Life is beautiful, learn it, live it, love it.

Only go
with what works. Follow the light. - MS Siazibulo
Contents
Reproduction; Genetics; Classification; Soil; Ecology
For the love of science we do these things. Factor non verba, our way of life © 2018

Reproduction is the giving of offspring by parent organisms to ensure the survival and continuity of
the species.

Two basic forms of reproduction

1.ASEXUAL
o Does not involve the fusion of the female and male gametes
o Occurs in fungi, amoeba, paramecium and bacteria
 In some organisms, unfertilised eggs give rise to new individuals. In animals this is called
parthenogenesis (parthenos = virgin ) e.g in sharks and aphids. In plants it is called
agamospermy (a = without; gamos = marriage; sperma = seed, hence: seed without
marriage).

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  Involves one parent and results in the production of genetically identical offspring 
 Characteristics of asexual reproduction
 No fusion of gametes

 Only one individual is needed for this to take place
 Offspring are exact copies of the parent

Advantages Disadvantages
Quick Little variation – adaptation to environment is
unlikely
Only one parent needed Offspring inherit bad characteristics
No gametes needed Lack of dispersal – creating competition
All good traits passed on to offspring
No dispersal – offspring grow in the same
favourable environment as parent

Types of asexual reproduction
o Spore formation (ferns and fungus) – involves development of spores in specific regions of
fungi e.g sporangium. At maturity the sporangium bursts to release the spores into air and
these spores germinate wherever they settle on organic matter.
o Binary fission (protozoa) – dividing of protozoa by mitosis or bacteria to give two exact
copies of itself.

o Budding (like in yeast) – spontaneous growth of a young organism on the parent plant
which eventually becomes independent.
 Vegetative propagation : any form of reproduction by plants which does not involve fusion
of gametes (occurs in grapes, bananas, sugarcanes, potato etc)

Vegetative reproduction maybe natural or artificial

i. Natural vegetative reproduction

Occurs via runners, buds, sucker, stem tubers(rhizomes), bulbs, root tubers etc

ii. Artificial vegetative reproduction

Occurs via grafting, layering, cutting etc

 Commercial applications

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 Natural vegetative propagation – to increase
global food production
Artificial vegetative propagation – to increase
food supply by growing high yielding crop
plants on a large scale and to ensure new
plants have some particular feature of the
parent
Bacteria and fungi are important as they are important for;

1. Decomposition of dead organic matter

2. Recycling of nutrients
3. Production of drugs
4. Production of alcohol and food (milk product
5. Some fungi are food (mushroom)

Bacteria and fungi may also cause disease and infections.

2.SEXUAL
 Involves the fusion of haploid (n) nuclei from two different parents to form a zygote and
the production of dissimilar offspring
 Involves a male and a female
 The male gamete fuses with the female gamete to form a zygote which grows and
develops into a multicellular individual.

In plants

 In flowering plants, flowers are the main reproductive organs. Flowers are seasonal.
 Flowers may be bisexual or unisexual

 The male sex organ is called the stamen – produces pollen grains.
 The female sex organ is called the carpel – consisting of an ovary, a style and one or more stigma.
 The female gametes are contained in the ovules produced by the ovary.

 Pollination is the transfer of pollen grains from the stamen to the stigma of the same or different
flower of the same species.

 Fertilisation occurs when the male gamete fuses with the female gamete of the same flower or
another flower of the same species.

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 Parts of a flower

 Floral parts of a flower are arranged in four whorls on the receptacle

 Floral parts consists of:

1. Calyx
Forms the outermost whorl
Made of green and leaf-like structures called sepal which enclose and protect the floral
parts during the bud stage
Epicalyx forms an extra whorl outside the calyx in some flowers such as the hibiscus
2. Corolla
Forms the second whorl of the flower
Components are called petals
Most conspicuous part of the flower – colourful and serve to attract insects to the flower;
protect the stamen and the carpels
3. Androecium
Forms the third whorl of the floral parts
Male organ of the flower comprises many stamens
Each stamen is made up of an anther attached to a filament
The number of stamens varies
The anther is bulged, each containing two pollen sacs
Pollen grains differ in shape and size depending on the species

4. Gynoecium
Forms the fourth and innermost whorl of the floral parts
Female sex organ comprises an ovary (may contains ovules), a style and a stigma
Style is a slender prolongation on the top of the ovary
The stigma is the apical portion of the style which receives the pollen grains

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  Comparing insect-pollinated and wind-pollinated flowers

Wind-pollinated flowers Insect-pollinated flowers

Small Large
No nectar Has nectar
Stamens with long slender Stamen not pendulous
filaments(pendulous)
Large number of pollen grains produced Few pollen grains produced
Pollen grains are small, light and with Pollen grains are larger heavier and have
smooth surfaces spikes on the surface
Feathery stigma with large surface area to Stigma has a sticky surface, usually
trap pollen grains in the wind compact – does not protrude
Stamen and stigma hung out of the whorl of Stamen and stigma within the whorl of
petals petals
No petals or dull coloured patals Brightly coloured petals, large and often
scented

 Pollination
The transfer of pollen grains from the anther to the stigma
ollen grains develop inside the anther
Then the anthers are matured, they split open and the pollen grains are released
ollen grains may be carried to the stigma by wind, insects or water (cross-pollination)
Pollen may simply fall from the anther onto the stigma of the same flower, resulting in
Self - pollination (E.g. peas have modified petals to ensure self-pollination).

1. Self-pollination – transfer of pollen grains from the anther of a flower to the stigma of the
same flower or another flower of the same plant
2. Cross-pollination – transfer of pollen grains from the anther of a flower to the stigma of
another flower of a different plant of the same species
 Fertilization
Pollen grains are put on the stigma by wind or an insect. The pollen grain produces a pollen
tube which grows down the style and into the ovary, where it releases two haploid sperm
nuclei. The pollen tube is created by the pollen-tube generating nuclei.
These two nuclei take part in a double fertilization (unique to flowering plants).
- One sperm nucleus fertilizes the egg nucleus to give rise to a 2n (diploid) zygote.
- The other sperm nucleus fertilises the polar nuclei, which results in a 3n endosperm
nucleus, which then rapidly divides giving rise to a triploid (3n) nutritive tissue: the
endosperm (cotyledon).
As the zygote develops into an embryo, the endosperm absorbs food from the parent
sporophyte, and the layers of the ovule wall develop into the seed coat. The ovary wall
develops into the fruit.
[Sporophyte = Diploid (2n) plant that produces haploid spores following meiosis ].

Revise on seed structure and germination from the topic growth and development .

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 Seed dispersal
The flowers produce seeds which can be dispersed by the wind or other animals, providing a
means of colonizing new areas.

1. Wind-dispersed seeds

Fruits contain seeds, and usually have a parachute

or a wing to help them be carried away from the
parent plant by the wind.
Examples: dandelion, sycamore
The dandelion fruit has a group of finehairs called a
pappus, which catches the wind and acts like a
parachute. The fruit counterbalances the pappus.
The sycamore has a wing with a large surface area.
When the fruit drops off the tree it spins, slowing
down in descent. If caught by the wind the seed will
be carried away from the parent plant, reducing
competition for nutrients, water and light.

2. Animal-dispersed seeds
There are 2 main modification of fruits for animal
dispersal: succulent fruits and hooked fruits.
Succulent fruits attract animals because they are
brightly coloured, juicy and nutritious.
When eaten, the seed pass through animal’s faeces,
which may be a long way from the parent plant. The
faeces provide nutrients when the seeds germinate.
Hooked fruits catch on to an animal’s fur as it
brushes past the parent plant. Eventually the seeds
drops off, or the animal grooms itself to remove
them. This disperses the seeds away from the parent
plant.

3. Self dispersed seeds

These are plants which bare fruits which at maturity the dry and pop, resulting into spreading of
seeds out of the pods e.g legumes (the bean plants). The seeds are not dispersed far from the
parent plant.

In animals

Male Reproductive System

The main reproductive organs are the testicles (testes).

