CRYSTAL BROOKS COLLEGE

THIRD TERM E-LEARNING NOTE

SUBJECT : BIOLOGY

CLASS: YEAR 11

WEEK: ONE

TOPIC: Reproduction (Cambridge page 283)

Sexual Reproduction In Humans

Male Reproductive System

Testes: have many coiled tubes that produce sperm, and the cells between tubes
produce testosterone.
Scrotum: holds testicles
Sperm duct: carries sperm from testicles to urethra. Prostate gland: makes
seminal îuid

Urethra: carries semen from the sperm duct to the tip of the penis

Penis: male sex organ used to transfer semen to the female.

Female Reproductive System

Ovary: contains follicles that develop into the ova and produces progesterone and
oestrogen

Oviduct (fallopian tube): carries the ovum to the uterus Uterus (womb): where the
fetus develops.

Cervix: neck of the uterus: a robust and rigid muscle, moist by mucus with a small
opening

Vagina: receives the penis during intercourse and way out for baby at birth. Moist tube
of muscle, îexible and secretes mucus

Fertilisation and Early Development

Fertilisation: The fusion of the nuclei from a male gamete (sperm) and a female gamete
(egg cell).
• Development of a Zygote:
One sperm penetrates
The ovum membrane alters to form a barrier against sperm

The head of the sperm (male nucleus) approaches and then fuses with the nucleus
of the ovum.

The zygote divides over and over to make a ball of cells called an embryo.

It implants itself in the uterus (implantation) wall, followed by conception.

Development of fetus: The zygote is changed through growth (mitosis) and

 development (organisation of cells into tissues and organs)

Umbilical cord: contains the umbilical artery, which carries deoxygenated blood and
waste products from the fetus to the placenta and the umbilical vein, which carries
oxygenated blood and soluble food from the

placenta to the fetus. (Contains fetus’ blood)

Placenta: organ for exchange of soluble materials such as foods, wastes and oxygen
between mother and fetus; physical attachment between uterus and fetus. (Contains
mother’s blood)

Amniotic Sac: membrane which encloses amniotic îuid, broken at birth.

Amniotic Fluid: protects the fetus against mechanical shock, drying out and
temperature îuctuations

Some pathogens and toxins can pass across the placenta and aìect the fetus.

Adaptive Features of Gametes

Sperm (Male Gamete)

1. Small in size
2. Elongated and streamlined with energy storage
3. Millions in numbers containing 23 chromosomes

Features Functions

Flagellum Propels the

sperm to swim

Mitochond Respiration to
ria release
energy for
swimming

Enzymes in the Release

acrosome digestive
enzymes to
digest the
jelly coat

Egg Cell (Female Gamete)

 1. Larger in size
2. Spherical protein/fat in the cytoplasm
3. Moved with the help of Cillia
4. Released once per month containing 23 chromosomes

Features Functions

Energy Development of
storage zygote

Jelly coat Changes at

fertilisation

Sexual Hormones in Humans

The roles of testosterone and oestrogen in the development and regulation of secondary
sexual characteristics during

puberty
Primary sexual characteristics: present during
development in the uterus and are the diìerences in reproductive organs etc.,
between males and females

Secondary sexual characteristics: are the changes that occur during puberty as
children become
adolescents
At puberty, the pituitary gland starts to stimulate the
primary sex organs: the testes in males and the ovaries in females.

They only aìect the target organs, which have receptors that can recognize them.
Causes secondary sexual characteristics such as the
growth of pubic hair and maturation of sexual organs.

The Menstrual Cycle

Day 1 to 5:
In the ovary, FSH secreted by the Pituitary Gland to
stimulate the maturation of ONE folicle in the ovary. In the uterus: the endometrium
breaks down;
 menstruation

Day 5 to 12:
In the ovary, the follicle keeps maturing
In the uterus, oestrogen is secreted by folicle and the
ovarian tissues to prepare the endometrium

Day 13/14/15:
In the ovary, LHis also secreted by the Pituitary
Gland to trigger the release of the egg from the
follicle into the fallopian tube. Ovulation happens on
Day 14.

Day 15 to 28:
In the ovary, LH triggers the formation of Corpus Luteum

In the uterus: progesterone is secreted by Corpus Luteum to keep endometrium thick,

waiting for
possible embryo implants.

Day 28 – Scenario 1: Egg not fertilised

No implantation takes place, and the Corpus Luteum degenerates, causing a lack of
progesterone.

This means that endometrium is no longer thick, back to Day 1

• Day 28 - Scenario 2: The egg is fertilised

Implantation occurs.
This makes the hormones keep the Corpus Luteum maintained, which means that
progesterone is high.
This keeps the Endometrium thick for pregnancy

Hormones in Menstrual Cycle

Oestrogen: secreted by the ovaries. It stops FSH from

 being produced - so that only one egg matures in a cycle, and it stimulates the pituitary
gland to release the
hormone LH.
Progesterone: secreted by the placenta during
pregnancy, while during the menstrual cycle is by the ovaries. Its primary function is
maintaining the uterus lining during the middle of the menstrual cycle and

pregnancy.
Follicle-stimulating hormone (FSH): secreted by the pituitary gland. It causes an egg
to mature in an ovary and stimulates ovaries to release oestrogen hormone.

Luteinizing hormone (LH): secreted by the pituitary gland and causes mature eggs
to be released from the ovary.

