IGCSE Biology - Keypoints
APRIL 18, 2016
COPYRIGHTED DOCUMENT
1 . Characteristic & Classification of Living Organisms
a.Describe the characteristics of living organisms by defining the terms:
Movement is an action by an organism or part of an organism causing a change of position or place.
Respiration describes the chemical reactions in cells that break down nutrient molecules and release energy for
metabolism.
Sensitivity is the ability to detect or sense stimuli in the internal or external environment and to make appropriate
responses.
Growth is a permanent increase in size and dry mass by an increase in cell number or cell size or both.
Excretion is the removal from organisms of the waste products of metabolism (chemical reactions in cells including
Respiration), toxic materials and substances in excess of requirements.
Nutrition is the taking in of materials for energy, growth and development. Plants require light, carbon dioxide, water
and ions. Animals need organic compounds and ions and usually need water.
Photosynthetic plants are called autotrophs and are usually the first organisms in food chains.
Species is a group of organisms that can reproduce to produce fertile offspring.
Binomial system is an internationally agreed system in which the scientific name of an organism is made up of two parts
showing the genus and the species
b. State that organisms can be cl assified into groups by the features that they share
A biologist looks for a natural system of classification using important features which are shared by as large a group as
possible. Birds all have wings, beaks and feathers; there is rarely any doubt about whether a creature is a bird or not. In
other cases it is not so easy. As a result, biologists change their ideas from time to time about how living things should
be grouped. New groupings are suggested and old ones abandoned.
c. Explain that classification systems aim to reflect evolutiona ry relationships
By classifying organisms it is also possible to understand evolutionary relationships. Vertebrates all have the presence of
a vertebral column, along with a skull protecting a brain, and a pair of jaws (usually with teeth). By studying the anatomy
of different groups of vertebrates it is possible to gain an insight into their evolution.
d. Explain that classification is traditionally based on studies of morphology and anatomy
Classification is traditionally based on studies of morphology (the study of the form, or outward appearance, of
organisms) and anatomy (the study of their internal structure, as revealed by dissection).
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e. Define and describe the binomial system
The binomial system of naming species is an internationally agreed system in which the scientific name of an organism is
made up of two parts showing the genus and the species. Binomial means ‘two names’; the first name gives the genus
and the second gives the species. For example, the stoat and weasel are both in the genus Mustela but they are
different species; the stoat is Mustela erminea and the weasel is Mustela nivalis.The name of the genus (the generic
name) is always given a capital letter and the name of the species (the specific name) always starts with a small letter.
Frequently, the specific name is descriptive, for example edulis means ‘edible’, aquatilis means ‘living in water’, bulbosus
means ‘having a bulb’, serratus means ‘having a jagged (serrated) edge’.
f. Explain that the sequences of bases in DNA and of amino acids in proteins are used as a more accurate
means of classification and explain that 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.
The use of DNA has revolutionized the process of classification. Eukaryotic organisms contain chromosomes made up of
strings of genes. The chemical which forms these genes is called DNA. The DNA is made up of a sequence of bases,
coding for amino acids and, therefore, proteins. Each species has a distinct number of chromosomes and a unique
sequence of bases in its DNA, making it identifiable and distinguishable from other species. This helps particularly when
different species are very similar morphologically (in appearance) and anatomically (in internal structure). The process of
biological classification called cladistics involves organisms being grouped together according to whether or not they
have one or more shared unique characteristics derived from the group’s last common ancestor, which are not present
in more distant ancestors. Organisms which share a more recent ancestor (and are, therefore, more closely related)
have DNA base sequences that are more similar than those that share only a distant ancestor.
g.List the features in the cells of all living organisms, limited to cytoplasm, cell membrane and DNA as
genetic material
All living organisms have certain features in common, including the presence of cytoplasm and cell membranes, and DNA
as genetic material.
h.List the features in the cells of all living organisms, limited to ribosomes for protein synthesis and enzymes
involved in respiration
All living organisms also contain ribosomes in the cytoplasm, floating freely or attached to membranes called rough
endoplasmic reticulum (ER). Ribosomes are responsible for protein synthesis.
i. List the main features used to place all organisms into one of the five kingdoms: Animal, Plant, Fungus,
Prokaryote, and Protoctist.
The Animal kingdom
Animals are multicellular organisms whose cells have no cell walls or chloroplasts. Most animals ingest solid food and
digest it internally.
Arthropods
The name arthropod means ‘jointed limbs’, and this is a feature common to them all. They also have a hard, firm
external skeleton, called a cuticle, which encloses their bodies. Their bodies are segmented and, between the segments,
there are flexible joints which permit movement. In most arthropods, the segments are grouped together to form
distinct regions, the head, thorax and abdomen.
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1. Crustacea
Like all arthropods, crustacea have an exoskeleton and jointed legs. They also have two pairs of antennae which are
sensitive to touch and to chemicals, and they have compound eyes. Compound eyes are made up of tens or hundreds of
separate lenses with light‐sensitive cells beneath. They are able to form a crude image and are very sensitive to
movement. Typically, crustacea have a pair of jointed limbs on each segment of the body, but those on the head
segments are modified to form antennae or specialised mouth parts for feeding.
2. Insects
Insects have segmented bodies with a firm exoskeleton, three pairs of jointed legs, compound eyes and, typically, two
pairs of wings. The segments are grouped into distinct head, thorax and abdomen regions. Insects differ from crustacea
in having wings, only one pair of antennae and only three pairs of legs. There are no limbs on the abdominal segments.
The insects have very successfully colonised the land. One reason for their success is the relative impermeability of their
cuticles, which prevents desiccation even in very hot, dry climates.
3. Arachnids
Their bodies are divided into two regions, the cephalothorax and the abdomen. They have four pairs of limbs on the
cephalothorax, two pedipalps and two chelicerae. The pedipalps are used in reproduction; the chelicerae are used to
pierce their prey and paralyse it with a poison secreted by a gland at the base. There are usually several pairs of simple
eyes.
4. Myriapods
They have a head and a segmented body which is not obviously divided into thorax and abdomen. There is a pair of legs
on each body segment but in the millipede the abdominal segments are fused in pairs and it looks as if it has two pairs of
legs per segment. As the myriapod grows, additional segments are formed. The myriapods have one pair of antennae
and simple eyes.
Vertebrates
Vertebrates are animals which have a vertebral column. The vertebral column is sometimes called the spinal column or
just the spine and consists of a chain of cylindrical bones (vertebrae) joined end to end. So‐called ‘warm‐blooded’
animals, for the most part, have a body temperature higher than that of their surroundings. The main difference,
however, is that these temperatures are kept more or less constant despite any variation in external temperature. There
are internal regulatory mechanisms (see Chapter 14) which keep the body temperature within narrow limits. It is better
to use the terms poikilothermic (variable temperature) and homoiothermic (constant temperature). However, to
simplify the terms, ‘cold blooded’ and ‘warm blooded’ will be referred to in this section.
1. Fish
Fish are poikilothermic (cold blooded) vertebrates. Many of them have a smooth, streamlined shape which offers
minimal resistance to the water through which they move . Their bodies are covered with overlapping
scales and they have fins which play a part in movement. Fish breathe by means of filamentous gills which are protected
by a bony plate, the operculum. Fish reproduce sexually but fertilisation usually takes place externally; the female lays
eggs and the male sheds sperms on them after they have been laid.
2. Amphibia
Amphibia are poikilothermic (cold blooded) vertebrates with four limbs and no scales. The class includes frogs, toads
and newts. The name, amphibian, means ‘double life’ and refers to the fact that the organism spends part of its life in
water and part on the land. In fact, most frogs, toads and newts spend much of their time on the land, in moist
situations, and return to ponds or other water only to lay eggs.
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Extensions (Difference between newts, frogs and toads)
Amphibia have four limbs. In frogs and toads, the hind feet have a web of skin between the toes. This offers a large
surface area to thrust against the water when the animal is swimming. Newts swim by a wriggling, fish‐like movement of
their bodies and make less use of their limbs for swimming. Amphibia have moist skins with a good supply of capillaries
which can exchange oxygen and carbon dioxide with the air or water. They also have lungs which can be inflated by a
kind of swallowing action. They do not have a diaphragm or ribs. Frogs and toads migrate to ponds where the males and
females pair up. The male climbs on the female’s back and grips firmly with his front legs. When the female lays eggs,
the male simultaneously releases sperms over them. Fertilisation, therefore, is external even though the frogs are in
close contact for the event.
3. Reptiles
Reptiles are land‐living vertebrates. Their skins are dry and the outer layer of epidermis forms a pattern of scales. This
dry, scaly skin resists water loss. Also the eggs of most species have a tough, parchment like shell. Reptiles, therefore,
are not restricted to damp habitats, nor do they need water in which to breed. Reptiles are poikilothermic (cold
blooded) but they can regulate their temperature to some extent. They do this by basking in the sun until their bodies
warm up. When reptiles warm up, they can move about rapidly in pursuit of insects and other prey.
4. Birds
Birds are homoiothermic (warm blooded) vertebrates. The vertebral column in the neck is flexible but the rest of the
vertebrae are fused to form a rigid structure. This is probably an adaptation to flight, as the powerful wing muscles need
a rigid frame to work against. The epidermis over most of the body produces a covering of feathers but, on the legs and
toes, the epidermis forms scales. The feathers are of several kinds. The fluffy down feathers form an insulating layer
close to the skin; the contour feathers cover the body and give the bird its shape and colouration; the large quill feathers
on the wing are essential for flight. Birds have four limbs, but the forelimbs are modified to form wings. The feet have
four toes with claws which help the bird to perch, scratch for seeds or capture prey, according to the species. The upper
and lower jaws are extended to form a beak which is used for feeding in various ways. In birds, fertilisation is internal
and the female lays hard‐shelled eggs in a nest where she incubates them.
5. Mammals
Mammals are homoiothermic (warm blooded) vertebrates with four limbs. They differ from birds in having hair rather
than feathers. Unlike the other vertebrates they have a diaphragm which plays a part in breathing. They also have
mammary glands and suckle their young on milk. Humans are mammals. All mammals give birth to fully formed young
instead of laying eggs. The eggs are fertilized internally and undergo a period of development in the uterus. In either
case, the youngster’s first food is the milk which it sucks from the mother’s teats. The milk is made in the mammary
glands and contains all the nutrients that the offspring need for the first few weeks or months, depending on the
species. As the youngsters get older, they start to feed on the same food as the parents. In the case of carnivores, the
parents bring the food to the young until they are able to fend for themselve.
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The plant kingdom
It is useful to have an overview of the classification of the plant kingdom, although only two groups (ferns and flowering
plants) will be tested in the examination.
1. Ferns
Ferns are land plants with quite highly developed structures. Their stems, leaves and roots are very similar to those of
the flowering plants. The stem is usually entirely below ground and takes the form of a structure called a rhizome. In
bracken, the rhizome grows horizontally below ground, sending up leaves at intervals. The roots which grow from the
rhizome are called adventitious roots. This is the name given to any roots which grow directly from the stem rather than
from other roots. The stem and leaves have sieve tubes and water conducting cells similar to those in the xylem and
phloem of a flowering plant (see Chapter 8). For this reason, the ferns and seed‐bearing plants are sometimes referred
to as vascular plants, because they all have vascular bundles or vascular tissue. Ferns also have multicellular roots with
vascular tissue. The leaves of ferns vary from one species to another, but they are all several cells thick. Most of them
have an upper and lower epidermis, a layer of palisade cells and a spongy mesophyll similar to the leaves of a flowering
plant. Ferns produce gametes but no seeds. The zygote gives rise to the fern plant, which then produces single‐celled
spores from numerous sporangia (spore capsules) on its leaves. The sporangia are formed on the lower side of the leaf
but their position depends on the species of fern. The sporangia are usually arranged in compact groups.
2. Flowering plants
Flowering plants reproduce by seeds which are formed in flowers. The seeds are enclosed in an ovary. Flowering plants
are divided into two subclasses: monocotyledons and dicotyledons. Monocotyledons (monocots for short), are flowering
plants which have only one cotyledon in their seeds. Most, but not all, monocots also have long, narrow leaves (e.g.
grasses, daffodils, and bluebells) with parallel leaf veins.
The dicotyledons (dicots for short), have two cotyledons in their seeds. Their leaves are usually broad and the leaf veins
form a branching network.
The fungi kingdom
Most fungi are made up of thread‐like hyphae, rather than cells, and there are many nuclei distributed throughout the
cytoplasm in their hyphae. There are also the less obvious, but very important, mould fungi which grow on stale bread,
cheese, fruit or other food. Many of the mould fungi live in the soil or in dead wood. The yeasts are single‐celled fungi
similar to the moulds in some respects.
The Prokaryote kingdom
These are the bacteria and the blue‐green algae. They consist of single cells but differ from other single‐celled organisms
because their chromosomes are not organized into a nucleus.
Bacterial structure
Bacteria (singular: bacterium) are very small organisms consisting of single cells rarely more than 0.01 mm in length.
They can be seen only with the higher powers of the microscope. Their cell walls are made, not of cellulose, but of a
complex mixture of proteins, sugars and lipids. Some bacteria have a slime capsule outside their cell wall. Inside the cell
wall is the cytoplasm, which may contain granules of glycogen, lipid and other food reserves.
Each bacterial cell contains a single chromosome, consisting of a circular strand of DNA (see Chapter 4 and
‘Chromosomes, genes and proteins. The chromosome is not enclosed in a nuclear membrane but is coiled up to occupy
part of the cell.
Individual bacteria may be spherical, rod‐shaped or spiral and some have fi laments, called flagella, projecting from
them. The flagella can flick and so move the bacterial cell about.
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The Protoctist kingdom
These are single‐celled (unicellular) organisms which have their chromosomes enclosed in a nuclear membrane to form
a nucleus. Some of the protoctista, e.g. Euglena, possess chloroplasts and make their food by photosynthesis. These
protoctista are often referred to as unicellular ‘plants’ or protophyta. Organisms such as Amoeba and Paramecium take
in and digest solid food and thus resemble animals in their feeding. They may be called unicellular ‘animals’ or protozoa.
Amoeba is a protozoan which moves by a fl owing movement of its cytoplasm. It feeds by picking up bacteria and other
microscopic organisms as it goes. Vorticella has a contractile stalk and feeds by creating a current of water with its cilia.
The current brings particles of food to the cell. Euglena and Chlamydomonas have chloroplasts in their cells and feed,
like plants, by photosynthesis.
Viruses
There are many different types of virus and they vary in their shape and structure. All viruses, however, have a central
core of RNA or DNA (see Chapter 4) surrounded by a protein coat. Viruses have no nucleus, cytoplasm, cell organelles or
cell membrane, though some forms have a membrane outside their protein coats. Virus particles, therefore, are not
cells. They do not feed, respire, excrete or grow and it is debatable whether they can be classed as living organisms.
