SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

WORK SCHEME

WEEK 1 REVISION/ HOMEOSTASIS

WEEK 2 TROPIC RESPONSES IN PLANTS
WEEK 3 HORMONAL COORDINATION- ANIMAL HORMONES
WEEK 4 COORDINATION- NERVOUS CONTROL IN HUMANS
WEEK 5 SENSE ORGANS-EYE
WEEK 6 DRUGS
WEEK 7 REPRODUCTION- ASEXUAL REPRODUCTION
WEEK 8 MID TERM BREAK
WEEK 9 SEXUAL REPRODUCTION IN PLANTS
WEEK 10 SEXUAL REPRODUCTION IN HUMANS
WEEK 11 SEX HORMONES IN HUMANS

HOMEOSTASIS
Homeostasis is the maintenance of a fairly constant internal environment.
Importance of homeostasis
living cells, all the chemical reactions are controlled by enzymes. The enzymes are very sensitive
to the conditions in which they work. A slight fall in temperature or a rise in acidity may slow
down or stop an enzyme from working.
Parts of an organism responsible for homeostasis
 The cell membrane controls the substances that enter and leave the cell.
 The tissue fluid supplies or removes these substances.
 The kidneys remove substances that might poison the enzymes. The kidneys also control
the level of salts, water and acids in the blood.
 The liver regulates the level of glucose in the blood. The liver stores any excess glucose as
glycogen, or turns glycogen back into glucose if the concentration in the blood gets too
low.
 The skin plays an important role in the regulation of body temperature.

Homeostasis and negative feedback

A negative feedback loop occurs in biology when the product of a reaction leads to a decrease
in that reaction. For example, a rise in blood glucose levels triggers responses that counteract the

1
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

rise (e.g. through the release of insulin). In this way, a negative feedback loop brings a system
closer to a target of stability or homeostasis.

Figure 1: Parts of a vertebrate involved in homeostasis

Blood sugar regulation

If the level of sugar in the blood falls, the islets in the pancreas release a hormone called glucagon
into the bloodstream. Glucagon acts on the cells in the liver and causes them to convert some of
their stored glycogen into glucose. This restores the blood sugar level.
Insulin has the opposite effect to glucagon. If the concentration of blood sugar increases (e.g. after
a meal rich in carbohydrate), insulin is released from the islet cells of the pancreas. When the
insulin reaches the liver, it stimulates the liver cells to take up glucose from the blood and store it
as glycogen.

Figure 2: Role of the pancrease in blood glucose regulation

2
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Type 1 diabetes
This happens when the islet cells of the pancreas do not produce enough insulin. This form of the
disease is sometimes called insulin-dependent diabetes. As a result the patient’s blood is low in
insulin.
The patient is unable to control the level of glucose in the blood. It may rise to such a high level
that it is excreted in the urine, or fall so low that the brain cells cannot work properly and the
person goes into a coma.
Symptoms
The symptoms of type 1 diabetes include:
 feeling tired,
 feeling very thirsty,
 frequent urination and
 weight loss.
Treatment
This condition can be managed by:
 taking a carefully controlled diet, to keep the blood sugar within reasonable limits,
 by engaging in regular exercise.
 having regular blood tests to monitor their blood sugar levels,
 taking regular injections of insulin to control blood sugar levels.

3
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Structure of the skin

Figure 3: Longitudinal section through the mammalian skin

Figure 4: Light microscope image of the skin

4
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Temperature regulation
Both the brain and the skin play a crucial role in regulating temperature.
Role of the brain
The brain plays a direct role in detecting any changes from normal by monitoring the temperature
of the blood. A region in the brain contains a thermoregulatory centre in which temperature
receptors detect temperature changes in the blood and co-ordinate a response to them. Temperature
receptors are also present in the skin. They send information to the brain about temperature
changes. The brain can controls the orientation of the skin hair through the hair erector muscles
in the skin.