Sexually Transmitted Infections

Human Immunodeíciency virus (HIV) is one example of a sexually transmitted infection.

Transmission: Intercourse, blood transfusion, organ transplant or sharing a needle

with an infected person
How it aìects the immune system:

Infects and destroys lymphocytes

Decreases the eïciency of the immune system The body becomes liable to
infection by other

pathogens
This may lead to AIDS and death from infection

CAMBRIDGE QUESTION
QUESTION SHEET 1

The The diagram shows the female reproductive system.

(a) Name the structures labelled A,B, C and D. Use
names from this list.

ovary urethra oviduct (fallopian tube) ureter cervix placenta uterus (womb) vagina

(b) Match one of the letters from the diagram with each of the following:

(i) an organ which produces eggs.

[ 1]

(ii) the normal site of fertilisation.

[ 1]

(iii) where sperm are deposited during intercourse

[ 1]

(iv) an organ where the embryo develops.

[ 1]

(c) State two ways in which egg and sperm cells are similar?
 .........................................................................................................................................................................[2]

WEEK : TWO
TOPIC: ASEXUAL REPRODUCTION IN PLANT (CAMBRIDGE PAGE 283)

Asexual Reproduction
Asexual Reproduction : the process resulting in the production of genetically identical offspring from one parent.

Bacteria:
Reproduced by binary íssion, each bacterium divides into two.

The generation time is the time taken for a cell to divide into 2.

Advantages Disadvantages

Fast: no need to índ a No genetic

mate,
variation/biodiversity
fertilise, etc.

Good characteristics are Harmful genes

kept transferred

Overcrowding: íghting
Do not need to carry
oìspring for
food/competition

Prone to extinction,
No pollinators
disease,
environmental change

Sexual Reproduction
Sexual reproduction: a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote and the production
of oìspring that are genetically diìerent from each other

Fertilisation: the fusion of gamete nuclei

The nuclei of gametes are haploid, and the nucleus of a zygote is diploid

Diploid: Full Set of Chromosomes

Haploid: Half Set of Chromosomes

Advantages Disadvantages

Produces genetically
It takes lots of time and
diìerent energy
oìspring

Reduced risk of extinction Mate required

 Energy on improving

appearances or pollen
volume

for pollination (plants)

Parts of a Flowering Plant

Flowers are the reproductive organ of the plant

They usually contain both male and female reproductive parts

The structure of insect and wind-pollinated îowers are slightly diìerent as each is adapted for their speciíc

function

Insect Pollinated Flowers. Wind Pollinated Flowers

Functions

Sepal: protect the îower bud.

Petal: brightly coloured and scented and may have

nectars, which are all used to attract insects. Petals in

wind-pollinated îowers are tiny and used for pushing the bracts (leaf-like structures) apart from exposing stamens and stigma.

Anther: has pollen sacs with pollen grains that contain the male nucleus (male gamete).

Stigma: platform on which pollen grains land

Ovary: hollow chamber, ovules grow from the walls.

WEEK: FOUR

TOPIC: POLLINATION

Pollination
Pollination: transfer of pollen grains from the male part of the plant (anther of stamen) to the female part of the plant (stigma).

Agents of pollination: insects, birds, mammals, water and wind

Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule

 Insect Pollinated Wind Pollinated

Bright, colourful petals – Dull petals

attract

Sweetly scented No scent

Contains nectar No nectaries

A moderate amount of Huge amount of pollen

pollen

Pollen is spiky/sticky, Pollen round and

large in size smooth, Small
and light

Pollen tube: pollen grain lands on the stigma and

creates a tunnel down the style, through the micropyle to ovules.

Ovule: seed

Ovary: fruit

Self Pollination
Self Pollination: the transfer of pollen grains from the anther of a îower to the stigma of the same îower or a diìerent îower
on the same plant.

Advantages Disadvantages

Genetically identical Lack of genetic variation

High chance of Increases competition

successful between plants
pollination

Susceptible to the
Fast and saves time
same
disease

Cross-Pollination
Cross-pollination: the transfer of pollen grains from the anther of a îower to the stigma of a îower on a diìerent

plant of the same species.

Advantages Disadvantages

Increases variation Reliance on

pollinators

Quick to adapt to Wastage of pollen

surroundings

Less susceptible to diseases More energy required

Fertilisation in Plants
 Pollen tube growing from a pollen grain

Pollen (tube/grain) releases enzymes

The pollen tube then grows down the style/grows into the ovary

Pollen nucleus travels down the pollen tube

Pollen tube grows and moves through the micropyle into the ovule

Fertilisation occurs

The pollen nucleus fuses with the female nucleus A zygote is formed

Germination
Germination: A process controlled by enzymes

Water: activates enzymes to turn insoluble food stores into soluble substances, and makes tissues swell so that the testa splits

Oxygen: enters through the gaps in the testa (along with water), and is used in aerobic respiration.

Temperature: must be suitable for enzymes to work (at optimum temperature).

WEEK: FIVE

TOPIC: Biotechnology and Genetic Modification

Introduction

Bacteria are useful due to their rapid reproduction rate and ability to make complex molecules.

Why are bacteria useful in biotechnology and genetic modification?