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1. Testes - Oval in shape. Are suspended in the scrotum outside the body cavity so that they are
kept 2–3°C cooler than the rest of the body where sperm production is optimum at this
temperature
Function - Produce male gametes known as sperms. Produce male sex hormones called
testosterone (androgens).

2. Scrotum - Sac formed by the skin to enclose the testes

Function - Protect the testes and regulates temperature.

4. Sperm duct - Connects the storage duct also known as epididymis with the urethra during
copulation

4. Male reproductive glands

Prostate gland – a single gland located at the part of the urethra where the two sperm ducts
join
Seminal vesicles – pair of glands which open directly into the sperm ducts
Cowper’s glands (bulbourethral gland) – open directly into the urethra
Function - Produce fluid which keeps the sperm alive (provide nutrients) and helps them to swim
vigorously together with the sperm, the fluid forms the semen. The fluids are alkaline in pH and this
aids in neutralization of the vagina acidic pH.
5. Urethra - Passes through the penis
Function - A tube which carries urine and semen at different times through the penis
6. Penis - An organ which gets erect when filled with blood.
Function - Carries urine and semen out of the body. Becomes stiff and erect so that copulation
may occur and release the sperm into the vagina

Female Reproductive System

The main reproductive organs are the ovaries
External sex organs (vulva)

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• Labia majora and minora (major and minor lips). They cover and protect the urinary and genital
openings and the surrounding tissue.
• Girls are born with a membrane: the hymen, covering the vaginal orifice. One or more slits in the
hymen allow the menstrual flow to pass.
• Clitoris: Develops from the same structure
that develops into the penis in a male
embryo. Its only function is to give a
pleasurable sensation when it is stimulated
by touch.
• Mons Veneris ("Mountain of Venus") is a
fatty pad over the pubic bone.
NOTE: opening of urethra (urinary tract) and
of the vagina (reprod. tract), are separate
(only with females of the higher mammals.)

Ovaries - Oval in shape. Attached to the

dorsal body wall below the left and right
kidneys
Function - Releases an egg or ovum
every 28 days into the oviduct or fallopian
tube
Produce female sex hormones –
oestrogen and progesterone
Oviduct - Also called the fallopian tube. A
narrow tube with a funnel-shaped opening
lying close to the ovary
Function - Contraction of the muscle wall
aids the ovum to move towards the uterus.
Fertilisation of the egg usually occurs here
Uterus or womb - Has a central cavity surrounded by thick muscular walls
Function - Adapted for the implantation of the embryo and its development into a foetus
Cervix - A ring of muscles at the lower end of the uterus
Function - Helps keep the foetus until it is ready to be born

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Vagina - Cervix opens into the vagina. A tube with thinner walls which opens to the outside
through the vulva

Function - Serves as an opening for the entry of the penis during copulation. Also serves as an
outlet for the birth of baby (birth canal)

This Sperm and the Egg

The sperm is the smallest cell in the

body while the oocyte (egg or
ovum) is the largest cell in the
human body.
Sperm - Extremely small
Consists of the head containing the
chromosomes which carry the
genes responsible for passing on
the characteristics of the father, a
middle piece and a tail, which helps it to swim
Egg (Ovum) - Larger than the sperm
Spherical in shape and consists of the nucleus containing chromosomes which carry genes
responsible for passing on the characteristics of the mother, surrounded by cytoplasm and
enclosed by a thin membrane with a jelly coat

Starlight fades in light years, children of light we are.- Manyepa S Siazibulo

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Menstrual cycle

Begins only when a female reaches puberty and stops when menopause begin
Cycle starts with menstruation – characterised by bleeding from the vagina caused by
the breaking down of the lining of the uterus or womb
Menstrual periods take place fairly regularly at intervals of about 28 days
Menstruation goes on for about five days
On the 14th day of the menstrual cycle, one of the ovaries releases an ovum into the
fallopian tube towards the uterus
If ovum is fertilised with a sperm, it attaches itself to the walls of the uterus from which
food and oxygen are obtained
If the ovum is not fertilised, the ovum eventually disintegrates and the lining of the
uterus wall breaks down
Uterine lining and blood flows out through the vagina 14 days after ovulation and this
signals the start of the next menstrual cycle

Fertile and infertile phases of the menstrual cycle. An ovum can live for 24 to 36 hours after
ovulation

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 A sperm cell remains active for two to three days after being released into the female
reproductive system
The fertile phase of the menstrual cycle is the time from day 11 to day 17 of the menstrual
cycle
If the sperm is released into the female reproductive system on day 12, the ovum can be
fertilised and pregnancy results
The infertile periods are from day 1 to day 10 when the uterus lining breaks down and then
gets repaired slowly again, and from day 18 to day 28 when the cells in the uterus wall
begin to die

Fertilisation = Human cells (somatic cells) have each 46 chromosomes (2n) which divide
by meiosis (spermatogenesis in males and oogenesis in females) in the gonads (testes
and ovaries) to form gamete cells, (spermatozoa and ova) which each have 23
chromosomes, i.e, and haploid. 2n cells are said to be diploid.
o During mating or sexual intercourse, a male’s penis enters the vagina of a female – semen
is ejaculated intothe vagina during sexual intercourse
o The sperms swim up the oviducts of the woman – if the sperm meets an egg, fertilisation
occurs
o Acrosome of the sperm releases an enzyme that disperses the follicle cells surrounding the
egg and breaks down part of the egg membranes
o The haploid sperm nucleus fuses with the haploid egg nucleus, forming a diploid zygote
External fertilization: The female lays eggs, and the male fertilizes them with his sperm. This
happens outside the body (e.g. fish, amphibians).
Internal fertilization: The ova (plural of ovum) are fertilized inside the female's body.
• Reptiles, birds: as soon as the ova are fertilized, eggs are laid without further development.
• Mammals: the ova are fertilized and remain in the body for further development
Conception = Period from fertilization to
implantation. Implantation marks the beginning
of pregnancy

Pregnancy = This is the period from

implantation to birth. This period is called
gestation period and it differs per species.
In humans gestation is about 270 days
(9months), cattle its 283 days, horse 11-
12months etc.
Organisms in which the young develops within
the parent’s body are referred to as viviparous
e.g mammals and those which lay eggs are
said to be oviviparous e.g reptiles and birds.
During pregnancy, a plug of mucus covers the
cervix.
Hermaphroditic animals = These have both male and female reproductive organs. 2 individuals
line up and while transferring their sperm; their ova get fertilized from the partner. (e.g.

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earthworms, snails). Some individuals change their sex during their lifetime. First they are males,
later on they become females (e.g. Blueheads = type of fish)
Development of the zygote
After fertilisation, the zygote passes along the oviduct to the uterus – zygote divides by mitosis
to form the embryo
The embryo implants itself in the uterine lining. The amnion encloses the embryo in the
amniotic cavity containing amniotic fluid. Villi containing the blood capillaries of the embryo
grow from the embryo into the uterine wall

The placenta
Allows the diffusion of oxygen, food
substances and antibodies from
the mother’s blood into the foetus’
blood
Embryo is attached to the placenta by
the umbilical cord – transports
deoxygenated blood and food from
the foetus to the placenta via the
umbilical arteries, and oxygenated
blood and food substances form
the placenta to the foetus via the
umbilical vein
The amniotic fluid = Thick fluid in which the foetus is suspended. It allows uniform
development of the foetus. The growth of the foetus is called development. The amniotic
fluid lubricates the birth-canal (vagina) during birth.
The yolk sac is a membranous sac which provides nutrients and blood cells to the foetus
until the placenta becomes fully functional. It is connected to the foetus via the allantois.
The umbilical cord is the passage of nutrients and oxygen in blood to the foetus and
wastes and carbon dioxide to the placenta.

 Labour
The body reactions which lead to birth are referred to as labour. Labour starts with mild
rhythmic contraction of the uterine walls, the contractions maybe hours apart and with time

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 occur more in time until they are tense leading to the amnion breaking and birth to occur.
Labour can occur in a few hours to a few days.
The baby comes out head-first during normal birth. When baby is born legs first it’s referred
to as bleach of birth and can lead to suffocation if not controlled quickly. The unmbilical
cord is cut after the baby is out and it leaves a scar called a navel. The placenta comes out
a few minutes and it is called the after-birth.
Parenting
The mother after birth is referred to as a lactating woman because she breastfeeds. The child
shoud be breast fed as much as possible especially in the first 6months because the first milk is
most nutritious and also offers immunity to the baby. The mother should thus, be on a balanced
diet. From day 1 to 5 years the child is to be taken to post-natal clinic check –ups for growth and
health monitoring on given dates.

