Cambridge IGCSE Biology Intensive 2022 Mr Andrew

IGCSE BIOLOGY INTENSIVE 2022

Table of Contents
Chapter 1: Characteristics and classification of living organisms ......................................... 2
Chapter 2: Organisation of the organisms............................................................................... 5
Chapter 3: Movement in and out of cells ................................................................................. 7
Chapter 4: Biological Molecule ................................................................................................ 8
Chapter 5: Enzymes .................................................................................................................. 9
Chapter 6: Plant nutrition ...................................................................................................... 10
Chapter 7: Human nutrition................................................................................................... 13
Chapter 8: Transport in plants ............................................................................................... 17
Chapter 9: Transport in animals ............................................................................................ 20
Chapter 10: Disease and immunity ........................................................................................ 26
Chapter 11: Gas exchange in humans ................................................................................... 27
Chapter 12: Respiration .......................................................................................................... 29
Chapter 13: Excretion in humans .......................................................................................... 30
Chapter 14: Coordination and response ................................................................................ 32
Chapter 15: Drugs................................................................................................................... 38
Chapter 16: Reproduction ...................................................................................................... 40
Chapter 17: Inheritance.......................................................................................................... 48
Chapter 18: Variation and selection ...................................................................................... 52
Chapter 19: Organisms and their environment ..................................................................... 56
Chapter 20: Biotechnology and genetic engineering ............................................................ 61
Chapter 21: Human influences on ecosystem ....................................................................... 63
EXERCISES............................................................................................................................ 68

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Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Chapter 1: Characteristics and classification of living organisms

1.1 Characteristics of living organisms

Movement An action by an organism or part of an organism causing a change of position or

place.
Respiration The chemical reactions in cells that break down nutrient molecules and release
energy for metabolism.
Sensitivity The ability to detect or sense stimuli in the internal or external environment and
to make appropriate responses.
Growth A permanent increase in size and dry mass by an increase in cell number or
cell size or both.
Reproduction The processes that make more of the same kind of organism.
Excretion Removal from organisms of the waste products of metabolism (all the chemical
reactions that occur in cells), toxic materials, and substances in excess of
requirements.
Nutrition Taking in of nutrients for energy, growth and development, absorbing and
assimilating them; plants require light, carbon dioxide, water and ions; animals
need organic compounds and ions and usually need water.

1.2 Concept and use of a classification system

➢ Organisms can be classified into groups by the features that they share.
➢ The binomial system of naming species as an internationally agreed system in which the
scientific name of an organism is made up of two parts showing the genus and species.

➢ Species: is a group of organisms that can reproduce to produce fertile offspring.

➢ The classification systems aim to reflect evolutionary relationships.
➢ The classification is traditionally based on studies of morphology and anatomy.
➢ The sequences of bases in DNA and of amino acids in proteins are used as a more
accurate means of classification.
➢ Organisms which share a more recent ancestor (are more closely related) have base sequences
in DNA that are more similar than those that share only a distant ancestor.

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

1.3 Features of organisms

Each kingdom has certain characteristics that all members of that group shared.

Plant kingdom

• Multicellular
• Cell wall made of cellulose
• Contain chlorophyll for photosynthesis. (at least some part
of a plant)
• Flowering plants

➢ Monocotyledons ➢ Dicotyledons
o One cotyledon in their seeds o Two cotyledons in their seeds • Not true living
o Long, narrow leaves o Broad leaves • Totally parasitic
o Parallel leaf vein o Branching network of veins • Only reproduce

Animal kingdom

• Multicellular
• No cell wall or chloroplast

Fungi kingdom

• Don’t have chlorophyll

• Don’t do photosynthesis
• Cell wall made of chitin
• Main body is mycelium
which is made of hyphae

Prokaryotes Protista
• Doesn’t have a nucleus • Mostly unicellular – amoeba
• Cell wall made of peptidoglycan • Some are multicellular – algae
• Have plasmids (some) • Do have a nucleus
• Have flagellum (some) • Prefer aquatic or moist environments

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Phylum Vertebrates

• Fur on skin
• External ears
• Internal fertilisation
• Lungs to breath
• Feathers on body and
scales on legs • Give birth to live
young
• Have wings and beak
• Have mammary
• Internal fertilisation
glands
• Lungs to breath
• Lay eggs • Dry scales
• Internal fertilisation
• Lungs to breath
• Lay eggs

• Slimy scales
• External fertilisation • Moist skin
• Gills to breath • External fertilisation
• Lay eggs • Gills / lungs to
breath
• Can live on land and
in water
• Lay eggs

Phylum Arthropods

• Invertebrate animal having exoskeleton, jointed legs and segmented body.

Insects Crustaceans Arachnids Myriapods

• 3 body segments • 2 body segment • 2 body • Fused head with
– head, thorax & – cephalothorax segment – thorax &
abdomen & abdomen cephalothorax segmented
• 3 pairs of legs • 5 pairs of legs & abdomen abdomen
• 1 pair of • 2 pairs of • 4 pairs of legs • 1 pair of legs on
antennae antennae • No antennae each segment
• Some with 1/2 • Compound eyes • Many simple • 1 pair of
pairs of wings • breathe through eyes antennae
• Compound eyes gills • Simple eyes

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 Cambridge IGCSE Biology Intensive 2022 15 Mr Andrew

Chapter 2: Organisation of 4the organisms

2.1 Cell structure and organisation

Cell membrane Cell wall

Cell membrane
Nucleus

Ribosome
Cytoplasm
Cytoplasm
Chloroplast
Mitochondria
Vacuole
Vesicle

Rough Nucleus
endoplasmic
reticulum
Animal cell Plant cell

Nucleus Controls all cell activities, contains genetic material.

Cell membrane Controls the movement of substances in and out of the cell, act a barrier
surrounding the cell.
Cytoplasm Region where chemical reactions take place. (E.g. protein synthesis)
➢ the cytoplasm of all cells contains structures such as ribosomes on
rough endoplasmic reticulum and vesicles
Mitochondria Power house of the cell, generate energy by cellular respiration.
➢ Aerobic respiration occurs in mitochondria
➢ Cells with high rates of metabolism require large numbers of
mitochondria to provide sufficient energy.
Ribosome Synthesise protein.
Cell wall Gives shape to the cell and withstand internal turgor pressure.
Chloroplast Contain chlorophyll which traps sunlight for photosynthesis.
• Starch is stored in the stroma of the chloroplast.
Vacuole Store water and dissolved nutrients.
© HENRICH ACADEMY 2019

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

2.2 Levels of organisation

Cell → Tissues → Organs → Organ Systems → Organism

Tissue is a group of cells with similar structures, working E.g. blood, retina, nerve
together to perform a shared function xylem, phloem.
Organ is a structure made up of a group of tissues, working E.g. tooth, artery, leaf,
together to perform specific functions. roots.
Organ is a group of organs with related functions, working E.g. respiratory, digestive,
system together to perform body functions. reproductive.

Specialised cells and their functions

2
Xylem vessels Root hair cells Palisade mesophyll cells
1 Breathing out combines which two characteristics of living organisms?

A excretion and movement

B excretion and respiration
C movement and sensitivity
D sensitivity and respiration

2 Scientists discover a new species of animal.

Conduction and support Absorption of water and mineral ions Photosynthesis
It has a segmented body with two pairs of legs on each segment.

Ciliated cells To which group

Redof blood
animalscells
does this new species belong?
Sperm and egg cells
A arachnids
88 B crustaceans
C insects
D myriapods

3 The diagram shows an insect.

Movement of mucus in the Transport of oxygen Reproduction
trachea and bronchi - cilia waft
mucus away from alveoli
towards mouth

2.3 Size of specimens 89

Use the key to identify the insect.

1 wings present ........................................... go to 2

I
wings absent ............................................ A
2 two pairs of wings ..................................... go to 3
M A one pair of wings ...................................... B
3 wings with circular markings ..................... C
𝑀𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 = 𝑖𝑚𝑎𝑔𝑒 𝐼 ÷ 𝑎𝑐𝑡𝑢𝑎𝑙 𝐴
wings without circular markings ................ D

4 Which feature shows that a cell is a plant cell?

90
A cell membrane
6
B cell wall
C cytoplasm
Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Chapter 3: Movement in and out of cells

3.1 Diffusion 3.2 Osmosis 3.3 Active transport

Diffusion is the net Osmosis is the net movement of water Active transport is the
movement of particles molecules down the water potential movement of particles through a
down a concentration gradient, through a partially cell membrane against the
gradient, as a result of permeable membrane. concentration gradient using
their random movement. energy from respiration.
Answering P4 osmosis questions
The energy for diffusion The active transport is carried
comes from the kinetic Compare the water potential of the out by protein molecules in the
energy of random solution given and water potential membrane, which bind to the
movement of molecules inside the cell. → therefore, water solute molecule, change shape
and ions. moves into / out of the cell → by and carry the molecule across
osmosis → down the water potential the membrane.
Factors that influence gradient → through a partially
diffusion permeable membrane. → Causing the The importance of active
• Distance (plant/animal) cell to … (describe the transport → ion uptake by root
• Surface area condition) hairs and glucose uptake by
• Temperature ➢ Animal cell epithelial cells of villi and

• Concentration • In – burst kidney tubules.

gradient • Out – shrink

➢ Plant cell
• In – turgid
• Out – flaccid (plasmolysis)

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Chapter 4: Biological Molecule

Carbohydrates Proteins

• Elements: Carbon, Hydrogen, Oxygen • Elements: Carbon, Hydrogen, Oxygen, Nitrogen

• Carbohydrates are used to store energy and • The basic units of proteins are amino acids.
they are stored as • Different sequences of amino acids give
➢ Glycogen in animals and humans different shapes to protein molecules.
➢ Starch in plants • Proteins are used to build new cells for growth
and replace damaged tissues.
Iodine solution (yellowish brown) to test for starch
• Protein is required in synthesis of enzymes,
→ (+) result – turn blue-black
antibodies and some hormones.