1. There are a few ethical concerns over their manipulation and growth
2. The presence of plasmids
3. Producing complex molecules
 4. Replicates rapidly

Biotechnology

Biofuel

Use plants to make sugars, which yeast then breaks down to make ethanol.
This process also uses anaerobic respiration.

Bread-Making

Flour, sugar, water and salt are mixed with yeast to make the dough.

Amylase breaks down some starch to make maltose and glucose. This is used by yeast
in respiration.

The dough is kept warm and moist (28°C). Yeast

ferments sugar, making carbon dioxide, which creates bubbles, so bread rises.

Cooking (at 180°C) – kills yeast, evaporates alcohol and

hardens the outer surface.
Use of Enzymes in Biotechnology

Pectinase:

Fruit juices are extracted using pectinase (breaks down pectin)

Pectin helps plant walls stick together
If pectin is broke down, it’s easier to squeeze juice from the fruit

Extraction of juice from fruit, making juice clear, not cloudy

Biological Washing powders:

Biological washing powders and liquids contain enzymes that help remove the stain

The enzymes are coated with a special wax that melts in the wash, releasing the enzyme

Once the stains have been broken down, they are easier for detergents to remove

Proteases: break down proteins in stains, e.g., grass, blood

Lipases: break down stains containing fats and oil

Amylases: break down carbohydrate-based stains, such as starch
Cellulases: break down cellulose fíbres

Lactase:
The enzyme that breaks down lactose (the sugar found in milk), people can stop making
lactase naturally and, therefore, can’t digest lactose.
 Lactose-free milk production

Lactase made from yeast

Lactase bound to the surface of alginate beads

Milk passed down beads

Lactose is broken down into glucose and galactose Immobilized enzymes are
reused

Fermenters

Penicillin: an antibiotic produced by a fungus called Penicillium.

They require proper temperature, pH, oxygen, nutrient supply and waste products.

The stainless steel fermentation vessel contains a medium containing sugars and
ammonium salts.

Penicillium is added to produce penicillin. They use sugar for respiration and ammonium
salts to make protein and nucleic acids

• The fermentation vessel consist of 'PAWS'

Probes monitor temperature and pH

Air provides oxygen for aerobic respiration in fungus
water-cooled jacket removes heat to maintain a temperature of 24°C.

Stirrer keeps the microorganism suspended (allowing access to nutrients and oxygen) while
maintaining an even temperature.
It is filtered to remove fungus and then can be crystallized to make capsules.

Mycoprotein
The fungus Fusarium is cultured (grown) on an industrial scale in fermenters.

These fermenters are large vats that can be kept at the optimum pH and temperature
to grow.

The fungus is grown in aerobic conditions and provided with glucose syrup as a food
source.

The fungus grows and multiplies within the fermenter

It is then harvested and puriíed to produce mycoprotein Mycoprotein is a protein-rich
food suitable for
vegetarians, eg. It is used in QuornTM products.

Genetic Modification

Genetic Modiícation: changing the genetic material of an organism by removing, altering,

or inserting individual genes

Examples of genetic modiícation:

the insertion of human genes into bacteria to produce human insulin

the insertion of genes into crop plants to confer resistance to herbicides

the insertion of genes into crop plants to confer resistance to insect pests

the insertion of genes into crop plants to provide additional vitamins

Human Insulin in Bacteria

• Isolation of the DNA making up a human gene using restriction enzymes, forming sticky ends.
Cutting of bacterial plasmid DNA with the same restriction enzymes, forming
complementary sticky ends.
Insertion of human DNA into bacterial plasmid DNA

using DNA ligaseto form a recombinant plasmid –

insertion of the plasmid into bacteria.
Replication of bacteria containing recombinant plasmids,

which make human protein as they express the gene

Genetically Modified Crops

 Advantages Disadvantag
es

Uniform in shape Natural species

– easy to may die
transport/appeal
to consumers

Growing season Decrease

shorter biodiversi
ty/genetic
diversity

Led to the
Drought resistant development of
– less water
superweeds –
stronger than
GM

Higher No one knows

yields the long-
term eìects
on humans

Solve global Expensive

hunger seeds

CAMBRIDGE QUESTION

1. TPAs can be produced by genetically-engineered bacteria.

Fig. 1 shows some of the stages involved in genetically engineering a bacterium to make a
TPA
(i). State the name of structure A in Fig. 1.[1]

(ii). In the flow chart, X represents the action of an enzyme on a molecule of DNA.

State the name of this enzyme.[1]

(iii). The TPA gene is inserted into structure A.

Explain how the gene is inserted into structure A to form structure B as shown in Fig. 1.

[3]

(iv). Before TPA was made by genetically-engineered bacteria it was only available from
blood donated by people.
Suggest one advantage of producing TPA by genetically-engineered bacteria.[1]

WEEK: SIX
TOPIC: Inheritance

Chromosomes, Genes and Proteins

Chromosomes: made of DNA, which contains genetic information in the form of genes
Gene: a length of DNA that codes for a protein
 Allele: an alternative form of a gene
Inheritance of sex in humans is used with X and Y chromosomes.

Haploid nucleus: a nucleus containing a single set of unpaired chromosomes (e.g.,

sperm and egg)

Diploid nucleus: a nucleus containing two sets of chromosomes (e.g., in body cells)

The sequence of bases in a gene determines the

sequence of amino acids used to make a speciíc protein.

Different sequences of amino acids give diìerent shapes to protein molecules.