Sexually Transmitted Diseases

Sexually transmitted diseases are diseases that are passed from an infected person to a healthy person
during sexual intercourse. Sexually transmitted diseases such as gonorrhoea and syphilis are caused by
bacteria which live and reproduce in the male and female reproductive systems.

Symptoms of gonorrhea
 Caused by Neisseria gonorrhea (Gonococci),
Burning sensation during urinating due to the inflammation of the urethra
Thick greenish-yellowish discharge from the tip of the penis or the vagina
Joints are swollen and painful
Results in sterility
Newborn baby may be infected as it passes through the vagina

Symptoms of syphilis
 Caused by Treponema pallidum
Painless sore appears on or near the genital organs usually just inside the vagina or on the
end of the penis
Mild fever occurs when the bacteria infect other parts of the body
Lymph nodes swell

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 Non-itchy rash appears on the body
Blindness, insanity and paralysis may occur when the bacteria attack the brain

Detection and treatment of gonorrhoea

With blood and urine tests to detect the presence of the bacteria
Both can be cured with antibiotics such as penicillin at an early stage of the infection

Acquired Immuno Deficiency Syndrome (AIDS)

Caused by a virus called HIV (human immunodeficiency virus)
Spread through
intimate sexual contact
blood transfusions using blood from an infected donor
sharing the same hypodermic needle with drug abusers who are AIDS patients
mothers who are AIDS patients, spreading the virus to their unborn babies
drug addicts
 Cannot spread through social contact
 More likely to be spread by the following groups
prostitutes
homosexuals with multiple sex partners
heterosexuals with multiple sex partners
mothers who are AIDS patients, spreading the virus to their unborn babies
drug addicts
Detection of AIDS - Blood test

Methods of control

Take precaution e.g. using condom.

Avoid having multiple sex partners
Ensure that instruments used for ear
piercing, acupuncture, tattooing and
injection are sterilized or disposable
Avoid sharing instruments that are likely
to break the skin and be contaminated
with blood

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Inheritance is the transmission of genetic information from one generation to the next,
leading to continuity of the species and variation within it.

Deoxyribonucleic Acid
 Deoxyribonucleic acid (DNA) is a molecule that carries genetic information and a gene is a
small segment of DNA that contains information used to make a single protein.

 Organisation of DNA inside cells

- Each DNA molecule consists of two parallel strands twisted around each other to form a
double helix (coiled structure)
- A molecule of DNA is wrapped around proteins to form a single chromatin thread
- During cell division, chromatin threads coil tightly into structures called chromosomes inside
the cell nucleus

 Basic unit that make up the DNA structure is known as nucleotide and each nucleotide is
made up of:
1. Deoxyribose (a sugar) 2. A phosphate group 3. A nitrogen-containing base, all joined
together

 Nucleotides are building blocks of DNA and they can be joined together to form long chains
called polynucleotides.

 The rule of base pairing states the base of one chain bonded to those of the opposite
chains and hence adenine (A) always bonds with thymine (T), and cytosine (C) always
bonds with guanine (G).

 Adenine and thymine are complementary bases. Cytosine and guanine are also
complementary bases.

 Each gene
- Is a small segment of DNA which controls the formation of a single protein such as an
enzyme
- Stores a message (genetic code) that determines how an enzyme or protein should be
made in the cell
- Consists of two polynucelotide chains
- Template – contains a sequence of nucleotides or bases

 A cell cannot directly use the DNA template to make proteins and this is done through a
two-step process
Transcription
- Occurs in the nucleus
- A process where the message stored in template DNA is copied to an mRNA molecule
Translation
- Occurs in the cytoplasm
- Involves the ribosomes
- Uses the message stored in the mRNA to make a protein molecule

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Key definitions
 Chromosome A thread of DNA, made up of genes.
 Allele An alternative form of a gene. Pairs of alleles occupy the same relative
positions on chromosome pairs.
 Gene A section of DNA, which codes for the formation of a protein controlling a
specific characteristic of the organism
 Haploid nucleus
A nucleus containing a single set of unpaired chromosomes, e.g. in sperm and
ova (eggs). In humans, the haploid number is 23.
 Diploid nucleus
A nucleus containing pairs of chromosomes, e.g. in somatic (body) cells, In
humans the diploid number is 46.
 Genotype The genetic make-up of an organism, e.g. Tt, where T and t are
alleles of a gene.
 Phenotype The characteristics visible in an organism, controlled by the
genotype, e.g. a tall plant or a dwarf plant.
 Homozygous Having a pair of identical alleles controlling the same
characteristics, e.g. TT, where T=tall. The organism will be pure-breeding for
that characteristics.
 Heterozygous Having a pair of dissimilar alleles for a characteristic, e.g. Tt.
 Dominant A gene, e.g. T, that always shows in the phenotype of an organism
whether the organism is heterozygous (Tt) or homozygous (TT).
 Recessive A gene, e.g. t, that only has an effect on the phenotype when the
organism is homozygous (tt)

In the nucleus of every cell there are a number of long threads (very large
molecules) called chromosomes.

Chromosomes
 Most of the time, the chromosomes are too thin to be seen except with an
electron microscope. But when a cell is dividing, they get shorter and fatter so
they can be seen with a light microscope.
 Human chromosomes and nucleus. Chromosomes are a packaged form of DNA.
The DNA normally exists in a non-condensed form in the cell nucleus (upper
right). It condenses into chromosomes (centre and lower left) during cell
replication.
 Human cells contain 46 chromosomes, which are in pairs. Sex cells (sperm and
ova) contain only 23 chromosomes. The 23 chromosomes comprise one from
each pair.
Inheritance of sex in humans
 Of the 23 pairs of chromosomes present is each human cell, one pair is the sex
chromosomes. These determine the sex of the individual. Male have XY, female
have XX. So the presence of a Y chromosome results in male features
developing.

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DNA

 Each chromosome contains one very long molecule of DNA. The DNA molecule
carries a code that instructs the cell about which kind of proteins it should
make. Each chromosome carries instructions for making many different
proteins.

Gene
 Each chromosome is
made up of a large
number of genes
coding for the
formation of different
proteins which give us
our characteristics. The
gene responsible for a
particular characteristic
is always on the same
relative position on the
chromosome. A part of
a DNA molecule coding
for one protein is called
a gene.

Alleles
When the chromosomes are in pairs, there may be a different form (allele) of the
gene on each chromosome.

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Cell division – Mitosis
and Meiosis
Mitosis is a nuclear
division giving rise to
genetically identical
cells in which the
chromosome number
is maintained by the
exact duplication of
chromosome.
Meiosis is a reduction
division in which the
chromosome number

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is halved from diploid to haploid.

Mitosis
Mitosis is the way in which any cell (plant or animal) divides when an organism is:
growing
repairing a damaged part of its body
replacing worn out cells
Growth means getting bigger. An individual cell can grow a certain amount, but not
indefinitely. Once a cell gets to a certain size, it becomes difficult for all parts of the
cell to obtain oxygen and nutrients by division. In order to grow any more, the cell
divides to form two smaller cells, each of which can then grow and divide again.
Mitosis is also used in asexual reproduction. For example, sweet potato plant can
reproduce by growing adventitious roots or runners which eventually produce new
plants.

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
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  During the process, all the chromosomes in the parent cell are copied in a
process called DNA replication.
Each copy remains attached to the original one --> each chromosome is made up of
2 identical threads joined together.
The parent cell (with 4 chromosomes) split to form 2 nuclei each with 2
chromosomes as the parent nucleus cell.
At the end of a mitotic cell division, the number of cells is doubled and the daughter
cells produced are genetically identical to the parent.