Viruses do reproduce, but only inside the cells of living organisms, using materials provided by the host cell. The nucleic
acid core is a coiled single strand of RNA. The coat is made up of regularly packed protein units called capsomeres each
containing many protein molecules. The protein coat is called a capsid.
2 . Organization of the Organism
a. Describe and compare the structure of a plant cell with an animal cell, as seen under a light microscope,
limited to cell wall, nucleus, cytoplasm, chloroplasts, vacuoles and location of the cell membrane
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b. State the functions of the structures seen under the light microscope in the plant cell and in the animal
cell
Organelles
Location
Description
Function
only in plant cell
Permeable, rigid outer layer,
nonliving and stiff
Protect the cell, provide shape and
rigidity
Cell
membrane
both plant cell and
animal cell
semipermeable, outer layer in
animal cell
control the movement of substances
in and out of the cell
Nucleus
both plant cell and
animal cell
Cytoplasm
both plant cell and
animal cell
membrane bounded organelle,
chromosomes are found inside
the nucleus
fluid matrix , all cell organelles
are seen in the cytoplasm
Mitochondria
both plant cell and
animal cell
Endoplasmic
reticulum
both plant cell and
animal cell
Ribosome
both plant cell and
animal cell
Golgi bodies
both plant cell and
animal cell
Cell wall
only in plant cell
Chloroplast
Vacuole
present in plant cell,
but in animal cell its
small or absent
rod-shaped organelles,
considered the power generators
of the cell
network of folded tubes and
membrane
small bodies floating free or
attached in the endoplasmic
reticulum
control the activities of the cell
all the bio chemical reactions occurs in
the cytoplasm
breakdown of glucose and release of
energy
carries proteins and other substances
from one part to the other
synthesis of proteins
flattened sacs or tubes
receives proteins and other materials
from the endoplasmic reticulum
green oval structure, containing
chlorophyll
carried out photosynthesis, convert
light energy into chemical energy
fluid filled sacs
storage area of the cell
c. State that the cytoplasm of all cells contains structures, limited to ribosomes on rough endoplasmic
reticulum and vesicles
Organelles present include the rough endoplasmic reticulum, a network of flattened cavities surrounded by a
membrane, which links with the nuclear membrane. The membrane holds ribosomes, giving its surface a rough
appearance. Rough endoplasmic reticulum has the function of producing, transporting and storing proteins. Ribosomes
can also be found free in the cytoplasm. They build up the cell’s proteins.
All living organisms also contain ribosomes in the cytoplasm, floating freely or attached to membranes called rough
endoplasmic reticulum (ER). Ribosomes are responsible for protein synthesis
d. State that almost all cells, except prokaryotes, have mitochondria and rough endoplasmic reticulum, state
that aerobic respiration occurs in mitochondria and also state that cells with high rates of metabolism
require large numbers of mitochondria to provide sufficient energy.
Mitochondria are tiny organelles, which may appear slipper‐shaped, circular or oval when viewed in section. In three
dimensions, they may be spherical, rod‐like or elongated. They have an outer membrane and an inner membrane with
many inward‐pointing folds. Mitochondria are most numerous in regions of rapid chemical activity and are responsible
for producing energy from food substances through the process of aerobic respiration. Note that prokaryotes do not
possess mitochondria or rough endoplasmic reticulum in their cytoplasm.
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e. Specialised cells
Most cells, when they have finished dividing and growing, become specialised. When cells are specialised: l they do one
particular job l they develop a distinct shape l special kinds of chemical change take place in their cytoplasm. The
changes in shape and the chemical reactions enable the cell to carry out its special function. Red blood cells and root
hair cells are just two examples of specialised cells.
The specialisation of cells to carry out particular functions in an organism is sometimes referred to as ‘division of labour’
within the organism.
1. Ciliated cells
These cells form the lining of the nose and windpipe,
and the tiny cytoplasmic ‘hairs’, called cilia, are in a
continual flicking movement which creates a stream of
fluid (mucus) that carries dust and bacteria through
the bronchi and trachea, away from the lungs.
2. Root hair cells
These cells absorb water and mineral salts from the soil. The hair‐
like projection on each cell penetrates between the soil particles
and offers a large absorbing surface. The cell membrane is able to
control which dissolved substances enter the cell
3. Xylem vessels
These cells transport mineral ions from the roots to the leaves. A substance called
lignin impregnates and thickens the cell walls making the cells very strong and
impermeable. This gives the stem strength. The lignin forms distinctive patterns in
the vessels – spirals, ladder shapes, reticulate (net‐like) and pitted. Xylem vessels are
made up of a series of long xylem cells joined end‐to‐end. Once a region of the plant
has stopped growing, the end walls of the cells are digested away to form a
continuous, fine tube. The lignin thickening prevents the free passage of water and
nutrients, so the cytoplasm in the cells dies. Effectively, the cells form long, thin,
strong straws.
4. Palisade mesophyll cells
These are found underneath the upper epidermis of plant
leaves. They are columnar (quite long) and packed with
chloroplasts to trap light energy. Their function is to make
food for the plant by photosynthesis using carbon dioxide,
water and light energy.
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5. Nerve cells
These cells are specialised for conducting electrical impulses
along the fiber, to and from the brain and spinal cord. The fibers
are often very long and connect distant parts of the body to the
CNS, e.g. the foot and the spinal column. Chemical reactions
cause the impulses to travel along the fiber.
6. Red blood cells
These cells are distinctive because they have no nucleus when mature. They
are tiny disc‐like cells which contain a red pigment called haemoglobin. This
readily combines with oxygen and their function is the transport of oxygen
around the body.
7. Sperm cell
Sperm cells are male sex cells. The front of the cell is oval shaped and
contains a nucleus which carries genetic information. There is a tip, called an
acrosome, which secretes enzymes to digest the cells around an egg and the
egg membrane. Behind this is a mid‐piece which is packed with
mitochondria to provide energy for movement. The tail moves with a whip‐
like action enabling the sperm to swim. Their function is reproduction,
achieved by fertilising an egg cell.
8. Egg cell
Egg cells (ova, singular: ovum) are larger than sperm cells
and are spherical. They have a large amount of cytoplasm,
containing yolk droplets made up of protein and fat. The
nucleus carries genetic information. The function of the egg
cell is reproduction.
f. Define tissue
A group of cells with similar structures, working together to perform a shared function.
g. Define organ
A structure made up of a group of tissues, working together to perform specific functions.
h. Define organ system
A group of organs with related functions, working together to perform body functions.
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3 . Movement In and Out of Cells
a. Define diffusion
The net movement of particles from a region of their higher concentration to a region of their lower concentration down
a concentration gradient, as a result of their random movement
b. State that the energy for diffusion comes from the kinetic energy of random movement of molecules and
ions
The energy for diffusion comes from the kinetic energy of random movement of molecules and ions. The speed with
which a substance diffuses through a cell wall/membrane will depend on temperature and many other conditions such
as:
1. Difference in concentration inside and outside the cell
2. Size of molecules
3. Surface area
c. Describe the importance of diffusion of gases and solutes
1. For respiration ‐ O2 and CO2
2. For photosynthesis – need carbon dioxide
3. Transpiration – water vapour
4. Mineral ion such as nitrates and magnesium – it diffuses through
the plant’s root
5. In ileum, vitamins such as vitamin B and C are absorbed in the
blood
6. In the kidneys, some solutes in the renal capsule, such as urea and
salts, pass back into the bloodstream by diffusion.
7. Initially, glucose is reabsorbed by diffusion, but active transport is
also involved.
8. Dialysis machines use diffusion to remove small solutes (urea, uric
acid and excess salts) from the blood.
d. Define osmosis
The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower
water potential (concentrated solution), through a partially permeable membrane
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e. Explain the effects on plant tissues of immersing them in solutions of different concentrations by using the
terms turgid, turgor pressure, plasmolysis and flaccid.
Plants do not burst in pure water. Plant cells are surrounded by a
cell wall. This is fully permeable, which means it will let any
molecules go through it. A plant cell in pure water will take in
water by osmosis through its partially permeable cell membrane in
the same way an animal cell. As the water goes in, the cytoplasm
and the vacuole will swell.
The cell wall is strong so it prevent the cell from bursting. A plant
cell in this state is rather like a blown‐up tyre – tight and firm. It is
said to be turgid. The cytoplasm shrinks, and stops pushing
outwards on the cell wall. Like a tyre when some of the air has leaked out, the cell becomes floppy. It is said to be
flaccid. If the cell becomes flaccid, the plant loses its firmness and begin to wilt.
When the cytoplasm and vacuole keeps shrinking and then the cytoplasm shrinks further into the center of the cell, the
cell wall gets left behind. The cell membrane, surrounding the cytoplasm tears away from the cell wall. A cell like this is
called plasmolysed. Plasmolysis usually kills the plant because the cell membrane is damaged as it tears away from the
cell wall.
f. Explain the importance of water potential and osmosis in the uptake of water by plants and on animal
cells and tissues
1. Plants
A plant cell with the vacuole pushing out on the cell wall is said to be turgid and the vacuole is exerting turgor pressure
on the inelastic cell wall. If all the cells in a leaf and stem are turgid, the stem will be firm and upright and the leaves held
out straight. If the vacuoles lose water for any reason, the cells will lose their turgor and become flaccid. If a plant has
flaccid cells, the leaves will be limp and the stem will droop. A plant which loses water to this extent is said to be
‘wilting’.
Root hair cells are in contact with water trapped between soil particles. When the water potential of the cell sap is lower
than that of the soil water, the water will enter the cells by osmosis providing the plant with the water it needs.
2. Animal cells and tissues
It is vital that the fluid which bathes cells in animals, such as tissue fluid or blood plasma, has the same water potential
as the cell contents. This prevents any net flow of water into or out of the cells. If the bathing fluid has a higher water
potential (a weaker concentration) than the cells, water will move into the cells by osmosis causing them to swell up. As
animal cells have no cell wall and the membrane has little strength, water would continue to enter and the cells will
eventually burst.
They avoid bursting by possessing a contractile vacuole. This collects the water as it enters the cell and periodically
releases it through the cell membrane, effectively baling the cell out.
g. Explain how plants are supported by the turgor pressure within cells, in terms of water pressure acting
against an inelastic cell wall
When plant cells have absorbed maximum amount of water by osmosis, they become very rigid due to the pressure
outwards on the cell wall. The end is that the stems and leaves are supported. When no pressure of water is pressing
outwards on the cell wall, at this point the plant becomes limp and wilts.
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h. Define active transport
The movement of particles through a cell membrane from a region of lower concentration to a region of higher
concentration using energy from respiration.
i. Discuss the importance of active transport as a process for movement across membranes
If diffusion were the only method by which a cell could take in substances, it would have no control over what went in or
out. Anything that was more concentrated outside would diffuse into the cell whether it was harmful or not. Substances
which the cell needed would diffuse out as soon as their concentration inside the cell rose above that outside it. The cell
membrane, however, has a great deal of control over the substances which enter and leave the cell. For example: ‐ ion
uptake by root hairs and uptake of glucose by epithelial cells of villi and kidney tubules.
j. Explain how protein molecules move particles across a membrane during active transport
The carrier molecules are protein molecules. They are responsible for transporting substances across the membrane
during active transport.
First the molecule or ion combines with a carrier protein. Energy from respiration enables the carrier protein to change
its shape to carry the ion or molecule to the inside of the membrane. The molecule or ion is released to the inside of the
membrane and the carrier protein reverts to its original shape
4 . Biological Molecules
a. List the chemical elements that make up:
– carbohydrates
– fats
– proteins
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b. Describe the use of:
– iodine solution to test for starch
– Benedict’s solution to test for reducing sugars
Test for:‐
Starch
Reducing sugars
Proteins
– biuret test for proteins
– ethanol emulsion test for fats and oils
– DCPIP test for vitamin C
Solution used
Procedure
Final result
Iodine solution
Half fill a test tube with
food extract you wish to
test for starch.
Add 2/3 drops of iodine
solution
A positive result for starch
is if the iodine solution
turns to blue black from
yellow brown
Benedict’s solution
Put a known value of the
extract you wish to test for
reducing sugars and place a
beaker on a heat proof
mat. Then half fill the
beaker with boiling water
and the same volume of
benedict’s solution
A positive test for reducing
sugars is if solution turns
red
Half fill a test tube with
food extract you wish to
test for proteins. Add 5/6
of biuret solution
A positive test for proteins
is if the biuret solution
turns purple/lilac from blue
color.
Safety: Take care as NaOH
is corrosive
Biuret test
Fats and oils
Ethanol emulsion
Vitamin C
DCPIP test
Chop up or grind a small
amount of material you
wish to test for fats. Put
the extract into a clean test
tube and add enough
ethanol to cover it and
then put a stopper and
shake it and add distilled
water then shake it again
Grind or chop a small
amount and put it into a
test tube. Add a similar
amount of distilled water
and stir with glass rod. One
drop at a time, to a test
tube containing a light blue
solution of DCPIP. If the
extract is acid the colour
will change from blue to
red. Continue to add more
and see if the colour
disappears altogether
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A white emulsion that
looks cloudy white/milk
color is a positive test for
fats.
Decolourisation of DCPIP
shows that a vitamin C is
probably present.
c. Explain that different sequences of amino acids give different shapes to protein molecules
Protein molecules are made up of long chains of simpler chemicals called amino acids. There are about 20 different
amino acids in animal proteins, including alanine, leucine, valine, glutamine, cysteine, glycine and lysine. (No need of
remembering these names). Each type of protein has its amino acids arranged in a particular sequence. The chain of
amino acids in a protein takes up a particular shape as a result of cross‐linkages.
d. Relate the shape and structure of protein molecules to their function, limited to the active site of enzymes
and the binding site of antibodies.
1. Enzymes
The shape of a protein molecule has a very important effect on its reactions with substances, as explained in ‘Enzymes’.
For example, the shape of an enzyme molecule creates an active site, which has a complementary shape to the
substrate molecule on which it acts. This makes enzymes very specific in their action.
2. Antibodies
Antibodies are proteins produced by white blood cells called lymphocytes. Each antibody has a binding site, which can
lock onto pathogens such as bacteria. This destroys the pathogen directly, or marks it so that it can be detected by other
white blood cells called phagocytes. Each pathogen has antigens on its surface that are a particular shape, so specific
antibodies with complementary shapes to the antigen are needed.
e. Describe the structure of DNA as:
‐ two strands coiled together to form a double helix
‐ each strand contains chemicals called bases
‐ cross‐links between the strands are formed by pairs of bases
‐ the bases always pair up in the same way: A with T, and C with G (full names are not required)
A DNA molecule is made up of long chains of nucleotides, formed into two strands. A nucleotide is a 5‐carbon sugar
molecule joined to a phosphate group and an organic base. In DNA the sugar is deoxyribose and the organic base is
either adenine (A), thymine (T), cytosine (C) or guanine (G).The nucleotides are joined by their phosphate groups to form
a long chain, often thousands of nucleotides long.
