them float, Some have shiny leaves to reduce water loss. The mangrove plants have roots that spread horizontally, and send some branches into the air.
These aerial roots are known as breathing roots or pneumatophores. They also have lenticel-Iike openings called pneumatothodes through which gaseous exchange takes place.
Xerophytes
These are plants that grow in dry habitats, i.e., in deserts and semi-deserts.
They have adaptations to reduce the rate of transpiration in order to save on water consumption. Others have water storage structures.
Adaptations include:
- Reduction of leaf surface area by having needle-like leaves, rolling up of leaves and shedding of leaves during drought to reduce water loss or transpiration.
- Thick cuticle; epidermis consisting of several layers of cells;
- Leafs covered with wax or resin to reduce evaporation.
- Sunken stomata, creating spaces with humid still air to reduce water holes.
- Few, small stomata, on lower epidermis to reduce water loss.
- Stomata open at night (reversed stomatal rhythm) to reduce water loss.
- Deep and extensive root systems for absorption of water.
- Development of flattened shoots and succulent tissue for water storage e.g. Opuntia.
These are the ordinary land plants which grow in well-watered habitats and have no special adaptations.
Stomata are found on both upper and lower leaf surfaces for efficient gaseous exchange and transpiration.
However, those found in constantly wet places e.g. tropical rain forests, have features that increase transpiration.
These plants are called hygrophytes.
The leaves are broad to increase surface areas for transpiration and thin to ensure short distance for carbon (IV) oxide to reach photosynthetic cells and for light penetration. The stomata are raised above the epidermis to increase the rate of transpiration. They have grandular hairs or byhathodes that expel water into the saturated atmosphere. This phenomenon is called guttation.
Hydrophytes (Water plants)
Water plants are either submerged, emergent or floating.
Submerged Plants
The leaves have an epidermis with very thin walls and a delicate cuticle.
They have no stomata.
Water is excreted from special glands and pores at the tips.
Other adaptations include the following:
- Presence of large air spaces and canals (aerenchyma) for gaseous exchange and buoyancy.
- Some plants have filamentous leaves In order to increase the surface area for absorption of light, gases and mineral salts.
- Some plants are rootless, hence support provided by water.
- Mineral salts and water absorbed by all plant surfaces.
- In some plants, the stem and leaves are covered with a waxy substance to reduce absorption of water. e.g. Ceratophyllum and Elodea sp.
Their structure is similar to that of mesophytes.
The leaves are broad to increase the surface area for water loss.
They have more stomata on the upper surface than on the lower surface to increase rate of water loss. Examples are Pistia sp. (water lettuce), Salvinia and Nymphea.
Halophytes (Salt plants)
These are plants that grow in salt marshes and on coastlines, have root cells that concentrate salts and enable them to take in water by osmosis; they also have salt glands which excrete salts.
Fruits have large aerenchymatous tissues for air storage that makes them float, Some have shiny leaves to reduce water loss. The mangrove plants have roots that spread horizontally, and send some branches into the air.
These aerial roots are known as breathing roots or pneumatophores. They also have lenticel-Iike openings called pneumatothodes through which gaseous exchange takes place.
Effect of Pollution on Human Beings and other Organisms
Pollution
This is the introduction of foreign material, poisonous compounds and excess nutrients or energy to the environment in harmful proportions. Any such substance is called a pollutant.
Effects and Control of causes of Pollutants in Air, Water and Soil
Industrialisation and urbanisation are the main causes of pollution.
As human beings exploit natural resources the delicate balance in the biosphere gets disturbed.
The disturbance leads to the creation of conditions that are un-favourable to humans and other organisms.
Sources of Pollutants
In most cases, chex, pical wastes from industries are discharged into water. Toxic chemicals such as mercury compounds may be ingested by organisms. Insecticides like DDT, and weedkillers eventually get into the water and contaminate it.
Oil and detergents also pollute water. Excess nitrates and phosphates from sewage and fertilisers cause overgrowth of algae and bacteria in water. This is called eutrophication.
As a result there is insufficient oxygen which causes the deaths of animals in the water.
Air pollution:
Smoke from industries and motor vehicles contains poisonous chemicals like carbon (II) oxide, carbon (IV) oxide, sulphur (IV) oxide and oxides of nitrogen.
When sulphur (IV) oxide and oxides of nitrogen dissolve in rain, they fall as acid rain.
Accumulation of carbon (IV) oxide in the atmosphere causes the infrared light to be confined within the atmosphere, the earth's temperature rises. This is called the greenhouse effect.
Carbon particles in smoke coat the leaves of plants and hinder gaseous exchange and photosynthesis. The particles also form smog in the air. Lead compounds are from vehicle exhaust pipes. All these have negative effects on man and the environment.
Soil/Land pollution:
Plastics and other man-made materials are biologically non-degradable i.e they are not acted upon by micro-organisms. Scrap metal and slag from mines also pollute land.
Failure to rehabilitate mines and quarries also pollute land.
Effects of Pollutants to Humans and other organisms
This is the introduction of foreign material, poisonous compounds and excess nutrients or energy to the environment in harmful proportions. Any such substance is called a pollutant.
Effects and Control of causes of Pollutants in Air, Water and Soil
Industrialisation and urbanisation are the main causes of pollution.
As human beings exploit natural resources the delicate balance in the biosphere gets disturbed.
The disturbance leads to the creation of conditions that are un-favourable to humans and other organisms.
Sources of Pollutants
- Motor vehicles release carbon (II) oxide, sulphur (IV) oxide, and nitrogen oxides and hydrocarbons.
- Agricultural chemicals, fertilisers and pesticides.
- Factories, manufacturing and metal processing industries.
- They release toxic substances and gases as well as synthetic compounds that are bio-undegradable.
- They release solid particles or droplets of poisonous substances e.g. arsenic, beryllium, lead and cadmium.
- Radioactive waste: Leakages from nuclear power stations and testing sites release radioactive elements like strontium-90 which can eventually reach man through the food chain.
- Domestic waste and sewage are released raw into water bodies.
- Oil spills from accidents in the seas and leakage of oil tankers as well as from offshore drilling and storage and processing.
In most cases, chex, pical wastes from industries are discharged into water. Toxic chemicals such as mercury compounds may be ingested by organisms. Insecticides like DDT, and weedkillers eventually get into the water and contaminate it.
Oil and detergents also pollute water. Excess nitrates and phosphates from sewage and fertilisers cause overgrowth of algae and bacteria in water. This is called eutrophication.
As a result there is insufficient oxygen which causes the deaths of animals in the water.
Air pollution:
Smoke from industries and motor vehicles contains poisonous chemicals like carbon (II) oxide, carbon (IV) oxide, sulphur (IV) oxide and oxides of nitrogen.
When sulphur (IV) oxide and oxides of nitrogen dissolve in rain, they fall as acid rain.
Accumulation of carbon (IV) oxide in the atmosphere causes the infrared light to be confined within the atmosphere, the earth's temperature rises. This is called the greenhouse effect.
Carbon particles in smoke coat the leaves of plants and hinder gaseous exchange and photosynthesis. The particles also form smog in the air. Lead compounds are from vehicle exhaust pipes. All these have negative effects on man and the environment.
Soil/Land pollution:
Plastics and other man-made materials are biologically non-degradable i.e they are not acted upon by micro-organisms. Scrap metal and slag from mines also pollute land.
Failure to rehabilitate mines and quarries also pollute land.
Effects of Pollutants to Humans and other organisms
- Chemical pollutants e.g. nitrogen oxides, fluorides, mercury and lead cause physiological and metabolic disorders to humans and domestic animals.
- Some hydrocarbons as well as radioactive pollutants acts as mutagens (cause mutations) and carcinogens induce cancer.
- Radioactive pollutants like strontium, caesium and lithium are absorbed into body surface and cause harm to bone marrow and the thyroid gland.
- Communicable diseases like cholera are spread through water polluted with sewage.
- Thermal pollution result in death of some fish due to decreased oxygen in the water.
- Oil spills disrupt normal functioning of coastal ecosystems.
- Birds that eat fish die due to inability to fly as feathers get covered by oil.
- Molluscs and crustaceans on rocky shores also die.
- Use of lead-free petrol and low sulphur diesel in vehicles.
- Use of smokeless fuels e.g electricity or solar.
- Filtration of waste gases to remove harmful gases.
- Liquid dissolution of waste gases.
- In Kenya, factories are subjected to thorough audits to ensure that they do not pollute the environment.
- Factories should be erected far away from residential areas.
- Reduce volume or intensity of sound.
- Use of ear muffs.
- Vehicle exhaust systems should be fitted with catalytic oxidisers.
- Regular servicing of vehicles to ensure complete combustion of fuel.
- Treatment of sewage.
- Treatment of industrial waste before discharge into water.
- Use of controlled amounts of agrochemicals.
- Organic farming and biological control.
- Avoid spillage of oils and other chemicals into water.
- Good water management.
- Stiff penalties for oil spillage.
- Use of Pseudomonas bacteria that naturally feed on oil and break it up.
- Addition of lime to farms to counteract the effect of agrochemicals.
- Recycling of solid waste.
- Compacting and incineration of solid waste.
- Use of biodegradable materials and chemicals.
- Good soil management to avoid soil erosion.
Human diseases
The term disease denotes any condition or disorder that disrupts the steady state of wellbeing of the body.
Health is a state of physical, mental and emotional wellbeing in the internal environment of the body.
Some of the causes of diseases are due to entry of pathogens and parasites. Pathogens include bacteria, viruses, protozoa and fungi.
Parasites are organisms which live on or in the body of another organisms.
Vectors are animals that carry the pathogen from one person to another. Most are ectoparasites that transmit the disease as they feed.
Health is a state of physical, mental and emotional wellbeing in the internal environment of the body.
Some of the causes of diseases are due to entry of pathogens and parasites. Pathogens include bacteria, viruses, protozoa and fungi.
Parasites are organisms which live on or in the body of another organisms.
Vectors are animals that carry the pathogen from one person to another. Most are ectoparasites that transmit the disease as they feed.
FEMALE ANOPHELES MOSQUITOES SPREAD MALARIA
Bacterial diseases - Cholera and Typhoid
Cholera
Causative agent is a bacterium Vibrio cholerae.
Transmission
It is spread through water and food contaminated by human faeces containing the bacteria. The bacteria produce a powerful toxin, enterotoxin that causes inflammation of the wall of the intestine leading to:
Carriers should be identified, isolated and treated during outbreaks.
Treatment
Causative agent is a bacterium Vibrio cholerae.
Transmission
It is spread through water and food contaminated by human faeces containing the bacteria. The bacteria produce a powerful toxin, enterotoxin that causes inflammation of the wall of the intestine leading to:
- Severe diarrhoea that leads to excessive water loss from body.
- Abdominal pain
- Vomiting
- Dehydration which may lead to death.
- Adequate sanitation such as water purification sewage treatment and proper disposal of human faeces.
- Public and personal hygiene e.g. washing hands before meals and washing fruits and vegetables, boiling drinking water.
Carriers should be identified, isolated and treated during outbreaks.
Treatment
- Use of appropriate antibiotics.
- Correcting fluid loss by injecting fluids or by administration of oral rehydration solutions.
Typhoid
Causative agent
The term disease causative agent usually refers to the biological pathogen that causes a disease, such as a virus, parasite, fungus, or bacterium. Technically, the term can also refer to a toxin or toxic chemical that causes illness. [Source: wikipedia.org]
Causative agent
The term disease causative agent usually refers to the biological pathogen that causes a disease, such as a virus, parasite, fungus, or bacterium. Technically, the term can also refer to a toxin or toxic chemical that causes illness. [Source: wikipedia.org]
- The disease is caused by Salmonella typhi.
- Transmission is through contaminated water and food. It is also transmitted by certain 'e.g. foods, e.g. oysters, mussels and shell fish.
- Fever
- Muscle pains
- Headache
- Spots on the trunk of the body
- Diarrhoea
- In severe cases mental confusion may result and death.
- Boil drinking water.
- Proper sewage treatment.
- Proper disposal of faeces, if not flushed use deep pit latrines.
- Observe personal hygiene e.g. washing hands before meals.
- Washing fruits and vegetables.
- Use of appropriate antibiotics.
Protozoa - Malaria and Amoebic dysentry (Amoebiasis)
Malaria
Use appropriate anti-malarial drugs.
- Malaria is caused by the protozoan plasmodium.
- The most common species of plasmodium are P. falciparum, P. vivax, P. rnalariae and P. ovale with varying degree of severity.
- Is by female anopheles mosquito as it gets a blood meal.
- Headache, sweating, shivering, high temperature (40-41 0C) chills and joint pains.
- The abdomen becomes tender due to destruction of red blood cells by the parasites.
- Destroy breeding grounds for mosquitoes by clearing bushes and draining stagnant water.
- Kill mosquito larvae by spraying water surfaces with oil.
- Use insecticides to kill adult mosquitoes
- Sleeping under a mosquito net.
- Take preventive drugs.
Use appropriate anti-malarial drugs.
Amoebic dysentry (Amoebiasis)
Causes
This disease is caused by Entamoeba histolytica. The parasites live in the intestinal tract but may occasionally spread to the liver. Transmission - They are transmitted through contaminated water and food especially salads.
Symptoms
Treatment of infected people with appropriate drugs.
Causes
This disease is caused by Entamoeba histolytica. The parasites live in the intestinal tract but may occasionally spread to the liver. Transmission - They are transmitted through contaminated water and food especially salads.
Symptoms
- Abdominal pain, nausea and diarrhoea.
- The parasites cause ulceration of the intestinal tract, which results in diarrhoea.
- Proper disposal of human faeces.
- Boiling water before drinking.
- Personal hygiene e.g. washing hands before meals.
- Washing vegetables and steaming particularly salads and fruits before eating.
Treatment of infected people with appropriate drugs.
Ascaris lumbricoides and Schistosoma
Ascaris lumbricoides
Ascaris lumbricoides lives in the intestines of a man or pig, feeding on the digested food of the host.
The body of the worm is tapered at both ends.
The female is longer than the male.
Mode of transmission
Deworm using appropriate drugs - ant-helminthic.
Ascaris lumbricoides lives in the intestines of a man or pig, feeding on the digested food of the host.
The body of the worm is tapered at both ends.
The female is longer than the male.
Mode of transmission
- The host eats food contaminated with the eggs, the embryo worms hatch out in the intestine.
- The embryo worms then bore into the blood vessels of the intestine.
- They are carried in the bloodstream to the heart and then into the lungs.
- As they travel through the bloodstream, they grow in size.
- After sometime, the worms are coughed out from the air passages and into the oesophagus.
- They are then swallowed, eventually finding their way into the intestines where they grow into mature worms.
- The parasites feed on the host's digested food.
- This results in malnutrition especially in children.
- If the worms are too many, they may block the intestine and interfere with digestion.
- The worms sometimes wander along the alimentary canal and may pass through the nose or mouth.
- In this way, they interfere with breathing and may cause serious illness.
- The larvae may cause severe internal bleeding as they penetrate the wall of the intestine.
- The female lays as many as 25 million eggs.
- This ensures the continuation of the species.
- Eggs are covered by a protective cuticle that prevents them from dehydration.
- The adult worms tolerate low oxygen concentration.
- Have mouth parts for sucking food and other fluids in the intestines.
- Has a thick cuticle or pellicle to protect it from digestive enzymes produced by the host.
- Personal hygiene e.g. washing hands before eating.
- Proper disposal of faeces.
- Washing of fruits and vegetables.
Deworm using appropriate drugs - ant-helminthic.
Schistosoma
Schistosoma or bilharzia worm is a flat worm, parasitic on human beings and fresh water snails. (Biomphalaria and Bulinus). The snail act as intermediate host.
Mode of Transmission
Schistosomiasis also known as a bilharsiasis is caused by several species of the genus schistosoma. Schistosoma haematobium - infects the urinary system mainly the bladder. S. japonicum and S. mansoni both infect the intestines. Schistosoma haemotobium is common in East Africa where irrigation is practised and where slow moving fresh water streams harbour snails.
It is spread through contamination of water by faeces and urine from infected persons. The embryo (miracidium) that hatch in water penetrates into snails of the species Biompharahia and Bulinus. Inside the snail's body, the miracidium undergoes development and multiple fission to produce rediae. The rediae are released into the water and develop to form cercariae which infect human through:
Effects on the host
Schistosoma or bilharzia worm is a flat worm, parasitic on human beings and fresh water snails. (Biomphalaria and Bulinus). The snail act as intermediate host.
Mode of Transmission
Schistosomiasis also known as a bilharsiasis is caused by several species of the genus schistosoma. Schistosoma haematobium - infects the urinary system mainly the bladder. S. japonicum and S. mansoni both infect the intestines. Schistosoma haemotobium is common in East Africa where irrigation is practised and where slow moving fresh water streams harbour snails.