Process of Meiosis
Meiosis is the way in which gametes (sex cells) are produced. Gametes have only half
the number of chromosome of a normal body cell. They have
1 set of chromosome instead of 2. When they fuse together, the zygote formed has 2
sets.
Human gametes are formed by the division of cells in the ovaries and testes
The gametes produced are haploid, but they are formed from diploid cells, so
meiosis involves halving the normal chromosome number - the pairs of chromosomes
are separated.

During meiosis, the new cells get a mixture of homologous chromosomes from father
and mother --> A sperm cell could contain
a chromosome 1 from father and a chromosome 2 from mother.
There are all sorts of combinations --> gametes are genetically different form the
parent cells. Meiosis produces genetic variation.
When ova are formed in a woman, all the ova will carry an X chromosome. When
sperm are formed in a man, half the sperm will carry an X chromosome; half will
carry a Y chromosome.

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Mendelian Genetics: Gregor Mendel was an Austrian monk in the 1860s, now called the father of
genetics because he observed characterictics of his pea plants from generation to generation and
came up with three laws of inheritance. Thus, the law of dominance, the law of segregation
and the law of independent assortment

Monohybrid cross and the punnett square

A monohybrid cross involves the crossing of

individuals and the examination of one
(mono) character (flower colour, pod
shape...) and different (hybrid) traits (red
colour, white colour) in their offspring.
The Punnett square is a useful tool for
predicting the genotypes and phenotypes of
offspring in a genetic cross involving
Mendelian traits.
Mendel crossed true-breeding plants that
differed for a given character.
Pollen from true-breeding pea plants with
purple flowers (one trait) was placed on

stigmas of true-breeding plants

with white flowers (another trait).
The F1 seeds were all purple; the
white flower trait failed to appear
at all.
Because the purple flower trait
completely masks the white
flower trait when true-breeding
plants are crossed, the purple
flower trait is called dominant, and
the white flower trait is called
recessive.
The F1 plants were allowed to
self-pollinate. This step was the
monohybrid cross. (or the F1 cross). The progeny, called F2, were examined: roughly
1/4 were white, and 3/4 were purple.

All the genetic crosses shown below will involve examples using pea plants, which can
be tall (T) of dwarf (t) – tall is dominant to dwarf.

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Co-dominance and inheritance of blood group

Sometimes, neither of a pair of alleles is completely dominant or completely recessive.

Instead of one of them completely hiding the effect of the other in a heterozygote,
they both have an effect on the phenotype. This is called co-dominance.
The result is that there can be three different phenotypes. When writing the
genotypes of co-dominant alleles, the common convention is to use a capital letter to
represent the gene involved, and a small raised letter for each phenotype.
Imagine a kind of flower which has two alleles for flower colour. The allele Cw
produces white flowers, while the allele CR produces red ones. If these alleles show
co-dominance, then the genotypes and phenotypes are: genotype phenotype
Cw Cw white flowers
Cw CR pink flowers
CR CR red flowers
In humans the gene for albinism is recessive to the gene for skin. The blue-eye colour
signifies absence of eye colour (recessive gene) therefore the brown gene for brown
eye-colour is dominant (brown eye colour is melanin).

Check!!
Co-dominance results in the appearance of a new characteristic, which is intermediate to the
parent’s features. For example, if the parents are pure-breeding for long fur and short fur, the
offspring will all have medium-length fur.

Inheritance of A, B, AB and O blood group - an example of

Co-dominance

In humans, there are 4 blood types (phenotypes): A, B,

AB, and O
Blood type is controlled by 3 alleles: IA, IB, IO (the base
letter = I stands for immunoglobulin)
IO is recessive; two IO alleles must be present for the
person to have type O blood
IA and IB are co-dominant but both are dominant to Io. If a
person receives an IA allele and an IB allele, their blood
type is type AB, in which characteristics of both A and B antigens are expressed. Co-
dominance is also known as incomplete dominance because the phenotype expression
is an intermediate.
Because IO is dominated by both IA and IB alleles, a person with blood group
A could have the genotype IA IO or IA IA. This has implication when having children
because, if both parents carry the IO allele, a child could be born with the genotype IOIO
(blood group O), even though neither of the parents have this phonotype.

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Complete dominance = Occurs when a pair of alleles occurs in heterozygous
condition. Therefore, only the dominant allele gets to express itself fully in the
phenotype.

Sex determination = Each cell has one pair of chromosomes that determine the sex of the animal
Males have an X and a Y chromosome
Females have two X chromosomes
The sperm has either an X or a Y chromosome
Each ovum has an X chromosome
Fertilization causes a zygote to form which grows into a male or a female

Variation = Variation is all the differences which exist between members of the same
species. It is caused by a combination of genetic and environmental factors.
There are two kinds of variation: continuous and discontinuous.
Continuous variation
- shows a complete range of the characteristic within a population
- Examples: weight, height, size of foot, skin colour, etc
- caused both by both genes (often a number of different genes) and environment:
Plants: availability of/competition for: nutrients, light, water; exposure to disease…
Animals: availability of food/balanced diet; exposure to disease (or the availability of
health serviced for humans).

Discontinuous variation
- seen where there are obvious, distinct categories for a feature.
- no intermediates between categories, the feature cannot usually change during life.
- caused by a single gen/a small number of genes, with no environmental influence.

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Mutation

Mutation is an unpredictable change in the genes or chromosome number, as a result of

fault copying when DNA is replicated, faulty separation of chromosomes during cell
division, or exposure to radiation or some chemicals. Can also be defined as the sudden change
in the structure of the gene or the number of chromosomes in an organism
 An occur in body cells and this may lead to cancer
 Can also occur in gametes resulting in genetic disorders in the off spring
 A mutant – an individual having characteristics altered by mutation
Gene mutation
 Involves change to the structure of the gene
 Sickle cell anaemia – the structure of the gene which controls the production of one amino
acid in the haemoglobin molecule of the red blood cell is altered
Caused by
 Exposure to atomic radiation such as alpha, beta, gamma, X-rays and cosmic rays
 Chemicals such as cyclamates (artificial sweetening agents) and mustard gas

Chromosome mutation
 Involves a change in the number of chromosomes
 The number of chromosomes may be more or less than 46
 Down’s syndrome and mongolism – caused by an extra chromosome in each body cell
Caused by
 Abnormality during gamete formation
 The number of chromosomes may be less or more than 46
 Part of a chromosome may be lost
 An additional part of a chromosome may be added
 The arrangement of the genes may be reversed

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Down’s syndrome is caused by a mutation. When ova are formed in the ovaries, the
chromosome number is halved. During this division process (meiosis), one of the
chromosomes (number 23) sticks to its partner. This result in one ovum with 24
chromosomes and one with only 22, and the ovum with 24 chromosomes is still
viable. If it is fertilized, the fetus formed will have 47 chromosomes instead of 46.
The presence of the extra chromosome causes unusual characteristics in the baby.
These usually include lowered life expectancy, mental retardation (although some
Down’s children are very intelligent), early puberty, and a distinctive round face and
short neck.

Effects of ionizing radiation and chemicals on the rate of mutation

Mutation are normally very rare. However, exposure to radiation and some
chemicals, such as tar in tobacco smoke, increases the rate of mutation.
Exposure can cause uncontrolled cell division, leading to the formation of tumours
(cancer).
Exposure of gonads (testes and ovaries) to radiation can lead to sterility or to
damage to genes in sex cells that can be passed on to children.
Some scientists argue that there is a higher incidence of leukaemia (a form a white
blood cells cancer) in the children of workers at nuclear power stations.

Sickle cell anaemia and its incidence to that of malaria

Sickle cell anaemia is caused by a mutation in the blood pigment haemoglobin. When
the faulty haemoglobin is present in a red blood cell, it causes the cell to deform and
become sickleshaped, especially when oxygen levels in the blood become low.
In this state the sickled red blood cells are less efficient at transporting oxygen and
more likely to become stuck in a capillary, preventing blood flow.
The faulty allele is dominated by the allele for normal haemoglobin, but still has some
effect in a heterozygous genotype.