The phosphate and sugar molecules are the same all the way down the chain but the bases may be any one of the four
listed above. The DNA in a chromosome consists of two strands (chains of nucleotides) held together by chemical bonds
between the bases. The size of the molecules ensures that A (adenine) always pairs with T (thymine) and C (cytosine)
pairs with G (guanine). The double
strand is twisted to form a helix (like a
twisted rope ladder with the base
pairs representing the rungs)
Note: for exam purposes, it is only
necessary to be able state the letters,
not the names of these bases.
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f. Describe the roles of water as a solvent in organisms with respect to digestion, excretion and transport
1. Excretion
Water plays an important role in excretion in animals. It acts as a powerful solvent for excretory materials, such as
nitrogenous molecules like urea, as well as salts, spent hormones and drugs. The water has a diluting effect, reducing
the toxicity of the excretory materials.
2. Digestion
In animals, water helps to break down and dissolve food molecules (see ‘Chemical digestion’ in Chapter 7).
3. Transport
Blood is made up of cells and a liquid called plasma. This plasma is 92% water and acts as a transport medium for many
dissolved substances, such as carbon dioxide, urea, digested food and hormones. Blood cells are carried around the
body in the plasma.
Note: Water is important as a solvent
5 . Enzymes
Catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction
Enzymes is a protein that function as biological catalysts
a. Describe why enzymes are important in all living organisms in terms of reaction speed necessary to
sustain life
Enzymes operate by lowering the activation energy of the reaction by providing alternate pathway for the reaction. This
saves the energy required to overcome the high activation energy levels and also increases the rates of the reactions.
Without the heightened rate of reactions, the human body (or animal bodies) will not be able to carry out the chemical
reactions at a fast enough rate to sustain life. It is estimated that enzymes speed up bodily reactions by about 1 million
times as compared to body without enzymes. Hence, enzymes enable our survival by increasing the rate of reactions.
b. Explain enzyme action with reference to the active site, enzyme‐substrate complex, substrate and product
The substance present at the beginning of reaction is called substrate and the substance which is made by the reaction
is called the product. [Example: Amylase has a dent that is called Active Site. This has a shape complementary to the
shape of part of a starch molecule. The starch fits into the active site of amylase forming an enzyme‐substrate complex.
When the starch molecule fits into the active site, the enzyme breaks it apart.]
c. Explain the specificity of enzymes in terms of the complementary shape and fit of the active site with the
substrate
Each enzyme has an active site that fits exactly its substrate. Meaning that each enzyme can only act on a
particular kind of substrate. [Example: Amylase cannot breakdown protein molecules, because it does not fit
in the active site.
16
d. Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy, shape and fit,
frequency of effective collisions and denaturation
Reactions occur faster in higher temperatures because the molecules have more kinetic energy. They move
around faster and bump into each other more frequently, meaning that an enzyme at high temperature is
more likely to bump into substrate more often than at lower temperature. After the optimum temperature,
the enzymes start getting damaged and lose their shape. The active site no longer fits perfectly with the
substrate. The enzyme is denatured and it can no longer catalyse the reaction.
e. Explain the effect of changes in pH on enzyme activity in terms of shape and fit and denaturation
Optimum pH in most enzymes is pH 7 (neutral). If the pH becomes too acidic or alkaline, the enzyme gets
denatured. Meaning that the active site no longer fits the substrate and no reaction will be catalyzed.
6 . Plant Nutrition
Photosynthesis is the process by which plants manufacture carbohydrates from raw materials using energy from light
Limiting factor is something present in the environment in such short supply that it restricts life processes
a. Explain that chlorophyll transfers light energy into chemical energy in molecules, for the synthesis of
carbohydrates
When sunlight falls on chlorophyll, some of the light is absorbed. Chlorophyll molecule then releases energy to make
CO2 combine with H2O so in this process light energy converted to chemical energy and is stored in the form of
carbohydrates
17
b. Outline the subsequent use andstorage of the carbohydrates made in photosynthesis
Use:
Used for respiration to release energy.
Cellulose ‐ which strengthens the cell wall
Proteins ‐ such as enzymes and chlorophyll
Storage:
Glucose is a simple sugar. It is soluble in water and can be quite reactive substance. Therefore, glucose is not a
good storage molecule because firstly of it being a reactive might get involved in chemical reactions where it is
not wanted. Secondly, it would dissolve in water and the water concentration in cell will be decreased (since
there will be lower water concentration outside of cell, the water diffuses out) and the cell will be damaged.
The glucose is therefore converted to carbohydrates (starch) to form a large molecule and it is not reactive. It
can be made into granules and stored inside chloroplast.
c. Investigate the necessity for chlorophyll, light and carbon dioxide for photosynthesis, using appropriate
controls
1. Chlorophyll is necessary for photosynthesis
Process
 Take a potted plant with variegated (green and white) leaves.
 Destarch the plant by keeping it in complete darkness for about
48 hours.
 Expose the plant to the sunlight for a few days.
 Test one of the leaves for starch with iodine solution.
Observations
‐ Areas with previously green patches test positive (turn blue
black).
‐ Areas with previously pale yellow patches test negative (remain brown).
2. Light is essential for photosynthesis
Process
 Take a potted plant.
 Destarch the plant by keeping it in complete darkness for about 48 hours.
 Test one of it leaves for starch, to check that is does not contain any.
 Fix a leaf of this plant in between two strips of a thick paper on leaf.
 Place the plant in light for a few days.
 Remove the cover from the leaf and test it for starch.
Observations
Positive starch test will be obtained only in the portion of the leaf exposed to light and
negative test in parts with paper strip.
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3. Carbon dioxide is essential for photosynthesis
Process
 Take two destarched potted plants.
 Cover both the plants with bell jars and label
them as A and B.
 Inside Set‐up A, keep NaHCO3 (sodium
bicarbonate). It produces CO2.
 Inside Set‐up B, keep NaOH (Sodium hydroxide).
It absorbs CO2.
 Keep both the set‐ups in the sunlight at least for
6 hours.
 Perform the starch test on both of the plants.
Observations
Leaf from the plant in which NaHCO3 has been placed gives positive test.
Leaf from the plant in which NaOH has been kept give negative test.
Conclusion
Plant in Set up A gets CO2 whereas plant in Set‐up B does not get CO2.
It means CO2 is must for photosynthesis.
d. Investigate and describe the effects of varying light intensity, carbon dioxide concentration and
temperature on the rate of photosynthesis, e.g. in submerged aquatic plants
1. Investigations need controls
‐ Control plant (or leave) has all substances it needs.
‐ Test plant lacks one substance (light/chlorophyll/CO2)
2. Plants must be destarched
‐ It is very important that the leaves you are testing should not have any starch in them at the beginning of the
experiment.
‐ So, first of all, you must destarch the plants. Leave them in the dark for 48 hours. The plants use up all stores
of starch in its leaves.
3. Starch test with Iodine solution
‐ After a few hours, carry out the starch test on both plants: Iodine solution is used; a blue‐black colour on the
leave is positive.
‐ Boil the leaf in water for 30 second. This kill the cells in the leaf à break down the
membrane à iodine solution gets through cell membrane to reach starch inside the
chloroplasts and react with them.
Boil the leaf in alcohol (ethanol) in a water bath: The green colour of the leaf and the
brown iodine solution can look black together, so you need to remove chlorophyll by
dissolving it out with alcohol. Leave it until all the chlorophyll has come out of the leaf.
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Rinse the leaf in water: Boiling the leaf in ethanol makes it brittle, the water softens
it.
Spread the leaf out on a white tile à easy to see the result.
Add iodine solution to the leaf and blue‐ black colour is positive, starch is present.
e. Identify and explain the limiting factors of photosynthesis in different environmental conditions
Temperature:
If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot. In
practice, any one of these factors could limit the rate of photosynthesis. After its optimum temperature, the
rate of photosynthesis will eventually decrease and stop because enzymes get denatured.
Light Intensity:
Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon
dioxide. Increasing the light intensity will boost the speed of photosynthesis. After it reaches it’s maximum
light intensity level, the rate of photosynthesis will be constant and light is not limiting factor.
20
Carbon Dioxide Concentration:
Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of
light, a plant cannot photosynthesise if there is insufficient carbon dioxide. After it reaches it’s maximum point
of photosynthesizing, the rate of photosynthesis will be constant and carbon dioxide is not a limiting factor.
f. Describe the use of carbon diox ide enrichment, optimum light and optimum temperatures in glasshouses
in temperate and tropical countries
Tropical Countries:
In tropical countries, the temperature and the light intensity may be too high. Both of these can be reduced by
shading the plants from direct sunlight. We can use closed glasshouse with windows that can be opened to let
hot air escape or grow taller plants nearby or provide a simple roof over the crop plants
Temperature:
If the temperature is too cold, the crops can be grown inside a heated glasshouse. The temperature in
glasshouse is kept optimum level to encourage the crop to grow fast, strong and produce a large yield of fruit
that ripens quickly.
g. Use hydrogencarbonate indicator solution to investigate the effect of gas exchange of an aquatic plant
kept in the light and in the dark
Hydrogencarbonate indicator is used to show carbon dioxide concentration in solution. The table shows the
colour that the indicator turns at different levels of carbon dioxide concentration.
Concentration
Indicator turns
Highest
Higher
Atmospheric level
Low
Lowest
Yellow
Orange
Red
Magenta
Purple
A leaf is placed in a stoppered boiling tube containing some hydrogen carbonate indicator solution. The effect
of light intensity can then be investigated.
21
h. Identify chloroplasts, cuticle, guard cells and stomata, upper and lower epidermis, palisade mesophyll,
spongy mesophyll, vascular bundles, xylem and phloem in leaves of a dicotyledonous plant
i. Explain how the internal structure of a leaf is adapted for photosynthesis
22
j. Explain the effects of nitrate ion and magnesium ion deficiency on plant growth
Nitrate ion deficiency
Magnesium ion deficiency
‐ Shorter plant / Reduced growth
‐ Lower leaves pale green and yellow
‐ Upper leaves pale green and bottom leaves yellow
‐ Upper leaves paler than normal
‐ Stem is thinner
‐ Root is smaller
7 . Human Nutrition
Balanced diet is a diet containing some of each of the different types of nutrients, in a suitable quantity and
proportions.
Ingestion: the taking of substances, e.g. food and drink, into the body through the mouth
a. Explain how age, gender and activity affect the dietary needs of humans including during pregnancy and
whilst breast‐feeding







Dietary requirements depend on your age, sex and activity;
The amount of energy needed is provided by our carbohydrate and fat intake;
Generally, males use more energy than females;
And generally the energy demand increases as we get older until we stop growing;
Someone doing physical work will use up more energy than an office worker;
While children are growing they need more protein per kilogram of body weight than adults do;
Pregnant women need extra nutrients for the development of the fetus.
b. Describe the effects of malnutrition in relation to starvation, constipation, coronary heart disease, obesity
and scurvy
Disease
Cause of malnutrition
Symptoms and consequences
Obesity
Too much food
(carbohydrate, fat or
protein)
Coronary heart disease
Too much saturated fat
(causes high cholesterol
levels in the blood)
Heart disease, strokes, diabetes
Extra weight can cause problem with joints
(knees)
Fat deposits build up on the inside of arteries
making them stiffer and narrower. If on coronary
arteries that supply blood, muscles run short of
oxygen and don’t work properly. Deposits also
cause blood clot and cause heart attack
Higher chance of heart disease
Starvation
(e.g. in anorexia nervosa)
Constipation
Too little food (e.g.
intense fear of gaining
weight)
Lack of fibre
Weight loss, organ damage, death
(depression, loneliness, insecurity)
Unable to defecate, pain
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c. List the principal sources of, and describe the dietary importance of: and Explain the causes and effects of
vitamin D and iron deficiencies
d. Explain the causes and effects of protein‐energy malnutrition, e.g. kwashiorkor and marasmus
Kwashiorkor
Cause: Wrong proportion of nutrients; too much carbohydrates and lack of protein
Effect: Underweight for the age
Marasmus
Cause: Not enough protein and energy in the diet
Effect: Low body weight and emaciated (abnormally thin or weak)
Mechanical digestion is the breakdown of food into smaller pieces without chemical change to the food
molecules
Chemical digestion is the breakdown of large, insoluble molecules into small, soluble molecules
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
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e. Describe diarrhoea as the loss of watery faeces
Diarrhoea is the loss of watery feaces. It happens when not enough water is absorbed from the feaces.
f. Outline the treatment of diarrhoea using oral rehydration therapy
Giving a drink containing water with a small amount of salt and sugar dissolved in it, or green coconut water,
or drink made from yoghurt and salt
g. Describe cholera as a disease caused by a bacterium
Cholera is caused by a bacterium
h. Explain that 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
The cholera bacterium lives and breeds in the small intestine. The bacteria produce toxin (poison) that
stimulates the cells lining the intestine to secrete chloride ions in the lumen of small intestine. This increase
the concentration of the fluid in the lumen, lowering the water potential. When the water potential becomes
lower than the blood flowing through vessels in the walls of the intestine, water moves out of the blood and
into the lumen by osmosis. Lots of water in the canal causes diarrhoea.
i. Identify the main regions of the alimentary canal and associated organs, limited to mouth, salivary glands,
oesophagus, stomach, small intestine (duodenum and ileum), pancreas, liver, gall bladder and large
intestine (colon, rectum, anus)
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k. Describe the functions of the regions of the alimentary canal listed above, in relation to ingestion,
digestion, absorption, assimilation and egestion of food
Region
Mouth
Oesophagus
Stomach
Duodenum
Pancreas
Liver
Ileum
Colon
Rectum
Anus
Functions
Food is ingested here; mechanical digestion by cutting, chewing and grinding of teeth;
Saliva added ‐ contains amylase to digest starch.
Boluses of food pass through by peristalsis, from mouth to stomach.
Gastric juice added‐ contains protease to digest protein and hydrochloric acid to
maintain pH 2 and kill bacteria.
Receives pancreatic juice containing protease, lipase and amylase. Juice also contains
sodium hydrogen carbonate which neutralizes acid from the stomach ‐ giving pH of 8.
Secretes pancreatic juice into the duodenum.
Makes bile, which is stored in gall bladder; bile contains salts that emulsify fats;
digested food is assimilated here, e.g. glucose is stored as glycogen.