It is spread through contamination of water by faeces and urine from infected persons. The embryo (miracidium) that hatch in water penetrates into snails of the species Biompharahia and Bulinus. Inside the snail's body, the miracidium undergoes development and multiple fission to produce rediae. The rediae are released into the water and develop to form cercariae which infect human through:
- Drinking the water
- Wading in water;
- Bathing in snail-infested water.
Effects on the host
- Inflammation of tissues where egg lodge.
- Ulceration where eggs calcify.
- Egg block small arteries in lungs leading to less aeration of blood.
- The body turns blue - a condition known as cyanosis.
- If eggs lodge in heart or brain, lesions formed can lead to death.
- Bleeding occurs as the worms burrow into blood vessels (faeces or urine has blood).
- Pain and difficulty in passing out urine.
- Nausea and vomiting.
- When eggs lodge in liver ulceration results in liver cirrhosis.
- Death eventually occurs.
- The female has a thin body and fits into small blood vessels to lay eggs.
- Eggs are able to burrow out of blood vessel into intestine lumen.
- Many eggs are laid to ensure the survival of the parasite.
- Large numbers of cercariae are released by snail.
- The miracidia and cercariae larvae have glands that secrete lytic enzymes which soften the tissue to allow for penetration into host.
- The male has a gynecophoric canal that carries the female to ensure that eggs are fertilised before being shed.
- Has suckers for attachment.
- Drain all stagnant water
- Boil drinking water.
- Do not wade bare feet in water.
- Wear long rubber boots and gloves (for those who work in rice fields).
- Eliminate snails, by spraying with molluscides.
- Reporting to doctor early when symptoms appear for early treatment.
Specific Objectives
By the end of the topic, the learner should be able to:
- Explain the significance of respiration in living organisms
- Distinguish between aerobic and anaerobic respiration
- Describe the economic importance of anaerobic respiration in industry and at home
- Describe experiments to show that respiration takes place in plants and animals.
topics/subtopics outline
Meaning and significance of respiration
Tissue respiration
1. Mitochondrion - structure and function
2. Aerobic respiration (Details of kreb's cycle not required)
3. Anaerobic respiration in plants and animals, the products and byproducts
4. Application of anaerobic respiration in industry and at home
5. Compare the energy output of aerobic and anaerobic respiration78
Practical Activities
1. Carry out experiments to investigate
2. The gas produced when food is burnt
3. The gas produced during fermentation
4. Heat production by germinating seeds
Tissue respiration
1. Mitochondrion - structure and function
2. Aerobic respiration (Details of kreb's cycle not required)
3. Anaerobic respiration in plants and animals, the products and byproducts
4. Application of anaerobic respiration in industry and at home
5. Compare the energy output of aerobic and anaerobic respiration78
Practical Activities
1. Carry out experiments to investigate
2. The gas produced when food is burnt
3. The gas produced during fermentation
4. Heat production by germinating seeds
Meaning and Significance of Respiration
Respiration is the process by which energy is liberated from organic compounds such as glucose.
It is one of the most important characteristics of living organisms.
Energy is expended (used) whenever an organism exhibits characteristics of life, such as feeding, excretion and movement.
Respiration occurs all the time and if it stops, cellular activities are disrupted due to lack of energy.
This may result in death e.g., if cells in brain lack oxygen that is needed for respiration for a short time, death may occur.
This is because living cells need energy in order to perform the numerous activities necessary to maintain life.
The energy is used in the cells and much of it is also lost as heat.
In humans it is used to maintain a constant body temperature.
It is one of the most important characteristics of living organisms.
Energy is expended (used) whenever an organism exhibits characteristics of life, such as feeding, excretion and movement.
Respiration occurs all the time and if it stops, cellular activities are disrupted due to lack of energy.
This may result in death e.g., if cells in brain lack oxygen that is needed for respiration for a short time, death may occur.
This is because living cells need energy in order to perform the numerous activities necessary to maintain life.
The energy is used in the cells and much of it is also lost as heat.
In humans it is used to maintain a constant body temperature.
Tissue Respiration
- Respiration takes place inside cells in all tissues.
- Every living cell requires energy to stay alive.
- Most organisms require oxygen of the air for respiration and this takes place in the mitochondria.
Mitochondrion Structure and Function
Structure
Adaptations of Mitochondrion to its Function
- Mitochondria are rod-shaped organelles found in the cytoplasm of cells.
- A mitochondrion has a smooth outer membrane and a folded inner membrane.
- The folding of the inner membrane is called cristae and the inner compartment is called the matrix.
Adaptations of Mitochondrion to its Function
- The matrix contains DNA ribosomes for making proteins and has enzymes for the breakdown of pyruvate to carbon (IV) oxide, hydrogen ions and electrons.
- Cristae increase surface area of mitochondrial inner membranes where attachment of enzymes needed for the transport of hydrogen ions and electrons are found.
- There are two types of respiration:
- Aerobic Respiration
- Anaerobic. Respiration
Aerobic Respiration
- This involves breakdown of organic substances in tissue cells in the presence of oxygen.
- All multicellular organisms and most unicellular organisms e.g. some bacteria respire aerobically.
- In the process, glucose is fully broken down to carbon (IV) oxide and hydrogen which forms water when it combines with the oxygen.
- Energy produced is used to make an energy rich compound known as adenosine triphosphate (ATP).
- It consists of adenine, an organic base, five carbon ribose-sugar and three phosphate groups.
- ATP is synthesised from adenosine diphosphate (ADP) and inorganic phosphate.
- The last bond connecting the phosphate group is a high-energy bond.
- Cellular activities depend directly on ATP as an energy source.
- When an ATP molecule is broken down, it yields energy.
- The breakdown of glucose takes place in many steps.
- Each step is catalysed by a specific enzyme.
- Energy is released in some of these steps and as a result molecules of ATP are synthesised.
- All the steps can be grouped into three main stages:
- The initial steps in the breakdown of glucose are referred to as glycolysis and they take place in the cytoplasm.
- Glycolysis consists of reactions in which glucose is gradually broken down into molecules of a carbon compound called pyruvic acid or pyruvate.
- Before glucose can be broken, it is first activated through addition of energy from ATP and phosphate groups.
- This is referred to as phosphorylation.
- The phosphorylated sugar is broken down into two molecules of a 3-carbon sugar (triose sugar) each of which is then converted into pyruvic acid.
- If oxygen is present, pyruvic acid is converted into a 2-carbon compound called acetyl coenzyme A (acetyl Co A).
- Glycolysis results in the net production of two molecules of ATP.
- The next series of reactions involve decarboxylation i.e. removal of carbon as carbon (IV) oxide and dehydrogenation, removal of hydrogen as hydrogen ions and electrons.
- These reactions occur in the mitochondria and constitute the Tri-carboxylic Acid Cycle (T.C.A.) or Kreb's citric acid cycle.
- The acetyl Co A combines with 4-carbon compound with oxalo-acetic acid to form citric acid - a 6 carbon compound.
- The citric acid is incorporated into a cyclical series of reactions that result in removal of carbon (IV) oxide molecules, four pairs of hydrogen, ions and electrons.
- Hydrogen ions and electrons are taken to the inner mitochondria membrane where enzymes and electron carriers effect release of a lot of energy.
- Hydrogen finally combines with oxygen to form water, and 36 molecules of ATP are synthesised.
Anaerobic Respiration
Anaerobic respiration involves breakdown of organic substances in the absence of oxygen.
It takes place in some bacteria and some fungi.
Organisms which obtain energy by anaerobic respiration are referred to as anaerobes.
Obligate anaerobes are those organisms which do not require oxygen at all and may even die if oxygen is present.
Facultative anaerobes are those organisms which survive either in the absence or in the presence of oxygen.
Such organisms tend to thrive better when oxygen is present e.g. yeast.
Products of Anaerobic Respiration
The products of anaerobic respiration differ according to whether the process is occurring in plants or animals.
Anaerobic Respiration in Plants
Glucose is broken down to an alcohol, (ethanol) and carbon (IV) oxide.
The breakdown is incomplete.
Ethanol is an organic compound, which can be broken down further in the presence of oxygen to provide energy, carbon (IV) oxide and water.
It takes place in some bacteria and some fungi.
Organisms which obtain energy by anaerobic respiration are referred to as anaerobes.
Obligate anaerobes are those organisms which do not require oxygen at all and may even die if oxygen is present.
Facultative anaerobes are those organisms which survive either in the absence or in the presence of oxygen.
Such organisms tend to thrive better when oxygen is present e.g. yeast.
Products of Anaerobic Respiration
The products of anaerobic respiration differ according to whether the process is occurring in plants or animals.
Anaerobic Respiration in Plants
Glucose is broken down to an alcohol, (ethanol) and carbon (IV) oxide.
The breakdown is incomplete.
Ethanol is an organic compound, which can be broken down further in the presence of oxygen to provide energy, carbon (IV) oxide and water.
Fermentation
This is the term used to describe formation of ethanol and carbon (IV) oxide from grains
Yeast cells have enzymes that bring about anaerobic respiration.
Lactate Fermentation
This is the term given to anaerobic respiration in certain bacteria that results in formation of lactic acid
Anaerobic Respiration in Animals
Anaerobic respiration in animals produces lactic acid and energy.
Yeast cells have enzymes that bring about anaerobic respiration.
Lactate Fermentation
This is the term given to anaerobic respiration in certain bacteria that results in formation of lactic acid
Anaerobic Respiration in Animals
Anaerobic respiration in animals produces lactic acid and energy.
When human muscles are involved in very vigorous activity, oxygen cannot be delivered as rapidly as it is required.
The muscle respire anaerobically and lactic acid accumulates.
A high level of lactic acid is toxic.
During the period of exercise, the body builds up an oxygen debt.
After vigorous activity, one has to breathe faster and deeper to take in more oxygen.
Rapid breathing occurs in order to break down lactic acid into carbon (IV) oxide and water and release more energy.
Oxygen debt therefore refers to the extra oxygen the body takes in after vigorous exercise.
The muscle respire anaerobically and lactic acid accumulates.
A high level of lactic acid is toxic.
During the period of exercise, the body builds up an oxygen debt.
After vigorous activity, one has to breathe faster and deeper to take in more oxygen.
Rapid breathing occurs in order to break down lactic acid into carbon (IV) oxide and water and release more energy.
Oxygen debt therefore refers to the extra oxygen the body takes in after vigorous exercise.
Practical Activities
To Show the Gas Produced When the Food is burned
- A little food substance e.g., maize flour or meat is placed inside a boiling tube.
- The boiling tube is stoppered using a rubber bung connected to a delivery tube inserted into a test-tube with limewater.
- The food is heated strongly to bum.
- Observations are made on the changes in lime water (calcium hydroxide) as gas is produced.
- The clear lime water turns white due to formation of calcium carbonate precipitate proving that carbon (IV) oxide is produced.
- Glucose solution is boiled and cooled. Boiling expels all air.
- A mixture of glucose and yeast is placed in a boiling tube, and covered with a layer of oil to prevent entry of air.
- A delivery tube is connected and directed into a test-tube containing lime water.
- The observations are made immediately and after three days the contents are tested for the presence of ethanol.
- A control experiment is set in the same way except that yeast which has been boiled and cooled is used.
- Boiling kills yeast cells.
- The limewater becomes cloudy within 20 minutes.
- This proves that carbon (IV) oxide gas is produced.
- The fermentation process is confirmed after three days when alcohol smell is detected in the mixture.
- Soaked bean seeds are placed in a vacuum flask on wet cotton wool.
- A thermometer is inserted and held in place with cotton wool.
- The initial temperature is taken and recorded.
- A control experiment is set in the same way using boiled and cooled bean seeds which have been washed in formalin to kill microorganisms.
- Observation is made within three days.
- Observations show that temperature in the flask with germinating seeds has risen.
- The one in the control has not risen.
Comparison between Aerobic and Anaerobic Respiration
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Aerobic Respiration
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Anaerobic Respiration
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Site
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In the mitochondria.
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In the cytoplasm.
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Products
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Carbon dioxide and water.
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Ethanol in plants and lactic acid in animals.
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Energy yield
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38 molecules of ATP (2880 KJ) from each molecule of glucose.
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2 molecules of ATP 210 KJ from each molecule of glucose.
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Further reaction
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No further reactions on carbon dioxide and water.
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Ethanol and lactic acid can be broken down further in the presence of oxygen.
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Comparison between Energy Output in Aerobic and Anaerobic Respiration
- Aerobic respiration results in the formation of simple inorganic molecules, water and carbon (IV) oxide as the byproducts.
- These cannot be broken down further. A lot of energy is produced.
- When a molecule of glucose is broken down in the presence of oxygen, 2880 KJ of energy are produced (38 molecules of ATP).
- In anaerobic respiration the by products are organic compounds.
- These can be broken down further in the presence of oxygen to give more energy.
- Far less energy is thus produced.
- The process is not economical as far as energy production is concerned.
- When a molecule of glucose is broken down in the absence of oxygen in plants, 210 KJ are produced (2 molecule ATP).
- In animals, anaerobic respiration yields 150 kJ of energy.
Substrates for Respiration
Carbohydrate, mainly glucose is the main substrate inside cells.
Lipids i.e. fatty acids and glycerol are also used.
Fatty acids are used when the carbohydrates are exhausted.
A molecule of lipid yields much more energy than a molecule of glucose.
Proteins are not normally used for respiration.
However during starvation they are hydrolysed to amino acids, dearnination follows and the products enter Kreb's cycle as urea is formed.
Use of body protein in respiration result to body wasting, as observed during prolonged sickness or starvation.
The ratio of the amount of carbon (IV) oxide produced to the amount of oxygen used for each substrate is referred to as Respiratory Quotient (RQ) and is calculated as follows:
Lipids i.e. fatty acids and glycerol are also used.
Fatty acids are used when the carbohydrates are exhausted.
A molecule of lipid yields much more energy than a molecule of glucose.
Proteins are not normally used for respiration.
However during starvation they are hydrolysed to amino acids, dearnination follows and the products enter Kreb's cycle as urea is formed.
Use of body protein in respiration result to body wasting, as observed during prolonged sickness or starvation.
The ratio of the amount of carbon (IV) oxide produced to the amount of oxygen used for each substrate is referred to as Respiratory Quotient (RQ) and is calculated as follows:
Carbohydrates have a respiratory quotient of 1.0 lipids 0.7 and proteins 0.8.
Respiratory quotient value can thus give an indication of types of substrate used.
Besides values higher than one indicate that some anaerobic respiration is taking place.
Respiratory quotient value can thus give an indication of types of substrate used.
Besides values higher than one indicate that some anaerobic respiration is taking place.
Application of Anaerobic Respiration in Industry and at Home
Industry
- Making of beer and wines.
- Ethanol in beer comes from fermentation of sugar (maltose) in germinating barley seeds.
- Sugar in fruits is broken down anaerobically to produce ethanol in wines.
- In the dairy industry, bacterial fermentation occurs in the production of several dairy products such as cheese, butter and yoghurt.
- In production of organic acids e.g., acetic acid, that are used in industry e.g., in preservation of foods.
- Fermentation of grains is used to produce all kinds of beverages e.g., traditional beer and sour porridge.
- Fermentation of milk.
respiration audio visuals
ENZYMES
AEROBIC VS ANAEROBIC RESPIRATION
LACTIC ACIDS
EXCRETION
BODY TEMPERATURE
HOMEOSTASIS
Respiration Questions
- Explain the roles of enzymes in respiration
- What is aerobic respiration
- Give a word equation for aerobic respiration
- What are the end products of aerobic respiration?
- What are obligate anaerobes?
- What are facultative anaerobes?
- State the word equation representing anaerobic respiration in plants
- Name the end products of anaerobic respiration in plants
- Give a word equation of anaerobic respiration in animals
- Name the end products of respiration in animals when there is insufficient oxygen supply
- Why is there a high rate of lactic acid production during exercise?
- Why does lactic acid level reduce after exercise?
- State why accumulation of lactic acid during vigorous exercise lead to an increase in heartbeat
- State the economic importance of anaerobic respiration
- What is oxygen debt?
- What is respiratory quotient (RQ)?
- Why are respiratory quotient important
- Name the respiratory substrates
- Why does anaerobic respiration of a given substrate yield a smaller amount of energy than aerobic respiration?
- Explain the disadvantages of anaerobic respiration
- Mention the types of experiments carried out for respiration
- Define the following terms
- Excretion
- Secretion
- Egestion
- Homeostasis
- Explain why excretion is necessary in plants and animals
- Describe how excretion takes place in green plants
- Why do plants lack complex excretory structures like those of animals?
- State the excretory products of plants and some of their uses to humans
- Describe excretion in unicellular organisms
- List excretory organs and products of mammals
- Draw and label a mammalian skin
- Explain how the mammalian skin is adapted to its functions
- What is the role of lungs in excretion?