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The possible genotypes are:
HNHN normal haemoglobin, no anaemia
HNHn some abnormal haemoglobin, sickle cells trait (not lifethreatening)
HnHn abnormal haemoglobin, sickle cells anaemia (life-threatening)

Malaria is a life-threatening disease caused by a parasite that invades red blood cells.
The parasite is carried by some species of mosquito.
A person who is heterozygous (HNHn ) for sickle cell anaemia has protection from
malaria, because the malaria parasite is unable to invade an reproduce in the sickle
cells.
A person who is homozygous for sickle cell anaemia (HnHn) also has protection, but is
at high risk of dying form sickle cell anaemia.
A person with normal haemoglobin (HNHN) in a malarial country is at high risk of
contracting malaria.
When the distributions of malaria and sickle cell anaemia are shown on a map of the
work, it is found that the two coincide in tropical areas because of the selective
advantage of the Hn allele in providing protection against malaria.

Haemophilia.
Certain forms of haemophilia are caused by a recessive allele located on the Xchromosome.
A person with haemophilia produces very little of a protein needed for blood to clot and so may
bleed to death after even a slight cut.
In case of a woman, she usually has a dominant normal allele on her other X chromosome, so
she does not have haemophilia. A man, who has only one X chromosome, will develop the
disease. A woman, in this case is said to be a carrier of the disease.
Sex linked genes
These are genes carried on the sex chromosomes (X and Y) but do not determine the sex of
the individual. Sex linked genes result into sex liked traits among which some may be imparing
to the individual e.g red-green colour blindness (common in males) and haemophilia (common
in males)

# Artificial and natural selection

Artificial selection is a method used by humans to produce varieties of animals and
plants which have an increased economic importance. People use selective breeding to
produce new varieties of a species, so that certain desirable traits are represented in
successive generations.
A variety is a type of a particular species that is different in some clear way from
other varieties of that species. The different breeds of domestic dogs and large ears of
maize corn are products of artificial selection.

Selective breeding of cows

Suppose you wanted a variety of cow that produced a lot of milk. This is what you
could do:
choose or select the cows in your herd that produce the most milk

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let only these cows reproduce
select the offspring that produce the most milk
let only these offspring reproduce
keep repeating the process of selection and breeding until you achieve your goal.

Natural selection is the process by which plants and animals that can adapt to changes
in their environment are able to survive and reproduce while those that cannot adapt
do not survive. It gives the greater chance of passing on of genes by the best adapted
organisms.

Check!
Farmers have carried out artificial selection to improve the breeds of some animals.
Some of the original breeds have become very rare and are in danger of becoming
extinct.

# Genetic engineering,

Putting human insulin genes into bacteria

Genetic engineering is a process of taking a gene from one species and putting it into
another species.
The control of all the normal activities of a bacterium depends upon its single
chromosome and small rings of genes called plasmids. In genetic engineering pieces of
chromosome from a different organism can be inserted into a plasmid. This allows the
bacteria to make a new substance.

Using genetic engineering to put human insulin genes into bacteria

1. Human cells with genes for healthy insulin are selected.
2. A chromosome (a length of DNA) is removed from the cell.
3. The insulin gene is cut from the chromosome using restriction endonuclease
enzyme.
4. A suitable bacterial cell is selected. Some of its DNA is in the form of circular
plasmids.
5. All the plasmids are removed from the bacterial cell.
6. The plasmids are cut open using the same restriction endonuclease enzyme.
7. The human insulin gene is inserted into the plasmids using ligase enzyme.
8. The plasmids are returned to the bacterial cells.
9. The bacterial cell is allowed to reproduce in a fermenter. All the cells produced
contain plasmids with the human insulin gene.

The importance of this process

Diabetics need a source of insulin to control their blood sugar level. In the past cow
insulin has been used, but some people are allergic to it.

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Human insulin produced from genetically engineered bacteria will not trigger an
allergic reaction.
The insulin is acceptable to people with a range of religious belief who may not be
allowed to use insulin form animals such as cows or pigs.
The product is very pure.
Human insulin can be made on a commercial scale, reducing costs.

Genetic engineering is also used in agriculture to improve crop quality. In involves

insertion of extra genetic material into a plant cell to make it 3n or 4n from being a 2n
(diploid) nucleus – a condition referred to as polyploidy. Polyploidy condition (and
many other mutations) is not harmful to plants. If chromosomes are more or less
than 2n in animals it can fatal (deadly) or result into serious physical deformations.

Also referred to as taxonomy. Involves the sorting of living things into distinct groups depending on
their common features. Usually external features are observed.

Swedish botanist Carolus Linnaeus is the Father of Systematic Biology.

He believed he could:
 Put every organism into a group (the science of TAXONOMY)
 Give every organism a name (the science of NOMENCLATURE)
In his binomial system, every living organism has a unique, two-part name:
 The first name is Genus, the second name is species.
 Names are written in Latin, printed in italics.
 The genus always has a capital letter, and the species always has a small letter. Both are
underlined separately.

All life forms are categorized into a scheme

that had 7 categorical terms.
The biggest group are Kingdoms, the
smallest one is Species.
Each kingdom is divided into smaller group,
which include genus and species

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Five Kingdoms of living things

These are animalia, plantae, fungi, monera

(bacteria), and protoctista.

o Each kingdom is divided into phyla

(division in plants)
o Each phylum divided into classes.
o Each class comprises of closely
related orders.
o Each order comprises of closely
related families.
o Each family comprises of closely
related genera.
o Each genus comprises of closely
related species.
o The species is the smallest group
(taxon)
o Each group (level of classification) is
called a taxon (plural – taxa)

Specie is a group of organisms with similar physical feature and capable of producing viable (fertile)
offspring. Species can be narrowed to breeds. The animal kingdom contains many phyla. Some of
them are: Vertebrates, Arthropods, Annelids, Molluscs, Nematodes.

Vertebrates
Vertebrates are animals with backbones. They are divided into 5 groups called classes:
Fish, Amphibians, Reptiles, Birds and Mammals

Features used in classification of animals:

1. Habitat – aquatic or terrestrial. If aquatic then into fresh or marine water (marine water is
saline)
2. The appendage system – these include mouth parts, numbers of legs, joints in legs etc
3. Presence or absence of exoskeleton.
4. Parts of the body
5. Mode of reproduction – lays eggs (oviparous) or lays eggs and watches after them
(oviviparous) or the egg develops in the female’s body (viviparous)
6. Type of organs used for breathing – lungs, books lungs, gills, spiracles, skin etc
7. Body symmetry.

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Various tools are used – microscopes and hand lenses are commonly used for smaller organisms.
Note that cells can be determined as either animal or plant via observation due to the presence or
absence of the cell wall.

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 Birds have a Beak - Feathers - Scales on
legs - Wings - 2 legs.

Mammals have four limbs - fur – mammary

glands in females.

Phylum arthropoda

There are more arthropods than any other group of animals, so they are divided into classes:
Insects, Crustaceans, Arachnids and Myriapods

Special features of arthropods

 They are invertebrates (no backbone)

 Waterproof exoskeleton-live in dry
places hence less water loss.
 Have segmented bodies
 Joint legs

Four classes of arthropods

1. Insects
Insects are a very successful group, due to
their exoskeleton and tracheae, which are
very good at stopping water from evaporating
from insect’s body, so they can live in very dry
places.

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Key features of insects:

 3 pair of jointed legs, 1 or 2 pairs of wings, 3 body segments-head, thorax and abdomen,
and Breath through trachea

2. Crustaceans
These are the crabs, lobsters and woodlice.
They breathe through gills, so most of them live
in wet places and many are aquatic.