Biuret test (blue solution) for proteins → (+) result –

turn into purple solution

Benedict’s solution (blue) to test for reducing

sugars → (+) result – brick-red precipitate formed.
• Heated using water bath

Fats DNA (deoxyribonucleic acid)

• Elements: Carbon, Hydrogen, Oxygen • DNA is the genetic material that organisms
• The two different kinds of organic molecules inherit from their parents.
that join to make fats and oils are: ➢ Structure – double helix
➢ Glycerol ➢ cross-links between the strands are
➢ Fatty acid formed by pairs of bases
• Fats and oils are important sources of ▪ T with A and G with C
energy.
• Function as heat insulator.
Provides physical protection to major
internal organs of the body
Water
Ethanol emulsion test for fats and oils → (+) result –
an emulsion of oil and water is formed.
• The importance of water in the cell
➢ As a solvent (digestion, excretion and transport)
➢ As a medium for biochemical reaction
➢ Maintaining body temperature

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Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Chapter 5: Enzymes

• Catalyst is a substance that increases the rate of a chemical reaction and is not changed
by the reaction.
Substrate Products
• Enzymes are proteins that function as Active site
biological catalysts.
• Enzymes are highly specific, it has
active site which is complementary
with the substrate it acts on. Enzyme

• Enzymes, like catalysts, can be used over and over again because they are not used up during
the reaction and only a small amount is needed to speed the reaction up.

Effect of temperature on enzymes

• As the temperature is increased, the molecules gain more kinetic
energy, so they move faster and the frequency of effective
collisions increases. Therefore, the rate of reaction increases.
• The optimum temperature in humans for enzyme-controlled reactions is 370C.
• Above the optimum temperature the reaction slows down. This is because enzyme molecules
are proteins. Protein molecules start to denature and lose their shape at higher temperatures,
so the active site becomes deformed.
• Substrate molecules cannot fit together with the enzyme, stopping the reaction. Most enzymes
are denatured above 500C.

Effect of pH on enzymes
• Different enzymes work best at different pH values.
• The optimum pH for an enzyme depends on where it
normally works.
• Each enzyme has an optimum pH, if this pH changes, an extreme pH can denature
enzymes, thus the substrate will not be able to fit in it, and the enzyme becomes useless.

Use of enzymes in the food industry Use of enzyme in biological washing powders
• Fruit juices are extracted using an enzyme • Biological washing powders contain
called pectinase. protease and lipase to remove protein
• Enzymes such as amylase, proteases and stains and fat/grease from clothes.
lipase are used to make baby foods so that
young babies can absorb the nutrients easily.

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Chapter 6: Plant nutrition

6.1 Photosynthesis

• Photosynthesis is the process by which plants manufacture carbohydrates from raw

materials (CO2 & H2O) using energy from light.
• In this process, light energy is converted to chemical energy for the formation of glucose
and its subsequent storage as starch.

Heat it in boiling ethanol for a few minutes

Starch testing on leaf
in a water bath - to remove chlorophyll
Rinse with water –
Heat a plant
to soften the leave.
leaf in boiling
water for 30
Spread onto a
seconds – white tile and
break down add iodine
solution – to
the membrane. see the colour
change clearly.

Photosynthesis investigations
• Experiments can be used to find out what factors are needed for photosynthesis.
• Before you begin your investigation, you must destarch the plants.
7 This is done by leaving
the plant in a dark place for14a long
A plant period
with stripedof timesimilar
leaves (2 days).
to the oneDue
below to
wasthe
keptlack oflight for six hours.
in bright

photosynthesis in this place, stored starch is used up.

white stripe

green stripe
7
Light Chlorophyll Carbon dioxide
14 A plant with striped leaves similar to the one below was kept in bright light for six hours.

A leaf was taken from the plant and the chlorophyll removed. It was then tested for starch using
white stripe
iodine solution.

Which diagram showsgreen

the result
stripe
of the test?

A B C D
A leaf was taken from the plant andyellow-brown
the chlorophyll removed. It waswhite blue-black
then tested for starch using yellow-brown
iodine solution.

Which diagram shows the result of the test?

Positive starch test will be A B C D

obtained only in the portion of yellow-brown white blue-black yellow-brown

blue-black blue-black green green

the leaf exposed to light and Potassium/Sodium hydroxide absorbs
Photosynthesis takes place only
negative test in parts with black 15 The diagram shows the human alimentary CO 2. Part of the leaf kept in
canal.
in green patches because green of the
paper strip. blue-black blue-black green
structure does not secrete digestive NaOH/KOH give negative test for
presenceWhich of chlorophyll. The enzymes?
15 The diagram shows the human alimentary canal. starch.
white stripe do not perform
Which structure does not secrete digestive enzymes?
photosynthesis because of the A
absence of chlorophyll.
A

D 10
D B
B C
C
Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Photosynthesis investigation in submerged aquatic plant

Inverted boiling Thermometer -
tube – to collect Measure the
the oxygen temperature of
released water.
Glass tank filled with water -
Water with sodium
Maintain constant temperature.
hydrogen carbonate
Prevent heat from the lamp
(NaHCO3) - To
heating the water.
provide carbon
dioxide.

Ruler - Measure the distance between the lamp and the plant.

Limiting factors in photosynthesis

➢ Limiting factor is something present in the environment in such short supply that it restricts
life processes.

In a glass house, several conditions can be manipulated to increase the rate

of photosynthesis to ensure maximum crop yields for farmers:
➢ artificial lighting (plants can photosynthesise for longer)
➢ increasing carbon dioxide content of the air inside (plants can photosynthesise quicker)
➢ regular watering
In tropical countries where temperatures are much hotter, glasshouses may need to be ventilated to
release hot air and avoid temperatures rising too high, which could cause the denaturation of the
enzymes controlling the photosynthesis reaction.

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 13 An experiment was done using the apparatus shown in the diagram.

The carbon dioxide content of the water in each tube was measured at the start and ag
hours later.

Mr Andrew
In which tube would there be a decrease in carbon dioxide content?
Cambridge IGCSE Biology Intensive 2022
A B C D

Hydrogen carbonate indicator

black
➢ can detect increases and decreases in carbon dioxide polythene
water
to keep
concentration. out light light light
water
➢ It is normally red. However, an increase plant
in carbon
water
dioxide changes the indicator to yellow and
snaila

decrease in carbon dioxide changes it to purple. Yellow Purple

5
6.2 Leaf structure
10 The diagram shows part of a leaf in cross-section. Upper epidermis – thin and transparent

Cuticle – minimise water lost by evaporation – allows light to pass through

© UCLES 2015 0610/12/O/N/15

Palisade mesophyll –
main region for
Xylem photosynthesis – cells
are columnar and
Phloem packed with
Spongy mesophyll chloroplasts
– loosely packed –
air spaces between Guard cell – control

cells allow gaseous the opening and

exchange closing of stomata

Stomata – site of gaseous exchange (diffusion)

6.3 Mineral requirements

• Plants need nitrate ions for making amino acids. Amino acids are important because they are
joined together to make proteins which is need for plant growth. If nitrate ions are in short
supply, the plant will show stunted growth and yellow leaves.
• Magnesium ions are needed to form chlorophyll. If the plant is deficient in magnesium, it
will not be able to make chlorophyll. The leaves turn yellow between the veins (a process
called chlorosis).

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Chapter 7: Human nutrition

7.1 Diet

• A balanced diet is a diet that contains all the Effects of malnutrition

main nutrients in the correct amounts and
proportions to maintain good health. • Obesity
• Humans need 7 classes of food in their diet: ➢ Too much calorie (carbohydrate or fat)
carbohydrates, proteins, fats, water, fibre,
vitamins and minerals. • Coronary heart disease
• The amount of energy needed is provided ➢ Too much saturated fat in the diet results in
mainly by our carbohydrate and fat intake. high cholesterol levels.
• Your dietary requirements depend on your ➢ CHD tends to develop when cholesterol
age, gender and activity (including pregnant builds up on the artery walls (coronary
and breast-feeding mother) arteries), creating plaques. These plaques
• Malnutrition is the result of not eating a cause the arteries to narrow, reducing blood
balanced diet. flow to the heart. A clot can sometimes
obstruct the blood flow, causing serious
health problems.
Nutrient Deficiency
Protein-energy malnutrition
Vitamin C Scurvy – bleeding gums.
Vitamin D Loss of bone density, which can
• Kwashiorkor
contribute to osteoporosis and
➢ It is caused by sufficient calorie intake, but
fractures. In children, it can cause
with insufficient protein consumption in
rickets.
young children.
Calcium Rickets, brittle bones and teeth,
➢ Symptoms - weight loss, hair loss, fatigue,
slow blood clotting
muscle wasting and more prone to disease.
Iron Anaemia (not enough RBC →
not enough 𝑂2 delivered to
• Marasmus
tissues): fatigue
➢ It is caused by starvation in children that
Fibre Constipation, long-term
don't ingest enough protein, calories and
deficiency leads to bowel cancer.
other important nutrients
Water Dehydration

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

7.2 – 7.4 Alimentary canal, Mechanical Digestion, Chemical digestion

Ingestion is the taking of substances, e.g. food and drink, into the body through the mouth.
Mechanical is the breakdown of food into smaller pieces without chemical change to the food molecules.
digestion Large pieces of food are broken down into smaller pieces → increases the surface area of
the food for chemical digestion.
Chemical is the breakdown of large, insoluble molecules into small, soluble molecules.
digestion The main places where chemical digestion happens are the mouth, stomach and small
intestine. Enzymes speed up the process. They work efficiently at body temperature (370C)
and at suitable pH.
Absorption is the movement of small food molecules and ions through the wall of the intestine into the
blood.
Assimilation is the movement of digested food molecules into the cells of the body where they are used,
becoming part of the cells.
Egestion is the passing out of food that has not been digested or absorbed, as faeces, through the anus.

Incisor
Types of human teeth Canine
Premolar
Incisor Canine Premolar Molar

Molar
Biting & cutting Tearing & biting Chewing and grinding

Structure of human teeth

Enamel - The hard-outer Nerves - Detect stimuli &
layer of the crown. transmit impulses.
Dentine - Forms the bulk of Cement - The layer of bone-like
the tooth. tissue covering the root. Not as
Pulp - Soft tissue hard as enamel.
containing the blood supply Gums - Soft tissue that protects
and nerves to the tooth. the bone & the roots of the teeth.