- State the functions of the liver
- Draw a labeled diagram of mammalian nephrone
- Describe how the human kidney functions
- Name the common kidney diseases
- Why is homeostatic control necessary?
- What is internal environment?
- Why is constant body temperature maintained by mammals?
- Explain the advantage gained by possessing a constant body temperature
- How do mammals regulate body temperature?
- Why does body temperature of a healthy person rise up to 37oC on a hot humid day?
- Name the structures in the human body that detect external temperature changes
- State the advantages that organisms with small surface area to volume ratio experience over those with larger
- Explain why individuals with smaller sizes require more energy per unit body weight than those with larger sizes.
- What is the meaning of osmoregulation?
- State the importance of osmoregulation
- State the ways by which desert mammals conserve water
- Explain why some desert animals excrete uric acid rather than water
- Explain why eating a meal with too much salt leads to production of a small volume of concentrated urine
- Explain how marine fish regulate their osmotic pressure
- What is the biological significance of maintaining a relatively constant sugar level in a human body?
- Discuss the role of the following hormones in blood sugar control
- Explain the part played by antidiuretic hormone in homeostasis
- What is the role of blood clotting in homeostasis?
- Describe the role of the following hormones in homeostasis
- Distinguish between diabetes mellitus and diabetes insipidus
- How can high blood sugar level in a person be controlled?
- Why does glucose not normally appear in urine even though it is filtered in the mammalian Bowman’s capsule?
- How would one find out from a sample of urine whether a person is suffering from diabetes mellitus?
CONTENTS
- Review of binomial nomenclature
- General principles of classification
- General characteristics of kingdoms
- Monera
- Protoctista
- Fungi
- Plantae
- Animalia
- Main characteristics of major divisions of plantae
- Bryophyta
- Pteridophyta
- Spermatophyta (cover only up to class level)
- Main Characteristics of the Phyla Arthropoda and Chordata (cover up to classes as shown)
- Arthropoda
- diplopoda chilopoda
- insecta
- crustacean
- arachnida
- Chordata
- Pisces
- Amphibian
- Reptilian
- Ayes
- mammalia
- Arthropoda
- Construction and use of simple dichotomous keys based on observable features of plants and animals
- Practical activities
- Examine live/preserved specimen or photographs of representatives of major divisions of plantae and phyla arthropoda and chordata
- Construct simple dichotomous keys using leaves/parts of common plants/arthropods/ common chordates in the local environment
- Use dichotomous keys to identify organisms
SPECIFIC OBJECTIVES
By the end of the topic, the learner should be able to:
- state briefly the general principles of classification of living organisms
- state general characteristics of each of the five kingdoms
- state the main characteristics of arthropoda, chordata and major divisions of plantae
- name classes of spermatophyta
- describe the main characteristics of classes of phyla arthropoda and chordata
- use observable external features to construct simple dichotomous keys of plants and animals
- use already constructed dichotomous keys to identify organisms.
Classification II
General Principles of Classification
- Classification is the science that puts organisms into distinct groups to make their study easy and systematic.
- Modern scientific classification is based on structure and functions.
- Organisms with similar anatomical and morphological characteristics are placed in one group while those with different structures are grouped separately.
- Modern studies in genetics and cell biochemistry are used to give additional help in classifying organisms.
- There are seven major taxonomic groups.
- The kingdom is the largest group.
- Others are phylum (division for plants) class, order, family, genus and species, the smallest.
- Living organisms are named using Latin or Latinised names.
- Every organism has two names.
- This double naming is called binomial nomenclature.
- This system of naming was devised by Carolus Linnaeus in the 18th Century.
- The first name is the generic name - the name of the genus.
- The second name is the name of the species.
- The generic name starts with a capital letter while that of the species starts with a small letter.
- The names are written in italics or are underlined in manuscripts.
- Bean =Phaseolus vulgaris.
- Phaseolus is the generic name,
- vulgaris is specific name.
- Dog =Canis familiaris.
- Canis is the generic name
- ,familiaris the specific name.
Organisms are classified into five kingdoms.
- Monera,
- Protoctista,
- Fungi,
- Plantae
- Animalia.
- They are simple and not cellular.
- They are metabolically inactive outside the host cell.
- Most of them can be crystallised like chemical molecules.
- Therefore they do not exhibit the characteristics of living organisms.
Examples of Organisms in Each Kingdom and Their Economic Importance
Kingdom Monera
General Characteristics
General Characteristics
- Unicellular and microscopic
- Some single cells, others colonial
- Nuclear material not enclosed within nuclear membrane-prokaryotic
- Have cell wall but not of cellulose.
- Have few organelles which are not membrane bound
- Mitochondria absent
- Mostly heterotrophic, feeding saprotrophically or parasitically, some are autotrophic.
- Reproduction mostly asexual through binary fission
- Most of them are anaerobes but others are aerobes
- Most move by flagella
- Examples include Escherichia coli, Vibrio cholerae and Clostridium tetani.
- Spherical known as Cocci.
- Rod shaped - e.g. Clostridium tetani
- Spiral shaped e.g. sprilla
- Coma shaped- Vibrios -e.g., Vibrio cholerae.
- They are used in food processing e.g., Lactobacillus used in processing of cheese, yoghurt.
- Involved in synthesis of vitamin Band K, in humans and breakdown of cellulose in herbivores.
- Bacteria are easily cultured and are being used for making antibiotics, amino acids and enzymes e.g. amylase, and invertase e.g. Escherichia coli.
Nutrient cycling:
- What is meant by the term binomial nomenclature?
- State briefly the general principles of classification of living organisms
- Describe the economic importance of:
- fungi
- bacteria
- State the importance of plants
- Give the general characteristics of phylum arthropoda
- State the economic importance of insects
- State the general characteristics of chordate
- What is a dichotomous key?
- State the necessity of using a dichotomous key.
- List the rules followed in constructing a dichotomous key.
- Describe the procedure of using a dichotomous key. Make a list of major features of the characteristics to be identified.
answers
QUESTION 1
scientific system of naming organisms using the generic(genus) and specific (species) names
QUESTION 2
- scientific names must be in Latin or should be latinised
- family names are formed by adding the suffix “idea” to the stem of the genus e.g. the genus Rana become Ranaidea
- generic names should be a single unique name
QUESTION 3
Fungi
- some cause decay to our food
- some cause diseases to humans and animals e.g. ringworms
- may be used as food e.g. mushrooms, yeast
- some are used in production of antibiotics e.g. penicillin, chloromycin, streptomycin
- yeast is used in brewing industry, baking and source of vitamin B
- many cause diseases to our crops e.g. late blight
- important in recycling nutrients in soil since they cause decay of organic matter
- mycorrhizal association in forest development may help in water intake/absorption
- help in nitrogen fixation
- are useful in the manufacture of antibiotics
- silage formation,
- fermentation of cheese, butter, milk yoghurt
- curing of tea, tobacco and retting flax
- formation of vitamin B12 and K
- enzymes such as amylase and invertase
- hormones such as insulin
- vinegar, acetic acid, lactic acid, citric acid
- in septic tanks and modern sewage works make use of bacteria
- biogas production
- saprophytic bacteria are used in compost decomposition or cause decay
- symbiotic bacteria are used in compost decomposition or cause decay
- symbiotic bacteria in herbivores/ruminants help in digestion
- some diseases in animals/humans and plants are caused by bacteria
- many bacteria cause food spoilage/decay
- nitrifying and nitrogen fixing bacteria increase soil fertility/make nitrates available
- denitrifying bacteria reduce soil fertility/convert nitrates into nitrogen/reduce nitrates
QUESTION 4
- balancing carbon IV oxide and oxygen in the atmosphere during photosynthesis and respiration
- influence water cycle
- reduce soil erosion by bind soil particles together
- useful products e.g. food, medicine, timber, paper and clothing
- habitat ( e.g. forests and grassland) for animals which may also be tourist attraction
- earn money from sales of products
- aesthetic value/beauty e.g. flowers, shade/shelter, live fences, windbreaks
- Some are harmful e.g. poisons, weeds, injurious (stinging nettles, thorns), water hyacinth.
QUESTION 5
- jointed appendages
- presence of exoskeleton
- triploblastic and coelomate
- segmented body
- bilateral symmetry (similar halves)
QUESTION 6
Beneficial effects
- food supply
- important in food chains
- pollinators
- biological control of pests and other organisms
- aesthetic value
- contribute to decomposition e.g. litter feeders like beetles
- pests
- vectors
- dirt and disease carriers
- injurious e.g. stings and bites
QUESTION 7
- notochord
- dorsal slits (pharyngeal cleft during development)
- bilateral symmetry
- triploblastic (three layer body-ectoderm, mesoderm and endoderm)
- clear cut head formation
- multilayered epidermis
- post anal tail
- closed circulatory system
- segmented muscle blocks(myotomes)
- single pair of gonads
QUESTION 8
A biological device (tool) which enables one to identify an organism by progressively opting between two alternative observable characteristics
QUESTION 9
- used to identify organisms quickly and accurately
- by following the statements in the key we are able to identify each organism on the basis of a characteristic which is not to be found in other specimens
QUESTION 10
- use observable characteristics only
- start with major characteristics, placing organisms into two groups at each stage
- use a single characteristics at a time
- use contrasting characteristics at each stage e.g 1(a) short, 1(b) tall
- avoid repeating the same characteristics
QUESTION 11
- look at the features of similarities
- look at the features of differences between the organisms
- we can then be able to identify the organisms by distinguishing one from another
- the key uses a method of elimination by following statements that are correct only for the organism
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SPECIFIC OBJECTIVES
By the end of the topic, the learner should be able to:
- distinguish between excretion and egestion
- explain the necessity for excretion in plants and animals
- state the uses of excretory products of plants
- describe the methods of excretion in a named unicellular organism
- relate the structures of the human skin, lungs, liver and kidney to their functions name common kidney diseases
- explain the concept of internal environment and homeostasis
- compare responses to changes in temperature by behavioural and physiological methods in animals
- relate heat loss to body size in
- describe methods by which mammals gain and lose heat
- explain how the functions of the following relate to homeostasis - skin, hypothalamus, liver and kidney
- discuss the role of antidiuretic hormone, insulin and glucagons
- describe simple symptoms of Diabetes mellitus and Diabetes insipidus.
TOPICS / SUB-TOPICS OUTLINE
Excretion in Plants
Methods of excretion in plants
Excretion in a named uni-cellular organism (protozoa)
Structure and functions of skin and kidney
Neuro-endocrine system and homeostasis
The role of the skin in thermoregulation, salt and water balance.
Major functions of the liver and their contributions to homeostasis.
Common diseases of the liver, their symptoms and possible methods of prevention and control
Practical Activities
Examine and draw the mammalian kidney
Make vertical sections of the kidney to identify cortex and medulla
Observe permanent slides of mammalian skin
Investigate effect of catalase enzyme on hydrogen peroxide
Methods of excretion in plants
- Useful and harmful excretory products of plants and their economic importance e.g. caffeine in tea and coffee, quinine, tannins, colchicines, cocaine, rubber, gum, papain (from pawpaw) and products of cannabis sativa (bhang) and khat (miraa)Excretion and homeostasis in Animals
Excretion in a named uni-cellular organism (protozoa)
Structure and functions of skin and kidney
Neuro-endocrine system and homeostasis
- Water balance (blood osmotic pressure)
- Blood sugar level (control)
- Temperature regulation (mention the role of hypothalamus)
The role of the skin in thermoregulation, salt and water balance.
Major functions of the liver and their contributions to homeostasis.
Common diseases of the liver, their symptoms and possible methods of prevention and control
Practical Activities
Examine and draw the mammalian kidney
Make vertical sections of the kidney to identify cortex and medulla
Observe permanent slides of mammalian skin
Investigate effect of catalase enzyme on hydrogen peroxide
Introduction Excretion and Homeostasis
- Excretion is the process by which living organisms separate and eliminate waste products of metabolism from body cells.
- If these substances were left to accumulate, they would be toxic to the cells.
- Egestion is the removal of undigested materials from the alimentary canals of animals.
- Secretion is the production and release of certain useful substances such as hormones, sebum and mucus produced by glandular cells.
- Homeostasis is a self-adjusting mechanism to maintain a steady state in the internal environment
Excretion in Plants
- Plants have little accumulation of toxic waste especially nitrogenous wastes.
- This is because they synthesise proteins according to their requirements.
- In carbohydrate metabolism plants use carbon (IV) oxide released from respiration in photosynthesis while oxygen released from photosynthesis is used in respiration.
- Gases are removed from the plant by diffusion through stomata and lenticels.
- Certain organic products are stored in plant organs such as leaves, flowers, fruits and bark and are removed when these organs are shed.
- The products include tannins, resins, latex and oxalic acid crystals.
- Some of these substances are used illegally.
- Khat, cocaine and cannabis are used without a doctor's prescription and can be addictive.
- Use of these substances should be avoided.
EXCRETION AND HOMEOSTASIS QUESTIONS AND ANSWERS
- Define the following terms
- Excretion
- Secretion
- Egestion
- Homeostasis
- Explain why excretion is necessary in plants and animals
- Describe how excretion takes place in green plants
- Why do plants lack complex excretory structures like those of animals?
- State the excretory products of plants and some of their uses to humans
- Describe excretion in unicellular organisms
- Draw and label a mammalian skin
- Explain how the mammalian skin is adapted to its functions
- What is the role of lungs in excretion?
- State the functions of the liver
- Draw a labeled diagram of mammalian nephrone
- Describe how the human kidney functions
- State the adaptations of proximal convoluted tubule to its function
- Name the common kidney diseases
- Why is homeostatic control necessary?
- What is internal environment?
- Why is constant body temperature maintained by mammals?
- Explain the advantage gained by possessing a constant body temperature
- How do mammals regulate body temperature?
- Why does body temperature of a healthy person rise up to 37oC on a hot humid day?
- Name the structures in the human body that detect external temperature changes
- State the advantages that organisms with small surface area to volume ratio experience over those with larger
- Explain why individuals with smaller sizes require more energy per unit body weight than those with larger sizes.
- What is the meaning of osmoregulation?
- State the importance of osmoregulation
- State the ways by which desert mammals conserve water
- Explain why some desert animals excrete uric acid rather than water
- Explain why eating a meal with too much salt leads to production of a small volume of concentrated urine
- Explain how marine fish regulate their osmotic pressure
- What is the biological significance of maintaining a relatively constant sugar level in a human body?
- Discuss the role of the following hormones in blood sugar control Insulin
- Explain the part played by antidiuretic hormone in homeostasis
- What is the role of blood clotting in homeostasis?
- Describe the role of the following hormones in homeostasis
- Distinguish between diabetes mellitus and diabetes insipidus
- How can high blood sugar level in a person be controlled?
- Why does glucose not normally appear in urine even though it is filtered in the mammalian Bowman’s capsule?
- When is glycogen which is stored in the liver converted into glucose and released into the blood?
- How would one find out from a sample of urine whether a person is suffering from diabetes mellitus?
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Gaseous Exchange in Animals
All animals take in oxygen for oxidation of organic compounds to provide energy for cellular activities.
The carbon (IV) oxide produced as a by-product is harmful to cells and has to be constantly removed from the body.
Most animals have structures that are adapted for taking in oxygen and for removal of carbon (IV) oxide from the body.
These are called "respiratory organs".
The process of taking in oxygen into the body and carbon (IV) oxide out of the body is called breathing or ventilation.
Gaseous exchange involves passage of oxygen and carbon (IV) oxide through a respiratory surface by diffusion.
The carbon (IV) oxide produced as a by-product is harmful to cells and has to be constantly removed from the body.
Most animals have structures that are adapted for taking in oxygen and for removal of carbon (IV) oxide from the body.
These are called "respiratory organs".
The process of taking in oxygen into the body and carbon (IV) oxide out of the body is called breathing or ventilation.
Gaseous exchange involves passage of oxygen and carbon (IV) oxide through a respiratory surface by diffusion.
Types and Characteristics of Respiratory surfaces
Different animals have different respiratory surfaces.
The type depends mainly on the habitat of the animal, size, shape and whether body form is complex or simple.
The type depends mainly on the habitat of the animal, size, shape and whether body form is complex or simple.
- Cell Membrane: In unicellular organisms the cell membrane serves as a respiratory surface.
- Gills: Some aquatic animals have gills which may be external as in the tadpole or internal as in bony fish e.g. tilapia. They are adapted for gaseous exchange in water.
- Skin: Animals such as earthworm and tapeworm use the skin or body surface for gaseous exchange. The skin of the frog is adapted for gaseous exchange both in water and on land. The frog also uses epithelium lining of the mouth or buccal cavity for gaseous exchange.
- Lungs: Mammals, birds and reptiles have lungs which are adapted for gaseous exchange.