DNA and Protein Synthesis

DNA: controls cell function by controlling the production of proteins, including enzymes,
membrane carriers, and receptors for neurotransmitters

DNA has 2 long strands and 4 nucleotides, AT and CG mRNA has AU and CG bases

Overall, protein synthesis occurs outside of the nucleus in the cytoplasm

Protein synthesis has two stages:
Transcription (rewriting the base code of DNA into bases of mRNA)

Translation (using mRNA base sequence to build

amino acids into a sequence in a protein)

How proteins are made:

the gene coding for the protein remains in the nucleus

messenger RNA (mRNA) is a copy of a gene

mRNA molecules are made in the nucleus and move to the cytoplasm

the mRNA passes through ribosomes

the ribosome assembles amino acids into protein molecules

the sequence determines the speciíc order of amino acids of bases in the mRNA

All body cells in an organism contain the same genes, but many genes in a particular cell
are not expressed

because the cell only makes the speciíc proteins it needs

Cell Division: Mitosis

Mitosis: The nuclear division gives rise to genetically identical cells

 Mitosis is needed for:
Growth: in animals, each tissue provides its own new cells when needed.

Repair damaged tissues: for example, when you cut your skin, mitosis provides new
cells to cover up cuts.
Replacement of worn-out cells

Asexual reproduction: in plants

The exact replication of chromosomes occurs before mitosis

During mitosis, the copies of chromosomes separate, maintaining the chromosome number
in each daughter cell
Stem Cells: unspecialised cells that divide by mitosis to produce daughter cells that can
become specialised for speciíc functions

Cell Division: Meiosis

Meiosis: Reduction division in which the chromosome number is halved from diploid
to haploid
Meiosis is involved in the production of gametes.
Meiosis results in genetic variation, so the cells produced are not all
genetically identical.

Gametes such as sperm and ovum are produced via meiosis.

Monohybrid Inheritance

Inheritance: The transmission of genetic information from generation to

generation.

Here are some common terminologies you should know to understand

monohybrid inheritance.

Terminologies

Genotype: the genetic makeup of an organism in terms of the alleles

present (e.g. Tt or GG)

Phenotype: the observable features of an organism (e.g. tall plant or

green seed)
genotype +environment + randomvariation →
phenotype
Homozygous: having two identical alleles of a particular gene (e.g. TT
or gg). Two identical homozygous

individuals that breed together will be pure-breeding

Heterozygous: having two diìerent alleles of a

particular gene (e.g. Tt or Gg), not pure-breeding

Dominant: an allele that is expressed if it is present (e.g. T or G)

Recessive: an allele that is only expressed when there is no dominant

allele of the gene present (e.g. t org)

Pedigree Diagram

Pedigree diagrams trace the inheritance pattern of a speciíc

characteristic (usually a disease) through generations of a family.

Pure Breeding: The individual is homozygous for that characteristic

This can determine the probability that someone in the family will
 inherit the genetic disorder.

Genetic Diagrams

Monohybrid Inheritance can be determined using a genetic diagram

known as a Punnett square.

A Punnett square diagram shows the possible

combinations of alleles that could be produced in the oìspring.

The dominant allele is shown using a capital letter, and the recessive
allele uses the

same letter but lowercase.

If you are asked to use your own letters to represent the alleles in a
Punnett square, try to choose a letter that is obviously diìerent as a
capital than the lowercase so the examiner is not left doubt as to which
is dominant and which is recessive.

3: 1 Monohybrid Crosses

In this cross, there is a 1:1 ratio of boy to girl, meaning a 50% chance
of the oìspring being a boy and a 50% chance of the offspring being a
girl.
 3:1 Monohybrid Crosses

There is more variation in this cross, with a 3:1 ratio of brown eyes: blue
eyes, meaning each oìspring has a 7 5 % chance of having brown eyes and a
2 5 % chance of having blue eyes

Modification of Mendelian Genetics

Codominance

Codominance: a condition where two alleles of a gene are equally

dominant (50%)

Both alleles are equally expressed in the phenotype of the

heterozygote.

For example, if the parent phenotype is red and white, a co-dominant

will have both red and white colour in the oìspring.

ABO Blood Group (Codominance and Multiple Allele)

Inheritance of bloodgroup is an example of

codominance

There are three alleles for the bloodgroup given by the symbols IA, IB
 and IO.

IA and IB are co-dominant giving bloodgroup AB or IAIB, and both

dominant to IO .

Sex-Linked Characteristics
Sex-linked characteristic: a characteristic in which the
gene responsible is located on a sex chromosome, making it more common in
one sex than in the other.

Generally, in the IGCSE syllabus, the most common is X- linked

recessive trait.

X-linked recessive disorders are more common in males than in

females.

Syllabus 17.4.18: You must be able to use genetic diagrams to predict the results
of monohybrid crosses involving codominance or sex linkage and calculate
phenotypic ratios.

CAMBRIDGE QUESTION

1. Haemophilia is a sex-linked blood disorder. The blood of people with

haemophilia takes longer to clot.

Fig. 1 is a pedigree diagram showing the inheritance of haemophilia.

 Fig. 1

The allele for normal clotting time is represented b y

XH . The allele for haemophilia is represented b y Xh .

(i). State the genotypes of the people identified as P, Q and R in Fig. 1. [3]
(ii). The couple S and T are expecting another child.