Causes of dental decay Proper care of teeth

Bacteria on the plaque • Avoid sugary food.

respire or breakdown sugars • Brush the teeth regularly – to remove plaque.
in the food, producing acid • Use fluoride toothpaste – fluoride hardens tooth enamel.
which dissolves the enamel • Use dental floss – to remove pieces of food and plaque trapped.
and dentine, forming a hole. • Visit a dentist regularly.

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

7.5 Absorption

• Absorption is the movement of digested food molecules from the digestive system into the blood (glucose
and amino acids) and lymph (fatty acids and glycerol).
• Water is absorbed in both the small intestine and the colon, but most absorption of water happens in
the small intestine.
• Absorption takes place in the second section of the small intestine, the ileum.
• The ileum is adapted for absorption as it is very long and has a highly folded surface with millions of villi,
massively increase the surface area, allowing absorption to take place faster and more efficiently.
• Microvilli on the surface of the villus further increase surface area for faster absorption of nutrients.
• Wall of villus is one cell thick meaning that there is only a short distance for absorption to happen by
diffusion and active transport.
• Well supplied with a network of blood capillaries that transport glucose and amino acids away from the
small intestine in the blood. A rich blood supply produces a steep concentration gradient for diffusion.
• The hepatic portal vein transports absorbed food from the small intestine to the liver.
• Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small
intestine in the lymph.

Diarrhoea Diarrhoea the loss of watery faeces. The treatment of diarrhoea is using oral
rehydration therapy.
Cholera Is a disease caused by a bacterium. The cholera bacterium produces a toxin that causes
secretion of chloride ions into the small intestine, causing osmotic movement of water
into the gut, causing diarrhoea, dehydration and loss of salts from blood.

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 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Chapter 8: Transport in plants

8.1 Transport in plants

Xylem tissue Phloem tissue

• Transport water and dissolved minerals • Transport food nutrients such as sucrose
(conduction) and amino acids (translocation)
• Support
the stem

• Unidirectional (moves up the plant’s stem) • Bidirectional (moves up or down the

• Dead tissue at maturity, so it is hollow with no plant’s stem from source to sink)
cell content. • Living tissue with little cytoplasm but no
• No end walls between cells, so a long, open nucleus. (its activities are controlled by a
tube is formed. companion cell next to it which has a
• The walls of the xylem vessel contain holes nucleus) 3

called pits for lateral movement of water. 4 • Cellsare

Which organelles present
have endinwalls
large numbers in cells that produce
with perforated sieve insulin?
A nuclei and mitochondria
• They have a thick lignified cellulose cell wall. plates.
B ribosomes and mitochondria
C
8 rough endoplasmic reticulum and cell walls
8
D vesicles and nuclei
Distribution of xylem and phloem in roots, stems and leaves
agrams show cross-sections through a root and 5a stem.
.m
The etsthickness
actual a dnaof tthe
ooleaf
r ashown
hginuotherhdiagram
t snoisit2000
cesμm,
-sbut
soitsrcthickness
woh in
is 50 mm.

Y Phloem
Y
Phloem W
Xylem
Z ZW
V V
Xylem

Phloem

root
Root etsWhat is thestem
mStem magnification of the diagram?
Leaf toor
A × 0.025 B × 25 C × 100 D × 100 000

labels are correct? 17 ?tcerroc er

6 The diagram shows an experiment on osmosis.

Which arrow shows the direction of the net movement of water at the start of the exp

V W Y Z Z Y A
W
 Cambridge IGCSE Biology Intensive 2022 Mr Andrew

8.2 Water uptake

• Plants take in water from the soil, through their root hairs. Elongated – increase
surface area
• The root hair increases the surface area of the cells as
it increases the rate of the absorption of water by osmosis
and mineral ions by active transport
• Water enters root hair cells by osmosis. This happens
when the water potential in the soil surrounding the root is Thin cell wall –
higher than in the cell. Water diffuses from the soil into shorter distance
for diffusion
the root hair by osmosis, down its water potential gradient
through a partially permeable membrane.
• Pathway taken by water through root, stem and leaf Mitochondria – provide energy for active transport

root hair cell root cortex cells xylem mesophyll cells

8.3 Transpiration

Transpiration is loss of water vapour from plant leaves by evaporation of water at the surfaces of the
mesophyll cells followed by diffusion of water vapour through the stomata.

Factors that affects rate of transpiration.

Temperature When temperature ↑, kinetic energy of water molecules ↑ causing them to diffuse
faster.
Air movement When air movement ↑, concentration gradient for diffusion ↑ as air removes water
molecules as they pass out the stomata.
Light intensity At high light intensity, stomata open to allow gas exchange for photosynthesis.
Water vapour can diffuse out through the stomata.
8
Humidity When humidity ↑, the concentration of water molecules outside the leave ↑ which
16 Which graph shows most clearly what will happen to the rate of transpiration as humidity
increases?
↓ the concentration gradient for diffusion.

A B

rate of rate of
transpiration transpiration

Temperature / Air movement / Light intensity

humidity Humidity
humidity

18
C D
Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Mechanism by which water moves upwards in the xylem

Water evaporate from surfaces of mesophyll cells into air spaces and the
water vapour is lost through stomata by diffusion. This reduces the water
potential at top of plant resulting in water moving upwards through the
xylem vessels in a continuous transpiration stream from roots to leaves via
the stem. Transpiration produces a pull that draws up a column of
water molecules held together by cohesion.

Wilting

How - If more water evaporates from the leaves of a plant than is

available in the soil to move into the root by osmosis, then wilting will
occur. This is when all the cells of the plant become flaccid, so the strength
of the cell walls cannot support the plant and
it starts to collapse.

Why – wilting closes stomata to prevent more water loss, therefore water
is conserved for other processes. It also decreases surface area of plant
exposed to the sun for absorption of heat.

8.4 Translocation

• Translocation is the movement of sucrose and amino acids in phloem; from regions of
production (source) to regions of storage OR to regions where they are used in respiration or
growth (sink).
• Some parts of a plant may act as a source and sink at different times during the life of a plant.
➢ During germination source is seed /
cotyledon. Once the leaves grow
and start to photosythesise, they
will become source during the
growing season.
➢ In early growth of a plant the root
is the sink. Later either the flowers
/ fruits / seed / tubers become sinks.

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Cambridge IGCSE Biology Intensive 2022 Mr Andrew

Ringing Experiment
• After a week there is:
➢ A swelling above the ring
➢ Reduced growth on the lower branch
➢ The leaves are unaffected. (normal)

Systemic pesticides
When sprayed onto the leaves of the plant, they are absorbed by it
through the cuticle or stomata and into the phloem tubes. They
move through the plant in the phloem by translocation and are
taken in by any insect eating the plant or sucking up phloem sap.

Chapter 9: Transport in animals

9.1 transport in animals

The single circulation of a fish

• Fish have a single-circulatory system because the blood
flows through the heart only once for each complete
circuit of the body.

The double circulation of a mammal

• Mammals have a double circulatory system because the
blood passes through the heart twice for each complete
circuit of the body.

The advantage of the double circulatory system

• Septum prevent mixing of oxygenated and deoxygenated blood.
• It allows different blood pressure in each loop. The pressure in systemic circulation is kept
higher than that in pulmonary circulation.
• Blood travelling through the small capillaries in the lungs loses a lot of pressure that was
given to it by the pumping of the heart, by returning the blood to the heart after going through
the lungs its pressure can be raised again before sending it to the body, meaning cells can
be supplied with the oxygen and glucose they need for respiration faster and more
frequently.

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9.2 Heart

• The heart valves maintain the one-way flow of blood:

➢ When the atria contract, atrioventricular (AV) valves open
➢ Blood flows from the atria and into the ventricles
➢ When the ventricles contract, the AV valves close and semilunar valves open
➢ This than forces blood out of the ventricles and into the arteries
➢ As arterial pressure rises, the semilunar valves close, ensuring the one-way flow of
blood
• The activity of the heart may be monitored by ECG, pulse rate and listening to sounds of
valves closing using a stethoscope.

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The effect of physical activity on the heart rate

• During exercise the heart rate increases to supply the muscles with more oxygen and
glucose. This allow the muscles to respire aerobically, so they have sufficient energy to
contract. This also allows for waste products to be removed at a faster rate.

Coronary heart disease (CHD)

• Coronary arteries supply oxygen and nutrients to heart

muscles.
• CHD normally happens when cholesterol accumulates on
the coronary artery walls, creating plaques. The arteries
become narrow, reducing blood flow to the heart muscles.
Sometimes, a clot can completely obstruct the flow of
blood to the heart muscles, leading to a heart attack.
• The possible risk factors are diet, stress, smoking, genetic predisposition, age and gender.

Possible treatment for CHD Prevention of CHD

• Drug treatment with aspirin to prevent • Diet and lifestyle play an important role.
formation of blood clot in arteries. ➢ Eat a healthy balanced diet
• Surgery ➢ Be more physically active
➢ By-pass - a piece of blood vessel attached to ➢ Give up smoking
carry blood around the blocked artery. ➢ Reduce alcohol consumption
➢ Stents - tube to hold arteries open to restore ➢ Keep blood pressure under control
blood supply to heart muscle.
➢ Angioplasty - tube or balloon inserted into
artery and inflated to widen artery.

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9.3 Blood and Lymphatic vessel

Heart → Artery → Arterioles → Capillaries → Venule → Veins → Heart

Artery • carry blood away from the heart.
• thick wall to withstand high blood pressure.
• small lumen to maintain high blood pressure.
Arterioles • transport blood from arteries to capillaries.
• constrict and dilate to regulate blood flow.
Capillaries • sites of exchange with the body tissues.
• thin wall (one cell thick walls) – short distance for diffusion.
• gaps in capillary walls ('leaky' walls) so that blood plasma can leak out and form
tissue fluid surrounding cells

Venule • allows deoxygenated blood to return from capillary beds to veins.

Veins • carry blood towards the heart.
• have valves to prevent back flow of blood.
• wide lumen offers less resistance to blood
flow.
Shunt • links an artery directly to a vein, allowing the blood to bypass the capillaries
vessel in certain areas.

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Chapter 10: Disease and immunity

• Pathogen is a disease-causing organism.

