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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2 Comments
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.
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