Figure 5: Role of skin hair in temperature regulation

Role of the skin

The skin helps to keep the body temperature steady. This is done by adjusting the flow of blood
near the skin surface and by sweating. Normal human body temperature varies between 35.8°C
and 37.7°C. The human skin ensures that body temperature stays at about 37oC. This is achieved
through:
 Insulation: The insulating properties of fatty tissue in the dermis help to reduce the amount
of heat lost. Humans also put on thick clothing as insulation.
 Sweating: the sweat glands secrete sweat on to the skin surface. When this layer of liquid
evaporates, it takes heat(latent heat) from the body and cools it down.
 Vasodilation: the widening of the arterioles in the dermis allows more warm blood to flow
through blood capillaries near the skin surface, resulting in heat loss.
5
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

 Vasoconstriction: narrowing (constriction) of the arterioles in the skin reduces the amount
of warm blood flowing through blood capillaries near the surface, reducing heat loss.

Figure 7: Vasodilation Figure 6: Vasoconstricton

 Shivering: uncontrollable bursts of rapid muscular contraction in the limbs release heat as
a result of respiration in the muscles.

TROPIC RESPONSES IN PLANTS

Although plants do not respond by moving their whole bodies, parts of them do respond to stimuli.
Some of these responses are described as tropic responses, growth responses or tropisms.
Tropisms are growth movements related to directional stimuli. If the plant organ responds by
growing towards the stimulus, the response is said to be ‘positive’. If the response is growth away
from the stimulus it is said to be ‘negative’. Auxin is unequally distributed in response to light and
gravity stimuli. Responses to light are called phototropisms; responses to gravity are
gravitropisms.
Phototropism
Plant growing tip (shoot and root) naturally produce the hormone auxin which stimulates cell
division and elongation. However, auxins migrate from brightly lit to shaded parts of a plant when
light is coming from only one direction (i.e. unilateral illumination). Both root and shoot cells
respond differently to high auxin concentration.
Phototropism in shoots
High auxin concentration in shoots stimulates growth. When a plant shoot experiences unilateral
illumination, auxins migrate to the shaded portion and cause cells on that side to divide and
elongate faster than the lit side, making the plant to grow, bending towards the light. Therefore, we
can conclude that plant shoots are positively phototropic.

6
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Figure 8: Phototropic response in Figure 9: Effect of a rotating klinostat on

plant shoot phototropism

However, a rotating klinostat causes all the sides of the plant shoot to be equally exposed to the
unilateral illumination. As a result, auxins are equally distributed in the shoot, so the plant grows
upright.
Moreover, plants grown in dim light or partial darkness can become etiolated. Etiolation in plants
occurs when they are grown in either partial or a complete absence of light. Etiolation is
controlled by the plant hormones called auxins, which are produced by the growing tip to maintain
apical dominance. Auxin diffuses, and is transported, downwards from the tip
Phototropism in roots
High auxin concentration in plant shoot cells inhibits cell division and elongation. If a plant root
tip were to be exposed to light, auxins would migrate to the shaded part, inhibiting growth on that
side. Cells on the lit side, having a much lower auxin concentration would divide faster, causing
the root to grow, bending away from the light. This shows that plant roots are negatively
phototropic.

Figure 11: Negative phototropism in

roots
Figure 10: Etiolation
7
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Gravitropism in plant shoot and root

Plant roots are positively gravitropic, while plant shoots are negatively gravitropic. The response is
controlled by the effect of gravity, concentrating auxins on the lower parts of a plant lying
horizontally. The varied response of shoot and root cells to auxin concentration causes them to
respond differently to gravity as a stimulus.

HORMONAL COORDINATION- ANIMAL HORMONES

Hormone is a chemical substance, produced by a gland, carried by the blood, which alters the
activity of one or more specific target organs and is then destroyed by the liver. The glands that
produce these hormones are called ductless/endocrine glands. Hormones are thus chemical
messengers used in coordination processes.

8
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Endocrine glands, their hormones and functions

Figure 12: Position of endocrine glands in the body

Table 1: Hormone, source and function

Endocrine Location Hormone secreted Function/Effect
gland
Pancreas Duodenal 1. Insulin (Beta cells) - Controls Glucose-glycogen
loop conversion
2. Glucagon (Alpha cells) - Controls Glycogen -glucose
conversion
Adrenals Top of each Adrenalin Prepares body for emergencies
kidney (fear & anxiety) by:
-increasing heartbeat &
respiration rates
-increasing blood sugar level
-dilating pupil
-increasing muscle tone
Gonads:
1.Testis Scrotum Testosterone -Stimulates pubertal changes
in males,
2. Ovary Within the i. Oestrogen -Stimulate pubertal changes in
ovaries females
ii. Progesterone i. prepares uterus for
9
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

implantation
ii. maintains foetal
development

The role of adrenaline in metabolism

As adrenaline circulates around the body it affects a number of organs, including the liver and
heart.
 In the liver it stimulates the conversion of glycogen to glucose.
 Increased levels of glucose available to cells enable them to respire faster, making more
energy available.
 Adrenalin increases heart rate.