• Transmissible disease is a disease in which the pathogen can be passed from one host to
another. They may be transmitted either through direct contact (through blood or other body
fluids) or indirectly (from contaminated surfaces or food, from animals, or from the air)
• The body has defences against disease:
➢ Mechanical barriers – skin and hairs in the nose
➢ Chemical barriers – stomach acid and mucus
➢ WBC cells - phagocytosis and antibody production by white blood cells

Antibody production
• Lymphocytes produced antibodies in response to the presence of pathogens or foreign cells
which have antigen on their surface. They make antibodies which are complementary
shape to the antigen.
• Antibodies clump pathogenic cells together
so they can’t move as easily and releasing
chemicals that signal destruction by
phagocytes or lock on to antigens leading to direct destruction of pathogens.

Active immunity Passive immunity

• Is the defence against a pathogen by • Is short-term defence against a pathogen
antibody production in the body by antibodies acquired from another
• This is long-term as memory cells are individual, e.g. mother to infant
produced. • This is temporary as memory cells are not
• Is gained after an infection by a produced.
pathogen, or by vaccination
Diseases Caused by the Immune System
The process of vaccination:
• Harmless pathogen given (injected) which Occasionally, the cells of the immune system start to
has antigens. attack the body’s own cells. One example of this type
• Antigens trigger an immune response by of disease is Type 1 diabetes. People who suffer
lymphocytes which produce antibodies. from this disease no longer make their own insulin
• Memory cells are produced that give and so are unable to regulate their blood glucose
long-term immunity. levels. This is because their immune system is
• Vaccination can be used to control the targeting and destroying the pancreatic cells
spread of diseases. which are responsible for making the insulin,
eventually leading to high glucose levels in the blood.

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Chapter 11: Gas exchange in humans

Main structures of the human respiratory system:

• lungs, diaphragm, ribs, intercostal muscles, larynx, trachea, bronchi, bronchioles, alveoli and
associated capillaries.

Cartilage in the trachea

• Keeps trachea open
which allows free flow of
air into the lungs.
• Can breathe even when
bending or swallowing.

Features of gas exchange surfaces in humans

• Large surface area to allow faster diffusion of a lot of
gases across the surface at the same time.
• Thin (one cell thick) walls to minimise the diffusion
distance.
• Good blood supply to maintain a high concentration gradient so diffusion occurs faster.
• Good ventilation with air so that diffusion gradients can be maintained.
• Moist to prevent the cells from drying and to allow gases to dissolve.

The differences in composition between inspired Cilia – waft

and expired air mucus away from
Inspired Air Expired Air alveoli towards
mouth
𝑂2 21% 16%
𝐶𝑂2 0.04% 4% Ciliated cell

𝑁2 78% 78%
Goblet cell – produce mucus which traps
Water vapour varies to climate Saturated
particles and microorganisms in the air

Limewater can be used as a test for 𝑪𝑶𝟐 to investigate the differences in composition between inspired and
expired air, because it changes colour from colourless to milky when the gas (𝐶𝑂2 ) is bubbled through. There is
more 𝐶𝑂2 present in expired air. Therefore, it makes limewater change colour more quickly (than inspired air)

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Inhalation & Exhalation

Inhalation Exhalation
Intercostal muscles External muscles contract Internal muscles contract
Internal muscle relax External muscle relax
Ribcage movement Upward & Outward Downward & Inward

Diaphragm muscles Contract & flattens Relax & curve upwards

Volume of thorax Increases Decreases

Air pressure in thorax Decreases Increases
(lower than atmospheric pressure) (higher than atmospheric pressure)
air rushes Into the lungs Out of the lungs

Link between physical activity and breathing

• Rate and depth of breathing increase when exercising.

• This is because muscles are respiring aerobically more and they need more oxygen to be
delivered to them to keep up with the energy demand. As respiration rates increase, more
carbon dioxide is produced and enters the blood. Carbon dioxide is an acidic gas in solution,
thus lowers the blood pH. As blood flows through the brain, this change is detected. Brain
stimulates an increase in breathing rate and increase in depth of breathing by negative
feedback mechanism.

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Chapter 12: Respiration

• Respiration is the chemical reactions in cells that break down nutrient molecules and
release energy for metabolism.
• In human’s body energy is used for:
➢ muscle contraction, protein synthesis, cell division, active transport, growth, the
passage of nerve impulses and the maintenance of a constant body temperature.
• Respiration involves the action of enzymes in cells.

• During vigorous exercise if the muscles cannot meet the energy demand they will respire
anaerobically producing lactic acid.
• After exercise, the lactic acid made will diffuse into the blood, transported to the liver, and
broken down by combining it with oxygen. (Aerobic respiration of lactic acid in the liver)
• This is known as ‘repaying the oxygen debt’.
• The oxygen debt is removed during recovery period.
• Increasing heart rate and deeper breathing will supply more oxygen to pay the oxygen
debt.

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Chapter 13: Excretion in humans

• Excretion is the removal from organisms of toxic materials, the waste products of
metabolism and substances in excess of requirements.
• Humans have organs which are specialised for the removal of certain excretory products
including the lungs, skin and kidneys. The liver also has a vital role in excretion.

Role of liver in excretion

• Deamination of excess amino acids. Deamination is the removal of nitrogen-containing
part of amino acids to form urea.
• Urea pathway (liver → heart → lungs → heart → kidney)
• Break down of hormones, toxins (drugs) and worn out red blood cells.

Structure of the urinary system

Renal
capsule

Collecting
duct

urethra

Function of the kidney – Filtration and Reabsorption

• The capillaries get narrower as they get further into the glomerulus which increases the
pressure on the blood moving through them causing smaller molecules to be forced out of
the capillaries and into the renal / Bowman’s capsule, forming filtrate. This process is
known as ultrafiltration.
• The role of the glomerulus – filtration from the blood of water, glucose, urea and salts
• The role of the tubule – reabsorption of all of the glucose, most of the water and some
salts back into the blood, leading to the concentration of urea in the urine as well as loss of
excess water and salts.
• As the filtrate flows through the tubule, all of the glucose is reabsorbed by active transport,
some salts are reabsorbed back into the blood by diffusion and water follows by osmosis.

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• Water is also reabsorbed from the collecting duct in different amounts depending on how
much water the body needs at that time. The volume and concentration of urine produced is
affected by:
➢ Water intake – the more fluids drunk, the more water will be removed from the body
and so a large quantity of dilute urine will be produced.
➢ Temperature – the higher the temperature the more water is lost in sweat and so less
will appear in urine, meaning a smaller quantity of concentrated urine will be
produced.
➢ Exercise – the more exercise done, the more water is lost in sweat and so less will
appear in urine, meaning a smaller quantity of concentrated urine will be produced.

Dialysis
• A patient with kidney failure needs to remove toxic
chemicals from the blood to stay alive.
• During dialysis, unfiltered blood is taken from an artery in
the arm, pumped into the dialysis machine and then
returned to a vein in the arm.
• Inside the machine the blood and dialysis fluid are
separated by a partially permeable membrane. The tubing
is very long to provide a large surface area.
• As the dialysis fluid has no urea in it, there is a large
Advantages and disadvantages of kidney
concentration gradient – meaning that
transplants compared with dialysis.
urea diffuses across the partially permeable
membrane, from the blood to the dialysis fluid.
Advantage
• As the dialysis fluid contains • Patients do not need to return to
a glucose concentration equal to a normal blood sugar clinic/hospital for dialysis.
level, this prevents the net movement of glucose across • No need for a restricted diet.
the membrane as no concentration gradient exists. • No long-term discomfort or pain.
• As the dialysis fluid contains a salt concentration similar • Time not taken up with dialysis.

to the ideal blood concentration, movement of salts • Lead a normal life.

across the membrane only occurs where there is Disadvantages

an imbalance (if the blood is too low in salts, they will • Difficult to find a compatible donor.
diffuse into the blood; if the blood is too high in salts, • Rejection of kidney
they will diffuse out of the blood) • Need to take immunosuppressant drugs.
• The dialysate needs to be changed regularly to maintain • Risk of infection during or after the

a concentration gradient. operation.

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Chapter 14: Coordination and response

11
14.1 Nervous control in humans
.cra xelfer a swohs margaid ehT 32

Sensory
neurone

Relay
neurone

Motor
elaneurone
cs ot ton

?X si tahW

• enoruentoyaler a
Sensory and motor neurones are covered with myelin sheath, which insulates the neurone A
make transmission of the impulse more efficient. espanys a B
• A nerve impulse is an electrical signal that passes along nerve cells called neurones. rotceffe eht C
rotpecer eht D

Reflex action
a ot aera til ylmid a morf sklaw nosrep a nehw eye eht fo siri eht ni rucco sesnopser hcihW 42
• A reflex action is an automatic (involuntary) and rapid response of effectors (muscles ?oraera til ylthgirb
glands) to a stimulus, which minimises any damage to the body from potentially harmful
elcsum laidar elcsum ralucric
conditions. It does not involve the conscious part of the brain.
tcartnoc tcartnoc A
• The nerve pathway followed by a reflex action is called a reflex arc.
xaler tcartnoc B
tcartnoc xaler C
xaler xaler D

?enilanerda fo esaeler eht fo tluser eht si hcihW 52

slipup fo noitcirtsnoc A
etar gnihtaerb ni esaerced B
etar eslup ni esaerced C
noitartnecnoc esoculg doolb ni esaercni D

revo nruT[ 71/J/M/22/0160 7 10 2 S E L C U ©

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Voluntary action Involuntary action

• Involve many stimuli • Automatic and rapid response
• Brain decides. • Does not involve thought.
• Consciously control skeletal muscles. • The same stimulus always results in
• Involve many effectors. the same response.

• Synapse: is a junction between two nuerones

• Electrical impulse triggers vesicles containing
neurotransmitter to move and fuse to the cell
membrane releasing the neurotransmitter which
diffuse across the synaptic gap and binds to the
receptor on cell surface which results in an
impulse in the next neurone.
• In a reflex arc the synapses ensure that impulses
travel in one direction only.
➢ Neurotransmitters released on one side of synapse
➢ Receptors only found on the opposite side of
synapse

14.2 Sense organs

• Sense organs are groups of receptor cells responding to specific stimuli: light, sound, touch,
temperature and chemicals.