3. Arachnids = these are spiders, ticks and

scorpions. They are land-dwelling (terrestrial)
organisms. Key features of arachnids:

 4 pairs of legs
 No wings
 2 pairs of antennae
 2 body segments: cephalothorax and abdomen
 Several pairs of compound eyes
 All have piercing jaws since all are predators
 Have pointed mouth parts for biting poisoning prey

4 Myriapods = These are centipedes and millipedes

 Long, thin body with many segments for moving

easily through soil and leaf litter
 No obvious thorax and abdomen
 Each segment has jointed legs (9pairs)
 1 pair of antennae as sence organs in dark
habitats
 Simple eyes

Other groups of invertebrates are:

Annelids (e.g segmented worms), Nematodes (e.g

smooth worms), Molluscs (snails and squids)

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Kingdom Bacteria

- Are: very small organisms

- Consisting of single cells (1 um)
- Reproducing by cell division
- Can form chains of individuals, clumps
or films over the surface of static water
- Individuals may be spherical, rod
shaped or spiral.
- Some have flagella which move the
bacterium about; others have pilli with
which E.Coli bacteria they attach
themselves.
- Some need oxygen to respire (aerobic
respiration) others are anaerobic (no oxygen is needed to break down compounds)
- Some can form spores (a resting stage) with a thick wall. This is used to survive severe
conditions (e.g. high temp., drought...)
- Bacteria are found everywhere: air, soil, water, food, humans...
- Some are pathogenic (causing disease) but most of them are NEEDED in nature: e.g. to
break down natural waste products, nitrogen cycle, to produce oxygen in ponds...

Kingdom: Fungi.

- Eukaryotic, multicellular organisms

- Fungi are saprobes or parasitic.
- Secrete digestive enzymes which hydrolyse
the organic matter.
- A fungus disperses itself by spores, usually
floating through the air. The spore falls on a
suitable food source and germinates. It
absorbs food and grows into a thread-like
hypha.
- The hypha grows rapidly and branches until
it resembles a tangled mass of threads.
- The body of a fungus, made up of many
hyphae, is called a mycelium, which is
well suited for absorbing food. A hypha
releases chemicals that cause other
hyphae to grow away from it. As a
result, the fungus spreads out through
its food source.
- Fungi are used as food (mushroom)
and also in production of drugs. They
also play an important role in nature as
decomposers thus, aid in recycle of nutrients.

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 - Examples of fungi are penicillin, rhizopus, mushroom, toadstool, yeast etc

Kingdom plantae

Plants are multicellular organisms,

with cell wall made of cellulose. They
include small organisms such as
mosses, ferns and flowering plants.
At least some parts of a plant are
green, thanks to pigment
chlorophyll. Chlorophyll absorbs
energy from sunlight for plant to
make glucose, using CO2 and H2O
from environment. This is called
photosynthesis.

Phylum: Angiosperm

Examples are; maize, banana, beans

etc

 Have broad leaves

 Have well defined vascular bundles
 Reproduce through seeds
 Flowers are the sexual organs
 Cells have chloroplast
 Cell made of cellulose
 Gaseous exchange takes place through the stomates and lenticels

 They are divided into 2 groups, depending on number of seed leaves (Cotyledon):
1. Monocotyledonous (Monocots)
2. Dicotyledonous (Dicots)

Class monocot Class dicot

1. Leaves are narrow with parallel Leaves are broad with net veination
veination
2. Leave are attached to the stem by the Leaves are attached to the stem by leaf petiole
sheath (stalk)
3. Have fibrous root system Have taproot system
4. Embryo has one cotyledon Embryo has two cotyledons
5. Vascular bundles in stem are Vascular bundles in stem arranged in a ring
scattered with no pith around the pith
6. Have no vascular cambium – no Have vascular cambium therefore exhibit
secondary growth secondary growth

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Phylum: Gymnosperm

Examples are pine, Cyprus, confers etc

o Bare naked seeds (not enclosed in an ovary)

o No fruit development
o Phloem have no companion cells
o They produce cones
o Leaves are commonly needles shaped

Phylum: Pteridophytes

Examples are fern plants.

- Have true stems, roots and leaves.

- Stems are called rhizomes which
grow horizontally underground and
bear adventitious roots
- Reproduce by spores formed in
leaves
- Vascular bundles present but
phloem has no companion cells.

Phylum: Bryophyta
Examples are mosses, liverwarts etc
- They are mostly terrestrial (land plants)
- They have rhizoids instead of roots
- They lack vascular bundles
Note that a phylum is also called a division in plants.

External features of plants considered when classifying;

i. Leaf structure, appearance and shape
a. Leaf venation – arrangement of veins. It can be parallel (in monocots) or net venation,
a.k.a reticulate venation (in dicots)
b. Number of blades per leaf. A simple leaf is whole and a compound leaf is one with
leaflets. A compound leaf is either palmate or pinnate.

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 c. Leaf margin – it may be smooth, toothed, wavy, or lobed.

ii. Leaf form = Leaves may be round, linear, heartshaped, elliptical, palmate etc
iii. Root system = True roots are those which develop from the radical (in the embryo
stage)
True root systems may be in form of a tap root system (in dicots) or fibrous root
system (in monocots).
Adventitious roots are not true as they develop from the stem.

Identification keys = The identification of biological organisms can be greatly simplified using
tools such as dichotomous keys and numbered keys. It is a written set of choices, each involving
two statements, that leads to the name of an organism. Scientists use these to identify unknown
organisms.

e.g

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Soil is a composition of soil particles, humus, air, moisture and micro-organisms. It makes up the
Earth’s crust. Soil is crucial for plants and life in general. It supports plants and provides nutrients
for their growth. The characteristics of soil determine the nature of the natural vegetation and the
crops that can be cultivated because they will be adapted to the soil and will provide good crop
performance. All soil contains four major elements:

 Air (20-30% of volume)

 Soil solution (20-30% of volume)
 Mineral fraction (inorganic matter) (45% of volume)
 Organic matter (humus) (5% of volume)

The porosity (air spaces) allows roots and micro-organisms to breath and it also stores water.

Types of Soil – Clay, Loam and Sand

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Drainage = the ability of soil to allow water to pass through, its fast in sandy soils.

Retention capacity = the ability to keep moisture (water). Its high in soil with fine particles (clay).

Soil fertility

This refers to the ability of soil to support both animal and plant life sustainably.

Soil is said to be fertile when it has essential components (micro-organisms, air, moisture, pH,
humus and inorganic material) in the right amounts depending on the crop it has to support as
each crop needs the essential components in different amounts. Loamy soils support a wider
range of plant and animal life, hence, they are said to be more fertile. Clay soils tend to have acid
pH.

Healthy soil contains soil-dwellers and decomposers. The decomposers break down plant and
animal tissue, forming humus (organic matter), which helps roots grow by trapping water and air.
The four main types of decomposers are:
- Bacteria
- Fungi (including moulds and mushrooms) - make nutrients available to plants
- Microscopic actinomycetes (a special type of bacteria)
- Earthworms (eat soil, grind, digest and mix it - their tunnels provide air and the mucus helps
stick soil particles together)

Loss of fertility
Activity and natural processes that promote fertility loss are:
i. Overgrazing – allowing either farm or game animals to exceed the carrying capacity of a
given area resulting in them over feeding on the lower vegetation (grass) leading to
erosion.
ii. Soil erosion – loss of top (fertile) soil via wind or water erosion. The top soil is further made
loose by rain before being washed away-this is referred to as the rain-drop-effect.
iii. Late burning – releases nitrogen into the atmosphere (it breaks down N2 - compounds)
iv. Poor farming methods – e.g chitemene.
v. Deforestation – uncontrolled cutting of trees
vi. Overuse of fertilizers lead into soil becoming acidic.

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Improving soil fertility

i. Re-aforestation – Re-planting of trees to improve

the rain cycle and reduce on the rain drop effect.
ii. Practicing crop rotation
iii. Applying fertilizers in regulated amounts.
iv. Weeding – removing unwanted plants to reduce
competition for nutrients.
v. Practice conservation farming – involves crop rotation, mixing crops and preserving the top
soil by covering it with suitable materials.

Distribution of soil animals

Earth worms and micro-organisms are distributed in their population according to how wet (or
amount of moisture is present) and how much organic matter (humus) is present in a given region.
Therefore they are more where there is more organic matter and moisture (wet lands) as they feed
on humus. Worms and other micro-organisms such as fungi and bacteria are referred to as
decomposers as they aid in the breakdown of organic matter (plant and animal material) and
recycle nutrients. Some bacteria also fix nitrogen into compounds to form nitrates important for
plant growth.