Difference between endocrine and nervous coordination

COORDINATION- NERVOUS CONTROL IN HUMANS

The nervous system is coordinating system in the body that employs the use of electrical
impulses/charges to transmit messages from one part of the body to another. The nervous
system plays a role in regulating and coordinating body functions.
The mammalian nervous system
The mammalian nervous system is made up of the Brain, the spinal cord and the nerves. It
is categorised into two parts:
• Central nervous system (CNS) - brain and spinal cord: coordinate all nervous
responses
• Peripheral nervous system (PNS) - nerves: connect all parts of the body to the CNS.
Together, they coordinate and regulate body functions.

Types of neurons
Three types of neurone are:
10
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

 Motor neurones: (also called effector neurones) which carry impulses from the central
 nervous system to muscles and glands.
 Sensory neurones: carry impulses from the sense organs to the central nervous system.
 Relay neurones: (also called connector or multipolar neurones) which make connections
to other neurones inside the central nervous system.
Impulses will travel in one direction in sensory fibres and in the opposite direction in motor fibres.

Structure of a typical neurone

Each neurone has a cell body consisting of a nucleus surrounded by cytoplasm. Dendrites are
fibres, which branch from the cell body to make contact with other neurones. A long filament of
cytoplasm, surrounded by an insulating sheath, runs from the cell body of the neurone. This
filament is called a nerve fibre.

Figure 13: Structure of the three types Figure 14: A typical neurone structure
of neurones (motor neurone)

11
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Simple reflex action

A reflex action is a rapid and automatic (involuntary) response to a stimulus e.g. coughing,
sneezing, blinking. It is a means of automatically and rapidly integrating and coordinating stimuli
with the responses of effectors (muscles and glands)

Figure 15: A simple reflex arc

A simple reflex arc

A simple reflex arc is the nervous pathway/route of a reflex action. It involves a sensory or
afferent neurone, an interneurone/relay neurone present within the spinal cord and a motor or
efferent neurone. The afferent is connected to the receptors (such as skin) and the efferent is
connected to the effectors (muscles or glands).

Figure 16: Structure of a synapse

How a synapse transmits an electrical impulse
At a synapse, a branch at the end of one fibre is in close contact with the cell body or dendrite of
another neurone. When an impulse arrives at the synapse,

12
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

• vesicles in the cytoplasm are stimulated to release a tiny amount of the neurotransmitter
molecules.
• The molecules rapidly diffuse across the synaptic gap and bind with neurotransmitter
receptor proteins in the membrane of the neurone on the other side of the synapse.
• This then stimulates a new impulse in the neurone.

SENSE ORGANS-EYE
These are a groups of receptor cells responding to specific stimuli: light, sound, touch, temperature
and chemicals

The eye
The human eye is the organ for sight and accommodation. The Longitudinal section of the eye
shows a 3 layered (Sclera, choroid, retina) eyeball filled with nutritious fluids-aqueous humour
and vitreous humour.

Figure 17: Structure of the eye

13
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Table 2: Descripton and functions of the parts of the eye

Pupil reflex
The change in size of the pupil is caused by exposure of the eye to different light intensities. It is
an automatic reaction done to protect the eye from damage by high-intensity lights.

When bright light falls on the eye, the iris responds by

 making the diameter of the pupil smaller (radial muscles relax, circular muscles
contract). R to r, C to c
 This restricts the amount of light reaching the retina,

If dim light falls on the eye, the iris responds by

 making the diameter of the pupil larger ( radial muscles contract, circular muscles
relax),
 so that as much light as is available can reach the retina to stimulate the light-sensitive cells

14
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

The circular and radial muscles of the iris act antagonistically. This means that they oppose
each other in their actions.