Epithelial lining secretes enzymes which breakdown maltose and peptides; contains
villi which increase the surface area for absorption of digested food.
Main function is reabsorption of water from undigested food
Stores faeces until it is egested
This has sphincter muscles to control when faeces is egested from the body
l. Identify the types of human teeth and describe their structure and functions
Type of teeth
Structure
Function
Chisel‐shaped (sharp edge)
Biting off pieces of food
Slightly more pointed than incisors
Similar function to incisors and also helps in
tearing flesh in carnivores
Premolar (4 in each jaw)
Have 2 pointed cusps; have 1‐2 roots
Chewing and Grinding food
Molar (6 in each jaw)
Have 4‐5 cusps; have 2‐3 roots.
Chewing and Grinding food
Incisor (4 in each jaw)
Canine (2 in each jaw)
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m. Describe the structure of human teeth, limited to enamel, dentine, pulp, nerves and cement, as well as
the gums
Section of an incisor tooth
Description
Part embedded in the gum called root
Part which can be seen is called crown
covered with enamel.
Enamel hardest substance made by animals
but can be dissolved by acids.
Under enamel is dentine which contains
living cytoplasm; dentine is hard.
Middle of the tooth is pulp cavity containing
nerve and blood vessels which supply
dentine with food and oxygen.
Root is covered with cement; it has fibres
growing out of it which attach the tooth to
the jawbone, but allow slight movement
when biting or chewing.
n. State the causes of dental dec ay in terms of a coating of bacteria and food on teeth, the bacteria respiring
sugars in the food, producing acid which dissolves the enamel and dentine
Bacteria are present on the surface of our teeth. Food deposits and bacteria form a layer called plaque.
Bacteria on the plaque feed on sugars, producing acid. This acid dissolves enamel, forming a hole. Dentine
underneath the enamel is softer – it dissolves more rapidly. If the hole reaches the pulp cavity, bacterial
infection can get to the nerve. This results in toothache and possibly, an abscess (an infection in the jaw).
o.Describe the proper care of teeth in terms of diet and regular brushing
 Avoid sugary food, especially between meals, so bacteria cannot make acid
 Clean teeth regularly to remove plaque (a fluoride toothpaste hardens tooth enamel);
 Use dental floss or a toothpick to remove pieces of food and plaque trapped between teeth;
 Visit a dentist regularly so any tooth decay is treated early and any stubborn plaque is removed
 Use antibacterial mouthwash
 Eat foods containing calcium / phosphate / vitamin D / vitamin C
 Rinse mouth with water after eating
27
p. State the significance of chemical digestion in the alimentary canal in producing small, soluble molecules
that can be absorbed
 Chemical digestion involves breaking down large, insoluble molecules into small, soluble ones;
 Enzymes speed up the process;
 Enzymes work efficiently at body temperature (370C) and at a suitable pH;
 Small, water soluble molecules of food are easily absorbed into the blood capillaries in the intestine.
q. State the functions of enzymes as follows:
– amylase breaks down starch to simpler sugars
– protease breaks down protein to amino acids
– lipase breaks down fats to fatty acids and glycerol
r. Describe the digestion of starch in the alimentary canal:
– amylase is secreted into the alimentary canal and breaks down starch to maltose
– maltose is broken down by maltase to glucose on the membranes of the epithelium lining the small intestine
s. State where, in the alimentary canal, amylase, protease and lipase are secreted and state the functions of
a typical amylase, protease and lipase, listing the substrate and end‐products.
Site of action
Special conditions
Substrate
End products
Amylase
Mouth, duodenum
Slightly alkaline
Starch
Maltose, glucose;
simple sugars
Protease
Stomach,
duodenum
Acid in stomach, alkaline in
duodenum
Protein
Amino acids
Lipase
Duodenum
alkaline
fat
Fatty acids and
glycerol
t. Describe pepsin and trypsin as two protease enzymes that function in different parts of the alimentary
canal:
Pepsin in the stomach:
Pepsin digests proteins by breaking them down into polypeptides.
Trypsin in the small intestine:
Breaks down proteins to polypeptides.
u. Explain the functions of the hydrochloric acid in gastric juice, limited to the low pH:
– denaturing enzymes in harmful microorganisms in food
– giving the optimum pH for pepsin activity
v. Outline the role of bile in neutralising the acidic mixture of food and gastric juices entering the duodenum
from the stomach, to provide a suitable pH for enzyme action
Bile is alkaline, watery liquid that helps to neutralize the acidic mixture from the stomach. If the mixture stays
acidic, the enzyme will be denatured and no reaction will occur. As we know enzymes work best at neutral
condition.
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w. Outline the role of bile in emulsifying fats to increase the surface area for the chemical digestion of fat to
fatty acids and glycerol by lipase
 Bile is made in the liver, stored in gall bladder and then flows along bile duct into duodenum;
 Bile does not contain any enzymes;
 Bile helps to digest fat by breaking the large drops of fat into very small ones;
 This makes it easier for lipase to digest them;
 This is called emulsification (a kind of mechanical digestion) and is done by bile salts.
x. Identify the small intestine as the region for the absorption of digested food
Most carbohydrates have been broken down to simple sugars, proteins to amino acids, and fats to fatty acids
and glycerol. These broken down molecules are small enough to pass through the wall of the small intestine
and into the blood. The features of small intestine is especially adapted to allow absorption to take place very
efficiently.
Feature
It is very long, about 5m in an adult human
It has villi. Each villus is covered with cells which
have even smaller projections on them, called
microvilli
Villi contains blood capillaries
Villi contains lacteals, which are part of the
lymphatic system.
Villi have walls only one cell thick
How this helps absorption take place
This gives plenty of time for digestion to be
completed, and for digested food to be absorbed as
it slowly passes through.
This gives the inner surface of the small intestine a
very large surface area.
The larger the surface area, the faster the nutrients
can be absorbed.
Monosaccharides, amino acids, water, minerals and
vitamins, and some fats, pass into blood, to be taken
to the liver and then round the body
Fats are absorbed into the lacteals
The digested nutrients can easily cross the wall to
reach the blood capillaries and lacteal.
y. Explain the significance of villi and microvilli in increasing the internal surface area of the small intestine
To provide large surface area to increase/maximize absorption by diffusion or active transport
29
30
In the wall of the intestine are the villi.
The villi make it possible for digested food
to be transferred from the intestine into
the blood by diffusion or active transport.
The Villi is a tiny
projection of the lining
of the small intestine
which increase the
surface area for the
absorption of digested
products.
The villi provide a large surface area
with an extensive network of
capillaries to absorb the products of
digestion by diffusion and active
transport.
It is important that the
villi has a rich blood
supply to absorb and
carry dissolved food
molecules to the cells of
the body to be used
during respiration and to
maintain a
concentration gradient.
Villi are adapted for the maximum absorption of digested food molecules because:
1. the folded villi greatly increase the surface area of the intestine
2. the villi are made of a single layer of thin cells (one cell thick) so there is a short diffusion
path
3. beneath the villi is an extensive blood capillary network to distribute the absorbed food
molecules. A rich blood supply produces a steep concentration gradient for diffusion.
Glucose is moved from
the small intestine into
the blood by active
transport.
The digested food
molecules have to move
against the
concentration gradient.
This makes sure that
none of the digested
food is wasted and lost
as faeces.
Each villus is covered in many microscopic microvilli.
This increases the surface area available for diffusion
even more.
The villi in the small intestine provide a large surface area with an extensive network of blood
capillaries. This makes the villi well adapted to absorb the products of digestion by diffusion and
active transport.
z. Describe the structure of a villus
z.i Describe the roles of capillaries and lacteals in villi
(Table Above)
z.ii. State that water is absorbed in both the small intestine and the colon, but that most absorption of water
happens in the small intestine
Small intestine is longer than colon (large intestine)
Small intestine has villis and microvillis to allow more absorption
8 . Transport in Plants
≥ State the functions of xylem and phloem
Xylem:
 To transport water / mineral salts / named salts / ions from roots to leaves.
 To provide structural support
 Transpiration
Phloem:
 Transport amino acids / sugars / sucrose / organic materials from leaves to storage area or place of use
 Translocation
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≥ Identify the position of xylem and phloem as seen in sections of roots, stems and leaves, limited to non‐
woody dicotyledonous plants
≥ Identify root hair cells, as seen under the light microscope, and state their functions
Function:
Increases the surface area of the root for absorption of water and mineral ions.
Provides anchorage for the plant
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≥ Explain that the large surface area of root hairs and root hair cells increases the rate of the absorption of
water by osmosis and ions by active transport
Root Hairs
 Each root hair is a long epidermal cell; this increases the surface area for absorption;
 Root hairs are long & thin and so can penetrate between the smallest soil particles for absorption
Root Hair Cells
 Large surface area to maximize absorption
 Membrane with proteins for active transport (of ions)
 Vacuole with high concentration of salts / sugars / solutes to give low water potential
 Thin cell walls provide short distance for diffusion
 More mitochondria to provide energy for active transport
≥ State the pathway taken by water through root, stem and leaf as root hair cell, root cortex cells, xylem
and mesophyll cells
Root hair cells  Root cortex cells  xylem of root  xylem of stem  xylem of leaf  mesophyll cells
≥ Investigate, using a suitable stain, the pathway of water through the above ground parts of a plant
Transpiration is the 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
≥ Explain how water vapour loss is related to the large surface area of cell surfaces, interconnecting air
spaces and stomata
 Transpiration is the loss of water vapour from the leaf;
 Water in the mesophyll cells form a thin layer on their surfaces;
 The water evaporates into the air spaces in the spongy mesophyll;
 This creates a high concentration of water molecules in the air spaces.
 Water vapour diffuses out of the leaf into the surrounding air, through the stomata, by diffusion.
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≥ Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that
draws up a column of water molecules, held together by cohesion
Mechanism of water uptake
1. Water enters root hair cells by osmosis (as the water potential in the soil surrounding the root is higher
than in the cell);
2. As the water enters the cell, its water potential becomes higher than in the cell next to it, e.g. in the
cortex;
3. So the water moves by osmosis, into the next cell;
4. This process is repeated until water reaches the xylem.
Mechanism of water movement through a plant
1. Transpiration continuously removes water from the leaf;
2. Thus water is constantly being taken from the top of the xylem vessels, to supply the cells in the leaves;
3. This reduces the effective pressure at the top of the xylem vessels;
4. This creates a transpiration stream or ‘pull’, pulling water up;
5. Water molecules have a strong tendency to stick together. This is called cohesion;
6. When the water is ‘pulled’ up the xylem vessels, the whole column of water stays together;
7. Roots also produce a root pressure, forcing water up the xylem vessels.
≥ Explain how and why wilting occurs
Young plant stems and leaves rely on their cells being turgid to keep them rigid. If the amount of water lost
from the leaves of a plant is more than the amount taken into the roots  the plant will have a water
shortage  cells become flaccid (soft) and will no longer press against each other  Stems and leaves lose
their rigidity, and wilt.
Why?
To prevent huge water loses through transpiration
≥ Describe the effects of variation of temperature, humidity and light intensity on transpiration rate.
FACTOR
Increase in temperature
Increase in air movement e.g. wind
Decrease in humidity
Increase in light intensity
EXPLANATION
Increases the kinetic energy of the water molecules, so they diffuse faster
Removes water molecules as they pass out of the leaf, maintaining a steep
concentration gradient for diffusion
Results in lower concentration of water molecules outside the leaf, making a
steeper concentration gradient for diffusion
Stomata open to allow gas exchange for photosynthesis, so water vapour can
diffuse out of the leaf
Translocation ‐ movement of sucrose and amino acids in phloem, from regions of production or of storage to
regions of use for respiration or growth
34
≥ Explain that some parts of a plant may act as a source and a sink at different times during the life of a
plant
'Source' is the part of a plant where substances are produced (e.g. leaves for sucrose, amino acids) or enter
the plant.
'Sink' refers to the part of the plant where the substrate can be stored (e.g. roots or stem for starch).
Examples:
Sources: Leaves ‐ sucrose is produced here  Root hairs ‐ Nitrates are absorbed here.
Sinks: Roots/Stems ‐ starch is stored here  Root tips ‐ amino acids are stored here.
1. During the summer, the leaves photosynthesise and send sucrose down
into underground stems. Here, swellings called tubers develop. The cells in
the root tubers change the sucrose to starch and store it.
2. In winter, the leaves die. Nothing is left of the potato plant above ground ‐ just the
stem tubers beneath the soil.
3. In spring, they begin to grow new shoots and leaves. The starch in the tubers
is changed back to the sucrose, and transported in the phloem to the
growing stems and leaves. This will continue until the leaves are above
ground and photosynthesise.
So in summer, the leaves are sources and the growing stem tubers are sinks.
In spring, the stem tubers are sources and the growing leaves are sinks.
35
9 . Transport in Animals
≥ Describe the circulatory system as a system of blood vessels with a pump and valves to ensure one‐way
flow of blood
 The main transport system of all mammals is the blood system, also known as the circulatory system;
 It is a network of tubes , called blood vessels;
 A pump, the heart, keeps blood flowing through the vessels;
 Valves in the heart and veins prevent backflow of blood.
≥ Describe the single circulation of a fish
A Single Circulatory System is a simple loop in which blood flows: Heart  Gills
 Body  Heart
Fish have a single circulatory system
Fish are not as active as other animals, so their single circulatory system is
sufficient for their needs, while more active animals like mammals need a
double circulatory system.
≥ Describe the double circulation of a mammal
Beginning at the lungs, blood flows into the left‐hand side of the
heart, and then out to the rest of the body. It is brought back to the
right‐side of the heart, before going back to the lungs again.
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Blood passes through the heart twice for each complete
circulation of the body;
The right side of the heart collects deoxygenated blood from the
body and pumps it to the lungs;
Thus there is a low pressure circulation in the lungs;
The left side collects oxygenated blood from the lungs and
pumps it to the body;
Thus there is a high pressure circulation to the body tissues.
The double circulatory system helps to maintain blood pressure,
making circulation efficient.
36
≥ Explain the advantages of a double circulation
 Oxygenated blood is kept separate from deoxygenated blood. The septum in the heart ensures this
complete separation. Oxygenated blood flows through the left side of the heart while deoxygenated blood
flows through the right.
 The blood pressure in the systemic circulation is kept higher than that in the pulmonary circulation. The
left ventricle, with a thicker wall, pumps blood under higher pressure to the body and delivers oxygenated
blood effectively to all parts of the body. The right ventricle has a thinner wall and pumps blood to the
lungs under lower pressure, thereby avoiding any lung damage.