Characteristics of Respiratory Surfaces
GASEOUS EXCHANGE IN ANIMALS
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Gaseous Exchange in Amoeba
- Gaseous exchange occurs across the cell membrane by diffusion.
- Oxygen diffuses in and carbon (IV) oxide diffuses out.
- Oxygen is used in the cell for respiration making its concentration lower than that in the surrounding water.
- Hence oxygen continually enters the cell along a concentration gradient.
- Carbon (IV) oxide concentration inside the cell is higher than that in the surrounding water thus it continually diffuses out of the cell along a concentration gradient.
Gaseous Exchange in Insects
Gaseous exchange in insects e.g., grasshopper takes place across a system of tubes penetrating into the body known as the tracheal system.
The main trachea communicate with atmosphere through tiny pores called spiracles.
Spiracles are located at the sides of body segments;
Two pairs on the thoracic segments and eight pairs on the sides of abdominal segments.
Each spiracle lies in a cavity from which the trachea arises.
Spiracles are guarded with valves that close and thus prevent excessive loss of water vapour.
A filtering apparatus i.e. hairs also traps dust and parasites which would clog the trachea if they gained entry.
The valves are operated by action of paired muscles.
Mechanism of Gaseous Exchange in Insects
The fine tracheoles are very thin about one micron in diameter in order to permeate tissue.
They are made up of a single epithelial layer and have no spiral thickening to allow diffusion of gases.
Terminal ends of the fine tracheoles are filled with a fluid in which gases dissolve to allow diffusion of oxygen into the cells.
Amount of fluid at the ends of fine tracheoles varies according to activity i.e. oxygen demand of the insect.
During flight, some of the fluid is withdrawn from the tracheoles such that oxygen reaches muscle cells faster and the rate of respiration is increased.
In some insects, tracheoles widen at certain places to form air sacs.
These are inflated or deflated to facilitate gaseous exchange as need arises.
Atmospheric air that dissolves in the fluid at the end of tracheoles has more oxygen than the surrounding cells of tracheole epithelium'.
Oxygen diffuses into these cells along a concentration gradient. '
Carbon (IV) oxide concentration inside the cells is higher than in the atmospheric.
Air and diffuses out of the cells along a concentration gradient.
It is then removed with expired air.
Ventilation in Insects
Ventilation in insects is brought about by the contraction and relaxation of the abdominal muscles.
In locusts, air is drawn into the body through the thoracic spiracles and expelled through the abdominal spiracles.
Air enters and leaves the tracheae as abdominal muscles contract and relax.
The muscles contract laterally so the abdomen becomes wider and when they relax it becomes narrow.
Relaxation of muscles results in low pressure hence inspiration occurs while contraction of muscles results in higher air pressure and expiration occurs.
In locusts, air enters through spiracles in the thorax during inspiration and leaves through the abdominal spiracles during expiration.
This results in efficient ventilation.
Maximum extraction of oxygen from the air occurs sometimes when all spiracles close and hence contraction of abdominal muscles results in air circulating within the tracheoles.
The valves in the spiracles regulate the opening and closing of spiracles.
Observation of Spiracle in Locust
Some fresh grass is placed in a gas jar.
A locust is introduced into the jar.
A wire mesh is placed on top or muslin cloth tied around the mouth of the beaker with rubber band.
The insect is left to settle.
Students can approach and observe in silence the spiracles and the abdominal movements during breathing.
Alternatively the locust is held by the legs and observation of spiracles is made by the aid of hand lens.
The main trachea communicate with atmosphere through tiny pores called spiracles.
Spiracles are located at the sides of body segments;
Two pairs on the thoracic segments and eight pairs on the sides of abdominal segments.
Each spiracle lies in a cavity from which the trachea arises.
Spiracles are guarded with valves that close and thus prevent excessive loss of water vapour.
A filtering apparatus i.e. hairs also traps dust and parasites which would clog the trachea if they gained entry.
The valves are operated by action of paired muscles.
Mechanism of Gaseous Exchange in Insects
- The main tracheae in the locust are located laterally along the length of the body on each side and they are interconnected across.
- Each main trachea divides to form smaller tracheae, each of which branches into tiny tubes called tracheoles.
- Each tracheole branches further to form a network that penetrates the tissues. Some tracheoles penetrate into cells in active tissue such as flight muscles.
- These are referred to as intracellular tracheoles.
- Tracheoles in between the cells are known as intercellular tracheoles.
- The main tracheae are strengthened with rings of cuticle.
- This helps them to remain open during expiration when air pressure is low.
The fine tracheoles are very thin about one micron in diameter in order to permeate tissue.
They are made up of a single epithelial layer and have no spiral thickening to allow diffusion of gases.
Terminal ends of the fine tracheoles are filled with a fluid in which gases dissolve to allow diffusion of oxygen into the cells.
Amount of fluid at the ends of fine tracheoles varies according to activity i.e. oxygen demand of the insect.
During flight, some of the fluid is withdrawn from the tracheoles such that oxygen reaches muscle cells faster and the rate of respiration is increased.
In some insects, tracheoles widen at certain places to form air sacs.
These are inflated or deflated to facilitate gaseous exchange as need arises.
Atmospheric air that dissolves in the fluid at the end of tracheoles has more oxygen than the surrounding cells of tracheole epithelium'.
Oxygen diffuses into these cells along a concentration gradient. '
Carbon (IV) oxide concentration inside the cells is higher than in the atmospheric.
Air and diffuses out of the cells along a concentration gradient.
It is then removed with expired air.
Ventilation in Insects
Ventilation in insects is brought about by the contraction and relaxation of the abdominal muscles.
In locusts, air is drawn into the body through the thoracic spiracles and expelled through the abdominal spiracles.
Air enters and leaves the tracheae as abdominal muscles contract and relax.
The muscles contract laterally so the abdomen becomes wider and when they relax it becomes narrow.
Relaxation of muscles results in low pressure hence inspiration occurs while contraction of muscles results in higher air pressure and expiration occurs.
In locusts, air enters through spiracles in the thorax during inspiration and leaves through the abdominal spiracles during expiration.
This results in efficient ventilation.
Maximum extraction of oxygen from the air occurs sometimes when all spiracles close and hence contraction of abdominal muscles results in air circulating within the tracheoles.
The valves in the spiracles regulate the opening and closing of spiracles.
Observation of Spiracle in Locust
Some fresh grass is placed in a gas jar.
A locust is introduced into the jar.
A wire mesh is placed on top or muslin cloth tied around the mouth of the beaker with rubber band.
The insect is left to settle.
Students can approach and observe in silence the spiracles and the abdominal movements during breathing.
Alternatively the locust is held by the legs and observation of spiracles is made by the aid of hand lens.
Gaseous Exchange in Bony Fish (e.g., Tilapia)
Gaseous exchange in fish takes place between the gills and the surrounding water.
The gills are located in an opercular cavity covered by a flap of skin called the operculum.
Each _gill consists of a number of thin leaf-like lamellae projecting from a skeletal base bronchial arch (gill bar) situated in the wall of the pharynx.
There are four gills within the opercular cavity on each side of the head.
Each gill is made up of a bony gill arch which has a concave surface facing the mouth cavity (anterior) and a convex posterior surface.
Gill rakers are bony projections on the concave side that trap food and other solid particles which are swallowed instead of going over and damaging the gill filaments.
Two rows of gill filaments subtend from the convex surface.
Adaptation of Gills for Gaseous Exchange
Gill filaments are thin walled.
Gill filaments are very many (about seventy pairs on each gill), to increase surface area.
Each gill filament has very many gill lamellae that further increase surface area.
The gill filaments are served by a dense network of blood vessels that ensure efficient transport of gases.
It also ensures that a favourable diffusion gradient is maintained.
The direction of flow of blood in the gill lamellae is in the opposite direction to that of the water (counter current flow) to ensure maximum diffusion of gases.
Ventilation
As the fish opens the mouth, the floor of the mouth is lowered.
This increases the volume of the buccal cavity.
Pressure inside the mouth is lowered causing water to be drawn into the buccal cavity.
Meanwhile, the operculum is closed, preventing water from entering or leaving through the opening.
As the mouth closes and the floor of the mouth is raised, the volume of buccal cavity decreases while pressure in the opercular cavity increases due to contraction of opercular muscles.
The operculum is forced to open and water escapes.
As water passes over the gills, oxygen is absorbed and carbon dioxide from the gills dissolves in the water.
As the water flows over the gill filaments oxygen in the water is at a higher concentration than that in the blood flowing, in the gill.
Oxygen diffuses through the thin walls of gill filaments/lamellae into the blood.
Carbon (IV) oxide is at a higher concentration in the blood than in the water.
It diffuses out of blood through walls of gill filaments into the water.
Counter Current Flow
In the bony fish direction of flow of water over the gills is opposite that of blood flow through the gill filaments.
This adaptation ensures that maximum amount of oxygen diffuses from the water into the blood in the gill filament.
This ensures efficient uptake of oxygen from the water.
Where the flow is along the same direction (parallel flow) less oxygen is extracted from the water.
Observation of Gills of a Bony Fish (Tilapia)
Gills of a fresh fish are removed and placed in a petri-dish with enough water to cover them.
A hand lens is used to view the gills.
Gill bar, gill rakers and two rows of gill filaments are observed.
The gills are located in an opercular cavity covered by a flap of skin called the operculum.
Each _gill consists of a number of thin leaf-like lamellae projecting from a skeletal base bronchial arch (gill bar) situated in the wall of the pharynx.
There are four gills within the opercular cavity on each side of the head.
Each gill is made up of a bony gill arch which has a concave surface facing the mouth cavity (anterior) and a convex posterior surface.
Gill rakers are bony projections on the concave side that trap food and other solid particles which are swallowed instead of going over and damaging the gill filaments.
Two rows of gill filaments subtend from the convex surface.
Adaptation of Gills for Gaseous Exchange
Gill filaments are thin walled.
Gill filaments are very many (about seventy pairs on each gill), to increase surface area.
Each gill filament has very many gill lamellae that further increase surface area.
The gill filaments are served by a dense network of blood vessels that ensure efficient transport of gases.
It also ensures that a favourable diffusion gradient is maintained.
The direction of flow of blood in the gill lamellae is in the opposite direction to that of the water (counter current flow) to ensure maximum diffusion of gases.
Ventilation
As the fish opens the mouth, the floor of the mouth is lowered.
This increases the volume of the buccal cavity.
Pressure inside the mouth is lowered causing water to be drawn into the buccal cavity.
Meanwhile, the operculum is closed, preventing water from entering or leaving through the opening.
As the mouth closes and the floor of the mouth is raised, the volume of buccal cavity decreases while pressure in the opercular cavity increases due to contraction of opercular muscles.
The operculum is forced to open and water escapes.
As water passes over the gills, oxygen is absorbed and carbon dioxide from the gills dissolves in the water.
As the water flows over the gill filaments oxygen in the water is at a higher concentration than that in the blood flowing, in the gill.
Oxygen diffuses through the thin walls of gill filaments/lamellae into the blood.
Carbon (IV) oxide is at a higher concentration in the blood than in the water.
It diffuses out of blood through walls of gill filaments into the water.
Counter Current Flow
In the bony fish direction of flow of water over the gills is opposite that of blood flow through the gill filaments.
This adaptation ensures that maximum amount of oxygen diffuses from the water into the blood in the gill filament.
This ensures efficient uptake of oxygen from the water.
Where the flow is along the same direction (parallel flow) less oxygen is extracted from the water.
Observation of Gills of a Bony Fish (Tilapia)
Gills of a fresh fish are removed and placed in a petri-dish with enough water to cover them.
A hand lens is used to view the gills.
Gill bar, gill rakers and two rows of gill filaments are observed.
Gaseous Exchange in an Amphibian - Frog
An adult frog lives on land but goes back into the water during the breeding season.
A frog uses three different respiratory surfaces.
These are the skin, buccal cavity and lungs.
Skin
The skin is used both in water and on land.
It is quite efficient and accounts for 60% of the oxygen taken in while on land.
Adaptations of a Frog's Skin for Gaseous Exchange
The skin is a thin epithelium to allow fast diffusion.
The skin between the digits in the limbs (i.e. webbed feet) increase the surface area for gaseous exchange.
It is richly supplied with blood vessels for transport of respiratory gases.
The skin is kept moist by secretions from mucus glands.
This allows for respiratory gases to dissolve.
Oxygen dissolved in the film of moisture diffuses across the thin epithelium and into the blood which has a lower concentration of oxygen.
Carbon (IV) oxide diffuses from the blood across the skin to the atmosphere along the concentration gradient.
Buccal (Mouth) Cavity
Gaseous exchange takes place all the time across thin epithelium lining the mouth cavity.
Adaptations of Buccal Cavity for Gaseous Exchange
It has a thin epithelium lining the walls of the mouth cavity allowing fast diffusion of gases.
It is kept moist by secretions from the epithelium for dissolving respiratory gases.
It has a rich supply of blood vessels for efficient transport of respiratory gases.
The concentration of oxygen in the air within the mouth cavity is higher than that of the blood inside the blood vessels.
Oxygen, therefore dissolves in the moisture lining the mouth cavity and then diffuses into the blood through the thin epithelium.
On the other hand, carbon (IV) oxide diffuses in the opposite direction along a concentration gradient.
Lungs
There is a pair of small lungs used for gaseous exchange.
Adaptation of Lungs
The lungs are thin walled for fast diffusion of gases.
Have internal folding to increase surface area for gaseous exchange.
A rich supply of blood capillaries for efficient transport of gases.
Moisture lining for gases to dissolve.
Ventilation
Inspiration
During inspiration, the floor of the mouth is lowered and air is drawn in through the nostrils.
When the nostrils are closed and the floor of the mouth is raised, air is forced into the lungs.
Gaseous exchange occurs in the lungs, oxygen dissolves in the moisture lining of the lung and diffuses into the blood through the thin walls.
Carbon (IV) oxide diffuses from blood into the lung lumen.
Expiration
When the nostrils are closed and the floor of mouth is lowered by contraction of its muscles, volume of mouth cavity increases.
Abdominal organs press against the lungs and force air out of the lungs into buccal cavity.
Nostrils open and floor of the mouth is raised as its muscles relax.
Air is forced out through the nostrils.
A frog uses three different respiratory surfaces.
These are the skin, buccal cavity and lungs.
Skin
The skin is used both in water and on land.
It is quite efficient and accounts for 60% of the oxygen taken in while on land.
Adaptations of a Frog's Skin for Gaseous Exchange
The skin is a thin epithelium to allow fast diffusion.
The skin between the digits in the limbs (i.e. webbed feet) increase the surface area for gaseous exchange.
It is richly supplied with blood vessels for transport of respiratory gases.
The skin is kept moist by secretions from mucus glands.
This allows for respiratory gases to dissolve.
Oxygen dissolved in the film of moisture diffuses across the thin epithelium and into the blood which has a lower concentration of oxygen.
Carbon (IV) oxide diffuses from the blood across the skin to the atmosphere along the concentration gradient.
Buccal (Mouth) Cavity
Gaseous exchange takes place all the time across thin epithelium lining the mouth cavity.
Adaptations of Buccal Cavity for Gaseous Exchange
It has a thin epithelium lining the walls of the mouth cavity allowing fast diffusion of gases.
It is kept moist by secretions from the epithelium for dissolving respiratory gases.
It has a rich supply of blood vessels for efficient transport of respiratory gases.
The concentration of oxygen in the air within the mouth cavity is higher than that of the blood inside the blood vessels.
Oxygen, therefore dissolves in the moisture lining the mouth cavity and then diffuses into the blood through the thin epithelium.
On the other hand, carbon (IV) oxide diffuses in the opposite direction along a concentration gradient.
Lungs
There is a pair of small lungs used for gaseous exchange.
Adaptation of Lungs
The lungs are thin walled for fast diffusion of gases.
Have internal folding to increase surface area for gaseous exchange.
A rich supply of blood capillaries for efficient transport of gases.
Moisture lining for gases to dissolve.
Ventilation
Inspiration
During inspiration, the floor of the mouth is lowered and air is drawn in through the nostrils.
When the nostrils are closed and the floor of the mouth is raised, air is forced into the lungs.
Gaseous exchange occurs in the lungs, oxygen dissolves in the moisture lining of the lung and diffuses into the blood through the thin walls.
Carbon (IV) oxide diffuses from blood into the lung lumen.
Expiration
When the nostrils are closed and the floor of mouth is lowered by contraction of its muscles, volume of mouth cavity increases.
Abdominal organs press against the lungs and force air out of the lungs into buccal cavity.
Nostrils open and floor of the mouth is raised as its muscles relax.
Air is forced out through the nostrils.
Gaseous Exchange in a Mammal -Human
The breathing system of a mammal consists of a pair of lungs which are thin-walled elastic sacs lying in the thoracic cavity.