Accommodation (focussing)
Accommodation/focusing is the ability to change the curvature of the lens, so that light rays
continue to be focused on the retina both from far and near objects. To do this the lens changes
its shape, becoming thinner for distant objects and fatter for near objects.

Figure 18: Focussing by the lens

Retina
There are two types of light-sensitive cells in the retina, the rods and the cones (named because of
their shape).
Cones
The cones enable us to distinguish colours, There are thought to be three types of cone cell. One
type respond best to red light, one to green and one to blue. If all three types are equally

15
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

stimulated, we get the sensation of white. The cone cells are concentrated in a central part of the
retina, called the fovea.
Rods
Rods are more sensitive to low intensities of light. They play an important part in night vision
when the light intensity is not enough to stimulate the cone cells. Images we form at night appear
as shades of grey.

DRUGS
A drug is any substance taken into the body that modifies or affects chemical reactions in the body.

Antibiotics
A tiny minority of bacteria are harmful (pathogenic). Antibiotics are drugs which fight against
pathogenic bacteria. Antibiotics attack bacteria in a variety of ways:
 Some of them disrupt the production of the cell wall to prevent the bacteria from
reproducing,
 or even cause them to burst open;
 some interfere with protein synthesis. This stops the growth of the bacteria.

Animal cells do not have cell walls, and the cell structures involved in protein production are
different. As a result, antibiotics do not damage human cells, although they may produce some
side-effects like allergic reactions.
Drug-resistant bacteria
Not all bacteria are killed by antibiotics. Some bacteria have the ability to mutate into forms that
are resistant to these drugs. For this reason, it is important:

 not to use antibiotics in a diluted form,

 or for too short a period or for minor complaints.

 not completing a course of antibiotics.

These practices lead to a build-up of a resistant population of bacteria. Antibiotic resistance

reduces the effectiveness of antibiotics. Also, antibiotic drug resistance can be passed from
harmless bacteria to pathogens.

MRSA (methicillin-resistant Staphylococcus aureus) is one type of bacteria that has developed
resistance to several widely used antibiotics.

16
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Antibiotics and viral diseases

Antibiotics are not effective in the treatment of diseases caused by viruses. The reason antibiotics
are not effective against viral diseases is because antibiotics work by disrupting structures in
bacteria like cell walls and membranes. They can also disturb processes to do with protein
synthesis and the replication of DNA. Viruses have totally different characteristics to bacteria, so
antibiotics do not affect them.

REPRODUCTION- ASEXUAL REPRODUCTION

Asexual reproduction is a process resulting in the production of genetically identical offspring
from one parent. This method of reproduction does not involve gametes (sex cells). Common
examples include budding, binary fission, multiple fission, fragmentation, sporogenesis,
vegetative propagation.

Examples of asexual reproduction in nature

Figure 20: Binary fisson Figure 19: Multiple fission

Figure 22: Budding in hydra

Figure 21: Fragmentation in

Planaria

Figure 23: Spore formation in fungi

17
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Vegetative propagation
This is the use of a part of a plant body, other than seeds, to produce offspring. Plant parts involved
include buds, leaves, roots, stems (stolons and rhizomes), etc. Vegetative propagation could be
natural or artificial

Stolons and rhizomes are modified stems for vegetative reproduction. While stolons grow above
the ground e.g. Strawberry, rhizomes grow beneath the ground e.g. grasses.
The bulb is the round, swollen part of the underground stem. Within the bulb lies the the central
shoot that grows into a new plant e.g. Onions, Garlic, and Tulips etc.
Corm are also swollen underground stems with dry-scale leaves covering them. Corms can be
cut into pieces and each piece planted to produce a new plant e.g. Coco-yam.
Artificial vegetative propagation
a. Cuttings: It is possible to produce new individuals from some plants by putting the cut end of a
shoot into water or moist earth. Roots grow from the base of the stem into the soil while the shoot
continues to grow and produce leaves e.g. in Cassava.
b. Tissue culture: In laboratory conditions, single plant cells can be stimulated to divide and grow
into complete plants. One method is to take small pieces of plant tissue (explant) from a root or
stem and treat it with enzymes to separate it into individual cells. The cells are then provided with
a plant growth substance, which stimulates cell division and goes on to form roots, stems and
leaves.