(iii). State the probability that the child will have haemophilia.

WEEK: SEVEN

TOPIC: Variation and Selection

Variation

Variation: diìerences between individuals of the same species

Both genetic and environmental factors cause

phenotypic variation
Continuous Variation: results in a range of phenotypes between two
extremes; examples include body length and body mass

Discontinuous Variation: results in a limited number of phenotypes

with no intermediates (e.g. ABO blood groups, seed shape in peas and
seed colour in peas)

It is usually caused by genes only, and genes and the environment

cause continuous variation.
Syllabus 18.1.5: You must be able to investigate and describe examples of
continuous and
discontinuous variation
 Mutation

Mutation: A genetic change.

Gene Mutation: a change in the base sequence of DNA Mutation is

the way in which new alleles are formed

Mutation, meiosis, random mating and random fertilisation are

sources of genetic variation in

populations
Ionising radiation and some chemicals increase the rate of mutation

Adaptive Features

Adaptive Feature: an inherited (structural) feature that helps an

organism to survive and reproduce in its environment.

XEROPHYTES

Xerophytes live in deserts where water is scarce, and evaporation is rapid

or in windy habitats. Their features
are:
Deep roots reach the water far underground
Leaves have reduced spines with minimum surface area for
 transpiration

Shallow spreading roots to collect occasional rain

Rolled leaves, leaf hairs, and stomata sunk in pits to trap moist air

Waxy leaf cuticle, impermeable to water

Stomata open at night and close at midday when evaporation is
highest
E.g. cactus and marram grass
Hydrophytes

Hydrophytes: live wholly or partly submerged in water. Their features

are:

Leaves are highly divided to create a large surface area for

absorption and photosynthesis
Minimal cuticle formation
Lack of xylem tubes, no stomata underside of leaves Stomata are
on the upper surface and have a thick waxy layer to repel water and to
keep the stomata open and clear

Roots are often reduced, and root hairs are often absent

Selection

Natural Selection

In any environment, the individuals that have the best adaptive features are the
ones most likely to survive and reproduce.

The greater chance of the best-adapted organisms passing on

genes.

The development of strains of antibiotic-resistant bacteria is an

example of natural selection.

The surviving organisms reproduce since they don’t get eaten up, so
variation has caused the species to evolve.
Process of Natural Selection:
1. genetic variation within populations
2. production of many oìspring
 3. struggle for survival, including competition for resources

4. Individuals better adapted to the environment have a greater chance

of reproduction than others; these individuals pass on their alleles to
the next generation.

Adaptation: the process of natural selection by which populations become

more suited to their environment over many generations.

Artificial Selection

Artiícial Selection: breeds organisms with valued characteristics together to

produce oìspring that share those valuable characteristics.
It can be used to produce organisms that are more economically
valued

For example, cows that produce more milk, wheat that is easier to
separate from grain, dogs that have a better appearance

Process of Selective Breeding:

Selecting by individuals with desirable features

Crossing these individuals to produce the next

generation
Selection of oìspring showing the desirable features

CAMBRIDGE QUESTION

QUESTIONSHEET

Read the following passage and answer the questions.

The speckled moth (Biston betularia) normally exists as a speckled

grey form. This moth spends much of its time resting on the lichen-
covered bark of trees where its colour provides good camouflage from
birds. Occasionally, a black form of the moth appears but rarely
survives. During the Industrial

Revolution in the nineteenth century coal came into widespread use

and many trees became covered with soot from the chimneys.

By the end of the nineteenth century the black form of the moth
made up 9 8 % of the moth population.
 Since the 1950's Britain's air has become much cleaner and the
speckled form of the moth is now the most common.

(a) What caused the first black form of the moth to appear?

....................................................................................................................................................................
.....[1]

(b) Explain why, prior to the Industrial Revolution, the black form of moth did not survive for
long.

....................................................................................................................................................................
.....[2]

(c) Explain how the black form of the moth came to make up 98% of the moth population.

..............................................................................................................................................................
...............

[5]

(d) The change in the populations of speckled and black moths is an example of evolution.
 What process had caused this evolution?

[ 1]

WEEK: EIGHT

TOPIC: Drugs

Drugs: Any substance taken into the body that modiíes or aìects
chemical reactions in the body. All drug metabolism is done in the Liver.

Antibiotics

Antibiotics work by disrupting crucial systems that

bacteria need to survive and multiply, such as their cell walls, DNA, or
protein synthesis, while not harming
human cells.
Some bacteria are resistant to antibiotics, which reduces the
eìectiveness of antibiotics.

The development of resistant bacteria such as MRSA can be minimized

by limiting antibiotics only when

essential and ensuring treatment is completed.

Antibiotics don’t work on viruses because they do not have a cell wall
and make the host cell perform their tasks.

Antibiotic Resistance

Antibiotic-resistant bacteria can be reproduced through the theory of

natural selection:

Mutation, giving rise to variation

Antibiotics kill bacteria without changing genes
 Competition for food space, among others
Reproduce via binary íssion
Then, alleles are passed on to oìspring to reproduce.