The thoracic cavity consists of vertebrae, sternum, ribs and intercostal muscles.
The thoracic cavity is separated from the abdominal cavity by the diaphragm.
The lungs lie within the thoracic cavity.
They are enclosed and protected by the ribs which are attached to the sternum and the thoracic vertebrae.
There are twelve pairs of ribs, the last two pairs are called 'floating ribs' because they are only attached to the vertebral column.
The ribs are attached to and covered by internal and external intercostal muscles.
The diaphragm at the floor of thoracic cavity consists of a muscle sheet at the periphery and a central circular fibrous tissue.
The muscles of the diaphragm are attached to the thorax wall.
The lungs communicate with the outside atmosphere through the bronchi, trachea, mouth and nasal cavities.
The trachea opens into the mouth cavity through the larynx.
A flap of muscles, the epiglottis, covers the opening into the trachea during swallowing.
This prevents entry of food into the trachea.
Nasal cavities are connected to the atmosphere through the external nares(or nostrils)which are lined with hairs and mucus that trap dust particles and bacteria, preventing them from entering into the lungs.
Nasal cavities are lined with cilia.
The mucus traps dust particles,
The cilia move the mucus up and out of the nasal cavities.
The mucus moistens air as it enters the nostrils.
Nasal cavities are winding and have many blood capillaries to increase surface area to ensure that the air is warmed as it passes along.
Each lung is surrounded by a space called the pleural cavity.
It allows for the changes in lung volume during breathing.
An internal pleural membrane covers the outside of each lung while an external pleural membrane lines the thoracic wall.
The pleural membranes secrete pleural fluid into the pleural cavity.
This fluid prevents friction between the lungs and the thoracic wall during breathing.
The trachea divides into two bronchi, each of which enters into each lung.
Trachea and bronchi are lined with rings of cartilage that prevent them from collapsing when air pressure is low.
Each bronchus divides into smaller tubes, the bronchioles.
Each bronchiole subdivides repeatedly into smaller tubes ending with fine bronchioles.
The fine bronchioles end in alveolar sacs, each of which gives rise to many alveoli.
Epithelium lining the inside of the trachea, bronchi and bronchioles has cilia and secretes mucus.
Adaptations of Alveolus to Gaseous Exchange
Each alveolus is surrounded by very many blood capillaries for efficient transport of respiratory gases.
There are very many alveoli that greatly increases the surface area for gaseous exchange.
The alveolus is thin walled for faster diffusion of respiratory gases.
The epithelium is moist for gases to dissolve.
Gaseous Exchange between the Alveoli and the Capillaries
The walls of the alveoli and the capillaries are very thin and very close to each other.
Blood from the tissues has a high concentration of carbon (IV) oxide and very little oxygen compared to alveolar air.
The concentration gradient favours diffusion of carbon (IV) oxide into the alveolus and oxygen into the capillaries.
No gaseous exchange takes place in the trachea and bronchi.
These are referred to as dead space.
Ventilation
Exchange of air between the lungs and the outside is made possible by changes in the volumes of the thoracic cavity.
This volume is altered by the movement of the intercostal muscles and the diaphragm.
Inspiration
The ribs are raised upwards and outwards by the contraction of the external intercostal muscles, accompanied by the relaxation of internal intercostal muscles.
The diaphragm muscles contract and diaphragm moves downwards.
The volume of thoracic cavity increases, thus reducing the pressure.
Air rushes into the lungs from outside through the nostrils.
Expiration
The internal intercostal muscles contract while external ones relax and the ribs move downwards and inwards.
The diaphragm muscles relaxes and it is pushed upwards by the abdominal organs. It thus assumes a dome shape.
The volume of the thoracic cavity decreases, thus increasing the pressure.
Air is forced out of the lungs.
As a result of gaseous exchange in the alveolus, expired air has different volumes of atmospheric gases as compared to inspired air.
The thoracic cavity consists of vertebrae, sternum, ribs and intercostal muscles.
The thoracic cavity is separated from the abdominal cavity by the diaphragm.
The lungs lie within the thoracic cavity.
They are enclosed and protected by the ribs which are attached to the sternum and the thoracic vertebrae.
There are twelve pairs of ribs, the last two pairs are called 'floating ribs' because they are only attached to the vertebral column.
The ribs are attached to and covered by internal and external intercostal muscles.
The diaphragm at the floor of thoracic cavity consists of a muscle sheet at the periphery and a central circular fibrous tissue.
The muscles of the diaphragm are attached to the thorax wall.
The lungs communicate with the outside atmosphere through the bronchi, trachea, mouth and nasal cavities.
The trachea opens into the mouth cavity through the larynx.
A flap of muscles, the epiglottis, covers the opening into the trachea during swallowing.
This prevents entry of food into the trachea.
Nasal cavities are connected to the atmosphere through the external nares(or nostrils)which are lined with hairs and mucus that trap dust particles and bacteria, preventing them from entering into the lungs.
Nasal cavities are lined with cilia.
The mucus traps dust particles,
The cilia move the mucus up and out of the nasal cavities.
The mucus moistens air as it enters the nostrils.
Nasal cavities are winding and have many blood capillaries to increase surface area to ensure that the air is warmed as it passes along.
Each lung is surrounded by a space called the pleural cavity.
It allows for the changes in lung volume during breathing.
An internal pleural membrane covers the outside of each lung while an external pleural membrane lines the thoracic wall.
The pleural membranes secrete pleural fluid into the pleural cavity.
This fluid prevents friction between the lungs and the thoracic wall during breathing.
The trachea divides into two bronchi, each of which enters into each lung.
Trachea and bronchi are lined with rings of cartilage that prevent them from collapsing when air pressure is low.
Each bronchus divides into smaller tubes, the bronchioles.
Each bronchiole subdivides repeatedly into smaller tubes ending with fine bronchioles.
The fine bronchioles end in alveolar sacs, each of which gives rise to many alveoli.
Epithelium lining the inside of the trachea, bronchi and bronchioles has cilia and secretes mucus.
Adaptations of Alveolus to Gaseous Exchange
Each alveolus is surrounded by very many blood capillaries for efficient transport of respiratory gases.
There are very many alveoli that greatly increases the surface area for gaseous exchange.
The alveolus is thin walled for faster diffusion of respiratory gases.
The epithelium is moist for gases to dissolve.
Gaseous Exchange between the Alveoli and the Capillaries
The walls of the alveoli and the capillaries are very thin and very close to each other.
Blood from the tissues has a high concentration of carbon (IV) oxide and very little oxygen compared to alveolar air.
The concentration gradient favours diffusion of carbon (IV) oxide into the alveolus and oxygen into the capillaries.
No gaseous exchange takes place in the trachea and bronchi.
These are referred to as dead space.
Ventilation
Exchange of air between the lungs and the outside is made possible by changes in the volumes of the thoracic cavity.
This volume is altered by the movement of the intercostal muscles and the diaphragm.
Inspiration
The ribs are raised upwards and outwards by the contraction of the external intercostal muscles, accompanied by the relaxation of internal intercostal muscles.
The diaphragm muscles contract and diaphragm moves downwards.
The volume of thoracic cavity increases, thus reducing the pressure.
Air rushes into the lungs from outside through the nostrils.
Expiration
The internal intercostal muscles contract while external ones relax and the ribs move downwards and inwards.
The diaphragm muscles relaxes and it is pushed upwards by the abdominal organs. It thus assumes a dome shape.
The volume of the thoracic cavity decreases, thus increasing the pressure.
Air is forced out of the lungs.
As a result of gaseous exchange in the alveolus, expired air has different volumes of atmospheric gases as compared to inspired air.
|
Component
|
Inspired %
|
Expired %
|
|
Oxygen
|
21
|
16
|
|
Carbon dioxide
|
0.03
|
4
|
|
Nitrogen
|
79
|
79
|
|
Moisture
|
Variable
|
Saturated
|
TABLE 1: COMPARISON OF INSPIRED AND EXPIRED AIR (% BY VOLUME)
Lung Capacity
The amount of air that human lungs can hold is known as lung capacity.
The lungs of an adult human are capable of holding 5,000 cm3 of air when fully inflated.
However, during normal breathing only about 500 cm3 of air is exchanged.
This is known as the tidal volume.
A small amount of air always remains in the lungs even after a forced expiration.
This is known as the residual volume.
The volume of air inspired or expired during forced breathing is called vital capacity.
Control of Rate of Breathing
The rate of breathing is controlled by the respiratory centre in the medulla of the brain.
This centre sends impulses to the diaphragm through the phrenic nerve.
Impulses are also sent to the intercostal muscles.
The respiratory centre responds to the amount of carbon (IV) oxide in the blood.
If the amount of carbon (IV) oxide rises, the respiratory centre sends impulses to the diaphragm and the intercostal muscles which respond by contracting in order to increase the ventilation rate.
Carbon (IV) oxide is therefore removed at a faster rate.
Factors Affecting Rate of Breathing in Humans
The rabbit is placed in a bucket containing cotton wool which has been soaked in chloroform.
The bucket is covered tightly with a lid.
The dead rabbit is placed on the dissecting board ventral side upwards.
Pin the rabbit to the dissecting board by the legs.
Dissect the rabbit to expose the respiratory organs.
Ensure that you note the following features.
Ribs, intercostal muscles, diaphragm, lungs, bronchi, trachea, pleural membranes, thoracic cavity.
The amount of air that human lungs can hold is known as lung capacity.
The lungs of an adult human are capable of holding 5,000 cm3 of air when fully inflated.
However, during normal breathing only about 500 cm3 of air is exchanged.
This is known as the tidal volume.
A small amount of air always remains in the lungs even after a forced expiration.
This is known as the residual volume.
The volume of air inspired or expired during forced breathing is called vital capacity.
Control of Rate of Breathing
The rate of breathing is controlled by the respiratory centre in the medulla of the brain.
This centre sends impulses to the diaphragm through the phrenic nerve.
Impulses are also sent to the intercostal muscles.
The respiratory centre responds to the amount of carbon (IV) oxide in the blood.
If the amount of carbon (IV) oxide rises, the respiratory centre sends impulses to the diaphragm and the intercostal muscles which respond by contracting in order to increase the ventilation rate.
Carbon (IV) oxide is therefore removed at a faster rate.
Factors Affecting Rate of Breathing in Humans
- Factors that cause a decrease or increase in energy demand directly affect rate of breathing.
- Exercise, any muscular activity like digging.
- Sickness
- Emotions like anger, flight
- Sleep.
- Students to work in pairs.
- One student stands still while the other counts (his/her) the number of breaths per minute.
- The student whose breath has been taken runs on the sport vigorously for 10 minutes.
- At the end of 10 minutes the number of breaths per minute is immediately counted and recorded.
- It is noticed that the rate of breathing is much higher after exercise than at rest.
The rabbit is placed in a bucket containing cotton wool which has been soaked in chloroform.
The bucket is covered tightly with a lid.
The dead rabbit is placed on the dissecting board ventral side upwards.
Pin the rabbit to the dissecting board by the legs.
Dissect the rabbit to expose the respiratory organs.
Ensure that you note the following features.
Ribs, intercostal muscles, diaphragm, lungs, bronchi, trachea, pleural membranes, thoracic cavity.
Diseases of the Respiratory System
Asthma
Asthma is a chronic disease characterised by narrowing of air passages.
Causes:
1)Allergy
Due to pollen, dust, fur, animal hair, spores among others.
If these substances are inhaled, they trigger release of chemical substances and they may cause swelling of the bronchioles and bring about an asthma attack.
2)Heredity
Asthma is usually associated with certain disorders which tend to occur in more than one member of a given family, thus suggesting' a hereditary tendency.
3)Emotional or mental stress
Strains the body immune system hence predisposes to asthma attack.
Symptoms
Asthma is characterized by wheezing and difficulty in breathing accompanied by feeling of tightness in the chest as a result of contraction of the smooth muscles lining the air passages.
Treatment and Control
Causes:
1)Allergy
Due to pollen, dust, fur, animal hair, spores among others.
If these substances are inhaled, they trigger release of chemical substances and they may cause swelling of the bronchioles and bring about an asthma attack.
2)Heredity
Asthma is usually associated with certain disorders which tend to occur in more than one member of a given family, thus suggesting' a hereditary tendency.
3)Emotional or mental stress
Strains the body immune system hence predisposes to asthma attack.
Symptoms
Asthma is characterized by wheezing and difficulty in breathing accompanied by feeling of tightness in the chest as a result of contraction of the smooth muscles lining the air passages.
Treatment and Control
- There is no definite cure for asthma.
- The best way where applicable is to avoid whatever triggers an attack (allergen).
- Treatment is usually by administering drugs called bronchodilators.
- The drugs are inhaled, taken orally or injected intravenously depending on severity of attack to relief bronchial spasms.
Bronchitis
This is an inflammation of bronchial tubes.
Causes
This is due to an infection of bronchi and bronchioles by bacteria and viruses.
Symptoms
Causes
This is due to an infection of bronchi and bronchioles by bacteria and viruses.
Symptoms
- Difficulty in breathing.
- Cough that produces mucus.
- Antibiotics are administered.
Pulmonary Tuberculosis
Tuberculosis is a contagious disease that results in destruction of the lung tissue.
Causes
It is characterised by a dry cough, lack of breath and body wasting.
Prevention
Treatment is by use of antibiotics.
Causes
- Tuberculosis is caused by the bacterium Mycobacterium tuberculosis.
- Human tuberculosis is spread through droplet infection i.e., in saliva and sputum.
- Tuberculosis can also spread from cattle to man through contaminated milk.
- From a mother suffering from the disease to a baby through breast feeding.
- The disease is currently on the rise due to the lowered immunity in persons with HIV and AIDS (Human Immuno Deficiency Syndrome).
- Tuberculosis is common in areas where there is dirt, overcrowding and malnourishment.
It is characterised by a dry cough, lack of breath and body wasting.
Prevention
- Proper nutrition with a diet rich in proteins and vitamins to boost immunity.
- Isolation of sick persons reduces its spread.
- Utensils used by the sick should be sterilised by boiling.
- Avoidance of crowded places and living in well ventilated houses.
- Immunisation with B.C.G. vaccine gives protection against tuberculosis.
- This is done a few days after birth with subsequent boosters.
Treatment is by use of antibiotics.
Pneumonia
Pneumonia is infection resulting in inflammation of lungs.
The alveoli get filled with fluid and bacterial cells decreasing surface are for gaseous exchange.
Pneumonia is caused by bacteria and virus.
More infections occur during cold weather.
The old and the weak in health are most vulnerable.
Symptoms
Pain in the chest accompanied by a fever, high body temperatures (39-40°C) and general body weakness.
Prevention
The alveoli get filled with fluid and bacterial cells decreasing surface are for gaseous exchange.
Pneumonia is caused by bacteria and virus.
More infections occur during cold weather.
The old and the weak in health are most vulnerable.
Symptoms
Pain in the chest accompanied by a fever, high body temperatures (39-40°C) and general body weakness.
Prevention
- Maintain good health through proper feeding.
- Avoid extreme cold.
- If the condition is caused by pneumococcus bacteria, antibiotics are administered.
- If breathing is difficult, oxygen may be given using an oxygen mask.
Whooping Cough
- Whooping cough is an acute infection of respiratory tract.
- The disease is more common in children under the age of five but adults may also be affected.
It is caused by Bordetella pertusis bacteria and is usually spread by droplets produced when a sick person coughs.
Symptoms:
- Severe coughing and frequent vomiting.
- Thick sticky mucus is produced.
- Severe broncho-pneumonia.
- Convulsions in some cases.
- Children may be immunised against whooping cough by means of a vaccine which is usually combined with those against diphtheria and tetanus.
- It is called "Triple Vaccine" or Diphtheria, Pertusis and Tetanus (DPT).
- Antibiotics are administered.
- To reduce the coughing, the patient should be given drugs.
Practical Activities
Observation of permanent slides of terrestrial and aquatic leaves and stems
Leaves
Leaves
- Observation of T.S. of bean and water lily are made under low and 'medium power objectives. Stomata and air space are seen.
- Labelled drawings of each are made.
- The number and distribution of stomata on the lower and upper leaf surface is noted.
- Also the size of air spaces and their distribution.
- Prepared slides (TS) of stems of terrestrial and aquatic plants such as croton and reeds are obtained.
- Observations under low power and medium power of a microscope are made.
- Labelled drawings are made and the following are noted:
- Lenticels on terrestrial stems.
- Large air spaces (aerenchyma) in aquatic stems.
Notes on Gaseous Exchange in plants and animals
SPECIFIC OBJECTIVES
GASEOUS EXCHANGE IN PLANTS AND ANIMALS
By the end of the topic, the learner should be able to:
- Explain the need for gaseous exchange in living organisms
- Explain the mechanism of gaseous exchange in plants
- Compare the internal structures of aquatic and terrestrial roots, stems and leaves
- Examine various types of respiratory structures in animals and relate them to their functions
- State the characteristics of respiratory surfaces
- Describe the mechanisms of gaseous exchange in protozoa, insects, fish, frog and mammal
- Describe the factors which control the rate of breathing in humans
- State the causes, symptoms and prevention of respiratory diseases.
