2/12/2018

TYPES OF GERMINATION

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previously: GROWTH AND DEVELOPMENT IN PLANTS

TYPES OF GERMINATION

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.

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.

Procedure

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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1/12/2018

GROWTH AND DEVELOPMENT IN PLANTS

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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

Bean seeds and maize grains which have been soaked overnight.
Scalpel or razor blades,
iodine solution,
Petri-dish and
hand lens.

Procedure

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.

2. Oxygen

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.

3. Hormones

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.

4. Viability

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.

5. Temperature

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.

6. Enzymes

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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24/10/2018

Introduction to Measurement of Growth

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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.

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.

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:

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 fact that most cells are fully differentiated.
Fewer cells still dividing,
Environmental factors (external and internal) such as:
1. shortage of oxygen and nutrients due to high demand by the increased number of cells.
2. space is limited due to high number of cells.
3. accumulation of metabolic waste products inhibits growth.
4. 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:

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

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.

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17/10/2018

Concept of Growth and Development - K.C.S.E Biology Notes

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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.

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.

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14/10/2018

Reproduction in Plants and Animals Practical Activities - K.C.S.E Biology Notes

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Reproduction in Plants and Animals Practical Activities

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.

Examining the stages of meiosis

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.

To observe the structure of Rhizopus

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.

To examine spores on sori of ferns

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

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.

Examine insect and wind pollinated flowers

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.

Classifying fruits

Obtain different fruits - oranges, mangoes, maize, castor oil, bean pod, black jack .
Observe the fruits, classify them into succulent, dry-dehiscent or indehiscent.

Dissection of Fruits

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.

Note that the fruit wall is not differentiated.
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.

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10/10/2018

SECONDARY SEXUAL CHARACTERISTICS - k.c.s.e biology notes

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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.

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7/10/2018

Role of placenta - K.C.S.E BIOLOGY NOTES

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ROLE OF PLACENTA

TABLE OF CONTENTS

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.

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.

Reproductive Hormones

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6/10/2018

Reproduction in Animals - K.C.S.E BIOLOGY NOTES

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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.

There are two types of fertilisation. External and internal.
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.

Internal fertilisation

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

Are two oval cream coloured structures found in lower abdomen below the kidneys.

Oviducts.

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.

Uterus

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.

Cervix

Has a ring of muscles that separates the uterus from the vagina.
It forms the opening to the uterus

Vagina

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:

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.

Seminiferous tubules

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.

Prostate gland

Produces an alkaline secretion to neutralise vaginal fluids.

Cowpers' gland

Secretes an alkaline fluid.
All these fluids together with spermatozoa form semen.

Urethra

Is a long tube through which the semen is conducted during copulation.
It also removes urine from the bladder.

Penis

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.

Implantation:

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

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.

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16/8/2018

Sexual reproduction in plants - k.c.s.e biology notes

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k.c.s.e biology reference notes Form 1-4

TYPES OF GERMINATION

Epigeal Germination

​Hyopgeal Germination

Practical Activity - To investigate epigeal and hypogeal germination

GROWTH AND DEVELOPMENT IN PLANTS

​STRUCTURE OF THE SEED

Dormancy in Seeds

Factors that Cause Dormancy

Ways of Breaking Dormancy

​Seed Germination

​Conditions Necessary for Germination

What is Measurement of Growth?

​Study Question

Lag phase (slow growth)

Exponential phase (log phase)

Decelerating Phase

Plateau (stationary) phase

PRACTICAL ACTIVITY I: PROJECT

Reproduction in Plants and Animals Practical Activities

​Male

Female

​Sexually transmitted infections (STl)

Menstrual Cycle

Advantages of Reproduction Asexual

Disadvantages of asexual reproduction

Advantages of sexual reproduction

Disadvantages of sexual reproduction

ROLE OF PLACENTA

Gestation period ​

Reproductive Hormones

Reproduction in Animals

Reproduction in Humans

​Concept of reproduction

Ecology Practical Activities

​Human diseases

​Energy Flow in an Ecosystem

​Abiotic factors (environmental factors)

wHAT IS ECOLOGY?

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Hyopgeal Germination

STRUCTURE OF THE SEED

Seed Germination

Conditions Necessary for Germination

Study Question

Male

Sexually transmitted infections (STl)

Gestation period

Concept of reproduction

Human diseases

Energy Flow in an Ecosystem

Abiotic factors (environmental factors)