An example of antibiotic-resistant bacteria is Methicillin- resistant

Staphylococcus aureus (MRSA)

WEEK: NINE
TOPIC: THE NERVOUS SYSTEM I

CONTENT:
(1) Organization of the nervous system
(i) Central Nervous System (CNS)
(ii) Peripheral Nervous System (PNS)
(2) The Brain-position, structure and functions
(3) The Spinal Cord-position, structure and functions

SUB-TOPIC 1: ORGANIZATION OF THE NERVOUS SYSTEM

 In a complex multicellular organism many activities go on almost
simultaneously. These activities are coordinated by the endocrine and nervous
system. The two systems are linked by the hypothalamus.
 The basic structural unit of the nervous system is the nerve cell (neurons). The
nervous system is made up of millions of neurons.
 The main parts of the nervous system are the central nervous system and the
peripheral nervous system.
THE CENTRAL NERVOUS SYSTEM (CNS)

 This consists of the brain and the spinal cord.

 The CNS coordinates the activities of the nervous system.
 It receives impulses from the organism’s internal and external environment,
processes and integrates the information and sends out impulses to appropriate
effector organs to take action.

The CNS has millions of interconnected nerves which are of two types;
i. the cranial nerves come out of the brain and enter mainly structures in the head
(e.g. the eyes and ears).
ii. The spinal nerves come out of the spinal cord and go into the arms, legs and
various structures in the trunk.

EVALUATION
1. State two differences between the endocrine system and the nervous system.
2. Mention the major parts of the nervous system

THE BRAIN.
The human brain is made up of billions of neurones which form the grey matter (nerve
fibres). The grey matter occupies the peripheral region, while the white matter is
situated in the central portion of the brain.

The adult human brain weighs about 1.2 to 1.4 kilograms and forms about 2% of the
body’s mass. The brain is protected by the cranium or brain case.

Human Brain

The human brain has three major structural components:

 the large dome-shaped cerebrum (top),

 the smaller somewhat spherical cerebellum (lower right),

 and the brainstem (center). Prominent in the brainstem are the medulla
oblongata (the egg-shaped enlargement at center) and the thalamus (between
the medulla and the cerebrum).
Functions:
 The cerebrum is responsible for intelligence and reasoning.
 The cerebellum helps to maintain balance and posture.
 The medulla is involved in maintaining involuntary functions such as respiration,
and
 the thalamus acts as a relay center for electrical impulses traveling to and from
the cerebral cortex.

The vertebrate brain is made up of three regions;

1. The Fore brain,
2. The Mid brain
3. The Hind brain.

1. THE FORE BRAIN,

This is associated with higher brain functions like intelligence and speech.

It is made up of three main parts, namely,

1. The Cerebrum,
2. The Thalamus and
3. The Hypothalamus.

A. Cerebrum:
This is made up of two halves, the right and left cerebral hemispheres. The two halves
are bound by fibres called the corpus callosum, which keeps each hemisphere informed
about the other.

Each hemisphere has four distinct lobes namely;

1. Frontal lobe (in front)
2. Parietal lobe (at the top)
3. Temporal lobe (at the side)
4. Occipital lobe (at the back)

The most active part of the cerebrum is its outer layer, the cerebral cortex, which is
composed of grey matter.
It is highly convoluted to increase its surface area and consequently the number of
neurones thus increasing the capabilities of the cerebrum.
The cerebral cortex is the seat of intelligence, speech, memory, learning, imagination
and creativity.
NB: The left hemisphere controls the right side of the body while the right hemisphere
controls the left part of the body.
B. The Thalamus
I. There are two thalami, each one is an oval body attached to the back end of the
cerebrum.
II. They act as the relay centres for receiving and transmitting sensory information
to relevant parts of the cerebral cortex.
III. They also transmit outgoing motor impulses from the cerebral cortex.

The Hypothalamus
a. This is an ovoid body projecting below the thalami.
b. It is a controlling centre for the autonomic nervous system.
c. It plays a homeostatic role by regulating temperature and endocrine secretions.
d. Signals from it also trigger feelings of hunger and thirst. It also influences
emotions like anger, pain and pleasure.

2. THE MIDBRAIN
a. This is the portion between the fore-brain and hind-brain.
b. Specific portions control the reflexes of sight and hearing.
c. Associated with these are the movements of the head when focusing on an
object and the detection of sound.

3. THE HINDBRAIN
It is composed of three parts;
1. The Cerebellum,
2. The Pons varolli and
3. The Medulla oblongata.

A. The Cerebellum
a. The Cerebellum is tri-lobed.
b. There is one median lobe and two lateral cerebellar hemispheres.
c. It controls and coordinates body posture and muscular movements, especially
those that maintain the body’s balance.

B. The Pons varolli

The Pons varolli is a wide band of fibres that connect the lateral cerebellar hemispheres.
C. The Medulla oblongata
a) The medulla oblongata is the posterior portion of the brain and continues into
the spinal cord.
b) It has an outer region of white matter and an inner region of grey matter.
c) It controls involuntary movements like those involving respiration, digestion,
heartbeat, constriction and dilation of blood vessels.

The Stem of the brain

EVALUATION
1. Discuss briefly the position and structure of the brain.
2. What are the functions of the brain?

THE SPINAL CORD

1. The spinal cord is composed of a soft white tissue running from the medulla
oblongata to the tail region.
2. It is protected by the bones of the vertebral column and passes through the
neural canal.
3. It is enveloped by three membranes called the menninges which further protect
it.
4. The spinal cord has an inner area of grey matter and an outer region of white
matter.
5. The grey matter is composed of the cell bodies of the neurones in the spinal
cord while the white matter is made up of the nerve fibres which emanate from
the cell bodies.