TOPIC/SUBTOPICS OUTLINE
GASEOUS EXCHANGE (36 LESSONS)
Gaseous exchange in living organisms (necessity)
Gaseous Exchange in Plants
Respiratory diseases: Asthma, Bronchitis, Pulmonary tuberculosis, Pneumonia and whooping cough
Practical Activities
Observe permanent slides of cross- sections of aerial and aquatic leaves and stems
Examine the distribution of spiracles on grasshopper or locust
Examine the gills of a bony fish
Dissect a small mammal and identify the structures of the respiratory system (demonstration) Construct and use models to demonstrate breathing mechanisms in a mammal (human) Demonstrate the effect of exercise on the rate of breathing
Gaseous exchange in living organisms (necessity)
Gaseous Exchange in Plants
- Mechanisms of opening and closing of stomata
- The process of gaseous exchange in root, stem and leaves of both aquatic (floating) and terrestrial plants
- Types and Characteristics of Respiratory Surfaces - cell membrane, gills, buccal cavity, skin and lungs
- Mechanism of gaseous exchange in
- Protozoa - amoeba
- Insect – grasshopper
- Fish – bonyfish
- Amphibia – frog
- Mammal - human
Respiratory diseases: Asthma, Bronchitis, Pulmonary tuberculosis, Pneumonia and whooping cough
Practical Activities
Observe permanent slides of cross- sections of aerial and aquatic leaves and stems
Examine the distribution of spiracles on grasshopper or locust
Examine the gills of a bony fish
Dissect a small mammal and identify the structures of the respiratory system (demonstration) Construct and use models to demonstrate breathing mechanisms in a mammal (human) Demonstrate the effect of exercise on the rate of breathing
INTRODUCTION TO GASEOUS EXCHANGE IN PLANTS AND ANIMALS
Necessity for Gaseous Exchange in Living Organisms
- Living organisms require energy to perform cellular activities.
- The energy comes from breakdown of food in respiration.
- Carbon (IV) oxide is a byproduct of respiration and its accumulation in cells is harmful which has to be removed.
- Most organisms use oxygen for respiration which is obtained from the environment.
- Photosynthetic cells of green plants use carbon (IV) oxide as a raw material for photosynthesis and produce oxygen as a byproduct.
- The movement of these gases between the cells of organisms and the environment comprises gaseous exchange.
- The process of moving oxygen into the body and carbon (Iv) oxide out of the body is called breathing or ventilation.
- Gaseous exchange involves the passage of oxygen and carbon (IV) oxide through a respiratory surface.
- Diffusion is the main process involved in gaseous exchange.
Gaseous Exchange in Plants
- Oxygen is required by plants for the production of energy for cellular activities.
- Carbon (IV) oxide is required as a raw material for the synthesis of complex organic substances.
- Oxygen and carbon (IV) oxide are obtained from the atmosphere in the case of terrestrial plants and from the surrounding water in the case of aquatic plants.
- Gaseous exchange takes place mainly through the stomata.
Structure of Guard Cells
FIGURE 1: STRUCTURE OF GUARD CELL
- The stoma (stomata - plural) is surrounded by a pair of guard cells.
- The structure of the guard cells is such that changes in turgor inside the cell cause changes in their shape.
- They are joined at the ends and the cell walls facing the pore (inner walls) are thicker and less elastic than the cell walls farther from the pore (outer wall).
- Guard cells control the opening and closing of stomata.
Mechanism of Opening and Closing of Stomata
- In general stomata open during daytime (in light) and close during the night (darkness).
- Stomata open when osmotic pressure in guard cells becomes higher than that in surrounding cells due to increase in solute concentration inside guard cells. Water is then drawn into guard cells by osmosis.
- Guard cells become turgid and extend.
- The thinner outer walls extend more than the thicker walls.
- This causes a bulge and stoma opens.
- Stomata close when the solute concentration inside guard cells become lower than that of surrounding epidermal cells.
- The water moves out by osmosis, and the guard cells shrink i.e. lose their turgidity and stoma closes.
Proposed causes of turgor changes in guard cells.
Accumulation of sugar.
- Guard cells have chloroplasts while other epidermal cells do not.
- Photosynthesis takes place during daytime and sugar produced raises the solute concentration of guard cells.
- Water is drawn into guard cells by osmosis from surrounding cells.
- Guard cells become turgid and stoma opens.
- At night no photosynthesis occurs hence no sugar is produced.
- The solute concentration of guard cells falls and water moves out of the guard cells by osmosis.
- Guard cells lose turgidity and the stoma closes.
- In day time carbon (IV) oxide is used for photosynthesis. This reduces acidity while the oxygen produced increases alkalinity.
- Alkaline pH favours conversion of starch to sugar.
- Solute concentration increases inside guard cells, water is drawn into the cells by osmosis. Guard cells become turgid and the stoma opens.
- At night when no photosynthesis, Respiration produces carbon (IV) oxide which raises acidity. This favours conversion of sugar to starch. Low sugar concentration lead to loss of turgidity in guard cells and stoma closes.
Explanation is based on accumulation of potassium
Ions
- In day time (light) adenosine triphosphate (ATP) is produced which causes potassium ions to move into guard cells by active transport.
- These ions cause an increase in solute concentration in guard cells that has been shown to cause movement of water into guard cells by osmosis.
- Guard cells become turgid and the stoma opens.
- At night potassium and chloride ions move out of the guard cells by diffusion and level of organic acid also decreases.
- This causes a drop in solute concentration that leads to movement of water out of guard cells by osmosis.
- Guard cells lose turgor and the stoma closes.
Process of Gaseous Exchange in Root Stem and Leaves of Aquatic and Terrestrial Plants
Gaseous Exchange in leaves of Terrestrial Plants
Gaseous exchange takes place by diffusion.
The structure of the leaf is adapted for gaseous exchange by having intercellular spaces that are filled.
These are many and large in the spongy mesophyll.
Gaseous exchange takes place by diffusion.
The structure of the leaf is adapted for gaseous exchange by having intercellular spaces that are filled.
These are many and large in the spongy mesophyll.
When stomata are open, carbon (IV) oxide from the atmosphere diffuses into the substomatal air chambers.
From here, it moves into the intercellular space in the spongy mesophyll layer.
The CO2 goes into solution when it comes into contact with the cell surface and diffuses into the cytoplasm. A concentration gradient is maintained between the cytoplasm of the cells and the intercellular spaces. CO2 therefore continues to diffuse into the cells.
The oxygen produced during photosynthesis moves out of the cells and into the intercellular spaces.
From here it moves to the substomatal air chambers and eventually diffuses out of the leaf through the stomata. At night oxygen enters the cells while CO2 moves out.
Gaseous exchange in the leaves of aquatic (floating) plants
- Aquatic plants such as water lily have stomata only on the upper leaf surface.
- The intercellular spaces in the leaf mesophyll are large.
- Gaseous exchange occurs by diffusion just as in terrestrial plants.
Transverse section of leaves of an aquatic plant such as Nymphaea differs from that of terrestrial plant.
The following are some of the features that can be observed in the leave of an aquatic plant;
- Absence of cuticle
- Palisade mesophyll cells are very close to each other i.e. compact.
- Air spaces (aerenchyma) in spongy mesophyll are very large.
- Sclereids (stone cells) are scattered in leaf surface and project into air spaces.
- They strengthen the leaf making it firm and assist it to float.
Gaseous Exchange through Stems
Terrestrial Plants
Stems of woody plants have narrow openings or slits at intervals called lenticels.
They are surrounded by loosely arranged cells where the bark is broken.
They have many large air intercellular spaces through which gaseous exchange occurs.
Oxygen enters the cells by diffusion while carbon (IV) oxide leaves.
Unlike the rest of the bark, lenticels are permeable to gases and water.
Stems of woody plants have narrow openings or slits at intervals called lenticels.
They are surrounded by loosely arranged cells where the bark is broken.
They have many large air intercellular spaces through which gaseous exchange occurs.
Oxygen enters the cells by diffusion while carbon (IV) oxide leaves.
Unlike the rest of the bark, lenticels are permeable to gases and water.
Aquatic Plant Stems
The water lily, Salvia and Wolfia whose stems remain in water are permeable to air and water.
Oxygen dissolved in the water diffuses through the stem into the cells and carbon (IV) oxide diffuses out into the water.
Oxygen dissolved in the water diffuses through the stem into the cells and carbon (IV) oxide diffuses out into the water.
Gaseous Exchange in Roots
Terrestrial Plants
Gaseous exchange occurs in the root hair of young terrestrial plants.
Oxygen in the air spaces in the soil dissolves in the film of moisture surrounding soil particles and diffuses into the root hair along a concentration gradient.
It diffuses from root hair cells into the cortex where it is used for respiration.
Carbon (IV) oxide diffuses in the opposite direction.
In older roots of woody plants, gaseous exchange takes place through lenticels.
Aquatic Plants
Roots of aquatic plants e.g. water lily are permeable to water and gases.
Oxygen from the water diffuses into roots along a concentration gradient.
Carbon (IV) oxide diffuses out of the roots and into the water.
The roots have many small lateral branches to increase the surface area for gaseous exchange.
They have air spaces that help the plants to float.
Mangroove plants grow in permanently waterlogged soils, muddy beaches and at estuaries.
They have roots that project above the ground level.
These are known as breathing roots or pneumatophores.
These have pores through which gaseous exchange takes place e.g. in Avicenia the tips of the roots have pores.
Others have respiratory roots with large air spaces.
Gaseous exchange occurs in the root hair of young terrestrial plants.
Oxygen in the air spaces in the soil dissolves in the film of moisture surrounding soil particles and diffuses into the root hair along a concentration gradient.
It diffuses from root hair cells into the cortex where it is used for respiration.
Carbon (IV) oxide diffuses in the opposite direction.
In older roots of woody plants, gaseous exchange takes place through lenticels.
Aquatic Plants
Roots of aquatic plants e.g. water lily are permeable to water and gases.
Oxygen from the water diffuses into roots along a concentration gradient.
Carbon (IV) oxide diffuses out of the roots and into the water.
The roots have many small lateral branches to increase the surface area for gaseous exchange.
They have air spaces that help the plants to float.
Mangroove plants grow in permanently waterlogged soils, muddy beaches and at estuaries.
They have roots that project above the ground level.
These are known as breathing roots or pneumatophores.
These have pores through which gaseous exchange takes place e.g. in Avicenia the tips of the roots have pores.
Others have respiratory roots with large air spaces.
TOPICAL QUESTIONS
These questions are good for group discussions in and out of a classroom environment they can also be used in a question and answer brainstorming sessions
- What is gaseous exchange?
- Why is gaseous exchange important to organisms?
- Name the structure used for gaseous exchange by plants
- Briefly describe the structure of stomata
- State the factors which affect stomatal opening
- Name the theories suggesting the mechanism of opening and closing of stomata
- Describe the mechanism of opening and closing of stomata
- What is the advantage of having stomata open during daytime and having them closed at night?
- State the ways in which leaves of plants are adapted to gaseous exchange
- Describe how gaseous exchange takes place in terrestrial plants
- State the ways in which floating leaves of aquatic plants are adapted to gaseous exchange
- How is aerenchyma tissue adapted to its function?
- Explain stomatal distribution in plants of different habitats
- List the types of respiratory surfaces of animals
- State the characteristics of respiratory surfaces in animals
- Describe gaseous exchange in protozoa
- Make a labeled drawing of a fish gill
- How is a fish gill adapted to its function?
- Discuss gaseous exchange in bony fish example is tilapia
- What is counter-flow system?
- What is the advantage of counter-flow system?
- Describe the mechanism of gaseous exchange in terrestrial insects
- State how traceholes are adapted to gaseous
- What is breathing?
- Name the structures in humans that are used in gaseous exchange
- Describe the mechanism of gaseous exchange in a mammal
- Explain how mammalian lungs are adapted to gaseous exchange
- Name the features of alveoli that adapt them to their function
- How is the trachea of a mammal suited to its function?
- State the advantages of breathing through the nose rather than through the mouth
- Give the conditions under which the carbon iv oxide level rises above normal in mammalian blood
- Explain the physiological changes that occur in the body to lower the carbon iv oxide level back to normal when it rises
- Describe the factors which control the rate of breathing in humans
- Name the respirator diseases
- Define respiration
- Explain the significance of respiration in living organisms
- Draw and label a mitochondrion
- Explain the roles of enzymes in respiration
- What is aerobic respiration?
- Give a word equation for aerobic respiration
- What are the end products of aerobic respiration?
- What is anaerobic respiration?
- What are obligate anaerobes?
- What are facultative anaerobes?
- State the word equation representing anaerobic respiration in plants
- Name the end products of anaerobic respiration in plants alcohol/ethanol carbon iv oxide
- Give a word equation of anaerobic respiration in animals
- Name the end products of respiration in animals when there is insufficient oxygen supply
- Why is there a high rate of lactic acid production during exercise?
- Why does lactic acid level reduce after exercise?
- State why accumulation of lactic acid during vigorous exercise lead to an increase in heartbeat
- State the economic importance of anaerobic respiration
- What is oxygen debt?
- What is respiratory quotient(RQ)?
- Why are respiratory quotient important?
- Name the respiratory substrates
- Why does anaerobic respiration of a given substrate yield a smaller amount of energy than aerobic respiration?
- Mention the types of experiments carried out for respiration
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SPECIFIC OBJECTIVES
By the end of the topic, the learner should be able to:
- define the cell
- state the purpose of a light microscope
- identify the parts of a light microscope and state their functions
- use and care for the light microscope and state the magnification
- identify the components of a cell as seen under the light and electron microscopes and relate their structure to functions
- compare plant and animal
- mount and stain temporary slides of plant cells
- describe animal cells as observed from permanent
- estimate cell size
- state the differences between cells, tissues, organs and organ systems.
TOPIC / SUB-TOPIC BREAKDOWN
- Definition of the cell
- Structure and functions of parts of a light microscope
- Use and care of the light microscope
- Cell structure and functions as seen under
- a light microscope
- an electron microscope
- Preparation of temporary slides of plant cells
- Estimation of cell size
- Cell specialization, tissues, organs and organ systems
- Observe, identify, draw and state the functions of parts of the light microscope
- Prepare and observe temporary slides of plant cells
- Observe permanent slides of animal cells
- Comparison between plant and animal cells
- Observe, estimate size and calculate magnification of plant cells
THE CELL
Introduction
- The cell is the basic unit of an organism.
- All living organisms are made up of cells.
- Some organisms are made up of one cell and others are said to be multicellular.
- Other organisms are made of many cells and are said to be multicellular.
- Cells are too little to see with the naked eye.
- They can only be seen with the aid of a microscope.
The microscope
The microscope is used to magnify objects.
Magnification
Magnification
- The magnifying power is usually inscribed on the lens.
- To find out how many times a specimen is magnified, the magnifying power of the objective lens is multiplied by that of the eye piece lens.
- If the eye piece magnification lens is x10 and the objective lens is x4, the total magnification is x40.
- Magnification has no units.
- It should always have the multiplication sign.e.g.x40
Microscope parts and their functions
- Eye piece - Has a lens which contributes to the magnification of the object under view.
- Coarse adjustment knob - Moves the body tube up and down for long distances and it brings the image into focus.
- Fine adjustment knob - Moves the body tube and brings the image into fine focus.
- Body tube - Holds the eye piece and the revolving nose piece. It directs light from objective lenses to the eye piece lens.
- Revolving nose piece - Holds and brings objective lenses into position.
- Objective lens - Contributes to the magnification of the object.
- Arm/limb - It is for handling the microscope and also tilting it.
- Stage - Is the flat platform onto which the slide with the object is placed.
- Clips - They hold the slide firmly onto the stage.
- Condenser - Concentrates light onto the object.
- Diaphragm - Regulates the amount of light passing through the object.
- Mirror - Reflects light into the condenser.
- Hinge screw - Fixes the arm to the base and allows for tilting of the arm.
- Base/stand - Provides support to the microscope
To View the Object
- Turn the low power objective lens until it clicks into position.
- Looking through the eye piece, ensure that enough light is passing through by adjusting the mirror.
- This is indicated by a bright circular area known as the field of view.
- Place the slide containing the specimen on stage and clip it into position.
- Make sure that the specimen is in the centre of the field of view.
- Using the coarse adjustment knob, bring the low power objective lens to the lowest point.
- Turn the knob gently until the specimen comes into focus.
- If finer details are required, use the fine adjustment knob.
- When using high power objective always move the fine adjustment knob upwards.