18
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Figure 24: Tissue culture

The advantages and disadvantages of asexual reproduction

SEXUAL REPRODUCTION
Unlike in asexual reproduction, Sexual reproduction is a process involving fertilization.
Fertilization is the fusion of the nuclei of two gametes to form a zygote. The zygote develops into
a new individual which is genetically unique. The process of cell division that produces the
gametes is called meiosis.

19
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Chromosome numbers
In normal body cells (somatic cells) the chromosomes are present in the nucleus in pairs. Humans,
for example, have 46 chromosomes: 23 pairs. Maize(sweetcorn) has 10 pairs. This is known as the
diploid number. When gametes are formed, the number of chromosomes in the nucleus of each sex
cell is halved. This is the haploid number.
During fertilisation, when the nuclei of the sex cells fuse, a zygote is formed. It gains the
chromosomes from both gametes, so it is a diploid cell.
Gametes
In flowering plants, the male gametes are found in pollen grains produced by the anther and the
female gametes, called egg cells, are present in ovules. In animals, male gametes are sperm and
female gametes are eggs.
In both plants and animals, the male gamete is microscopic and mobile. The sperm swim to the
ovum; the pollen cell moves down the pollen tube. The female gametes are always larger than the
male gametes and are not mobile. Pollination in seed-bearing plants and mating in most animals
bring the male and female gametes close together.

Figure 25: Gametes in plants and animals

Advantages and disadvantages of sexual reproduction

20
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Sexual reproduction in plants

Flowers are reproductive structures; they contain the reproductive organs of the plant. The male
organs are the stamens, which produce pollen. The female organs are the carpels. The male gamete
is a cell in the pollen grain. The female gamete is an egg cell in the ovule. After fertilisation, part
of the carpel becomes the fruit of the plant and contains the seeds. In the flowers of most plants
there are stamens and carpels. So, these flowers are both male and female.

Structure of a flower

Figure 26: TS of an insect pollinated flower

Figure 27: Structure of a wind pollinated flower

21
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Petals
Petals are usually brightly coloured and sometimes scented. They are arranged in a circle or a
cylinder. The colour and scent of the petals attract insects to insect-pollinated flowers. The flowers
of grasses and many trees do not have petals. Instead they have small, leaf-like structures that
surround the reproductive organs.
Sepals
Outside the petals is a ring of sepals. They are often green and much smaller than the petals. They
may protect the flower when it is in the bud.
Carpels
Also called pistil, these are the female reproductive organs. Each carpel consists of an ovary,
bearing a style and a stigma. Inside the ovary there are one or more ovules. A flower may have one
or more carpels.
Stamens
The stamens are the male reproductive organs of a flower. Each stamen has a stalk called the
filament with an anther on the end. Each anther is made of four pollen sacs in which the pollen
grains are produced by meiotic cell division. When the anthers are ripe, the pollen sacs split open
and release their pollen.
Receptacle
The flower structures just described are all attached to the expanded end of a flower stalk. This is
called the receptacle and, in a few cases after fertilisation, it becomes fleshy and edible (e.g. apple
and pear).
Pollen grains
Insect-pollinated flowers tend to produce smaller amounts of pollen grains. These are often round
and sticky, or covered in tiny spikes to attach to the furry bodies of insects.
Wind-pollinated flowers tend to produce larger amounts of smooth, light pollen grains. This
means that they are easily carried by the wind. Large amounts are needed because much of the
pollen is lost so there is a low chance of it reaching another flower of the same species.

Figure 28: Insect Figure 29:

pollen Wind pollen

22
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Pollination
Pollination is the transfer of pollen grains from an anther to a stigma. The anthers split open,
exposing the microscopic pollen grains. The pollen grains are then carried away on the bodies of
insects, or simply blown by the wind, and may land on the stigma of another flower. There are two
types of pollinnaton and these are:
1. Self pollination: the transfer of pollen grains from the anther of a flower to the stigma of the
same flower or a different flower on the same plant. This is very efficient because pollination can
occur in the absence of pollinators (perhaps because of the over-use of insecticides), but offers a
low chance of genetic variety.
2. Cross-pollination: as the transfer of pollen grains from the anther of a flower to the stigma of a
flower on a different plant of the same species. This is very risky, since no nearby plants of the
same species may be avalable. However, it offers a greater chance of genetic variety.