Functions of the Spinal Cord

1. It coordinates simple reflex actions such as knee jerk and automatic reflexes such as
sweating.
2. It connects all peripheral pathways to the brain.

EVALUATION
1. Describe the spinal cord.
2. What are the functions of the Spinal cord?

ESSAY TEST
1. What are the structural differences between the brain and spinal cord?
2. In a table differentiate the functions of the brain and spinal cord.

WEEKEND ASSIGNMENT
Examine the brain and spinal cord of sheep and make well labeled diagrams

WEEK 10

TOPIC: THE NERVOUS SYSTEM II

CONTENT: 1.The Peripheral nervous system

2. Structure and functions of a neurone
3. Reflex and voluntary actions

SUB-TOPIC 1. THE PERIPHERAL NERVOUS SYSTEM (PNS)

The peripheral nervous system links the CNS with the body’s receptors and effectors in
mammals.
When receptors pick up impulses of change in the environment, messages are sent to
the CNS which integrates the information and sends appropriate messages to the
effectors accordingly.

The peripheral nerves are of two types;

1. the spinal nerves connected to the spinal cord and
2. the cranial nerves, connected to the brain.

The spinal nerves serve the receptors and effectors in the other body parts.
The cranial nerves are associated chiefly with the receptors and effectors in the head,
while

The PNS consists of

1) The Somatic nervous system (SNS) and
2) The Autonomic nervous system (ANS).

Somatic Nervous System

 The nerves of the SNS principally serve the parts of the body which take part in
responses to external stimuli (e.g. sense organs, limb muscles and glands) and
voluntary activities.
 The motor neurones stimulate the effectors.
 The SNS also controls the emptying of the bladder and the opening of the anal
sphincters.

Autonomic Nervous System

The ANS is concerned with control of the bodies involuntary activities e.g. heartbeat,
movements of the gut and secretion of sweat.

The ANS consists of two parts;

1. The Sympathetic and
2. The Parasympathetic systems.

Both contain nerve fibres serving structures over which the body has little or no
voluntary control. In both cases nerve fibres from the brain or spinal cord pass into the
organs concerned. Along the course of each pathway there is a complex set of
synapses forming a ganglion.

In the sympathetic system, the ganglia lie alongside the vertebrae close to the spinal
cord.
In the parasympathetic system, the ganglia are embedded in the wall of the effector
itself. The effects produced by the two systems generally oppose one another
(antagonistic).
Thus, if the sympathetic system causes a certain muscle to contract, the
parasympathetic system relaxes it.

The following is a diagrammatic representation of the autonomic nervous system

showing its connections with the central nervous system and its effects on some
internal organs.

The Autonomic nervous system

The Neurone

 The neurone is the basic structural unit of the nervous system.

 The nervous system is made of bundles of cells called neurons.
 They send electrical signals that direct all of your body’s activities, including
thinking, breathing, and moving.
 These signals travel along the length of one neuron and jump to another
neuron over a gap called a synapse.
 It consists of a cell body and protoplasmic processes called nerve fibres
which are tied up in bundles called nerves.
 It is specialized for transmitting electric impulses. Mature neurones have lost
 their ability to regenerate.

Nerve cells

Structure of a Neurone
A Neurone has three basic parts;
1. A cell body
2. Dendron
3. The axon

i. A cell body: this may be star-shaped, oval or angular. It has a large nucleus and dense
granulated cytoplasm which gives it a greyish colour. The golgi apparatus manufactures
vesicles containing chemicals needed for the transfer of electric impulses.
The cell body relays impulses to the axon

ii. Dendron with branches called dendrites: dendrons carry nerve impulses that their
dendrites receive to the cell body.

iii The axon ending in synaptic knob(s): this carries electric impulses away from the cell
body to their destination. The synaptic
knobs release chemicals that bring about
transfer of electrical impulses from an
axon to the target cells.
TYPES OF NEURONE

There are different types of neurons

 Based on their functions
 Based on number of axons they
possess
Based on their functions
a. Sensory (afferent) neurone: this receives impulses from receptors and passes them
towards the CNS.
b. Motor (efferent) neurone: this receives impulses from the CNS and passes them to
the effector.
c. Relay/ association neurone: this transfers impulses from the sensory neurones to
the motor neurones.

Based on number of axons they possess

Neurones may also be grouped according to the number of axons they possess, thus,
there are
1. Unipolar (one axon)
2. Bipolar and (two axons)
3. Multipolar neurons (more than two)

NERVE IMPULSES
A nerve impulse is a wave of electrical activity travelling along a neurone.

Nerve impulses are transmitted along a neurone in two main ways;

1. Electrical and
2. Ionic (chemical) means.

Electrical Transmission
a) When an axon is in the resting state, its inside is negatively charged and its
outside is positively charged. Thus the membrane surrounding the axon is
polarized. This is called its resting potential.
b) When an impulse passes through the axon, its inside becomes positively
charged and its outside becomes negatively charged. This is the action potential
and the nerve membrane becomes depolarized for a short time after which the
original resting potential is restored.
c) Once an action potential is set up, it moves rapidly along the neurone until it
reaches the end of the axon.