Care of a Microscope
- Great care should be taken when handling it.
- Keep it away from the edge of the bench when using it.
- Always hold it with both hands when moving it in the laboratory.
- Clean the lenses with special lens cleaning paper.
- Make sure that the low power objective clicks in position in line with eye piece lens before and after use.
- Store the microscope in a dust-proof place free of moisture.
Cell Structure as Seen Through the Light Microscope
The cell as seen above has the following:
Cell membrane (Plasma membrane):
- This is a thin membrane enclosing cell contents.
- It controls the movement of substances into and out of the cell.
Cytoplasm:
- This is a jelly-like substance in which chemical processes are carried out.
- Scattered all over the cytoplasm are small structures called organelles.
- Like an animal cell, the plant cell has a cell membrane, cytoplasm and a nucleus.
Vacuole:
- Plant cells have permanent, central vacuole. It contains cell sap where sugars and salts are stored.
Cell wall:
- This is the outermost boundary of a plant cell.
- It is made of cellulose.
- Between the cells is a middle lamella made of calcium precipitate.
Chloroplasts;
- With special staining techniques it is possible to observe chloroplasts.
- These are structures which contain chlorophyll, the green pigment responsible for trapping light for photosynthesis.
The Electron Microscope (EM)
- Capable of magnifying up to 500,000 times.
- The specimen is mounted in vacuum chamber through which an electron beam is directed.
- The image is projected on to a photographic plate.
- The major disadvantage of the electron microscope is that it cannot be used to observe living objects.
- However, it provides a higher magnification and resolution (ability to see close points as separate) than the light microscope so that specimen can be observed in more detail.
Cell Structure as Seen Through Electron Microscope
The Plasma Membrane
- Under the electron microscope, the plasma membrane is seen as a double layer.
- This consists of a lipid layer sandwiched between two protein layers.
- This arrangement is known as the unit membrane and the shows two lipid layers with proteins within.
- Substances are transported across the membrane by active transport and diffusion.
The Endoplasmic Reticulum (ER)
- This is a network of tubular structures extending throughout the cytoplasm of the cell.
- It serves as a network of pathways through which materials are transported from one part of the cell to the other.
- An ER encrusted with ribosomes it is referred to as rough endoplasmic reticulum.
- An ER that lacks ribosomes is referred to as smooth endoplasmic reticulum.
- The rough endoplasmic reticulum transports proteins while the smooth endoplasmic reticulum transports lipids.
The Ribosomes
- These are small spherical structures attached to the ER.
- They consist of protein and ribonucleic acid (RNA).
- They act as sites for the synthesis of proteins.
Golgi Bodies
- Golgi bodies are thin, plate-like sacs arranged in stacks and distributed randomly in the cytoplasm.
- Their function is packaging and transportation of glycol-proteins.
- They also produce lysosomes.
Mitochondria
- Each mitochondrion is a rod-shaped organelle.
- Made up of a smooth outer membrane and a folded inner membrane.
- The folding of the inner membrane are called cristae.
- They increase the surface area for respiration.
- The inner compartments called the matrix.
- Mitochondria are the sites of cellular respiration, where energy is produced.
Lysosomes
- These are vesicles containing hydrolytic enzymes.
- They are involved in the breakdown of micro-organisms, foreign macromolecules and damaged or worn-out cells and organelles.
The Nucleus
- The nucleus is surrounded by a nuclear membrane which is a unit membrane.
- The nuclear membrane has pores through which materials can move to the surrounding cytoplasm.
- The nucleus contains proteins and nucleic acid deoxyribonucleic acid (DNA) and RNA.
- The chromosomes are found in the nucleus.
- They are the carriers of the genetic information of the cell.
- The nucleolus is also located in the nucleus but it is only visible during the non-dividing phase of the cell.
The Chloroplasts
- These are found only in photosynthetic cells.
- Each chloroplast consists of an outer unit. Membrane enclosing a series of interconnected membranes called lamellae.
- At various points along their length the lamellae form stacks of disc like structures called grana.
- The lamellae are embedded in a granular material called the stroma.
- The chloroplasts are sites of photosynthesis.
- The light reaction takes place in the lamellae while the dark reactions take place in the stroma.
Comparison between animal cell and plant cell
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PLANT CELL
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ANIMAL CELL
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Has a cell wall and a cell membrane
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Has cell membrane only
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Nucleus at periphery
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Nucleus at the center
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Have chloroplasts
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Have no chloroplasts
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Are usually large
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Are usually small
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Has a large central vacuole
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Has no vacuoles, they are small and scattered
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Are regular in shape
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Irregular in shape
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Has no centriole
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Has centrioles
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Stores starch, oils and protein
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Store glycogen and fats
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Cell Specialization
Cells are specialized to perform different functions in both plants and animals.
Example;
Example;
- Palisade cells have many chloroplasts for photosynthesis.
- Root hair cells are long and thin to absorb water from the soil.
- Red blood cells have haemoglobin which transports oxygen.
- Sperm cells have a tail to swim to the egg.
- Multicellular organisms cells that perform the same function are grouped together to form a tissue.
- Each tissue is therefore made up of cells that are specialised to carry out a particular function.
Animal Tissues
Examples of animal tissues;
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Type of tissue
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Functions
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1. Epithelial Tissue
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Covering, allowing movement of materials
Covering of internal organs, lining for body cavity. Secretion, absorption e.g. in the alimentary canal. Covering surfaces, protection e.g. the skin. Absorption e.g. in the kidney tubules. |
Thin flat cells.
Cells that are longer than they are wide. Several layers of epithelial cells (either squamous. cuboidal or columnar). Cube like cells. |
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2. Muscular Tissue
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Contraction, bringing about movement of body parts.
Contract and allow movement. Cover internal organs; allow movement e.g. peristalsis. Cause contraction of the heart. |
Consists of units called myofibrils.
Are multinucleated; have transverse striations; Controlled by voluntary nervous system. Are spindle-shaped. mononucleated; Controlled by involuntary nervous system. contract rhythmically; are myogenic (ability to contract is within) |
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3. Supporting Tissue
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Support the body. provide a rigid
Framework, protect soft tissue. |
Cells that produce hard materials.
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4. Blood
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Transport of materials, protection against disease.
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A complex tissue consisting of three types of cells suspended in a fluid medium (Plasma)
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5. Nerve Tissue
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Receive stimuli and transmit impulses; co-ordinate body activities
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Consists of cells called neurons which are interconnected through axons to enable transmission of impulses
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Plant Tissues
Example of plant tissues;
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Type of Tissue
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Functions
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Characteristics
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Meristematic
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Undergo division and cause growth, e.g. increase in length and girth
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Small thin-walled cells, contain a lot of cytoplasm; found mostly at the tip of shoots and roots.
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Parenchyma
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Photosynthesis gaseous exchange; support; storage.
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Thin walled cells; vary in shape and size; many intercellular spaces.
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Collenchyma
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Strengthening
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Thickened walls; no intercellular spaces; found in cortex of stems.
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Sclerenchyma
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Strengthening
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Vary in shape; thick cell walls; are usually dead.
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Vascular
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Transport materials.
Transport of water and mineral salts. Transport of organic materials (manufactured food). |
Tubular vessels and trancheids joined end to end.
Sieve elements joined to each other through sieve pores. |
Organs
- An organ is made up of different tissues e.g. the heart, lungs, kidneys and the brain in animals and roots, stems and leaves in plants.
Organ systems
- Organs which work together form an organ system.
- Digestive, excretory, nervous and circulatory in animals and transport and support system in plants.
Organism
- Different organ systems form an organism.
Practical Activities
Observation and Identification of parts of a light microscope and their functions
- A light microscope is provided.
- Various parts are identified and observed.
- Drawing and labelling of the microscope is done.
- Functions of the parts of the microscope are stated.
- Calculations of total magnification done using the formula.
- Eye piece lens magnification objective lens magnification.
Preparation and Observation of Temporary Slides of Plant Cells
- A piece of epidermis is made from the fleshy leaf of an onion bulb. It is placed on a microscope slide and a drop of water added.
- A drop of iodine is added and a cover slip placed on top.
- Observations are made, under low and medium power objective.
- The cell wall and nucleus stain darker than other parts.
- A labelled drawing is made.
- The following are noted: Nucleus, cell wall, cytoplasm and cell membrane.
Observation of permanent slides of animal cells
- Permanent slides of animal cells are obtained e.g, of cheek cells, nerve cells and muscle cells.
- The slide is mounted on the microscope and observations made under low power and medium power objectives.
- Labelled drawings of the cells are made.
- A comparison between plant and animal cell is made.
Observation and Estimation of Cell Size and Calculation of Magnification of Plant Cells.
- Using the low power objective, a transparent ruler is placed on the stage of the microscope.
- An estimation of the diameter of the field of view is made in millimeters.
- This is converted into micrometres (1mm=1000u)
- A prepared slide of onion epidermal cells is mounted.
- The cells across the centre of the field of view are counted from left and right and top to bottom.
- The diameter of field of view is divided by the number of cells lying lengthwise to give an estimate of the length and width of each cell.
These are fats and oils.
Fats are solid at room temperature while oils are liquid.
They are made up of carbon, oxygen and hydrogen atoms.
The structural units of lipids are fatty acids and glycerol.
Fatty acids are made up of hydrocarbon chain molecules with a carboxyl group (-COOH) at one end.
In the synthesis of a lipid, three fatty acid molecules combine with one glycerol molecule to form a triglyceride.
Three molecules of water are lost in the process.
This is a condensation reaction and water is given off.
Lipids are hydrolysed e.g. during digestion to fatty acids and glycerol, water is added.
Condensation = Glycerol + 3 Fatty hydrolysis Lipid + Water acids
Fats are solid at room temperature while oils are liquid.
They are made up of carbon, oxygen and hydrogen atoms.
The structural units of lipids are fatty acids and glycerol.
Fatty acids are made up of hydrocarbon chain molecules with a carboxyl group (-COOH) at one end.
In the synthesis of a lipid, three fatty acid molecules combine with one glycerol molecule to form a triglyceride.
Three molecules of water are lost in the process.
This is a condensation reaction and water is given off.
Lipids are hydrolysed e.g. during digestion to fatty acids and glycerol, water is added.
Condensation = Glycerol + 3 Fatty hydrolysis Lipid + Water acids
Properties of Lipids
- Fats are insoluble in water but dissolve in organic solvents e.g. in alcohols.
- They are chemically inactive, hence used as food storage compounds.
- Structural materials - as structural material they make up the cell membrane.
- Source of energy - they are energy rich molecules. One molecule of lipid provides more energy than a carbohydrate molecule.
- Storage compound - They are stored as food reserves in plants. In animals e.g. mammals, all excess food taken is converted to fats which are stored in adipose tissue, and around internal organs such as the heart and kidneys.
- Insulation - They provide insulation in animals living in cold climates. A lot of fat is stored under the skin e.g. blubber in seals.
- Protection - Complex lipids e.g. wax on leaf surfaces protects the plant against water-loss and overheating. Fats stored around some internal organs acts as shock absorbers, thus protecting the organs.
- Source of Metabolic Water -:-lipids when oxidised produce metabolic water which supplements water requirements in the body. Desert animals e.g. the camel accumulate large quantities of fat in the hump which when oxidised releases metabolic water.
Proteins
- Proteins are the most abundant organic compounds in cells and constitute 50% of total dry weight.
- Proteins are compounds which are made up of carbon, hydrogen, nitrogen, oxygen and sometimes sulphur and phosphorus.
- The structural units of proteins are amino acids.
- The nature of a protein is determined by the types of amino acids it is made of.
- There are about 20 common amino acids that make up proteins.
Essential and Non-Essential Amino Acids
- Essential amino acids are those which cannot be synthesised in the body of an organism and must therefore be provided in the diet.
- There are ten amino acids which are essential for humans.
- These are valine, leucine, phenylalanine, lysine, tryptophan, isoleucine, methionine, threonine, histidine and arginine.
- Non-essential amino acids are those which the body can synthesise and therefore need not be available in the diet.
- There are ten of them.
- These are glycine, alanine, glutamic acid, aspartic acid, serine, tyrosine, proline, glutamine, arginine and cysteine.
- Proteins are essential in the diet because they are not stored in the body.
- Excess amino acids are deaminated.
Formation of Proteins
- Proteins are made up of many amino acid units joined together through peptide bonds.
- When two amino acids are joined together a dipeptide is formed.
- The chemical process involved is called condensation and a molecule of water is eliminated .
- When many amino acids are joined together a polypeptide chain is formed.
- The nature of a particular protein depends on the types, number and sequence of amino acids from which it is made.
Functions of Proteins
As structural materials proteins-
As functional chemical compounds.
Examples are hormones and enzymes that act as regulators in the body.
Respiratory pigments.
Examples are haemoglobin that transports oxygen in the blood and myoglobin that stores up oxygen in muscles.
Contractile proteins - make up muscles, i.e. myosin and actin.
Proteins combine with other chemical groups to form important substances e.g. mucin in saliva.
Source of energy.
Proteins are a source of energy in extreme conditions when carbohydrates and fats are not available e.g. in starvation.
As structural materials proteins-
- These are the basic building structures of protoplasms
- Proteins in conjunction with lipid form the cell membrane.
- Keratin (in hair, nails, hoofs, feathers and wool)
- Silk in spider's web.
- Elastin forms ligaments that join bones to each other.
- Antibodies that protect the body against foreign antigens.
- Fribrogen and thrombin are involved in clot formation, preventing entry of micro-organisms when blood vessel is cut.
As functional chemical compounds.
Examples are hormones and enzymes that act as regulators in the body.
Respiratory pigments.
Examples are haemoglobin that transports oxygen in the blood and myoglobin that stores up oxygen in muscles.
Contractile proteins - make up muscles, i.e. myosin and actin.
Proteins combine with other chemical groups to form important substances e.g. mucin in saliva.
Source of energy.
Proteins are a source of energy in extreme conditions when carbohydrates and fats are not available e.g. in starvation.
Enzymes
- Enzymes are biological catalysts that increase the rate of chemical reaction in the body.
- They are all produced inside cells.
- Some are intracellular and they catalyse reactions within the cells.
- Others are extracellular and are secreted out of the cells where they work. E.g. digestive enzymes.
Properties of Enzymes
- Enzymes are protein in nature.
- Enzymes are specific to the type of reaction they catalyse.
- This is referred to as substrate specificity.
- Enzymes work in very small amounts.
- They remain unchanged after the reaction.
- They catalyse reversible reactions.
- They work very fast (high turnover numbers) e.g. the enzyme catalase works on 600 thousand molecules of hydrogen peroxide in one second.
Naming of enzymes
Enzymes are named by adding the suffix -ase to:
Name of substrate that they work on e.g.
Enzymes are named by adding the suffix -ase to:
Name of substrate that they work on e.g.
- Carbohydrates - carbohydrases e.g.sucrase.
- Starch (amylose) - amylase
- Protein - proteinase (protease)
- Lipids -lipases
- Oxidation - oxidase
- Reduction - reductase
- Hydrolysis - hydrolase
Factors Affecting Enzyme Action
Temperature
- Enzymes are sensitive to temperature changes.
- Generally, the rate of an enzyme-controlled reaction doubles with every 10OC increase in temperature.
- However, temperatures above 40°C do not favour enzyme reaction.
- This is because enzymes are denatured by high temperatures.
- Every enzyme has a particular pH range over which it works best.
- Some enzymes work best in acidic media while others function better in alkaline media.
- Many enzymes function well under neutral conditions.
- Under conditions where the substrate is in excess, the rate of an enzyme-controlled reaction increases as the enzyme concentration is increased.
- If the concentration of the substrate is increased while that of the enzyme remains constant, the rate of the reaction will increase for some time and then become constant.
- Any further increase in substrate concentration will not result in corresponding increase in the rate of the reaction.
- These are substances that either compete with substrates for enzyme active sites or combine with enzymes and hence they inhibit the enzyme reaction; e.g. certain drugs, cyanide and nerve gas.
- Most enzymes require the presence of other compounds known as co-factors which are non-proteins.
- There are three groups of co-factors.
- Inorganic ions - e.g. iron, magnesium, copper and zinc.
- Complex organic molecules known as prosthetic groups are attached to the enzyme e.g. flavin adenine dinucleotide (FAD) derived from vitamin B2 (riboflavin).
- Co-enzymes e.g. coenzyme A is involved in respiration.
- All co-enzymes are derived from vitamins.