Figure 30: Self- and Cross-pollination, compared

Fertilisation
Fertilization in plants usually follows pollination. For fertilisation to occur, the pollen grain
absorbs liquid from the stigma and a microscopic pollen tube grows out of the grain. This tube
grows down the style and into the ovary, where it enters a small hole, the micropyle, in an ovule.
The nucleus of the pollen grain travels down the pollen tube and enters the ovule. Here it combines
with the nucleus of the egg cell. Each ovule in an ovary needs to be fertilised by a separate pollen
grain.

23
Figure 31: Fertilization in plants
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Structural adaptations of insect-pollinated and wind-pollinated

flowers

Germination
Germination is the process of development of a plant from a seed.
Environmental conditions that affect germination
Three important external factors in seed germination are temperature, water and oxygen.
1. Temperature: germination happens more rapidly at high temperatures, up to about 40°C. Above
45°C, the enzymes in the cells are denatured and the seedlings would be killed. Below certain
temperatures (e.g. 0–4°C) germination may not start at all in some seeds.
2. Water: When first dispersed, most seeds contain very little water. In this dehydrated state their
metabolism is very slow, and their food reserves are not used up. Before the metabolic changes
needed for germination can take place, water is absorbed through a tiny hole in the seed coat called
the micropyle, and then through the whole seed coat. The absorbed water help to:
 activate the enzymes in the seed

24
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

 help the conversion of stored starch to sugar, and proteins to amino acids
 transport the sugar in solution from the cotyledons to the growing regions
3. Oxygen: In some seeds the seed coat is not very permeable to oxygen, which suggests that the
early stages of germination are anaerobic. When soaked or split open, the seed coat allows oxygen
to enter. The oxygen is used in aerobic respiration. This provides the energy for the chemical
changes involved in activating the food reserves.

SEXUAL REPRODUCTION IN HUMANS

In human reproduction, the two sexes, male and female, each produce special types of
reproductive cells called gametes. The male gametes are the sperm and the female gametes are the
ova (singular = ovum) or eggs.

Female reproductive system

Figure 33: Female reproductive system (side

view)

Figure 32: Female reproductive system (front

view)

Table 3: Functions of parts of the female reproductive system

25
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Male reproductive system

Figure 34: Male reproductive system (side

view)

Figure 35: Male reproductive system (front

view)

Table 4: Functions of parts of the male reproductive system

Fertilization in humans
To produce a new individual, a sperm needs to reach an ovum and fuse with it. The sperm nucleus
then passes into the ovum and the two nuclei also fuse. This is fertilisation. The cell formed after

26
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

the fertilisation of an ovum by a sperm is called a zygote. A zygote will grow by cell division to
produce first an embryo that implants into the lining of the uterus and then develops into a fully
formed animal.

Figure 36: Fertilisation and development

Comparing male and female gametes

Figure 38: Human egg cell

Figure 37: Human sperm cell

27
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Sperm cell
Sperm are much smaller than eggs and are produced in much larger numbers (over 300 million in a
single ejaculation). The tip of the cell carries an acrosome. This secretes enzymes which can digest
the jelly coat of an egg cell so the sperm nucleus can fuse with the egg nucleus. The cytoplasm of
the mid-piece of the sperm contains many mitochondria. They carry out respiration, providing
energy to make the flagellum (tail) move and propel the sperm forward.
Egg cell
The egg cell is much larger than a sperm cell. Only one egg is released each month while the
woman is fertile. It is surrounded by a jelly coat, which protects the contents of the cell and that
changes at fertilisation, preventing more than one sperm from entering and fertilising the egg. The
egg cell contains a large amount of cytoplasm, which is rich in fats and proteins. The fats act as
energy stores. Proteins are available for growth if the egg is fertilised.