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The heart is a pump, made of muscle, which moves blood around the body;
The muscle is constantly active and coronary arteries to provide it with oxygen and glucose;
The left and right side of the heart is completely separated from each other by a septum;
RIGHT side receives deoxygenated blood from the body and pumps it to the lungs for oxygenation;
LEFT side receives oxygenated blood from the lungs and pumps it to the body;
There are four chambers ‐ two atria and two ventricles;
The right atrium (RA) receives blood from vena cava and the left atrium (LA) from pulmonary vein.
Both atria then squeeze the blood into the ventricles;
The tricuspid valve allow blood to flow from RA to right ventricle and the bicuspid valve allow blood to
flow from LA to left ventricle preventing backflow;
The right and left ventricles then squeeze the blood into arteries;
Right ventricle (RV) pumps blood into the pulmonary artery & the left ventricle (LV) into the aorta;
The semilunar valves allow blood to move into the arteries and prevent backflow
The wall of the LV is much thicker than the RV because it needs to build up enough pressure to send the
blood to all the main organs (not just to the lungs).
Thus the blood in the aorta has a much higher pressure than in the pulmonary artery.
37
≥ Explain the effect of physical activity on the heart rate
Heart beats about 70 times a minute, more if you are younger;
The rate becomes lower the fitter you are;
During exercise the heart rate increases to supply the muscles with more oxygen and glucose;
These are needed to allow the muscles to respire aerobically, so they have sufficient energy to contract;
Regular exercise is needed to keep the heart muscle in good tone;
This results in the heart being more efficient in maintaining blood pressure and reduces the risk of coronary
heart disease.
After Exercise:
 Oxygen debt since oxygen not supplied fast enough from heart to muscles
 Removal of excess carbon dioxide
 Anaerobic respiration in muscles produce lactic acid that builds up in muscle and not carried away fast
enough in blood lowers blood pH which makes person feel tired and the muscle cannot contract any more.
 Lactic acid is broken down and converted to glucose
During Exercise:
 Increase in energy demand in muscle for contraction (of muscle)
 Increase in respiration in muscle
 Increase in blood flow supplies more oxygen for aerobic respiration / more glucose / more fatty acids
 Increase in blood flow removes carbon dioxide and lactic acid from anaerobic respiration
≥ Discuss the roles of diet and exercise in the prevention of coronary heart disease
Taking care of your diet also decreases the risk of getting CHD. Having a diet with wide range of food and
eating food with low saturated fat will help to reduce CHD. Fast foods also contain lots of saturated fat and
moderation of these types of food can help reduce risk of CHD.
Regular exercise is very beneficial on many parts of body, including the heart. Exercise prevents excessive
weight gain and decreases blood pressure.
≥ Describe ways in which coronary heart disease may be treated, limited to drug treatment with aspirin and
surgery (stents, angioplasty and by‐pass)
Treatment 1:
Give drug to the patient like statins, and also other drugs that help to lower the blood pressure, or to decrease
the risk of blood clots by giving aspirin.
Treatment 2:
1. Doing surgery is the patient’s second choice. The blocked or severely damaged coronary artery will be
replaced with a length of blood vessel taken from another part of the body. This is called coronary bypass
operation.
2. Insert little mesh tube called stent inside the artery to keep it open
3. Use tiny balloon that is inserted into the collapsed artery and then inflate it using water. This pushes the
artery open. The balloon is then removed. This is called angioplasty
38
≥ Describe coronary heart disease in terms of the blockage of coronary arteries and state the possible risk
factors as diet, stress, smoking, genetic predisposition, age and gender
1. Coronary arteries supply blood (nutrients and oxygen) to the heart muscles.
2. If a coronary artery gets blocked (e.g. by a blood clot), the cardiac muscle runs short of oxygen;
3. Blockage of the coronary arteries is called coronary artery disease;
4. The cardiac muscle cannot respire, so it cannot obtain energy to contract;
5. The heart therefore stops beating; this is called a heart attack or cardiac arrest.
Age:
Risk of developing CHD increases as you get older
Stress:
Some stress and excitement is good for you. However, if your stress is long‐term it increases the risk of
developing CHD.
Prevention: Avoid severe or long term stress
Gender:
Men are more likely to develop CHD than woman
Diet:
A diet with high in salt, saturated fat or cholesterol increases the chance of CHD.
Prevention: Eat wide variety of food; Oils from plant and fish can help to prevent CHD
Smoking:
Components of cigarette smoke (nicotine) cause damage to the circulatory system.
Prevention: Stop smoking
Genetic predisposition:
Some people have genes that had CHD in their family before that could increase the risk of you having CHD.
Preventing: Live a healthy lifestyle
≥ Describe the functioning of the heart in terms of the contraction of muscles of the atria and ventricles and
the action of the valves
 Heart beats as the cardiac muscles in its walls contract and relax;
 When they contract, heart becomes smaller, squeezing blood out. This is called systole;
 When they relax, the heart becomes larger, allowing blood to flow into the atria and ventricles. This is
called diastole;
 The rate at which heart beats is controlled by a patch of muscle in the right atrium called pacemaker;
 The pacemaker sends electrical signals through the walls of the heart, which make the muscle contract;
 Between atria and ventricles are atrio‐ventricular valves (bicuspid on left & tricuspid on right);
 When the ventricles contract, these valves stop blood flowing back into atria;
 As the ventricles contract, the blood pushes the semilunar valves upwards;
 The tendons attached to them stop them from going up too far.
39
≥ Describe the structure and functions of arteries, veins and capillaries and how they are adapted
Blood
vessel
Artery
Vein
Capillary
Structure
How structure is related to function
1.Thick, tough wall with muscles
and elastic tissue,
2. Narrow lumen
3. Valves absent
1. Thick walls to withstand and maintain blood pressure (prevents
bursting).
2. Narrow lumen maintains high blood pressure.
3. High pressure prevents backflow of blood.
4. Folded endothelium allows artery to stretch
1. Thin walls allow muscles to exert pressure on the veins.
2. Wide lumen allows great volume of blood to pass or reduces
resistance to blood flow.
3. Valves prevent backflow of blood.
1. One cell thick wall allows diffusion of materials between capillary
and surrounding tissues.
Pores in the wall allow white blood cells to exit.
2. Narrow lumen allows blood cells to pass through slowly and
increases oxygen diffusion from red blood cell.
1. Thin wall with less muscles
and elastic tissue
2. Large lumen
3. Valves present
1. Permeable wall (one cell
thick) with no muscle and
elastic tissue
2. Lumen approximately one
red blood cell wide
≥ Name the main blood vessels in heart, lungs and kidney:
Organ
Heart
Lungs
Liver
Kidney
To
Vena cava and pulmonary vein
Pulmonary artery
Hepatic portal vein & hepatic artery
Renal artery
From
Pulmonary artery and aorta
Pulmonary vein
Hepatic vein
Renal vein
40
≥ Outline the lymphatic system in terms of lymphatic vessels and lymph nodes
≥ Describe the function of the lymphatic system in the circulation of body fluids and the protection of the
body from infection
Circulation:
Tissue fluid is a fluid surrounding the cells of a tissue. It is leaked
plasma ‐ Plasma from the blood capillaries move to the tissue through
gaps in the walls and become tissue fluid. Tissue fluid play an
important role in substance exchange between blood and cells. It
supplies cells with O2 and nutrients and takes away waste products
including CO2. At the end of the capillary bed, the tissue fluid leaks
back into the blood, and becomes plasma again, but not all of it. A
little of it is absorbed by the lymphatic vessel and becomes lymph. The
lymphatic vessel takes the lymph to the blood stream by secreting
them in a vein near the heart, called subclavian vein. The lymph in the
lymphatic vessels are moved along by the squeeze of muscles against
the vessel, just like some veins. The return of tissue fluid to the blood
in the form of lymph fluid prevents fluid built up in the tissue.
Protection:
The lymphatic system is an important component of the immune system, which fights infection. One group of
white blood cells, the lymphocytes, are made in lymph glands such as the tonsils, adenoids and spleen. The
glands become more active during an infection because they are producing and releasing large numbers of
lymphocytes. The lymphocytes can live and multiply in the lymphatic system, where they attack and destroy
foreign organisms. Lymphoid tissue scattered throughout the body filters out pathogens, other foreign matter
and cellular debris in body fluids.
41
≥ List and identify the components of blood as red blood cells, white blood cells, platelets and plasma and
their functions
Components of blood
Red blood cells
White blood cells
Platelets
Plasma
Function
Red due to hemoglobin which carries oxygen and transports it to the tissues.
Fights infection by phagocytosis and antibody production.
Causes blood clotting.
Transport of blood cells, ions, soluble nutrients, hormones & carbon dioxide.
≥ Identify lymphocyte and phagocyte white blood cells, as seen under the light microscope, on prepared
slides and in diagrams and photomicrographs
≥ State the functions of lymphocytes and phagocytes:
Phagocytes:
Bacteria is ingested into the vacuole and digested and broken down by enzymes
Lymphocytes:
Attach to bacteria and cause them to stick together and stop them spreading
Help phagocytes engulf them
42
≥ Describe the process of clotting as the conversion of fibrinogen to fibrin to form a mesh
Platelets stimulate clotting. Thrombin converts soluble fibrinogen is converted into insoluble fibrin which
forms a mesh. Mesh traps red blood cells and platelets and dries to form a scab. This prevents loss of blood
and prevents infection
1 0 . Diseases & Immunity
Pathogen is a disease‐causing organism
Transmissible disease is a disease in which the pathogen can be passed from one host to another
Active immunity is defence against a pathogen by antibody production in the body
Antibodies lock on to antigens leading to direct destruction of pathogens, or marking of pathogens for
destruction by phagocytes
The body has defences:
– mechanical barriers, limited to skin and hairs in the nose
– chemical barriers, limited to mucus and stomach acid
– cells, limited to phagocytosis and antibody production by white blood cells
– which can be enhanced by vaccination
Memory cells are not produced in passive immunity
The pathogen for a transmissible disease may be transmitted either through direct contact, e.g. through blood
or other body fluids, or indirectly, e.g. from contaminated surfaces or food, from animals, or from the air
Some diseases are caused by the immune system targeting and destroying body cells, limited to Type 1
diabetes. The cells of the pancreas do not produce enough insulin. When the person eats and digests food the
blood sugar level rises. Treatment is with diet, monitoring blood sugar level and injections of insulin.
≥ Explain how each pathogen has its own antigens, which have specific shapes, so specific antibodies which
fit the specific shapes of the antigens are needed
Pathogens have markers on their surface membranes called antigens
Antibodies stick to these antigens and destroy the pathogen. or marking them for phagocytes to act on them.
≥ Explain that active immunity is gained after an infection by a pathogen, or by vaccination
A person has active immunity to a disease if they have made their own antibodies and memory cells that
protect against it. These memory cells can last for many years. You can develop active immunity by having
disease and getting over it or being vaccinated with weakened pathogens.
43
≥ Explain the process of vaccination (harmless pathogen given which has antigens, antigens trigger an
immune response by lymphocytes which produce antibodies, memory cells are produced that give long‐
term immunity):
A vaccine contains weakened or dead viruses or bacteria that normally cause disease. These pathogens have
the same antigens as the normal ones but they aren’t able to cause disease. These pathogens are injected into
the body and recognized by the lymphocytes that can make antibodies that will lock onto their antigens. These
lymphocytes multiply and produce antibodies (like a real infection). They will also make memory cells which
gives long‐term immunity.
≥ Explain the role of vaccination in controlling the spread of diseases
Vaccines immunize diseases caused by pathogens. Vaccine is a dead virus or bacteria that stimulate
lymphocytes to produce antibodies and be immune to that particular disease. So the next time the disease
comes, it will be killed before spreading
≥ Explain the importance of hygienic food preparation, good personal hygiene, waste disposal and sewage
treatment in controlling the spread of disease
Hygienic Food
Personal hygiene
Means keeping your body clean. This can reduce the risk of getting, or passing on transmissible diseases. The
skin makes oil that helps to keep it supple and waterproof. If the skin is not washed regularly, this oil can build
up dirt from things that we have touched. When we are hot, sweat is produced and if the sweat, oil and dirt
stays on the skin for long, it provides breeding ground for bacteria.
Waste Disposal
Animals forage for food in waste and bacteria breed in there. Some of the rubbish in the landfill site is rotten
by decomposers (bacteria). This produces a gas called methane which can cause explosion if build up. Using
pipes can allow methane to escape.
Sewage Treatment
Sewage is mostly water but contains other substances too. (urine, faces, toilet paper, etc). Sewage that is run
into rivers or sea before being treated can harm the environment and people. Raw sewage contains many
bacteria and other microorganisms, some which are likely to be pathogens. If people get contact with raw
sewage can get ill. Poliomyelitis and cholera are two serious diseases caused by sewage. Treating the sewage
can prevent these.
≥ Explain that passive immunity is short‐term defence against a pathogen by antibodies acquired from
another individual, e.g. mother to infant
Passive immunity lasts for a short time because the antibodies eventually break down. No lymphocytes have
been stimulated to make clones and the body hasn’t made memory cells. Antibodies are passed from mother
to baby through breast feeding or across the placenta during pregnancy.
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≥ Explain the importance of passive immunity for breast‐fed infants
Immune system of the baby has not been developed yet so the mother’s antibodies can protect it against any
diseases she is immune to.
≥ Describe the immune system in terms of antibody production, tissue rejection and phagocytosis.
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The immune system is the body’s defence against disease and foreign bodies. There are two main types of white
blood cells – lymphocytes & phagocytes:
Antibody production:
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All cells have proteins on their surface called antigens;
Lymphocytes recognize foreign antigens from foreign cells (such as bacteria) and make antibodies to them;
A different antibody is produced for each antigen;
Antibodies make bacteria clump together in preparation for action by phagocytes or neutralize the toxins produced
by the bacteria;
Tissue rejection:
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Transplants involve replacing a damaged organ with a donor organ;
However lymphocytes detect the foreign antigens of the donor organ and make antibodies to it;
The donor organ is rejected as antibodies ‘fight’ the foreign tissue;
To prevent this happening:
o The donor organ needs to be a similar tissue type to the patient e.g. from a close relative;
o Immunosuppressive drugs are used, which switch off the body’s immune response;
However the drawback of this drug is that the patient needs to be kept in isolation as they are at the risk of dying
from any disease they are exposed to.
Phagocytosis:
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Phagocytes have the ability to move out of capillaries to the site of infection;
They then engulf (ingest) the infecting pathogen and kill them by digesting them. A process called phagocytosis.
1 1 . Gas Exchange in Humans
≥ List the features of gas exchange surfaces in humans, limited to large surface area, thin surface, good
blood supply and good ventilation with air
 Wall of the alveolus is thin (a single layer of cells) to allow gases to diffuse across them quickly;
 They are moist to prevent the cells from drying and to allow gases to dissolve;
 They have a large surface area, so that a lot of gas can diffuse across at the same time;
 They have a high concentration gradient ‐ maintained by the movement of air & blood.