Structure and function of the eye

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Cornea refracts light

Iris controls how much light enters pupil
Lens focuses light onto retina
Retina contains light receptors, some sensitive to light of
different colours.
Rods Sensitive to low light intensity – Provide night
vision – Detect shades of grey – Can recognise
shapes but not colour
Cones Sensitive only to high light intensity – Detect
colour – There are three types, sensitive to red,
green and blue light → colour seen white
Optic nerve carries impulses to the brain.

In bright light
In bright light
• Circular muscle contract
• Circular muscle contract
• Radial muscle relax
• Radial muscle relax
• Pupil constricts Pupil reflex
• Pupil constricts
• To prevent the light damaging the light-sensitive cells in the retina
• To prevent the light damaging the light-sensitive cells in the retina
In dim light
In dimlight Accommodation
• Circular muscle relax
• Circular muscle relax of eye to view
• Radial muscle contract
• Radial muscle contract near and distant
• Pupil dilates
• Pupil dilates
• To allow a maximal amount of light into the eye
objects.
• To allow a maximal amount of light into the eye

DistantDistant
vision vision
• The ciliary
• The muscle relax relax
ciliary muscle
• This•pulls
Thisonpulls
the on
suspensory ligaments
the suspensory (tense)
ligaments (tense)
• This•makes the lens
This makes thinner
the (decrease
lens thinner in curvature)
(decrease in curvature)

MeMe ga ga

Near vision
Near vision r r
• The ciliary
• The muscle contract
ciliary muscle contract
• This•removes
This removes the tension
the tension on theon the suspensory
suspensory ligaments.
ligaments.
• The
• The lens lens become
become thickerthicker (increase
(increase in curvature)
in curvature)

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14.3 Hormones in humans

• Hormone is a chemical substance, produced by a gland, carried by the blood, which alters
the activity of one or more specific target organs and is then destroyed by the liver.
• An endocrine gland is a ductless gland. It produces and secretes hormones which diffuse
directly into the bloodstream.

Endocrine gland Hormone Function

• Adrenaline is a hormone secreted in ‘fight or flight’
Adrenal gland Adrenaline situations and its effects are increased breathing
and pulse rate, increased blood glucose
concentration and widened pupils.
Insulin • Lowers blood glucose level by stimulating glucose
Pancreas storage as glycogen.
Glucagon • Raises blood glucose level by stimulating the
conversion of glycogen to glucose.
• Regulates the development of secondary sexual
Ovary Oestrogen characteristics.
• Stimulates the thickening of the uterine wall
Progesterone • Maintains the thickening of the uterine wall.
Testis Testosterone • Regulates the development of secondary sexual
characteristics.

Features Nervous system Endocrine system

Speed Fast Slow
Longevity Short term Long term
of action

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14.4 Homeostasis
• Homeostasis is the maintenance of a constant internal environment.
• Homeostasis is the control of internal conditions within set limits by negative feedback.
• When there is a change in internal environment, the body will respond to keep it at the normal
by producing a corrective mechanism in the opposite direction.

The control of the glucose concentration of the blood by the liver and the roles of insulin and
glucagon from the pancreas.

• Both hormones are secreted by the pancreas and are transported to the liver in the
bloodstream.
• Insulin control blood glucose level by increasing the uptake of glucose by cells and
stimulate cells to convert glucose to glycogen.

Type 1 diabetes.
Symptoms Treatment
• Increased glucose in urine • Insulin by injection
• Blurred vision • Regular blood glucose test
• Slow wound healing • Controlled diet

The maintenance of a constant internal body temperature in humans in terms of vasodilation and
vasoconstriction of arterioles supplying skin surface capillaries.

When you are cold, body produces and saves heat When you are hot, the body loses more heat:
• shivering: muscles contract and relax • sweating: droplets of sweat evaporate,
spontaneously → produces heat cooling the body
• vasoconstriction: arterioles near skin become • vasodilation: arterioles near skin
narrower → conserve heat become wider, more blood flows near
• shunt vessels near the skin open skin surface → lose heat
• hair stands up. In animals it acts as an • shunt vessels near the skin close
insulator. • hair lies flat → heat is lost faster by
conduction, convection or radiation.

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Human skin
• limited to: hairs, hair erector muscles, sweat
glands, receptors, sensory neurones, blood
vessels and fatty tissue.

14.5 Tropic responses

• Geotropism – is a response in which parts of a

plant grow towards or away from gravity.
• Phototropism – is a response in which parts of a
plant grow towards or away from the direction
which light is coming.

Role of auxin in controlling shoot growth

Auxin in phototropism Auxin in geotropism

• Auxin is made in shoot tip • Auxin is made in shoot tip
• If a shoot is exposed to light from one • If a shoot is placed horizontally in the
side, more auxins move to the shaded absence of light, auxins accumulate on
side from the shoot tip. the lower side of the shoot, due to
• On this side, auxin stimulates cell gravity.
elongation by the absorption of water. • On this side, auxin stimulates cell
• Shoot bends toward the light. elongation by the absorption of water.
• This is called positive phototropism • The shoot bends upwards.
• This is called negative geotropism.

Weed killers - synthetic plant hormone 2,4-D

• 2,4-D is primarily used as a selective herbicide which kills many terrestrial and aquatic
broadleaf weeds, but not grasses. It acts by mimicking the action of the plant growth
hormone auxin, which results in uncontrolled growth and eventually death in susceptible
plants.

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Chapter 15: Drugs

15.1 Drugs
• Drug is any substance taken into the body that modifies or affects chemical reactions in the
body.

15.2 Medicinal drugs

Antibiotics
• Used for the treatment of bacterial infection. • Some bacteria have mutated and
• Antibiotics do not work against viruses become resistant to antibiotics which
because… reduces the effectiveness of antibiotics.
➢ Viruses are not cells and they have no Development of resistant bacteria such as
metabolism. MRSA can be minimised by:
➢ Antibiotics stop cell wall growth, viruses ➢ Using antibiotics only when essential
have no cell wall ➢ Ensuring the treatment is complete –
➢ Antibiotics stop enzymes working, viruses all bacteria need to be killed. Any
have no enzymes remaining bacteria might mutate, survive
• Antibiotics are made by growing the fungus and reproduce becoming resistant to the
in a large fermenter provided with oxygen antibiotics. Since the antibiotic is no
and nutrients. The mixture is then filtered longer effective, new antibiotics have to
and purified. be developed.

15.3 Misused drugs

Heroin
• Heroin is a powerful depressant drug: it relieves severe pain and produce short-lived feelings of
wellbeing and freedom from anxiety.
• Heroin affects the nervous system by interacting with receptor molecules at synapse, heroin diffuses
into synapse binds to receptors (for neurotransmitter). heroin being complementary to receptor,
blocks neurotransmitter entering receptor site.
• Heroin can lead to tolerance and physical dependence within weeks. Withdrawal symptoms of
heroin can be very unpleasant - involving anxiety, muscle aches, sweating, abdominal cramping,
diarrhoea, nausea and vomiting.
• When heroin injected using unsterilized and shared needles, there is a risk of infections such as HIV.
• Addiction creates financial problems leading to family breakdown, criminal activity and sexual
promiscuity.

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Alcohol
• Alcohol is a CNS depressant, it slows down brain functioning and neural activity.
• Larger amount of alcohol slows down the transmission of electrical impulses in the brain, so
reactions are depressed, coordination is impaired and reasoned judgements become
difficult.
• Liver is the site of breakdown of alcohol and other toxins. Excessive alcohol consumption
can cause liver damage.
• Some people build up a tolerance to alcohol and this may lead to both emotional and physical
dependence (alcoholism).
• Alcohol can also lead to irresponsible behavior such as vandalism and aggression.
• Drinking alcohol during pregnancy can present a major risk to the developing fetus.

Tobacco smoking
• Carbon monoxide - Binds permanently with haemoglobin in RBC, thus preventing them
transporting oxygen.
• Nicotine - causes addiction.
• Tar - a carcinogen which increase the risk of lung cancer, increase mucus production and
paralysing cilia on the respiratory tract.
• Tobacco smoking can cause chronic obstructive pulmonary disease (COPD), lung cancer and
coronary heart disease.

COPD Chronic bronchitis.

Emphysema (break down of alveoli) → shortness of breath.
Lung cancer Carcinogen in cigarette smoke increase the risk of lung cancer
Coronary heart disease Increase risk of blood clot formation in blood vessels (coronary artery)

Use of hormones to improve sporting performance

• Taking testosterone supplements leads to increased muscle and bone mass which can
enhance a sportsperson’s performance.
• Anabolic steroids affect protein metabolism, increasing muscle development and reducing
body fat. Long-term effects are sterility, masculinisation in women, and liver and kidney
malfunction.

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Chapter 16: Reproduction

16.1 Asexual reproduction

• Asexual reproduction is a process resulting in the production of genetically identical
offspring from one parent.

Advantages Disadvantages
• Quick • No variation → unlikely to adapt in
• Only one parent needed. new environment.
• No gametes needed. • Lack of dispersal → competition
• All good characteristics are passed on. • Offspring inherit bad characteristics.
• No dispersal. Thus, grow in the same (no resistance towards a disease)
favorable environment as parent.

16.2 Sexual reproduction

• Sexual reproduction is the process involving the fusion of haploid nuclei of two gametes
(sex cells) to form a diploid zygote and the production of offspring that are genetically
different from each other.
• It is the formation of a new organism by fertilisation - the fusion of gamete nuclei

Advantages Disadvantages
• More variation – allow adaptation to • Two parents needed.
new/changing environment. • Slow growth
• Fewer offspring – less competition for resources. • Fewer offspring – lesser
• New variation created – disease resistance. chance of survival.

16.3 Sexual Reproduction in plants

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Insect pollinated flower vs wind pollinated flower

Pollination
• Pollination is the transfer of pollen grains from the anther to the stigma.

Self-pollination Cross-pollination
• Transfer of pollen grains from the anther of • Transfer of pollen grains from the anther
a flower to the stigma of the same flower of a flower to the stigma of a flower on
or different flower on the same plant. a different plant of the same species.