TOPICS
- Meaning of cell physiology
- Structure and properties of cell membrane (Theories of membrane structure not required)
- Physiological processes - diffusion, osmosis and active transport
- Factors affecting diffusion, osmosis and active transport
- Role of diffusion, osmosis and active transport in living organisms
- Water relations in plant and animal cells: turgor, plasmolysis, wilting and haemolysis
- Practical Activities
- Diffusion as demonstrated with Potassium permanganate or potassium iodide/flower dyes/coloured plant extracts/smoke
- Experiments with visking tubing and living tissues: fresh arrow roots/cassava/sweet potatoes/leaf petioles/Irish potatoes/carrots
- Plasmolysis can be demonstrated by using any of the following: spirogyra, epidermal cells of onion or raw egg that has been put in dilute hydrochloric acid overnight
Lesson Objectives
By the end of the topic, the learner should be able to:
- Define cell physiology
- Correlate the membrane structure with cell physiology in relation to permeability
- Differentiate between diffusion, osmosis and active transport
- State and describe factors affecting diffusion, osmosis and active transport
- Carry out experiments on diffusion and osmosis
- Explain the roles of diffusion, osmosis and active transport in living organisms
- Explain turgor and plasmolysis in terms of osmotic pressure.
Meaning of cell physiology
The term physiology refers to the functions that occur in living organisms.
Cell physiology refers to the process through which substances move across the cell membrane.
Several physiological processes take place inside the cell e.g. respiration.
Oxygen and glucose required enter the cell while carbon (IV) oxide and water produced leave the cell through the cell membrane.
Cell physiology refers to the process through which substances move across the cell membrane.
Several physiological processes take place inside the cell e.g. respiration.
Oxygen and glucose required enter the cell while carbon (IV) oxide and water produced leave the cell through the cell membrane.
Structure and properties of cell membrane
- The cell membrane is the protective barrier that shelter cellular contents.
- Movement of all substances into and out of the cells takes place across the cell membrane.
- It is made up of protein and lipid molecules.
- Lipid molecules have phosphate group attached to it on one end.
- They are then referred to phospholipids.
- The phospholipids are arranged to form a double layer.
- The ends with phosphate group face outwards.
- The proteins are scattered throughout the lipid double layer.
- Some of these proteins act as carrier molecules that channel some material in and outside the cells.
- The cell membrane allows certain molecules to pass through freely while others move through with difficulty and still others do not pass through at all.
- This is selective permeability and the cell membrane is described as semi-permeable.
Properties of cell membrane
Permeability
- The cell membrane is semi-permeable.
- It allows small molecules that are soluble in lipid to pass through with more ease than water soluble molecules.
- This is due to the presence of the phospholipids double layer.
- The cell membrane has electrical charges across its surface.it has positive charged ions on the outside and negatively charged ions on the inside. This property contributes to electrical impulses sent along nerve cells.
- Sensitivity to changes in temperature and pH
- Very high temperatures destroy the semi-permeability nature of the cell membrane because the proteins are denatured by extreme pH values have the same effect on the membrane permeability.
- Physiological processes
- Some of the physiological processes include diffusion, osmosis and active transport.
- Diffusion is the movement of molecules or ions from a region of high concentration to a region of low concentration aided by a concentration gradient.
- Diffusion continues to occur as long as there is a difference in concentration between two regions (concentration gradient).
- Stops when an equilibrium is reached i.e., when the concentration of molecules is the same in both regions.
- Diffusion is a process that occurs inside living organisms as well as the external environment..
- Does not require energy.
Concentration Gradient
An increase in the concentration of molecules at one region results in a steeper concentration gradient which in turn increases the rate of diffusion.
Temperature
High temperature increases kinetic energy of molecules. They move faster hence resulting in an increase in rate of diffusion, and vice versa.
Size of Molecules or Ions
The smaller the size of molecules or ions, the faster their movement hence higher rate of diffusion.
Density
The denser the molecules or ions diffusing, the slower the rate of diffusion, and vice versa.
Medium
The medium through which diffusion occurs also affects diffusion of molecules or ions. For example, diffusion of molecules through gas and liquid media is faster than through a solid medium.
Distance
This refers to the thickness or thinness of surface across which diffusion occurs. Rate of diffusion is faster when the distance is small i.e., thin surface.
Surface Area to Volume Ratio
The larger the surface area to volume ratio, the faster the rate of diffusion.
For example, in small organisms such as Amoeba the surface area to volume ratio, is greater hence faster diffusion than in larger organisms.
An increase in the concentration of molecules at one region results in a steeper concentration gradient which in turn increases the rate of diffusion.
Temperature
High temperature increases kinetic energy of molecules. They move faster hence resulting in an increase in rate of diffusion, and vice versa.
Size of Molecules or Ions
The smaller the size of molecules or ions, the faster their movement hence higher rate of diffusion.
Density
The denser the molecules or ions diffusing, the slower the rate of diffusion, and vice versa.
Medium
The medium through which diffusion occurs also affects diffusion of molecules or ions. For example, diffusion of molecules through gas and liquid media is faster than through a solid medium.
Distance
This refers to the thickness or thinness of surface across which diffusion occurs. Rate of diffusion is faster when the distance is small i.e., thin surface.
Surface Area to Volume Ratio
The larger the surface area to volume ratio, the faster the rate of diffusion.
For example, in small organisms such as Amoeba the surface area to volume ratio, is greater hence faster diffusion than in larger organisms.
Factors Affecting Diffusion
Role of Diffusion in Living Organisms
Some processes that depend on diffusion include the following:
- Gaseous exchange: Movement of gases through respiratory surfaces is by diffusion.
- Absorption of materials into cells: cells obtain raw materials and nutrients from the surrounding tissue fluid and blood through diffusion, e.g., glucose needed for respiration diffuses from blood and tissue fluid into cells.
- Excretion: Removal of metabolic waste products like carbon (IV) oxide, and ammonia out of cells is by diffusion.
- Absorption of the end-products of digestion from the intestines is by diffusion.
Osmosis
- Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration through a semi-permeable membrane.
- Osmosis is a special type of diffusion that involves the movement of water molecules only and not solute molecules.
- Osmosis takes place in cells across the cell membrane as well as across non-living membranes e.g. cellophane or visking tubing which are also semi-permeable,
- It is purely a physical process.
Factors Affecting Osmosis
Size of solute molecules-
Osmosis' occurs only when solute molecules are too large to pass through a semi-permeable membrane.
Concentration Gradient.
Osmosis occurs when two solutions of unequal solute concentration are separated by a semi-permeable membrane.
Temperature.
High temperatures increase movement of water molecules hence influence osmosis. However, too high temperatures denature proteins in cell membrane and osmosis stops.
Pressure
Increase in pressure affects movement of water molecules.
As pressure increases inside a plant cell, osmosis decreases.
Osmosis' occurs only when solute molecules are too large to pass through a semi-permeable membrane.
Concentration Gradient.
Osmosis occurs when two solutions of unequal solute concentration are separated by a semi-permeable membrane.
Temperature.
High temperatures increase movement of water molecules hence influence osmosis. However, too high temperatures denature proteins in cell membrane and osmosis stops.
Pressure
Increase in pressure affects movement of water molecules.
As pressure increases inside a plant cell, osmosis decreases.
Roles of Osmosis in Living Organisms
The following processes depend on osmosis in living organisms:
- Movement of water into cells from the surrounding tissue fluid and also from cell to cell.
- Absorption of water from the soil and into the roots of plants.
- Support in plants especially herbaceous ones, is provided by turgor pressure, which results from intake of water by osmosis.
- Absorption of water from the alimentary canal in mammals.
- Re-absorption of water in the kidney tubules.
- Opening and closing stomata.
Water Relations in Plant and Animal Cells
- The medium (solution) surrounding cells or organisms is described by the terms hypotonic, hypertonic and isotonic.
- A solution whose solute concentration is more than that of the cell sap is said to be hypertonic. A cell placed in such a solution loses water to the surroundings by osmosis.
- A solution whose solute concentration is less than that of the cell sap is said to be hypotonic. A cell placed in such a solution gains water from the surroundings by osmosis.
- A solution which has the same solute concentration as the cell sap is said to be isotonic. When a cell is placed in such a solution there will be no net movement of water either into or out of the cell.
Osmotic Pressure
- The term osmotic pressure describes the tendency of the solution with a high solute concentration to draw water into itself when it is separated from distilled water or dilute solution by a semi-permeable membrane.
- Osmotic pressure is measured by an osmometer.
- When plant cells are placed in distilled water or in a hypotonic solution, the osmotic pressure in the cells is higher than the osmotic pressure of the medium.
- This causes the water to enter the cells by osmosis.
- The water collects in the vacuole which increases in size.
- As a result the cytoplasm is pushed outwards and it in turn presses the cell membrane next to the cell wall.
- This builds up water pressure (hydrostatic pressure) inside the cell.
- When the cell is stretched to the maximum, the cell wall prevents further entry of water into the cell.
- Then the cell is said to be fully turgid.
- The hydrostatic pressure developed is known as turgor pressure.
Plasmolysis
- When a plant cell is placed in a hypertonic medium, it loses water by osmosis.
- The osmotic pressure of the cell is lower than that of the medium.
- The vacuole decreases in size and the cytoplasm shrinks as a result of which the cell membrane loses contact with the cell wall.
- The cell becomes flaccid. The whole process is described as plasmolysis.
- Incipient plasmolysis is when a cell membrane just begins to lose contact with the cell wall.
- Plasmolysis can be reversed by placing the cell in distilled water or hypotonic solution.
- However, full plasmolysis may not be reversed if cell stays in that state for long.
Wilting
- The term wilting describes the drooping of leaves and stems of herbaceous plants after considerable amounts of water have been lost through transpiration.
- It is observed in hot dry afternoons or in dry weather.
- This is when the amount of water lost through transpiration exceeds the amount absorbed through the roots.
- Individual cells lose turgor and become plasmolysed and the leaves and stems droop.
- The condition is corrected at night when absorption of water by the roots continue while transpiration is absent.
- Eventually, wilting plants may die if the soil water is not increased through rainfall or watering.
Water Relations in Plants and Animals
Haemolysis
- Haemolysis is the bursting of cell membrane of red blood cells releasing their haemoglobin.
- It occurs when red blood cells are placed in distilled water or hypotonic solution.
- This is because the cell membrane does not resist further entry of water by osmosis after maximum water intake.
Crenation
- Takes place when red blood cells are placed in hypertonic solution.
- They lose water by osmosis, shrink and their shape gets distorted.
- Animal cells have mechanisms that regulate their salt water balance (osmoregulation) to prevent above processes that lead to death of cells.
- An Amoeba placed in distilled water, i.e. hypotonic solution, removes excess water using a contractile vacuole.
- The rate of formation of contractile vacuoles increases.
Active Transport
- Active transport is the movement of solutes such as .glucose, amino acids and mineral ions;
- From an area of their low concentration to an area of high concentration.
- It is movement against a concentration gradient and therefore energy is required.
- As such it only takes place in living organisms.
- The energy needed comes from respiration.
- Certain proteins in the cell surface membrane responsible for this movement are referred to as carrier proteins or channel proteins.
- The shape of each type of carrier protein is specific to the type of substances conveyed through it.
- It has been shown that the substance fits into a particular slot on the protein molecule,
- As the protein changes from one form of shape to another the substance is moved across and energy is expended.
Factors Affecting Active Transport:
Availability of oxygen
- Energy needed for active transport is provided through respiration.
- An increase in the amount of oxygen results in a higher rate of respiration.
- If a cell is deprived of oxygen active transport stops.
Temperature
- Optimum temperature is required for respiration, hence for active transport.
- Very high temperatures denature respiratory enzymes.
- Very low temperatures inactivate enzymes too and active transport stops.
Availability of carbohydrates
- Carbohydrates are the main substrates for respiration.
- Increase in amount of carbohydrate results in more energy production during respiration and hence more active transport.
- Lack of carbohydrates causes active transport to stop.
Metabolic poisons
- Metabolic poisons e.g. cyanide inhibit respiration and stops active transport due to lack of energy.
Role of Active Transport in Living Organisms
Processes requiring active transport:
- Absorption of mineral salts from the soil into plant roots.
- Absorption of end products of digestion e.g. glucose and amino acids from the digestive tract into blood stream.
- Excretion of metabolic products e.g. Urea from the cells.
- Re-absorption of useful substances and mineral salts back into blood capillaries from the kidney tubules.
- Sodium-pump mechanism in nerve cells.
- Re-absorption of useful materials from tissue fluid into the blood stream.
Practical Activities
1. Experiment to Demonstrate Diffusion
4. Experiment to Demonstrate Turgor and Plasmolysis in Onion Epidermal Cells
- Various coloured substances such as: dyes, plant extracts and chemicals like potassium permanganate are used.
- Potassium manganate (VII) crystals are introduced to the bottom of a beaker filled with water using a glass tubing or drinking straw which is then removed.
- Observations are made and the disappearance of the crystals and subsequent uniform colouring of water noted.
- A strip of visking tubing 8-10 cm is cut and tied at one end using strong thread.
- About 2 ml of 25% sucrose solution is put inside and the other end tied with thread.
- The tubing is washed under running water and then blotted to dry.
- It is immersed in a beaker containing distilled water and left for at least one hour or overnight.
- It will then be observed that the visking tubing has greatly increased in size and has become firm.
- A control experiment can be set up using distilled water inside the visking tubing in place of sucrose solution.
- Irish potato tubers are peeled and scooped out to make hollow space at the centre.
- Sucrose solution is placed inside the hollow, and the potato tuber placed in a beaker or petri-dish with distilled water. A control is set using a boiled potato.
- Another one using distilled water inside hollow in place of sugar solution.
- The experiment is left for 3 hours to 24 hours.
4. Experiment to Demonstrate Turgor and Plasmolysis in Onion Epidermal Cells
- Two strips of onion epidermis are obtained.
- One is placed on a slide with distilled water while the other is placed on a slide with 25% sucrose solution and a coverslip placed on top of each.
- The mounted epidermis is observed under low power microscope and then left for 30 minutes.
- After 30 minutes, observations are made again.
- The cells in distilled water have greatly enlarged. Cells in 25% sucrose have shrunk.
CELL PHYSIOLOGY QUESTIONS
1. 1994 Q6 P1
Give a reason for each of the following
a) A mature plant cell does not lose its shape even after losing water.
b) Xylem vessels do not collapse even when they do not contain water.
2. 1995 Q4 P1
Explain what would happen to red blood cells if they are placed in a concentrated salt solution ( 2 marks)
3. 1995 Q10 P1
An experiment was carried out to investigate the rate of reaction shown below
Sucrose →Fructose + Glucose
For the products fructose and glucose to be formed, it was found that substance K was to be added and the temperature maintained at 370C. When another substance L was added, the reaction slowed down and eventually stopped.
(a) Suggest the identify of substances K and L (2 marks)
(b) Other than temperature state three ways by which the rate of reaction could be increased (3 marks)
(c) Explain how substance L slowed down the reaction (2 marks)
4. 2000 Q8 P1
Why is oxygen important in the process of active transport in cells?
5. 2004 Q16 P1
a) What is diffusion (2 marks)
b) How do the following factors affect the rate of diffusion?
i) Diffusion gradient (1 mark)
ii) Surface area volume ratio (1mark)
iii) Temperature (1mark)
c) Outline three roles of active transport in the human body (3 marks)
6. 2005 Q7 P1
State the importance of osmosis in plants. (3 marks)
7. 2009 Q13 P1
(a) Distinguish between diffusion and active transport (2 marks)
(b) State one role that is played by osmosis in (1 mark)
(i) Plants
(ii) Animals
8. 2010 Q7 P1
Distinguish between haemolysis and plasmolysis. (2 marks)
Give a reason for each of the following
a) A mature plant cell does not lose its shape even after losing water.
b) Xylem vessels do not collapse even when they do not contain water.
2. 1995 Q4 P1
Explain what would happen to red blood cells if they are placed in a concentrated salt solution ( 2 marks)
3. 1995 Q10 P1
An experiment was carried out to investigate the rate of reaction shown below
Sucrose →Fructose + Glucose
For the products fructose and glucose to be formed, it was found that substance K was to be added and the temperature maintained at 370C. When another substance L was added, the reaction slowed down and eventually stopped.
(a) Suggest the identify of substances K and L (2 marks)
(b) Other than temperature state three ways by which the rate of reaction could be increased (3 marks)
(c) Explain how substance L slowed down the reaction (2 marks)
4. 2000 Q8 P1
Why is oxygen important in the process of active transport in cells?
5. 2004 Q16 P1
a) What is diffusion (2 marks)
b) How do the following factors affect the rate of diffusion?
i) Diffusion gradient (1 mark)
ii) Surface area volume ratio (1mark)
iii) Temperature (1mark)
c) Outline three roles of active transport in the human body (3 marks)
6. 2005 Q7 P1
State the importance of osmosis in plants. (3 marks)
7. 2009 Q13 P1
(a) Distinguish between diffusion and active transport (2 marks)
(b) State one role that is played by osmosis in (1 mark)
(i) Plants
(ii) Animals
8. 2010 Q7 P1
Distinguish between haemolysis and plasmolysis. (2 marks)
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