≥ State the functions of the cartilage in the trachea
 To connect bones together
 Provide smooth surfaces enabling tissue to slide easily
 Epiglottis closes trachea and stop food going down the trachea when you swallow
 Allows ribs to swing up and down
45
≥ Name and identify the lungs, diaphragm, ribs, internal and intercostal muscles, larynx, trachea, bronchi,
bronchioles, alveoli and associated capillaries
46
≥ Explain the role of the ribs, the internal and external intercostal muscles and the diaphragm in producing
volume and pressure changes in the thorax leading to the ventilation of the lungs
Breathing in:
1. External intercostal muscles contract
2. Internal intercostal muscles relax
3. Ribs lift upwards
4. Diaphragm contracts and flattens
5. Volume of thorax increases
6. Pressure in thorax decreases
7. Air flows in down a pressure gradient
Breathing out:
1. External intercostal muscles relax
2. Internal intercostal muscles contract
3. Ribs fall in
4. Diaphragm relaxes and goes back into its domed shape
≥ Explain the differences in composition between inspired and expired air
Gas
Nitrogen
Oxygen
Carbon dioxide
Water vapour
Temperature
Inspired air %
79
21
0.04
Variable
Expired air %
79
16
4
Saturated
Variable
Always warm
Explanation
Not used or produced by body processes
Used up in the process of respiration
Produced in the process of respiration
Produced in the process of respiration, moisture
evaporates from the surface of the alveoli
Air is warmed as it passes through the respiratory
passages.
≥ Use limewater as a test for carbon dioxide to investigate the differences in composition between inspired
and expired air
Apparatus Needed:
 Rubber Tubing
 Test Tube
Experiment:
The rubber tubing must be sterilized before you use it. Do not blow or suck hard when doing this experiment,
just breathe gently. Use either limewater or hydrogencarbonate indicator solution for this experiment.
Limewater changes from clear to cloudy when CO2 dissolves in it and
hydrogencarbonate from red to yellow.
1. Set up the apparatus as show in the diagram
2. Breathe in and out gently using the rubber tubing. Keep doing
this until one the liquids in tube changes colour
47
≥ Explain the link between physical activity and rate and depth of breathing in terms of the increased
carbon dioxide concentration in the blood, detected by the brain, causing an increased rate of breathing
* tidal volume: amount of air during normal, relaxed breathing
vital capacity; maximum amount of air breathed in or out in one breath
During normal breathing:
‐ depth (tidal volume) : ≈ 0.5L
‐ rate: 12 breaths/ minute
During exercise:
‐ depth: ≈ 5L (depending on age, sex, size & fitness of person)
‐ rate: over 20 breaths/ minute
The total lung volume is greater than vital capacity (some air always remains in the lungs). If not, alveoli wall
would stick together, the lung would collapse.
Link between physical activity and rate and depth of breathing
 when you run, muscles in your legs use up a lot of energy.
 cells in the muscles need a lot of O2 very quickly.
 they combine O2 + glucose as fast as they can, to release energy for muscle construction ‐‐‐> a lot of O2 is
needed
 you breath deeper and faster to get more O2 into your blood.
 your heart beast faster to get O2 to the leg muscles as quickly as possible.
 a limit is reached ‐ the heart and the lung cannot supply O2 to the muscles any faster.
 some extra energy (not much) is produced by anaerobic respiration: some glucose is broken down without
combing with O2:
 Glucose ‐‐‐> lactic acid + energy.
 CO2 and lactic acid concentration in tissue and in the blood ↑ ‐‐‐> blood pH ↓
 Brain senses the change ‐‐‐> nerve impulses sent to the diaphragm and the intercostal muscles, stimulating
them to contract harder and more often ‐‐‐> faster and deeper breathing.
Past Paper Answer:
 requires more oxygen
 oxygen debt
 lactic acid produced during exercise as a result of anaerobic respiration
 not enough oxygen supplied, to muscles (during running)
 lactic acid lowers pH of blood
 high concentration of carbon dioxide in blood
 from aerobic respiration
 (carbon dioxide) detected by, brain / receptors
 (carbon dioxide) stimulates high ventilation rate
 (carbon dioxide) increases depth of breathing
 lactic acid is, broken down / respired / converted to glucose
 ref. to homeostasis (increase in temperature  revert back to normal)
48
≥ Explain the role of goblet cells, mucus and ciliated cells in protecting the gas exchange system from
pathogens and particles
 Goblet cells produce mucus which traps dirt/particles. Cilia beats (create wave motion) to move fluid out
of the airway. This reduces the risk of pathogens entering the lungs
 Mucus also protects the lining
1 2 . Respiration
Respiration: The chemical reactions that break down nutrient molecules in living cells to release energy
Aerobic respiration is the chemical reactions in cells that use oxygen to break down nutrient molecules to
release energy
Balanced Chemical Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O
Word Equation: Glucose + Oxygen → Carbon dioxide + Water
Anaerobic respiration as the chemical reactions in cells that break down nutrient molecules to release energy
without using oxygen
Word Equation (Exercise): Glucose → Lactic acid
Word Equation (Yeast): Glucose → Alcohol + Carbon dioxide
Balanced Chemical Equation (Yeast): C6H12O6 → 2C2H5OH + 2CO
Respiration involves the action of enzymes in cells
≥ State the uses of energy in the body of humans
 Muscle contraction
 Protein synthesis
 Cell division
 Growth
 The passage of nerve impulses
 Maintenance of a constant body temperature
Respiration involves the action of enzymes in cells
≥ Investigate the effect of temperature on the rate of respiration of germinating seeds
49
≥ Investigate the uptake of oxygen by respiring organisms, such as arthropods and germinating seeds
Apparatus Needed:
Capillary tube
Beaker / Container
Ruler
Rubber Stoppers
Soda lime contains chemicals that absorb carbon dioxide. It’s important not to let any animals touch the soda
lime as it could harm them. As the seeds respire, they will produce carbon dioxide which is absorbed by soda
lime (or pellets of sodium hydroxide). The volume of air in the flask decreases as oxygen is used up.
Consequently, the coloured water in the 1 ml pipette rises (oil drop). After adjusting the pressure changes in
the volume of air in the flask, the rate of oxygen uptake can be measured
Experiment:
1. Set up both pieces of apparatus as shown in the diagrams. You can use any small living organisms
(maggots) or germinating seeds in apparatus B. Make sure that the connections between the capillary
tubes, rubber stoppers and contains are completely airtight.
2. Dip the end of the capillary tube of each set of apparatus into oil. You should find that a small drop of oil
goes into the capillary tube.
3. Record the initial position of the oil drop in each apparatus. Then continue to record this at regular
intervals until you feel that you have enough readings.
4. Plot a line graph of your results for both sets of apparatus. Draw both lines on one set of axes.
≥ State that anaerobic respiration releases much less energy per glucose molecule than aerobic respiration
Aerobic respiration
Uses oxygen
No alcohol or lactic acid made
Large amount of energy released from each
molecule of glucose
Carbon dioxide made
Anaerobic respiration
Does not use oxygen
Alcohol (in yeast and plants) or lactic acid (in animals)
is made
Much less energy released from each molecule of
glucose
Carbon dioxide is made by yeast and plants, but not
by animals
50
≥ State that lactic acid builds up in muscles and blood during vigorous exercise causing an oxygen debt
1. Not enough oxygen is supplied to muscles
2. Oxygen debt
3. Anaerobic respiration occurs and lactic acid is produced
4. Lactic acid builds up in muscles
≥ Outline how the oxygen debt is removed during recovery, limited to:
– aerobic respiration of lactic acid in the liver
– continuation, after exercise, of fast heart rate to transport lactic acid in blood from muscles to the liver
– continuation, after exercise, of deeper breathing supplying oxygen for aerobic respiration of lactic acid
1 3 . Excretion in Humans
Deamination is the removal of the nitrogen‐containing part of amino acids to form urea
Urea is formed in the liver from excess amino acids
Carbon dioxide is excreted through the lungs
Kidneys excrete urea and excess water and salts
≥ Explain that the volume and concentration of urine produced is affected by water intake, temperature and
exercise
The kidneys adjust the amount of urine that they produce, according to the needs of your body. If your body is
short of water because you have been doing exercise in the heat, and have lost lots of water by sweating. The
kidney produces small volume of concentrated urine (less water). If your body contains too much water (too
much water intake), your kidneys produce large volume of dilute urine, which helps to get rid of excess water.
≥ Identify on drawings, diagrams and images, the ureters, bladder and urethra
51
≥ Describe the role of the liver in the assimilation of amino acids by converting them to proteins, including
plasma proteins, e.g. fibrinogen
When you ingest proteins, digestive enzymes (in stomach, duodenum, and ileum) break them down into
amino acids. The amino acids are absorbed into the blood capillaries in the villi. The blood capillaries all join up
to the hepatic portal vein, which takes the absorbed food to the liver. The liver allows some of the amino acids
to carry on in the blood, to other parts of your body but if you have excess amount (more than you need)
some should be removed. It is wasteful to excrete extra amino acids since they contains energy that may need
to be used for later. So enzymes in the liver split each amino acid molecule and the part which contains energy
is converted and stored as carbohydrates. The rest which contains nitrogen is turned into urea. (Deamination).
52
≥ Explain the need for excretion, limited to toxicity of urea and carbon dioxide
All living cells have metabolic reactions going inside them. Metabolic reactions often produce substances that
the cells don’t need. If these substances are allowed to remain in cells, it might become poisonous or toxic.
Respiration for example does not only produce energy but CO2 and water. Animas might need the water and
the energy but not the CO2 (waste product). CO2 is excreted from the lungs, gills or other gas exchange
surfaces. If allowed to stay, it would harm the cells.
≥ Outline the structure of the kidney, limited to the cortex, medulla and ureter
≥ Outline the structure and functioning of a kidney tubule, the
role of the glomerulus in the filtration from the blood of water,
glucose, urea and salts and the role of the tubule in the
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 (details of these
processes are not required)
Filtration:
Blood is brought to the renal capsule in a branch of the renal
artery. Small molecules, including water and most of the things
dissolved in its, are squeezed out of the blood into the renal
capsule.
There are thousands of renal capsules in the cortex of each kidney.
Each one is shaped like a cup. It has a tangle of blood capillaries,
called a glomerulus, in the middle. The blood vessels bringing
blood to each glomerulus is quite wide, but the one taking blood
away is narrow. This means that the blood in the glomerulus
cannot get away easily. Quite a high pressure builds up, squeezing
the blood in the glomerulus against the capillary walls.
These walls have small holes in them. So do the walls of the renal capsules. Any molecules small enough to go
through these holes will be squeezed through, into the space in the renal capsule.
Only small molecules can go through. These include water, salt, glucose and urea. Most protein molecules are
too big, so they stay in the blood, along with the blood cells.
53
Reabsorption:
The fluid in the renal capsule is a solution of glucose, salts and urea
dissolved in water. Some of the substances in this fluid are needed by
the body. All of the glucose, some of the water and some of the salts
need to be kept in the blood.
Wrapped around each kidney tubule are blood capillaries. Useful
substances from the fluid in the kidney tubule are reabsorbed, and pass
back into the blood in these capillaries.
The remaining fluid continues on its way along the tubule. By the time it
gets to the collecting duct, it is mostly water, with urea and salts
dissolved in its. It is called urine. The kidneys are extremely efficient at
reabsorbing water. Over 99% of the water entering the tubules is
reabsorbed.
The relative amount of water reabsorbed depends on the state of hydration of the body (how much water is in
the blood), and is controlled by secretion of the hormone ADH.
 On a hot day: we sweat more to cool down  the body needs to conserve water  produce a small
amount of concentrated urine.
 On a cold day: little sweat is being produced  we tend to produce a larger volume of dilute urine.
Filtered blood returns to the vena cava (main vein) via a renal vein. The urine formed in the kidney passes
down a ureter into the bladder, where it is stored. A sphincter muscle controls the release of urine through
urethra.
≥ Explain dialysis in terms of salt balance, the maintenance of glucose concentration and the removal of
urea
 Dialysis membrane is partially permeable so minerals / salts / ions / urea move by diffusion from high
concentration to low concentration gradient
 Water moves by osmosis from high water potential to lower water potential across membrane.
 Proteins / blood cells too large to move across membrane
 Glucose is not removed by dialysate (same concentration)
 Dialysate contains glucose so glucose / sugar diffuses until blood is at correct concentration
 Fresh dialysate maintains a concentration gradient
Concentration of substances when blood enters the dialysis machine
 urea (concentration) decreases
 water (content) increases / decreases
 salt (concentration), decreases
54
≥ Describe the use of dialysis in kidney machines


Provide liquid conditions to allow substance transfer
Maintain the concentration gradient so only urea and little salt will diffuse out while not allowing glucose
and other valuable substances to be diffused out.
≥ Discuss the advantages and disadvantages of kidney transplants, compared with dialysis
Advantages
 Person no longer needs regular dialysis
 Dialysis is tiring, discomforting, takes a long time and fails eventually
 Better quality of life
 More efficient control of composition of blood
 Can have wider diet
 Economic benefit
Disadvantages
 Need immunosuppressant
 Risk of death or infection during or after the operation
 Rejection of kidney
 Finding a compatible donor
 Expensive operation
 Transplantation is not accepted by some religions
55
1 4 . Coordination & Response
Synapse is a junction between two neurones
Sense organs are groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and
chemicals
≥ Describe the human nervous system in terms of: the central nervous system consisting of brain and spinal
cord; the peripheral nervous system; coordination and regulation of body functions
 The human nervous system is made of two parts: central nervous system (CNS) and peripheral nervous
system(PNS);
 CNS ‐ brain and spinal cord, which have the role of coordination;
 PNS ‐ nerves, which connect all parts of the body to the CNS;
 Sense organs are linked to the PNS; they contain groups of receptor cells;
 When exposed to a stimulus they generate an electrical impulse, which passes along peripheral nerves to
the CNS, triggering a response.
 Peripheral nerves contain sensory and motor neurons;
 Sensory neurons transmit nerve impulses from sense organs to the central nervous system;
 Motor neurons transmit nerve impulses from the CNS to effectors (muscles or glands)
 Neurons are covered with a myelin sheath, which insulates them to make transmission of the impulse
more efficient;
 Relay neurons pick up messages from other neurons and pass them on to other neurons.
 The cytoplasm (mainly axon and dendron) is elongated to transmit the impulse for long distances.