Ecology
 The study of living and non-living organisms in the
natural environment
 How they interact with one another
 How the interact with their nonliving environment
 A person who studies ecology is called an
ecologist

The Sun is the principal source of. Energy input to biological systems.
The Earth receives 2 main types of Energy from the Sun: light (solar)
And heat. Photosynthetic plants and some bacteria can trap light energy
And convert it into chemical energy

Ecosystem = An ecosystem is an ecological system formed by the interaction of living organisms

and their non-living environment.

Biotic factors = these are the living components of the ecosystem e.g grass, flies, birds, worms
etc

Abiotic factors = non-living components of the ecosystem e.g water, air, rocks, pH, temperature,
salinity (salt concentration) etc

Community = All the populations of the différent species living and inter-acting in the same
ecosystem.

Species = A group of organisms that can breed to produce fully fertile offspring e.g. Snow geese

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Population = A group of organisms of the same species which live in the same habitat at the
same time where they can freely interbreed

Habitat = a place where an organism lives.

Biodiversity = The total number of different species in an ecosystem and their relative abundance

Habitat = The characteristics of the type of environment where an organism normally lives

Energy and organisms

 Energy mainly comes from the sun (the source)

 Part of it absorbed by the earth, part of it reflected back into space and part of it is utilized
by plants in photosynthesis.

 Only about 1% of energy from the sun is used in photosynthesis. At every trophic level 90%
of the obtained energy is lost.

 Plants make complex organic molecules from simple inorganic ones, hence, they are called
producers because from them all other organisms benefit directly and indirectly.

 Photosynthetic algae also use solar energy.

 Via photosynthesis, solar energy (light) is converted to chemical energy stored in various
molecules.

Trophic levels

Trophic means nutrition.

 Producers = green plants

 Primary (1st degree) consumers. ie, herbivores e.g rhinos

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  Secondary (2nd degree) consumers ie, lower carnivores (small carnivores) and omnivores

 Tertiary (3rd degree) consumers ie, top carnivores e.g lions, eagles and leopards

Non-cyclical nature of energy flow

Heterotrophic organisms obtain their energy by eating plants or animals that have eaten plants.
So all organisms, directly or indirectly, get their energy from the Sun. The energy is passed
from one organism to another in a food chain but, unlike water and elements such as carbon
and nitrogen, energy does not return in a cycle. Energy give out by organisms is lost to the
environment.

By nutrition the organisms are classified as:

Heterotrophs = Organisms who must obtain complex, energy rich, organic compounds form the
bodies of other organisms (dead or alive)

Detritivores = Heterotrophic organisms are those which ingest dead organic matter. (e.g.
earthworms, woodlice, millipedes)

Saprotrophs = Heterotrophic organisms who secrete digestive enzymes onto dead organism
matter and absorb the digested material. (e.g. fungi, bacteria)

The place of an organism in its environment

 Niche = An organism’s habitat + role + tolerance limits to all limiting factors

The niche of a species therefore consists of:

 Its role in the ecosystem (herbivore, carnivore, producer etc)

 Its tolerance limits (e.g. soil pH, humidity)

 Its requirements for shelter, nesting sites etc etc, all varying through time

LIVING RELATIONSHIPS

Symbiosis = A relationship between organisms in which at least

one of them benefits. Three types of symbiosis in ecosystems are
mutualism, commensalism, and parasitism

Mutualism (+, +) = both species benefit from being in relationship

with one another ex. Honey bee & flower.

Commensalism (+, 0) = One organism benefits while the other is

unaffected (neither helped nor harmed) e.g. Sparrow in a tree

Parasitism (+, -) = One organism benefits at the expense of the other

 One organism benefits, the other harmed but not killed e.g. dog tick on a dog

 Parasites are either:

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 a. Endoparasites – live inside the host e.g. worms in intestines or blood or the malaria
parasite etc

b. Ectoparasites - live outside but on the host e.g. lice, ticks, fleas etc

Predation (+, -) = One organisms benefits by hunting, killing, and feeding on another organism

 A.k.a predator – prey relationship e.g lion & zebra

 predator = organism that hunts, kills, and feeds off another

 prey = organism that is hunted & killed

Competition = Occurs when organisms in the same ecosystem are competing with each
other for resources such as food, water, sunlight, and living spaces

Food chain = A series of organisms, each of which provides the food supply for the next in line.
(E.g. leaves >caterpillars > sparrow > hawk)

Food web = A food web is made up of two or more food chains linked together

Pyramids = Because energy is lost at each step (in a food chain), there are rarely more than five
trophic levels in an ecosystem.

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  Pyramid of numbers = A pyramid of numbers can be used to depict the progressively
smaller numbers of organisms at successive trophic levels.

 Show organisms at different trophic levels in different numbers e.g 1 mango feeds
10monkeys and each monkey feeds 200fleas.

 Sometimes these pyramids are inverted, for example, when a single tree is attacked by
many individual insects

Pyramids of energy
The flow of energy through an ecosystem can be
represented in the form of a pyramid of energy,
which shows the total amount of incoming energy
for successive trophic levels. Unlike pyramids of
numbers or biomass, however, pyramids of energy
must always be “right side up ", because some
energy is always lost as heat, sound or light in
going from one trophic level to the next. Thus, they
have a wide base.
Pyramid of biomass = allows for the comparison of the mass of organisms present in each
trophic level at a particular time.
- Biomass is the total weight of living mass
- Biomass decreases with each successive level in the food chain
- iomass decreases as the trophic level increases
- Producers are present in the largest quantity of biomass

Above is a table comparing pyramids of biomass to those of energy/

BIOMES

 A large region that contains similar plant and animal ecosystems and is characterized by
certain climate conditions. Biomes can be terrestrial (land) or aquatic (water).

Nutrient cycles

1. The Carbon cycle

Food chains and food webs are but one link in the constant use and re-use of the Earth's chemical
resources.

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• Green plants perform photosynthesis, so the carbon-dioxide is removed from the atmosphere or
water in which they grow. The carbon is incorporated into the carbohydrates (sugar, starch) and
proteins and pigments. When the plants get eaten by animals, the organic matter will be digested
and will become incorporated into animal tissue.
 Dissolution of carbon dioxide in sea water to form carbonates which are absorbed by animals to
form shells
• Respiration: Plants and animals get their E by oxidising the carbohydrates to CO2 and H2O. This
gets excreted and the carbon-dioxide escapes back into the atmosphere.
• Decay: Bacteria and fungi use the organic matter of dead animals and plants as a source of E. In
the process, CO2 is produced.
• Combustion: Burning C- containing fuels (wood, coal, petroleum) oxidises the C to
CO2.
 Volcanic eruption – carbon dioxide is released from the materials deep in the earth
 Limestone – the action of acid rain on limestone hills causes carbon dioxide to be released

2. The water cycle

• Animals lose water by evaporation (sweat), defecation, urination, and exhalation.
• They gain water from their food and drink. Plants take up water from the soil and lose it by
transpiration. Millions of tonnes of water are transpired, but only a tiny fraction of it has taken part
in the reactions of respiration and photosynthesis.
• The great proportion of water is recycled without the intervention of animals or plants:
• The sun shining and the wind blowing over the oceans evaporate water from their vast, exposed
surfaces.
• The water vapour enters the atmosphere and forms clouds. Water from these clouds will be lost
as rain or snow (precipitation).
• The rain collects in streams and rivers and finds its way back to the oceans.

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• Some of this water is used by man for drinking, washing, cooking, irrigation, hydroelectric
schemes and industrial processes before it is allowed to go back to the oceans.