• Can occur without pollinating agent • Lower chance of successful pollination,

• Higher chance of fertilization needs pollinating agent
• Less variation • Lower chance of fertilisation
• Less adapted to environmental change • More variation
• More adapted to environmental change

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Fertilisation
• After pollination, the pollen grains may germinate to form a pollen
tube. The pollen tube contains the male nucleus, which is needed
to fertilise the ovule inside the ovary.
• The pollen tube grows down the style, through the ovary wall, and
through the micropyle of the ovule. Fertilisation occur when a
pollen nucleus fuses with a nucleus in an ovule.
• If the ovary contains a lot of ovules, each will need to be fertilised
by a different pollen nucleus.

Formation of seed
• The fertilised ovule divides by mitosis to form a seed containing the
embryo plant and food stores called cotyledons.
• Conditions affecting germination
Water Activate enzymes for converting insoluble food stores in the cotyledons
down to soluble food → for growth & energy production of embryo.
Oxygen Respiration → release energy → growth
Warmth Enzyme work best at optimum temperature

16.4 Sexual reproduction in humans

• Reproduction in humans is when the male gamete (sperm) fuses together with the female
gamete (ovum/egg). This fusion is called fertilisation.

Male reproductive system

• Testes: produce sperm and testosterone
• Scrotum: a sac that holds and keeps testes cool
(outside body)
• Sperm ducts: link testis to urethra to allow passage
of semen containing sperm.
• Prostate gland: produce seminal fluid
• Urethra: carries semen from sperm duct to tip of
penis and also carry urine
• Penis: become firm, inserted into vagina during
sexual intercourse to transfer semen to the vagina.

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Female reproductive system

• Ovaries: contains follicles which
develop into ovum and produce
oestrogen and progesterone.
• Oviducts: carries ovum to uterus
and site of fertilisation
• Uterus: where the fetus develops
• Cervix: neck of uterus: a strong
rigid muscle, moist by mucus with
a small opening
• Vagina: receives semen from erect penis during intercourse and way out for baby at birth.

Human sperm Human ovum

Size Small Large

Movement Can move (flagellum to swim) Cannot move. (moved by cilia)
Number Millions constantly produced Once a month (after puberty until
produced menopause)
Adaptive Flagellum – movement/swim Jelly coat – prevents too many sperm from
features Mitochondria – energy getting to the egg at the same time
Enzymes in acrosome - help the sperm get
through the egg's protective coat

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Formation of the fetus – fertilisation and implantation

• Fertilisation happens in the oviduct.

• The sperm nucleus then fuses with the nucleus of the ovum forming a diploid zygote.
• The zygote moves slowly down the oviduct. As it goes, it divides by mitosis to make a ball of
cells called an embryo.
• It implants itself into the wall
of the uterus (implantation).
• Placenta is formed linking the
embryo with the uterus lining.
• Zygote is changed through
growth (increase in size and
dry mass) and development
(increase in complexity) into
fetus.

• Placenta and umbilical cord play a role in exchange of

dissolved nutrients, gases and excretory products and also
provide a barrier to some toxins and pathogens.
• Placenta prevent mixing of blood between mother and fetus.
• Placenta also provide protection from mother’s high blood pressure.
• Umbilical arteries carry carbon dioxide and urea from fetal blood to maternal blood.
• Umbilical vein carries glucose, amino acids, oxygen and antibodies from maternal blood to
fetal blood.
• Amniotic sac: contain or encloses amniotic fluid.
• Amniotic fluid: protects fetus from physical damage, act as shock absorber and prevent
unequal pressures from acting on fetus.

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Antenatal care
Dietary needs The mother’s diet needs to be balanced for the healthy growth and development
of the fetus. Her diet should contain plenty of amino acids, calcium, iron and
energy (carbohydrates/ fats).
Things to avoid Drugs, smoking, alcohol & viruses (can pass across the placenta, risking the
fetus health).

Breast feeding Formula milk

advantages Has antibodies → passive immunity. Other people can easily feed the
Correct temperature. baby.
Builds mother-child bond. May contain additional supplements
No cost/preparation. (vitamins & minerals)
Sterile – no additives/preservatives
disadvantages Painful nipples. Transfer of virus. Mother Expensive. Allergic reactions or
needs to be present. illness.

Stages of birth
1. Hormone oxytocin trigger the contractions of the muscles in the uterus wall, breaking the amniotic sac.
2. Contraction gradually become more frequent.
3. Cervix dilate to allow baby to pass through.
4. The vagina too stretches for the passage of the baby.
5. Umbilical cord is tied and cut.
6. The placenta breaks away from the wall of the uterus and passed out

16.5 Sex hormones in humans

Secondary sexual characteristics at puberty

Male Female
Voice becomes much lower (breaks) Breasts grow, nipples enlarge
Hair start to grow on chest, face, under arms Hair develops under arms and in pubic area
and in pubic area
Body becomes more muscular Hip become wider
Penis becomes larger Uterus and vagina become larger
Testis start to produce sperm Ovaries start to release eggs and period begin
(menstruation)

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Hormone Site of production Functions

Testosterone Testis • Regulates the development of secondary sexual characteristics.

FSH Pituitary gland • Stimulate the development & growth of follicles in ovary.

LH • Stimulate ovulation and the development of corpus luteum.

Oestrogen Follicle cells of ovary • Stimulate the repair of uterus lining to prepare for implantation.
• Inhibit the release of FSH – stops production of more eggs.
• Stimulate the release of LH

Progesterone Corpus luteum • Maintain the thickness of uterus lining to prepare for
implantation.
• Inhibit the release of FSH & LH – prevent development of
follicle and ovulation.
• Prevent menstruation in pregnancy

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16.6 Method of birth control in humans

• There are 4 main groups of birth control methods:
➢ Natural – abstinence, monitoring body temperature and cervical mucus
➢ Chemical – IUD, IUS, contraceptive pill, implant and injection
➢ Mechanical barrier – condom, femidom, diaphragm
➢ Surgical – vasectomy and female sterilization

Artificial insemination (AI)

• Sperm collected from male (donor) inserted into oviduct near the time of ovulation.

In vitro fertilization (IVF)

• Fertilisation by extracting eggs (fertility drugs are used to stimulate multiple release of eggs),
retrieving a sperm sample, and then manually combining an egg and sperm in a
laboratory dish. The embryo(s) is then transferred to the uterus.

16.7 Sexually transmitted infections (STIs)

• STI is an infection that is transmitted via body fluids through sexual contact.
• AIDS (Acquired Immune Deficiency Syndrome) is a disease caused by the HIV (Human
Immunodeficiency Virus).
• It is transported in body fluids. You can only become infected with HIV through direct
contact of your body fluid with those of someone with the virus.

How HIV affects the immune system

• The HIV virus attacks some types of lymphocyte in the blood stream.
• Lymphocytes produce antibodies → attack the antigens on invading microbes.
• HIV prevents this immunity being retained, so the AIDS sufferer has no protection against
diseases such as tuberculosis (TB) and pneumonia.
Methods of transmission Prevention methods
• Unprotected sexual intercourse with • Condom for sexual intercourse
infected person • Refuse sexual intercourse
• Drug use involving sharing needle • Screen blood (for transfusion)
used by infected person • Use sterilized needles
• Transfusion of infected blood • Feed baby with bottled powdered
• Infected mother to fetus (through milk (if mom has HIV)
placenta or breast feeding) • Use sterilised surgical instruments.
• Unsterilized surgical instruments

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Chapter 17: Inheritance

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

17.2 Chromosomes, DNA, genes and proteins

Chromosomes Is a thread-like structure of DNA, carrying genetic information in the form of

genes.
Gene Is a length of DNA that codes for a protein
• The sequence of bases in a gene is the genetic code for putting together
amino acids in the correct order to make a specific protein.

Allele Is a version of a gene

• Alternate forms of
the same gene
occupying the same
relative positions on
a certain pair of
homologous
chromosomes.

Haploid Is a nucleus containing a single set of unpaired chromosomes, e.g. in gametes

nucleus
Diploid Is a nucleus containing two sets of chromosomes, e.g. in body cells
nucleus
Sex in humans XX Female
XY Male

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Protein synthesis
• the gene coding for the protein remains in the nucleus
• mRNA molecules carry a copy of the gene to the cytoplasm
• the mRNA passes through ribosomes
• the ribosome assembles amino acids into protein molecules
• the specific order of amino acids is determined by the
sequence of bases in the mRNA

17.3 Mitosis 17.4 Meiosis

• Mitosis is a nuclear division giving rise to • Meiosis is a reduction division in which
genetically identical cells. the chromosome number is halved from
• Mitosis plays an important role in growth, diploid to haploid resulting in genetically
repair of damage tissues, replacement of different cells.
cells and asexual reproduction. • Meiosis is the way in which gametes (sex
• Exact duplication of chromosomes occurs cells) are produced.
before mitosis. • During meiosis, the new cells get a mixture
• During mitosis, the copies of chromosomes of homologous chromosomes from father
separate, maintaining the chromosome and mother.
number. • There are different sorts of combinations.
• Stem cells are unspecialised cells that divide Gametes are genetically different form the
by mitosis to produce daughter cells that can parent cells. Meiosis produces genetic
become specialised for specific function. variation.

17.5 Monohybrid inheritance

Genotype Is the genetic make-up of an organism in terms
of the alleles present
• E.g. Tt, where T & t are alleles of a gene

Phenotype Is the observable features of an organism

• E.g. a tall plant or a dwarf plant

Dominant Is an allele that is expressed if it is present

• T - to represent the dominant allele for tallness.

Recessive Is an allele that is only expressed when there is

no dominant allele of the gene present
• t - to represent the recessive allele for dwarfness.