Ionic (chemical) Transmission

 a) When an axon is at rest, the membrane is polarized i.e. its outside is positively
charged and the inside is negatively charged. A resting neuron actively pumps
+
out sodium ions (Na ) out through the cell membrane and retains chloride ions
- +
(Cl ). As each sodium ion is pumped out a potassium ion (k ) is pumped into the
cell. The potassium ions leak out again but the sodium ions cannot move in
because the sodium gates are closed. This results in the polarization of the
neurone. An electric potential difference thus exists across the membrane of the
neurone.

b) When an impulse passes along the axon, the membrane suddenly becomes
depolarized and permeable to sodium ions. This reverses the resting potential i.e.,
the inside of the axon becomes positively charged and the outside negatively
charged, thus an action potential is set up. Small local currents on both sides of
the membrane (at the leading end of the region of polarization) excite the next
part of the axon, so that an action potential is propagated along the whole length
of the axon.

c) Impulses are set up in nerve cells as a result of excitation of the receptors.

Nerves are stimulated by mechanical, osmotic, chemical, thermal and electrical
stimuli. If the strength of a stimulus is below certain threshold intensity no action
potential is evoked. Further increase in intensity of the stimulus however does
not give a larger potential. A stimulated neurone therefore acts in an all-or-none
manner.

d) Transmission of the impulse across the synapse occurs by chemical means.

When an impulse arrives at a synapse a chemical substance, acetylcholine, is
released. This diffuses across the gap and causes excitation of the adjacent
nerve cell.

e) The synapse prevents impulses from going in the wrong direction i.e. an
impulse can only go in one direction across a synapse but it can go in either
direction along an axon.

REFLEX AND VOLUNTARY ACTIONS

Actions are responses to stimuli. They involve the nervous and endocrine system. There
are two main action patterns;
i. The Reflex action
ii. The Voluntary action.
Reflex Action
Responses to a stimulus that are not controlled by will i.e. involuntary responses are
called reflex actions. We are often not aware of our reflex actions though sometimes we
may become aware of them shortly after doing them. Reflex actions help to protect us
against danger and also to maintain equilibrium in both our internal and external
environment.
Other examples of reflex actions are;
i. blinking of the eyes.
ii. Withdrawing the hand from a hot object.
iii. The knee jerk e.t.c.

The Reflex Arc

The reflex arc is the simplest pathway taken by a nerve impulse in mediating a simple
response. In the simplest form it involves only two neurones; a sensory neurone and a
motor neurone. For example in the knee jerk a sensory neurone synapse directly with a
motor neurone.

The structures which take part in a reflex arc are;

1. The sensory receptor that detects the stimulus.
2. The afferent neurone along which the sensory impulse is transmitted.
3. The relay neurone in the central nervous system which passes the impulse
from the afferent neurone to the motor neurone.
4. The motor neurone which receives the impulse from the relay neurone
5. The effector muscle or gland which responds to the motor impulse with an
appropriate action.
Some reflex actions involve only the spinal cord and are known as spinal reflexes e.g.
the knee jerk while others involve the brain and are called cranial reflexes e.g.
contraction of the pupils when a light source approaches them.

Complex Reflex Actions

A reflex action could be complex when the actions involve neurones at different levels
of the spinal cord or the brain. Complex reflexes are also fast and automatic and
produce stereotyped activities like simple reflexes, but they involve ascending and
descending nerve fibres within and between the spinal cord and the brain.

Voluntary Actions
These are actions which we think about first before doing them. These actions involve
the brain and are usually the acts of will. They are consciously carried out e.g. a sudden
withdrawal of the foot from a sharp object is a reflex action but going back to examine
the foot and extract the object is a conscious or voluntary action.

Voluntary actions therefore;

i. Involve higher centres of the brain.
ii. Involve numerous neurones.
iii. Bring about comparatively sloe responses.
iv. Bring about responses that vary with circumstances.

The brain may also initiate a voluntary action without any sensory stimulation.

ANIMAL BEHAVIOUR
An animal’s response to the changes in its environment is referred to as its behavior.
There are two main patterns of behavior;
i. Instinctive behavior.
ii. learned behavior.

Instinctive Behaviour
Reflexes which originate from birth are described as instinctive or innate. Example are
the sucking reflex of an infant and the pecking action of a newly-hatched chick.

Learned Behaviour
Behaviours which are not innate/ instinctive develop through use. These are learned
from experience. When a reflex action is modified by experience, it becomes a
conditioned reflex.
The conditioned reflex was first demonstrated by a Russian scientist, Pavlov (1910)
who noticed that a dog will salivate when food was presented to it. Pavlov changed the
experience by ringing a bell just before food was presented to the dog. This was
repeated several times, and then he decided to ring the bell without presenting food. He
noticed that the dog salivated on hearing the bell. Thus in a conditioned reflex the
stimulus and response do not have to be related, just like the bell was in no way related
to the food.

Many simple reflex actions are consciously modified by manipulating conditions; the
results are learned (conditioned) behaviours. With time these become almost automatic.
The learned behaviours of walking, speaking, typing, swimming, playing on an
instrument and driving a car are almost automatic.

EVALUATION
1. Define the following terms (a) neuron (b) reflex action (c) behaviour (d) conditioned
reflex (e) voluntary action
2. Discuss two of the terms you have defined
WEEKEND ASSIGNMENT

In a tabular form, differentiate between the reflex action and conditioned reflex.