Development of the fetus

Figure 39: Growth and development in the uterus (not to scale)

The early embryo travels down the oviduct to the uterus. Here it implants or sinks into the lining
of the uterus. The embryo continues to grow and produces new cells that form tissues and organs.
After 8 weeks, when all the organs are formed, the embryo is called a fetus.
As the embryo grows, the uterus enlarges to contain it. Inside the uterus the embryo becomes
enclosed in a fluid-filled sac called the amniotic sac, which protects it from damage and prevents
unequal pressures from acting on it. The fluid is called amniotic fluid. The oxygen and food
needed to keep the embryo alive and growing are obtained from the mother’s blood by means of a
structure called the placenta. The placenta becomes closely attached to the lining of the uterus and
is attached to the embryo by a tube called the umbilical cord.

28
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Figure 40: The exchange of substances

Function of the placenta and umbilical cord

There is no direct communication between the mother’s blood system and that of the embryo. The
exchange of substances takes place across the thin walls of the blood vessels. In this way,
 the mother’s blood pressure cannot damage the delicate vessels of the embryo and
 it is possible for the placenta to select the substances allowed to pass into the embryo’s
blood.
 the placenta can also prevent some toxins (harmful substances) in the mother’s blood from
reaching the embryo.
It cannot prevent all of them, however: alcohol and nicotine can pass to the developing fetus. If the
mother is a drug addict, the baby can be born addicted to the drug.
Some pathogens like the rubella virus and HIV can pass across the placenta. Rubella (German
measles), although a mild infection for the mother, can infect the fetus and results in major health
problems. HIV is potentially fatal.

SEX HORMONES IN HUMANS

Hormones are chemical messengers produces by ductless glands, transported by the blood, which
control target organs with specific receptors for such hormones. Hormones produced by both the
male and female organs, or those targeted at them, are referred to as sex hormones.

29
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

Development and regulation of secondary sexual

characteristics during puberty
In girls
Although the ovaries of a young girl contain all the ova she will ever produce, they do not start to
be released (ovulation) until she reaches the age of about 10–14 years. This stage in her life is
known as puberty.
At about the same time as the first ovulation, the ovary also releases female sex hormones into the
bloodstream. These hormones are called oestrogens and when they circulate around the body they
cause the development of secondary sexual characteristics which include:
 the increased growth of the breasts,
 widening of the hips and
 the growth of hair in the pubic region and in the armpits.
 increase in the size of the uterus and vagina.
 Commencement of menstruation
Once all these changes are complete, the girl is capable of having a baby.

In boys
Puberty in boys occurs at about the same age as in girls. The testes start to produce sperm for the
first time. They also release a hormone called testosterone into the bloodstream. The male
secondary sexual characteristics, which begin to appear at puberty, are
 enlargement of the testes and penis,
 deepening of the voice,
 growth of hair in the pubic region, armpits, chest and, later, the face.
 Sponteneous release of semen during sleep

The menstrual cycle

The ovaries release an ovum about every 4 weeks. In preparation for this the lining of the uterus
wall thickens. This is to enable an embryo to embed itself if the released ovum is fertilised. If no
embryo implants, the uterus lining breaks down. The cells, along with blood, are passed out of the
vagina. This is called a menstrual period. After menstruation, the uterus lining starts to re-form
and another ovum starts to mature.

Hormones and the menstrual cycle

1. At the start of the cycle, the lining of the uterus wall has broken down (menstruation)

30
SS2 FIRST TERM NOTE 2023/2024 ACADEMIC SESSION OTOTE O.

2. Follicle-stimulating hormone (FSH) is then produced by the pituitary gland to stimulates

the growth of eggs in the ovaries in preparation for ovulation.
3. As each follicle in the ovaries develops, the amount of oestrogens produced by the ovary
increases.
4. The oestrogens act on the uterus and cause its lining to become thicker and develop more
blood vessels (in anticipation of fertilization and implantation)
5. Luteinising hormone, or lutropin (LH) is then released from the pituitary gland to trigger
the release of the ovum from an ovary at ovulation.
6. Once the ovum has been released, the follicle that produced it develops into a solid body
called the corpus luteum
7. Corpus luteum produces a hormone called progesterone, which affects the uterus lining in
the same way as the oestrogens.
8. If the ovum is fertilised, the corpus luteum continues to release progesterone, but if the
ovum is not fertilised, the corpus luteum stops producing progesterone.
9. As a result, the thickened lining of the uterus breaks down and loses blood, which escapes
through the cervix and vagina as menstruation.

Figure 41: The mentrual cycle

31