≥ Identify motor (effector), relay (connector) and sensory neurones from diagrams
56
≥ Describe a simple reflex arc in terms of receptor, sensory neurone, relay neurone, motor neurones and
effector
≥ Describe a reflex action as a means of automatically and rapidly integrating and coordinating stimuli with
the responses of effectors (muscles and glands)





A reflex arc describes the pathway of an electrical impulse in response to a stimulus;
In diagram above, the stimulus is a pin sticking in the finger;
The response is the withdrawal of the arm due to contraction of the biceps;
Relay neurons are found in the spinal cord, connecting sensory neurons to motor neurons;
Neurons do not connect directly with each other: there is a gap called a synapse.
The sequence of events is:
Stimulus (sharp pin in finger)
↓
Receptor (pain receptors in skin)
↓
Coordinator (spinal cord)
↓
Effector (biceps muscle)
↓
Response (biceps muscle contracts, hand is withdrawn from pin
COMPARISON OF MOTOR AND SENSORY NEURON
Structure
1.Cell body
2.Dendrites
3. Axon (takes impulses
away from cell body)
4. Dendron
Sensory neuron
Near end of the neuron, just
outside the spinal cord
Present at the end of neuron
Very short stretch into spinal cord
Very long stretches to a receptor
57
Motor neuron
At start of neuron, inside the
spinal cord
Attached to cell body and inside
the spinal cord
Very long, stretches from spinal
cord into a muscle
None
1. Receptors detects heat / stimulus
2. Electrical impulses are generated by skin receptor that travels to spinal cord along sensory neurones within
spinal nerve
3. Relay neurone
4. Motor neurone’s nerve impulses sent to effector (biceps / muscle)
5. Biceps contracts
≥ Distinguish between voluntary and involuntary actions
 Voluntary action involves (brain in) decision making / conscious
 Involuntary action doesn't require thinking
 Voluntary action is slow and involuntary action is fast
 Voluntary action is not automatic and involuntary action is automatic
 Voluntary action can be learned
 Voluntary action can give different responses to same stimulus
 Involuntary action give same response to same stimuli all the time
≥ Describe the structure of a synapse, including the presence of neurotransmitter containing vesicles, the
synaptic cleft and neurotransmitter receptor molecules
58
≥ Describe how an impulse triggers the release of a neurotransmitter from vesicles into the synaptic gap and
how the neurotransmitter diffuses across to bind with receptor molecules, in the membrane of the neurone
after the synaptic gap, causing the impulse to continue
When an impulse arrives along the axon of the sensory neurone, it causes these vesicles to move to the cell
membrane and empty their contents into the synaptic cleft. The neurotransmitter quickly diffuses across the
tiny gap, and attaches to receptor molecules in the cell membrane of the relay neurone. This can happen
because the shape of the neurotransmitter molecules is complementary to the shape of the receptor
molecules. The binding of the neurotransmitter with the receptors triggers a nerve impulse in the relay
neurone. This impulse sweeps along the relay neurone, until it reaches the next synapse. Here, a similar
process occurs to transmit the impulse to the motor neurone.
≥ State that in a reflex arc the synapses ensure that impulses travel in one direction only
Synapses act like one‐way valves. There is only neurotransmitter on one side of the synapse, so the impulses
can only go across from that side. Synapses ensure that nerve impulses only travel in one direction.
≥ State that many drugs, e.g. heroin act upon synapses
59
≥ Identify the structures of the eye, limited to cornea, iris, pupil, lens, retina, optic nerve and blind spot
≥ Describe the function of each part of the eye
Part of the eye
Fovea
Blind spot
Optic nerve
Conjunctiva
Sclera
Choroid
Retina
Ciliary body
Suspensory
ligament
Cornea
Iris
Lens
Pupil
Rods
Cones
Function
An area of the retina containing a high concentration of cones, where light is
usually focused and colours are detected
Part of the retina in front of the optic nerve that lacks rods or cones
Transmits electrical impulses from the retina to the brain
A transparent, sensitive layer on the surface of the cornea
A tough, white layer that protects the eyeball
Produces a black pigment to prevent reflection of light inside the eye
A light sensitive layer made of rods and cones
A ring of muscle that controls the shape of the lens to allow focusing
Attaches the lens to the ciliary body, so the lens is held in place
A transparent layer at the front of the eye that refracts the light entering to help
to focus it
A coloured ring of circular and radial muscle that controls the size of the pupil
A transparent, convex, flexible, jelly‐like structure that refracts light to focus it
A hole in the centre of the iris that controls the amount of light reaching the
retina
Sensitive to dim light, do not respond to colour
Function when the light is bright, able to distinguish between different colours
of light
60
≥ Explain the pupil reflex in terms of light intensity and antagonistic action of circular and radial muscles in
the iris
This reflex action changes the size of the pupil to control the amount of light entering the eye
In bright light:
 Retina detects the brightness of light entering the eye;
 An impulse passes to the brain along sensory neurons and travels back to the muscles of the iris along
motor neurons, triggering a response:
 Circular muscles contract; radial muscles relax; so iris gets bigger
 Pupil constricts (gets smaller) so less light falls on the retina (to prevent damage).
In dim light:
 Retina detects the brightness of light entering the eye;
 An impulse passes to the brain along sensory neurons and travels back to the muscles of the iris along
motor neurons, triggering a response:
 Radial muscles contract; circular muscles relax; so iris gets smaller
 Pupil size is increased (dilated) to allow as much light as possible to enter the eye;
≥ Explain accommodation to view near and distant objects in terms of the contraction and relaxation of the
ciliary muscles, tension in the suspensory ligaments, shape of the lens and refraction of light
To focus on a distant object
Slightly diverging rays of light enter the eye
Ciliary muscles relax
Suspensory ligaments are pulled tight
Lens becomes thin
The thin lens bends the light rays slightly
To focus on a nearby object
Greatly diverging rays enter the eye
Ciliary muscles contract
Suspensory ligaments slacken (loosen)
Lens get fatter
The thick lens bends the light rays greatly
61
≥ State the distribution of rods and cones in the retina of a human
Receptors
Distribution
Rods
Found throught the retina, but none in the centrer of
the fovea or in the blind spot
Concentrated in the fovea
Cones
≥ Outline the function of rods and cones, limited to greater sensitivity of rods for night vision and three
different kinds of cones absorbing light of different colours for colour vision
We have two kinds of receptors cells in the retina. Rod cells and Cone cells. Rode cells are sensitive to quite
dim light, but they do not respond to colour. Cone cells are able to distinguish between the different colours
of light, but they only function when the light is quite bright. We have three different kinds of cones, sensitive
to red, green and blue light. Rods therefore allow us to see in dim light but only in black and white, while
cones give us colour vision.
How they work?
1. Light absorbed by a pigment
2. Rods detect low light intensity and give ‘black and white’ vision (provide night vision)
3. Cones detect high light intensity and colour (red, green and blue)
4. Convert light into electrical impulses and it is sent to the brain via neurons / sensory / optic nerve
≥ Describe a nerve impulse as an electrical signal that passes along nerve cells called neurones
Receptor sends impulses. Impulse is then picked up by a sensory receptor in your finger. It travels to the spinal
cord along the axon from the receptor cell. In the spinal cord, the neurone passes an impulse on to several
other neurones. These neurones are called relay neurones, because they relay the impulse on to other
neurones. The relay neurones pass the impulse on to the brain. They also pass it on to an effector. In this case,
the effectors are the muscles in your arm. The impulse travels to the muscle along the axon of a motor
neurone. The muscle then contracts, so that your hand is pulled away.
62
Hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of
one or more specific target organs
≥ Identify specific endocrine glands and their secretions, limited to adrenal glands and adrenaline, pancreas
and insulin, testes and testosterone and ovaries and oestrogen
Gland
Hormone that it secretes
Adrenal Gland
Pancreas
Testis
Ovary
Adrenaline
Insulin
Testosterone
Oestrogen
≥ Describe adrenaline as the hormone secreted in ‘fight or flight’ situations and its effects, limited to
increased breathing and pulse rate and widened pupils
There are two adrenal glands, one above each kidney. They make a hormone called adrenaline. When you are
frightened, excited or keyed up, your brain sends impulses along a nerve to your adrenal glands which
secretes adrenaline into your blood. Adrenaline cause your heart beat faster, supplying oxygen to your brain
and muscles more quickly. This provides them more energy for fighting or running away. Adrenaline also
increases breathing rate, so that more oxygen can enter the blood in the lungs. Adrenaline also causes the
pupils in the eye to widen (allows more light enter the eye so can see danger clearly).
≥ Give examples of situations in which adrenaline secretion increases
 Examination
 You see something scary
≥ State the functions of insulin, oestrogen and testosterone
Insulin
Reduces the concentration of glucose in the blood
Oestrogen
Causes development of female secondary sexual characteristics, helps in the control of the menstrual cycle
Testosterone
Causes development of male secondary sexual characteristics
≥ Discuss the role of the hormone adrenaline in the chemical control of metabolic activity, including
increasing the blood glucose concentration and pulse rate
 Adrenaline is secreted by adrenal glands located one above each kidney;
 Adrenaline helps us to cope with danger by increasing the heart rate;
 Thus supplying oxygen to brain and muscles more quickly, this increase the rate of metabolic activity and
gives more energy for fighting or running away;
 The blood vessels in skin and digestive system contract so that they carry very little blood, as a result we
get ‘butterflies in our stomach’, and more blood goes to brain and muscles;
 Adrenaline also causes the liver to release glucose into the blood;
 This provides extra glucose to the muscles, thus more respiration and more energy is released for
contraction.
63
≥ Compare nervous and hormonal control systems in terms of speed and longevity of action
Feature
Nervous
Hormonal (endocrine)
What are they made of
Form of transmission
Transmission pathway
Speed of transmission
Duration of effect
Response
Neurons
Electrical impulses
Nerves
Fast
Short term
Localized
Secretory cells
Chemical (hormones)
Blood vessels
Slow
Long term
Widespread (although there may
be a specific target organ)
Homeostasis is the maintenance of a constant internal environment
≥ Explain that homeostasis is the control of internal conditions within set limits
It is important that the internal environment of the body is controlled. Maintaining a constant internal
environment is called homeostasis. The nervous system and hormones are responsible for this. These are
some of the internal conditions that are controlled.
Water content of the body
This is controlled to protect cells by avoiding too much water entering or leaving them. Water content is
controlled by water loss from:
 the lungs when we exhale
 the skin by sweating
 the body, in urine produced by the kidneys
Ion (salts) content of the body
This is controlled to protect cells by avoiding too much water entering or leaving them. Ion content is
controlled by loss of ions from:
 the skin by sweating
 the body in urine produced by the kidneys
Temperature of the body
This is controlled to maintain the temperature at which enzymes work best. Body temperature is controlled
by:
 controlling blood flow to the skin
 sweating
 shivering
Blood sugar levels
This is controlled to provide cells with a constant supply of energy. Blood sugar level is controlled by the
release and storage of glucose controlled by insulin.
64
≥ Explain the concept of control by negative feedback
 A change from normal, for instance an increase in blood glucose levels, triggers a sensor, which stimulates
a response in an effector;
 However, the response in this case is the secretion of insulin hormone, which would eventually result in
glucose levels dropping below normal;
 As glucose levels drop, the sensor detects the drop and instructs the effector (pancreas) to stop secreting
insulin (negative effect);
 This is negative feedback‐ the change is fed back to the effector.
≥ Describe the control of the glucose concentration of the blood by the liver and the roles of insulin and
glucagon from the pancreas
 Liver is a homeostatic organ; it controls the levels of glucose;
 Two hormones – insulin and glucagon control blood glucose levels;
 Both hormones are secreted by pancreas and are transported to the liver in the bloodstream.
Role of insulin in controlling blood glucose levels:
 When blood glucose levels are high, then insulin is secreted by pancreas;
 Insulin passes in the bloodstream and then to the liver;
 Insulin stimulates the liver to absorb glucose;
 Insulin converts glucose to glycogen;
 Insulin also increases the rate of respiration; so more blood glucose is absorbed by cells and used up, to
reduce blood glucose levels.
Role of glucagon in controlling blood glucose levels:
 When blood glucose levels drop below normal, glucagon is secreted by the pancreas;
 Glucagon passes in the bloodstream and then to the liver;
 Glucagon converts glycogen to glucose in the liver;
 Glucose is then released into the bloodstream.
≥ Name and identify on a
diagram of the skin:
hairs
hair erector muscles
sweat glands
receptors
sensory neurones
blood vessels
fatty tissue
65
≥ Describe the maintenance of a constant internal body temperature in humans in terms of insulation,
sweating, shivering and the role of the brain (limited to blood temperature receptors and coordination)
≥ Describe the maintenance of a constant internal body temperature in humans in terms of vasodilation and
vasoconstriction of arterioles supplying skin surface capillaries
Humans maintain a body temperature of 37oC;
 A part of the brain called the hypothalamus keeps internal temperature constant by acting like a
thermostat;
 If the temperature is above or below 37oC, the hypothalamus receives information from thermo receptors
in our skin and sends electrical impulses, along nerves, to the parts of the body which have the function of
regulating our body temperature.
When cold, the body produces and saves heat in the following ways:
I.
Shivering: Muscles in some parts of the body contract and relax very quickly. This produces heat and is
called shivering.
II.
Metabolism may increase;
III.
Hair stands up: This produces ‘goose flesh’ and traps a thicker layer of warm air next to the skin, acting as
an insulator;
IV.
Vasoconstriction: The arterioles that supply the skin blood capillaries becomes narrower, thus less blood
flows in them and thus less heat is lost to the air by radiation.
When hot, the body loses more heat in the following ways:
I.
Hair lies flat: No insulation
II.
Vasodilation: The arterioles that supply the skin blood capillaries gets dilated, thus more blood flows
through them and thus heat is readily lost from the blood into the air by radiation;
III.
Sweating: Sweat gland secretes sweat on the surface of skin, which evaporates, taking heat from the skin
with it, thus cooling the body;
IV.
Metabolism slows down.
66
≥ Outline the symptoms and treatment of Type 1 diabetes (detail of β cells is not required)
Symptoms:
 Feeling tired
 Feeling very thirsty
 Frequent urination
 Weight loss
Treatment:
 Avoid large amounts of carbohydrate
 Eat little and often
 Inject insulin
Gravitropism 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 from which
light is coming
≥ Investigate gravitropism and phototropism in shoots and roots
≥ Explain phototropism and gravitropism of a shoot as examples of the chemical control of plant growth
Control of plant growth by auxins
 Auxins are growth hormones;
 They are produced by the shoot and root tips of growing plants;
 An accumulation of auxin in a shoot stimulates cell growth by the absorption of water;
 However, auxins have the opposite effect in roots, when they build up, they slow down cell growth
67
≥ Explain the role of auxin in controlling shoot growth, limited to:
– auxin is unequally distributed in response to light and gravity
– auxin made in shoot tip (only)
– auxin spreads through the plant from the shoot tip – auxin stimulates cell elongation
Phototropism
 When a shoot is exposed to light from one side, auxins produced from the shoot tip towards the shaded
side of the shoot;
 Cells on shaded side stimulated to absorb more water than those on
the light side;
 Thus unequal growth causes the stem to bend towards light;
 This is called positive phototropism.