3. Nitrogen cycle

Nitrogen is an essential constituent of many organic compounds especially proteins, nucleic

acids...
Molecular nitrogen gas (N2) making up 78 % of the atmosphere is more abundant than carbon-
dioxide.
It is a macro-nutrient for plants along with phosphorus and potassium.
Few kinds of organisms can use molecular nitrogen. Only certain species of bacteria can fix
molecular nitrogen by reducing it to ammonia, which is washed away into the soil where it forms
ammonium compounds.
Nitrifying bacteria
Nitrite bacteria: oxidise the ammonium compounds to nitrites (NO2-)
Nitrate bacteria: oxidise nitrites to nitrates (NO3-) and these can be taken up in solution by plants.
Faeces of animals are rich in nitrogenous waste products ammonia Nitrite nitrate.
Nitrogen fixing bacteria
Since green plants can not absorb the nitrogen in the air, some plants have developed some sort
of Symbiosis with bacteria which can. These bacteria combine it with other elements making
nitrogen compounds. These bacteria can be found in the soil as free living organisms, or they live
in root nodules or swellings (e.g. Clover).
Denitrifying bacteria
Live in the soil and obtain their energy by breaking down compounds of nitrogen to gaseous
nitrogen which escapes into the atmosphere

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.
Population
A population is a group of organisms of one species, living in the same area at the same time.
Factors affecting the rate of population growth include food supply, predation and disease

1. The rate of growth of a population depends on:

= Food supply – abundant food will enable organisms to breed more successfully to produce
more offspring; shortage of food can result in death or force emigration, reducing the population.
= Predation- if there is heavy predation of a population, the breeding rate may not be sufficient to
produce enough organisms to replace those eaten, so the population will drop in numbers. There
tends to be a time lag in population size change for predators and their pray: as predator numbers
increase, prey number drops; and as predator numbers drop, prey numbers rise again (unless
there are other limiting factors).
= Disease – this is a particular problem in large populations, because disease can spread easily
from one individual to another. Epidemics can reduce population sizes very rapidly.
= Use of contraceptives (for humans)

2. Population growth in an environment with limited resources

When a limiting factor influences population growth, a sigmoid (S-shaped) curve is created. You
need to be able to place the terms lag, log, stationary and death phase on a graph of population
growth.

Lag phase – the new population takes time to settle and mature before breeding begins. When
this happens, a doubling of small numbers does not have a big impact on the total population size,
so the line of the graph rises only slowly with time.

Log (exponential) phase – there are no limiting factors. Rapid breeding in an increasing
population causes a significant in numbers. A steady doubling in numbers per unit of time
produces a straight line.
Stationary phase – limiting factors, such as shortage of food, cause the rate of reproduction to
slow down and there are more deaths in the population. When the birth rate and death rate are
equal, the line of the graph becomes horizontal. Death phase - as food runs out, more organisms
die than are born, so the
number in the population
drops

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 3. Population growth in the absence of limiting factors

If there are no limiting factors, there will be no stationary or death phase – the log phase will
continue upwards, instead of the line leveling off. This has happened with human population
growth. Human population size has increased exponentially because of improvements on food
supply and the development of medicine to control diseases. Infant mortality has decreased, while
lifer expectancy has increased
Such a rapid increase in population size has social implications:
= Increase demand for basic resources (food, water, space, medical care, fossil fuels)
= Increase pressures on the environment (more land needed for housing, growing crops, road
buildings, more wood for fuel and housing) and more pollution.
= Larger population of young people --> greater demands on education
= More old people --> greater demands on healthcare.
Abundant food supplies can leads to more people becoming obese --> greater demands on
healthcare (heart disease, diabetes, blindness…). In the long term ---> reduce average life
expectant, as poor health becomes a limiting factor.

Population data is represented using pie-charts, bar-graphs, pyramids and graphs.

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Effects of man on the ecosystem
1. Natural resources are resources supplied by nature that are used by humans and these can be:
- Renewable – can be replaced by natural cycles
- Non-renewable – cannot be replaced once they are used

2. Deforestation is the clearing of forests and this give rise to:

Soil erosion
Flooding
Desertification
Climate changes

3. Pollution is the process in which potentially harmful substances are released into the
environment.
- Water pollution by sewage
Sewage is waste water
Effects of untreated sewage discharge in the ecosystem
 Organic waste such as urine and faeces contain bacteria which causes diseases to
spread
 Sewage is a rich source of nutrients for bacteria and algae to multiply – they strive very
wells
- Water pollution by inorganic wastes
Inorganic wastes are discharged by industries into rivers and seas e.g.
 Phosphate ions form phosphate detergents
 Fertilizers not absorbed by the soil are washed into rivers.
 Many industrial wastes are non-biodegradable e.g. mercury, cadmium, nickel and
chromium
- Effects of inorganic wastes on the ecosystem
 Mercury released into the water is absorbed by primary consumers and becomes
more concentrated from one trophic level to the next trophic level in a food chain
 Phosphate detergents and inorganic fertilisers decrease the amount of oxygen
that is dissolved in the water and encourage the growth of bacteria and algae –
fishes die due to lack of oxygen
- Air pollution by sulphur dioxide
Released into the atmosphere by industries and car exhausts. Sulphur dioxide
combines with moisture in the air to form acids and resulting in acid rain effects.
Sulphur dioxide gas penetrates the leaves and stems resulting in the destruction of
plant tissues
Gases cause respiratory diseases such as bronchitis and lung cancer
Acid rain decreases the pH of lakes and ponds, causing fishes and other pond
animals to die and other animals in the food chain are also affected
Acid rain causes skin irritation

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 Corrodes stone or cement buildings as well as metal structures such as zinc roofs
and bridges
- Pollution due to insecticides
 Insecticides are frequently used to kill the pests which attack and damage crops
 Chemical insecticides such as DDT are used on a large scale to kill pets which
attack vegetables and fruit trees
 Insecticides such as DDT are non-biodegradable – they are not chemically broken
down into simpler, harmless, inactive substances
 DDT is very persistent – it accumulates in the fatty tissues of organisms and its
toxicity accumulates along the food chain
 DDT is non-specific – kills both target and non-target animals
 DDT are initials for Dichlorodiphenylchloroethane (C14H9Cl5)

4. Conservation is the protection of the natural environment.

5. Conservation includes ways of:
 Protecting wildlife
 Keeping the environment clean
 Saving the natural resources so that the natural balance of nature can be maintained

6. Conservation of species is done for various reasons such as:

 Ecological value
 Each species of plant and animal is part of the ecosystem
 Extinction of one or more species will upset the natural balance of nature in the ecosystem
 Economic value
 Forest is the source of many useful products such as rubber, fibres
 Products from the forest provide raw materials for industries
 Chemicals are extracted from plants
 Scientific value
 Plants and animals serve as a source of
- Genetic materials
- Natural drugs and antibiotics

7. Recycling
 Many of our natural resources are non-renewable
 Recycling helps to conserve resources
 Reasons for recycling
- Reduces wastes
- Garbage can be burnt or buried in landfills
- Whether burnt or buried, toxic gases are released. Toxic gases pollute the surrounding
ecosystem; therefore, recycling technology and systematic garbage collection reduces
waste pollution. It also saves energy e.g recycling paper uses up to 64% less energy than
making new ones. Conserves natural resources - recycled water from sewage can be used
in industries, flushing toilets and watering of plants and recycled paper can be used for
printing and manufacture of paper bags.

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Water purification

Water from the tap has been purified to make it fit for consumption.
• It has been filtered through beds of sand to remove suspended solids and to allow bacteria, living
in the sand, to remove harmful impurities.
• It will have had chlorine added to it. This oxidizes other impurities that might give bad tastes and
smells and disinfects the water by killing any bacteria.
Other possibilities:
· It may be passed through activated carbon to remove org. compounds that give the water taste,
colour and smell and
· It may have had oxygen bubbled through it to oxidize other impurities.
People shouldn't take water just for granted. Take a shower instead of a bath.

In cases of you not being sure of the safety of the tap water, boil or add chlorine to kill
possible harmful bacteria!

Biodiversity

 This is the study of the diversity or variety of animal and plant life in a given habitat (or in
the whole world). The habitat could be aquatic (water) or terrestrial (land).
 It is important as it makes biologists understand the importance or equilibrium of organisms
in an ecosystem.
 Different should tendencies of dominance in some parts of the world due to their
adaptations to that climate, ie, organisms are adapted differently to their environment.
 Human activities should be checked to prevent extinction of some species or disturbing the
balance in ecosystems e.g fishing, cutting down of forests for charcoal, pouching (e.g
elephants) etc.
 Biodiversity provides medicine, food, income from tourism, building materials and maintains
the rain cycle and balance of oxygen and carbon dioxide.

Remember!! For the love of science, we do these things.

Factor, non verba is our way of life.
1st Ed © March 2018

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