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Homozygous Is having two identical alleles of a particular

gene
• Two identical homozygous individuals that breed together
will be pure-breeding
• E.g. TT or tt

Heterozygous Is having two different alleles of a particular

gene
• A heterozygous individual will not be pure-breeding.
• E.g. Tt

Test cross
• The purpose of the test cross is to determine the genetic makeup of the dominant organism.
• The organism with the dominant trait is always crossed with an organism with the recessive
trait
➢ if ANY offspring show the recessive trait, the unknown genotype is heterozygous
➢ if ALL the offspring have the dominant trait, the unknown genotype is homozygous
dominant

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Codominance
• 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 codominance.
• The inheritance of the human ABO blood groups provides an example of codominance.
• The gene controlling human ABO blood groups has three allele (IA, IB, IO )
• IA and IB are codominant but both are dominant to Io

Sex-linked Inheritance
• Sex-linked inheritance is the inheritance genes carried on the sex chromosomes. However,
these genes determine body characters and have nothing to do with sex.
• For example, the character of colour-blindness is found on the X chromosome.
• Sex-linked characteristic as a characteristic in which the gene responsible is located on a sex
chromosome and that this makes it more common in one sex than in the other.

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Chapter 18: Variation and selection

18.1 Variation
• Variation is the differences between individuals of the same species.

Continuous variation Discontinuous variation

Results in range of phenotypes between two Results in a limited number of phenotypes

extremes within a population. with no intermediates.
Controlled by both genes (many different genes) Controlled by one or a few genes.
and environment
Tends to be quantitative. Tends to be qualitative.
E.g. height, weight, foot length and skin colour. E.g. blood group (A, B, AB, O), types of ear
lobes (attached or free), hair (naturally curly
or straight hair) and tongue rolling.

Mutation
• Mutation is a genetic change.
• Mutation is the way in which new alleles are formed.
• 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 ionising radiation or some chemicals (such as tar in tobacco smoke).

Gene mutation
• Is a change in the base sequence of DNA
• Sickle cell anaemia is an example of gene
mutation.

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Sickle cell anaemia

• Sickle cell anaemia is caused by a change in the base sequence of the gene for haemoglobin (gene
mutation) resulting in abnormal haemoglobin and sickle-shaped red blood cells.
• Sickle-shaped red blood cells are less efficient at
transporting oxygen, less flexible and more likely to
become stuck in a capillary, preventing blood flow to
tissues leading to death of tissues.
• The possible genotypes are:
➢ HbAHbA – homozygous dominant → normal
➢ HbAHbS – heterozygous / carrier → sickle cell trait (not life-threatning)
➢ HbSHbS – homozygous recessive → sickle cell anaemia (life-threatening)
• Allele for sickle cell anaemia is recessive; thus, it is only present in the phenotype if two copies of HbS
allele are present (homozygous).
• Sickle cell trait – is an example of codominance, because both HbA and HbS alleles are expressed (in
heterozygous). Both alleles make two different form of haemoglobin.
• The allele for HbS is commonly found in areas where malaria is common. This shows that natural
selection for this gene is occurring in these areas, as people who are heterozygous HbAHbS have
sickle cell trait and have resistance to malaria. HbS continue to appear due to selective advantage.

18.2 Adaptive features

• Adaptive feature is the inherited functional features of an organism that increase its fitness.
• Fitness is the probability of an organism surviving and reproducing in the environment in which
it is found.
• Evolution is the change in adaptive features of a population over time as the result of natural selection.
• The process of adaptation is the process, resulting from natural selection, by which population
become more suited to their environments over many generations.

Adaptive features of hydrophytes

Stems and leave Large air spaces Creates buoyancy – absorb more light for
stalks photosynthesis.
stomata On upper surface Allows diffusion of CO2 for the air for
(floating leaves) photosynthesis.
Cuticle Thin (submerged No need to reduce water loss by evaporation.
leaves)
Submerged leaves highly divided Minimises water resistance & large surface area
for absorption and photosynthesis

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Adaptive features of xerophytes

Roots Long/tap To absorb water from deep down.
Shallow/fibrous To absorb water over wide area
Leaves No/small leaves ↓ the surface area for transpiration
reduced to spines Act as a protection – prevent being eaten.
Roll up in dry weather Trap moisture,
Fine hairs thus ↑ humidity &
Stomata Sunken ↓ transpiration

Open during night only ↓ transpiration

Cuticle Thick waxy Prevent evaporation from leave surface
Stem Fleshy/succulent Store water
Green/chlorophyll For photosynthesis (due to reduction of leaves)

8.3 Selection
Pass on
Adapt Survive Reproduce
favorabel gene
Natural selection

• Individuals within a population have variations.

• When many offspring are produced, not all of them are likely to survive because of
competition for resources such as food, water and shelter. The same is true for plants (they
compete for resources such as nutrients, light, water and space).
• Due to the struggle for survival, those that are poorly adapted to their environment are less
likely to survive and reproduce. This means that their genes are less likely to be passed on to
the next generation.
• Individuals that are better adapted to the environment are more likely to survive and
reproduce passing on of their alleles to the next generation.
• This gradual change in the species through natural selection over time, in response to changes
in the environment, is a possible mechanism for evolution.

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Antibiotic resistance
• This is an example of evolution by natural selection.
• In a large population of bacteria, there may be some that are not affected by an antibiotic.
These survive and reproduce - producing more bacteria that are not affected by the antibiotic.
• The main steps in the development of resistance are:
➢ random mutations occur in the genes of individual bacterial cells
➢ some mutations protect the bacterial cell from the effects of the antibiotic
➢ bacteria without the mutation die and cannot reproduce when the antibiotic is present
➢ resistant bacteria can reproduce with less competition from normal bacterial strains

Artificial selection

• Artificial selection is a method used by humans to produce varieties of animals and plants
which have an increased economic importance.
• Selective breeding by artificial selection is carried out over
many generations to improve crop plants and domesticated
animals. It is a selection by humans of individuals with
desirable features crossing these individuals to produce the
next generation and selecting the offspring that shows the
desirable features.
• These are the main steps involved:
1. decide which characteristics are important enough to select
2. choose parents that show these characteristics
3. choose the best offspring from these parents to produce the
next generation
4. repeat the process continuously

Problems with selective breeding

• Future generations will all share very similar genes. This could
make some diseases more dangerous as all the organisms
would be affected. Also, there is an increased risk of genetic
disease caused by recessive alleles.
• Inbreeding can lead to the loss of alleles from the gene pool,
making it more difficult to produce new varieties in the future.

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Chapter 19: Organisms and their environment

19.1 Energy flow

• The Sun is the principal source of energy input to biological systems.
• Photosynthetic organisms can trap light energy and convert it into chemical energy and its
eventual transfer to the environment.
• Energy flow is a non-cyclical process – once the energy gets to the top of the food chain or
web, it is not recycled but ‘lost’ to the environment.

19.2 Food chains and food webs

Food chain Shows the transfer of energy from one organism to the next, beginning with a
producer. (E.g. maize → locust → lizard → snake)
Food web Is a network of interconnected food chains. A more accurate way of showing
feeding relationships than food chains, because most animals have more than one
food source.
Producer Is an organism that makes its own organic nutrients, usually using energy from
sunlight, through photosynthesis.
Consumer Is an organism that gets its energy from feeding on other organisms. Consumers
may be classed as primary, secondary and tertiary according to their position in a
food chain.
Herbivore Is an animal that get its energy by eating plants.
Carnivore Is an animal that get its energy by eating other animals.
Decomposer Is an organism that gets its energy from dead or waste organic material.
Trophic level Is the position of an organism in a food chain, food web, pyramid of numbers or
pyramid of biomass.

• In term of conversations of energy, there is a greater efficiency in supplying green plants as

human food and a relative inefficiency in feeding crop plants to livestock that will be used
as food.
• Short food chains are more efficient than long ones in providing energy to the top consumer.
• Below are two food chains where human being as the top consumer.
Food chain 1: Maize → cow → human Food chain 2: Maize → human
• More energy is available to the human in the second food chain than in the first.

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Why food chains usually have fewer than 5 trophic levels?

• Only a small percentage of energy from sun is converted to chemical energy by producers.
Not all of the energy plants receive goes into making new cells that can be eaten.
• About 90% of the energy is lost between each trophic level along a food chain. Only 10%
energy is transferred to the next trophic level
• The energy is lost or used through:
➢ making waste products (urine) that get
removed from the organism
➢ as movement
➢ as heat in respiration
➢ as undigested waste (faeces) that is removed
from the body.
• Only small total percentage of energy is reaching forth tropic level and not enough to sustain
another level.

Pyramid of numbers
• Shows the relative number of organisms at each stage of a food chain.

E.g. 1: clover → snail → thrush → hawk E.g. 2: Oak tree → Insects → Woodpecker E.g. 3: Grass → Rabbit → Flea

Pyramid of biomass
• Shows the biomass (total dry mass)
at each trophic level, rather than the
population

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19.3 Nutrient cycles

The carbon cycle

• Main processes involved: photosynthesis, respiration, feeding, decomposition,
fossilisation and combustion.

The water cycle

• Main processes involved: evaporation, transpiration, condensation and precipitation.

Transpiration
Precipitation

Condensation

Evaporation

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The nitrogen cycle

The stages of the nitrogen cycle

• Decomposition of plant and animal protein to ammonium ions.
• Nitrification - Oxidation of ammonia or ammonium to nitrite followed by the oxidation of
the nitrite to nitrate. Nitrifying bacteria convert ammonium into nitrates.
• Nitrogen fixation by lightning and bacteria - Nitrogen is fixed in nature as nitric oxide by
lightning and ultraviolet rays, but more significant amounts of nitrogen are fixed as ammonia,
nitrites, and nitrates by soil microorganisms. (nitrogen-fixing bacteria live freely in the soil.
Others live in the roots nodules of leguminous plants)
• Absorption of nitrate ions by plants - Non-legume plants absorb nitrates from the soil into
their roots and use the nitrates to produce their proteins.
• Production of amino acids and proteins - The plants then use the nitrate ions to produce
proteins from amino acids.
• Feeding and digestion of proteins - Animals consume plant protein, digest it and absorb the
free amino acids.
• Deamination - Animals cannot store excess protein in their bodies. They break it down in the
liver and turn it into waste products and excrete them from their bodies.
• Denitrification - This is when bacteria in the soil convert the nitrate back into nitrogen gas
which then gets released back into the atmosphere.

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19.4 Population size

Population Is a group of organisms of one species, living and interacting in the same area
at the same time.
Community Is all of the populations of different species in an ecosystem.
Ecosystem Is a unit containing the community of organisms and their environment,
interacting together, eg. a decomposing log or a lake.

Factors affecting the rate of population growth for a population of an organism:

• Food supply
• Predation
• Disease

Sigmoid population growth curves

Lag phase • The new population takes time to settle and mature before breeding
begins.

Log (exponential) • No limiting factors

phase • birth rate > death rate

Stationary phase • Limiting factors, such as shortage of food, cause the rate of
reproduction to slow down
• birth rate = death rate

Death phase • birth rate < death rate

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Chapter 20: Biotechnology and genetic engineering

20.1 Biotechnology and genetic engineering

• Microorganisms such as bacteria are useful in biotechnology and genetic engineering because
➢ Rapid reproduction rate and easily grown in a laboratory.
➢ Able to make complex molecules such as proteins.
➢ Lack of ethical concerns over their manipulation and growth.
➢ Bacteria has same genetic code as other organisms.
➢ have plasmids - easy to transfer and move genes from cells to cells.

20.2 Biotechnology
• Biotechnology is the application of biological organisms, systems or processes to
manufacturing and service industries.

Making use of yeast

• Yeast able to respire anaerobically. When it does, it produces ethanol and carbon dioxide.
Yeast are used in the production of ethanol for biofuels (sustainable resource) and bread
making (causing dough to rise).

Making use of enzymes

• Biological washing powders contain enzymes such as proteases (blood stains) and lipases
(oil/ grease)
• Fruit juices are extracted using an enzyme called pectinase. Pectin
is a substance which helps to stick plant cells together. The breaking
down of pectin makes it much easier to squeeze juice from the fruit.
Pectinase is widely used in order to:
➢ increase extraction of juice.
➢ Pectin is converted to sugars so juice is sweeter.
➢ Cell wall material is removed from juice (pectin digested to soluble products)
so the juice is clearer.
• Lactase is an enzyme that breaks down lactose (glucose + galactose), the sugar
found in milk. People with lactose intolerance (their body stops making lactase
meaning they cannot digest lactose) can drink lactose-free milk which can be
produced using lactase.

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Use of microorganisms to manufacture antibiotic penicillin

• Antibiotics are substances which kill bacteria without harming human cells. They help to
cure bacterial infections.
• Penicillin is made by growing the fungus Penicillium in
a large fermenter.

Fermenter (PAWS)
➢ Probes monitor temperature and pH
➢ Air provides oxygen for aerobic respiration in fungus
➢ Water-cooled jacket removes heat to maintain a constant
optimum temperature
➢ Stirrer keeps the microorganism suspended (allowing
access to nutrients and oxygen) while maintaining an
even temperature.

20.3 Genetic engineering

• Genetic engineering is changing the genetic material of an organism by removing,
changing or inserting individual genes.

Genetic engineering using bacterial production of human protein

1. Isolation of the DNA making up a human gene

using restriction enzymes, forming sticky ends.
2. Cutting of bacterial plasmid DNA with the
same restriction enzymes, forming
complementary sticky ends.
3. Insertion of human DNA into bacterial plasmid
DNA using DNA ligase to form a recombinant
plasmid.
4. Insertion of plasmid into bacteria.
5. Replication of bacteria containing recombinant
plasmids which make human protein as they
express the gene.

Examples of genetic engineering:

➢ The insertion of human genes into bacteria to produce human insulin.
➢ The insertion of genes into crop plants to confer resistance to herbicides and insect pests.
➢ The insertion of genes into crop plants to provide additional vitamins.

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Chapter 21: Human influences on ecosystem

21.1 Food supply

Use of modern technology for increasing food production:

• Agricultural machinery is used to clear larger areas of land and to harvest crops to improve
efficiency.
• Chemical fertilisers are used to provide minerals to improve yield of crops.
• Pesticide is a chemical that destroys agricultural pests or competitors:
➢ Herbicides are used to reduce competition (for root space, soil minerals and sunlight)
with weeds.
➢ Insecticides are used to kill insects that eat and damage the crops.
• Selective breeding to improve production by crop plants and livestock, eg. cattle, fish and
poultry.

The negative impact of monocultures:

• When a crop of a single species is grown on the same land, year after year.
• Every attempt is made to destroy organisms that feed on, compete with or infect the crop
plant. The habitat for other species is reduced (deforestation) → Low biodiversity.

The negative impact of livestock production:

• Livestock are kept in small area in a temperature-controlled building to reduce movement and
conserve energy.
• Disease can spread easily among livestock.
• Waste from intensive farming cause pollution if it gets into streams and rivers.
• Overgrazing → soil becomes dry and hard → soil erosion.

Problems which contribute to famine:

• Natural disasters such as flooding and drought
• Increasing population – reduce the land available to produce enough food.
• Unequal distribution of food.
• Urbanisation
• Poor education of farmers and outmoded farming practices.
• Wars & poverty

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21.2 Habitat destruction

Reasons for habitat destruction

• Increased area for food crop growth, livestock production and housing
• Extraction of natural resources
• Marine pollution which damage the habitat.

Deforestation:

• The removal of large numbers of trees to provide land for agriculture and roads, and to
provide timber (wood) for building, furniture and fuel.
• Undesirable effects:
➢ Extinction
➢ Loss of soil
➢ Flooding
➢ Increase of carbon dioxide in the atmosphere

21.3 Pollution

Sources and effect of pollution of land and water.

• Insecticides - enter food chains and accumulate as it moves up them.

• Herbicides - kill aquatic plants, removing the producers from food chains.
• Nuclear fall-out - the radioactive material bioaccumulates in food chains and can cause cancer
(mutation) in top carnivores.

Sources and effects of pollution of water (river, lakes and the sea)

• Chemical waste – waste from factories release into the rivers poisons aquatic organism and
also humans.
• Discarded rubbish – kill aquatic organisms and spread disease.
• Untreated sewage – spread disease like typhoid & cholera and cause eutrophication
• Fertilisers – when nitrates and phosphates from farmland and sewage escape into water they
cause excessive growth of microscopic green plants – eutrophication.

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Eutrophication: The greenhouse effect and global warming:

• When fertilisers and untreated sewage • Light from the sun enters our
leach into the river it causes an increase atmosphere as shortwave radiation in
in the levels of nitrate and phosphate the form of ultraviolet (UV) rays and
in the water which encourages the visible light which passes through the
growth of algae. CO2 layer.
• These algal bloom over the water • The ground heats up and re-emits
surface, preventing sunlight reaching energy as longwave radiation in the
other water plants. These plants die form of heat.
because they are unable to carry out • This heat is trapped in atmosphere by
photosynthesis. greenhouse gases such as carbon
• Decomposition increase after the death dioxide and methane.
of producers. • Open burning, deforestration and
• Decomposers respire aerobically using combustion of fossil fules - Increase of
up the dissolved oxygen in the water. carbon dioxide in the atmosphere.
• The low oxygen levels make it difficult • Additional amounts of these gases lead
for aquatic animals to live, and to more heat being trapped enhancing
eventually the lake may be left the greenhouse effect.
completely lifeless. • This extra heat causes global warming
that leads to climate change.

Effects of non-biodegradable plastics in the environment, in both aquatic and terrestrial

ecosystems:
• Plastics that are non-biodegradable are not decomposed by decomposers.
• When plastics are accidentally ingested by marine organisms they stay in the gut or prevent
the gills from working efficiently.
• Some marine organisms get trapped or stuck around the plastics.
• Floating plastics also blocks light for photosynthesis.
• Plastics also block the flow of water in streams and rivers.
• Plastics dumped in landfill sites or left as litter remain in the environment, taking up
valuable space or causing visual pollution.
• When plastic is burned, it can release toxic gases.

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Causes and effects on the environment of acid rain Pollution by female contraceptive
• Burning of fossil fuels, power stations and hormones
factories release sulfur dioxide and oxides of • When women use the
nitrogen into the atmosphere. contraceptive pill, the hormones in
• These gases are carried by the wind and it are excreted in urine and become
combines with water vapour in the air to present in sewage.
form acids and fall to the ground as acid rain. • The process of sewage treatment
• Effects – damage leaves & killing the plant, does not remove the hormones, so
acidification of lakes & killing aquatic they end up in water systems.
organisms, corrosion of stone work on • Their presence in this water causes
buildings, release of aluminum from the soil feminisation in aquatic
into the lakes that are toxic to fish → loss of organisms and reduce the sperm
biodiversity and disrupts the food chains. count in men.

21.4 Conservation

• Sustainable resource is one that is produced as rapidly as it is removed from the

environment so that it does not run out.
• Sustainable development is development providing for the needs of an increasing human
population without harming the environment.
➢ it needs to management of conflicting demands and involves planning &
cooperation done at local, national and international levels.
• Non-renewable resources such as fossil fuels need to be conserved because the stocks of them
on the planet are finite. It can be conserved in the following ways:
➢ By increasing the use of renewable energy
➢ By improving the efficiency of energy use (better insulation, smaller car engines,
more public transport).

Sustaining forest and fish stocks:

• Resources such as forests and fish stocks can be maintained with careful management. There
are three main ways of sustaining them.
• These are:
➢ Education
➢ Legal quotas
➢ Restocking

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Recycling:

• Products such as paper, glass, plastic and metal can be reused or recycled.

Sewage treatment:

• Large object such as sticks screened out of raw sewage.

• Suspended grit (sand) allowed to settle out by gravity in grit settling tank.
• Organic matter allowed to settle out by gravity in sludge-settling tank – after anaerobic
digestion in a sludge digester, sludge can be used as fertiliser on farmland – methane gas can
also be generated for use as a fuel.
• Remaining liquid sprinkled on to the aeration tank where microbes on surface of stones digest
any remaining organic matter.
• Water passing out will be chlorinated to kill any bacteria, so it is safe to drink.

Organisms become endangered or extinctic Endangered species (at risk of extinction) can be
due to: conserved by:
• Climate change • Monitoring and protecting species and
• Habitat destruction habitats
• Pollution • Education
• Introduced species • Captive breeding programmes
• Hunting • Seed banks

Reasons for conservation programmes:

• Reducing extinction
• Protecting vulnerable environments
• Maintaining ecosystem functions
➢ Nutrient cycling and resource provision (e.g. food, drugs, fuel and genes)

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EXERCISES

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