If a root is exposed to light in the absence of gravity, auxins produced
by the root tip moves towards the shaded side of the root;
Cells on the shaded side are stimulated to absorb less water than
those on the light side;
Thus unequal growth causes the root to bend away from the light;
This is called negative phototropism.
Geotropism
 Shoot and roots also respond to gravity;
 If a shoot is placed horizontally in the absence of light, auxins accumulate on the lower side of the shoot,
due to gravity;
 This makes the cells on the lower side grow more quickly than on the upper side, so the shoot bends
upwards ‐ negative geotropism;


If a root is placed horizontally in the absence of light,
auxins accumulate on the lower side of the root, due to
gravity;
Thus the cells on the lower side grow more slowly than
those on the upper side, so the root bends downwards ‐
positive geotropism
.
68
≥ Describe the use in weedkillers of the synthetic plant hormone 2,4‐D
 To kill weeds in lawns, cereal, crops [wheat, millet, maize and sorghum] (Weeds are affected by the auxin
but doesn’t affect the grass)
 Weed killers contain plant hormones that contain type of auxin, usually a synthetic form
 The weeds respond by growing very fast then die leaving more space, nutrients and water for the grass to
grow
1 5 . Drugs
Drug is any substance taken into the body that modifies or affects chemical reactions in the body
Injecting heroin can cause infections such as HIV
Excessive alcohol consumption can cause liver damage
Tobacco smoking can cause chronic obstructive pulmonary disease (COPD), lung cancer and coronary heart
disease
The liver is the site of breakdown of alcohol and other toxins
≥ Describe the use of antibiotics for the treatment of bacterial infection
Antibiotics are substances that kill bacteria or prevent their growth, but do not harm other living cells. Most
of them are made by fungi. It is thought that the fungi make antibiotics to kill bacteria living near them –
bacteria and fungi are both decomposers, so they might compete for food.
The first antibiotic to be discovered was penicillin. It is made by the fungus Penicillium. Penicillin kills bacteria
by: preventing the production of peptidoglycan that form the cell wall:  the cell continue to grow without
dividing or developing new cell wall  the wall gets weaker  ruptures (lysis).
Since the discovery of penicillin in 1928, many more antibiotics have been developed and used to treat
bacterial infections. Some bacteria have mutated and become resistant to antibiotics, but new drugs are
constantly being developed and tested.
≥ Explain why antibiotics kill bacteria, but do not affect viruses
Antibiotics do not work against viruses. Many antibiotics kill bacteria by damaging their cell walls. Viruses do
not have cell walls, so they are unharmed by antibiotics. It is difficult to develop drugs that kill viruses without
damaging the body’s tissues
69
≥ Explain how development of resistant bacteria such as MRSA can be minimised, limited to using
antibiotics only when essential and ensuring treatment is completed
 Use antibiotics less often
 Don't use antibiotics for not viral / fungal infections
 Make sure people complete the course of antibiotics
 Develop new antibiotics
 Do not use the same antibiotics for too long
 Use combinations of antibiotics
≥ Describe the effects of excessive alcohol consumption and abuse of heroin, limited to:
Heroin:
 Heroin is a powerful depressant.
 It is a narcotic, producing a dream‐like feeling of relaxation and reducing severe pain.
 It is very addictive, leading to dependency (addiction).
 Withdrawal symptoms can be very unpleasant – involving cramp, sleeplessness, violent vomiting, sweating
and hallucinations.
 The body develops a tolerance to the drug, so an addict needs to take increasing amount to achieve the
same feeling. This leas t the risk of overdosing on the drug.
 When injected using unsterilized and shared needles, there is a risk of infections such as hepatitis and HIV.
 Addiction creates financial problems leading to family breakdown, criminal activity and sexual promiscuity.
Alcohol:
 Small amounts – alcohol can relax the body and create a sense of wellbeing.
 Alcohol is a depressant: larger amounts slow down the transmission of electrical impulses in the brain, so
reactions are depressed, coordination is impaired and reasoned judgments become difficult. Mood swings
involving violence can result.
 Decrease in reaction time makes driving and handling machinery dangerous.
 Poor judgments may leads to criminal activity and sexual promiscuity.
 Long‐term excessive drinking can lead to addiction (alcoholism).
 This can lead to financial difficulties and family problems.
 As the liver removes alcohol from the blood, heavy drinking can leas to liver damage such as cirrhosis.
 Drinking can cause brain damage, peptic ulcers in the stomach and obesity.
 Drinking during pregnancy can damage the fetus, increase the risk of miscarriage or premature birth, and
reduce the average birth weight.
70
≥ Describe the effects on the gas exchange system of tobacco smoke and its major toxic components,
limited to carbon monoxide, nicotine and tar
Chemical
Effects on gas exchange system
Carbon monoxide
A poisonous gas; combines with hemoglobin in RBC, preventing them from
transporting oxygen
Nicotine
Addictive; increases heart rate & blood pressure
Smoke particles
Irritate the air passages, causing inflammation & increased mucus production,
resulting in chronic bronchitis; coughing and the presence of particles in the alveoli
can lead to emphysema (breaking the walls of the alveoli)
Tar
A carcinogen ‐ increases the risk of lung cancer; lines the air passages, increasing
mucus production and paralyzing and damaging cilia, causing bronchitis.
≥ Explain how heroin affects the nervous system, limited to its effect on the function of synapses
Endorphins help to reduce sensations of pain, affect mood and reduce sensations of hunger and thirst. When
it enters the brain, heroin is metabolised to morphine. Morphine molecules fit into some of the endorphin
receptors. This is why heroin makes people feel good. Unfortunately, taking heroin can reduce the production
of natural endorphins, and also affect the brain's production of other important neurotransmitters. Users
often find that they have to keep taking more and more heroin to get the same effect and, if they stop using it,
will suffer extremely unpleasant withdrawal symptoms.
≥ Discuss the evidence for the link between smoking and lung cancer
It was in the 1950s that people first began to realise that there was a link between smoking cigarettes and
getting lung cancer. The person at the forefront of this new understanding was a medical researcher called
Richard Doll (Figure 15.11). At that time, doctors were becoming concerned about the rapid rise of lung cancer
in the British population. No‐one knew why this was happening.
Richard Doll interviewed lung cancer patients in 20 hospitals in London,
trying to find out if they had anything in common. His initial theory was
that this was something to do with the new substance, tarmac, that
was being used to build roads. However, it rapidly became clear to him
that all of these people were smokers. Very quickly, he himself stopped
smoking. Doll published the results of his research in a journal in 1950,
but it was many years before everyone was prepared to accept the link
between smoking and lung cancer. The difficulty was that you could
not really do a controlled experiment on it. Instead, researchers had to
rely on looking for a correlation between these two factors. The graphs
in Figure 15.12 show that there is a correlation between the number of
cigarettes smoked per year and the number of deaths from lung
cancer. For many years, tobacco companies tried to play down this link.
They suggested many other possible reasons for the correlation,
because they did not want people to stop smoking. However, much
research has now been done on the effects of smoking on health, and
we now understand how smoking — both passive and active ‐ can
cause lung and other cancers. For example, we know that tar contains
chemicals that affect the DNA in cell nuclei. These chemicals can damage the normal control mechanisms of a
cell, so that it begins to divide over and over again. This is how cancer begins. Chemicals that can cause this to
happen are called carcinogens. Tar in cigarette smoke contains many different carcinogens.
71
≥ Discuss the use of hormones to improve sporting performance, limited to testosterone and anabolic
steroids
Some hormones belong to a class of chemicals called the steroids. Steroid hormones include the reproductive
hormones testosterone, oestrogen and progesterone. Many steroid hormones stimulate metabolic reactions
in body cells that build up large molecules from small ones. These reactions are called anabolic reactions.
Steroid hormones that stimulate these reactions are called anabolic steroids. One type of reaction that is
stimulated by anabolic steroids is the synthesis of proteins from amino acids.
 Testosterone causes more proteins to be made in muscles, so that muscles become larger and stronger
 Athletes and others have taken anabolic steroids to increase their muscle size and strength
 These hormones can help athletes to train harder and for longer periods of time
1 6 . Reproduction
Asexual reproduction is a process resulting in the production of genetically identical offspring from one parent
≥ Identify examples of asexual reproduction from information provided
Potatoes, for example, reproduce using stem tubers (Figure 16.2). Some of
the plant's stems grow normally, above ground, producing leaves, which
photosynthesize. Other stems grow under the soil. Swellings called tubers
form on them. Sucrose is transported from the leaves into these
underground stem tubers, where it is converted into starch and stored.
The tubers grow larger and larger. Each plant can produce many stem
tubers. The tubers are harvested, to be used as food. Some of them,
however, are saved to produce next year's crop. These tubers are planted
underground, where they grow shoots and roots to form a new plant.
Because each potato plant produces many tubers, one plant can give rise
to many new ones. To get more plants, tubers can be cut into several
pieces. As long as each piece has a bud on it, it can grow into a complete
new plant.
≥ Discuss the advantages and disadvantages of asexual reproduction:
Advantages
 The process is quick
 Only one parent is needed
 No gametes are needed
 All the good characteristics of the parent are passed on to the offspring;
 They usually store large amounts of food that allow rapid growth when conditions are suitable
 Dense colonies outcompete other species
 Less energy / resources used
Disadvantages
 There is little variation created, so adaptation to a changing environment (evolution) is unlikely;
 If the parent has no resistance to a particular disease, none of the offspring will have resistance;
 Lack of dispersal (e.g. potato tubers) can lead to competition for nutrients, water and light.
72
Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote
and the production of offspring that are genetically different from each other
Fertilisation as the fusion of gamete nuclei
Nuclei of gametes are haploid and that the nucleus of a zygote is diploid
≥ Discuss the advantages and disadvantages of sexual reproduction:
Advantages
 There is variation in the offspring so adaptation to a changing or new environment is likely, enabling
survival of the species
 New varieties may be created which may have resistance to disease
 In plants, seeds are produced, which allow dispersal away from the parent plant, reducing competition
(colonization)
Disadvantages
 Two parents are usually needed (although not always‐ some plants can self‐pollinate)
 Growth of a new plant to maturity from a seed is slow
 Much pollen / many seeds wasted
 Fertilization may not happen
 Loss of lots of energy
Pollination is the transfer of pollen grains from the anther to the stigma
Self‐pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same flower or
different flower on the same plant
Cross‐pollination is transfer of pollen grains from the anther of a flower to the stigma of a flower on a
different plant of the same species
≥ Identify and draw, using a hand lens if necessary, the sepals, petals, stamens, filaments and anthers,
carpels, style, stigma, ovary and ovules, of an insect‐pollinated flower
73
≥ State the functions of the sepals, petals, anthers, stigmas and ovaries
Part
Function
Petal
Sepal
Petiole (stalk)
Often large and coloured, to attract insects
Protects the flower while in bud
Supports the flower to make it easily seen by insects, and to be able to
withstand wind
The male reproductive part of the flower, made of anther and filament
Contains pollen sacs, in which pollen grains are formed. Pollen contains
male sex cells
Supports the anther
The female reproductive part of the flower, made of stigma, style and ovary
A sticky surface that receives pollen during pollination
Links the stigma to the ovary, through which pollen tubes grow
Contains ovules, which develop into seeds when fertilised
Stamen
Anther
Filament
Carpel
Stigma
Style
Ovary
≥ Use a hand lens to identify and describe the anthers and stigmas of a wind‐pollinated flower
≥ Distinguish between the pollen grains of insect‐pollinated and wind‐pollinated flowers
Wind‐Pollinated Flowers:
Pollen grains are smooth, light and very small to be easily carried by the wind  produced in large quantities
Insect‐Pollinated Flowers:
Pollen grains are big, and with hooks to attach to insect’s legs  produced in smaller quantities
74
≥ Investigate and state the environmental conditions that affect germination of seeds, limited to the
requirement for water, oxygen and a suitable temperature
Environmental
condition
Water
Oxygen
Suitable temperature
Light
Explanation
Absorbed through micropyle, needed to activate enzymes
which convert insoluble food stores into soluble foods needed
for growth and energy production.
Needed for respiration, to release energy for growth and
chemical changes for mobilization of food reserves
For enzymes to work as enzymes work best at optimum
temperature
Not usually a requirement for germination but some seeds
need a period of exposure to light before they germinate
75
≥ Describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (details of
production of endosperm and development are not required)
1. Pollen grain germinates and grows pollen tube
2. Pollen tube grows down the style
3. Secretes enzymes to digest a pathway through the style
4. Ovule is surrounded by (layers of) integuments, at one end, there is a small
hole called micropyle
5. Pollen tube grows through the micropyle and reaches the ovule
6. Tip of pollen tube breaks open
7. Male gamete(s) travels down the pollen tube and enter the ovule
8. Male gamete fuses with female gamete and zygote is formed
≥ Describe the structural adaptations of insect‐pollinated and wind‐pollinated flowers
Feature
Insect‐pollinated
Wind‐pollinated
Petals
Absent or small and inconspicuous
Nectar
Stamen
Present‐ often large, coloured and
scented
Produced by nectaries to attract insects
Present inside the flower
Stigmas
Small surface area, inside the flower
Pollen
Smaller amounts‐ grains are often
round and sticky, or covered in spikes to
attach to the furry bodies of insects
Absent
Bracts (modified
leaves)
Absent, or small and green
Long filaments, allowing the anthers to hang
freely outside the flower so the pollen is
exposed to the wind
Large and feathery, hanging outside the
flower to catch pollen
Larger amounts of smooth and light pollen
grains, which are easily carried by the wind
Sometimes present
≥ Compare male and female gametes in terms of size, structure, motility and numbers
Types of gamete
Structure
1. Is large in size 0.1mm because it has all cell
components that is needed for the cell to grow
and multiply; has yolk to nourish the embryo.
2. During ovulation, only one egg is released every
month.
3. Ovum is immobile as the sperm moves towards
it to fertilise it.
1. Size is very small 0.05mm.
2. During ejaculation millions of sperms are
produced into the women’s vagina.
3. Sperms are highly mobile and can swim towards
the oviduct with the help of its tail.
76
≥ Identify and name on diagrams of the male reproductive system: the testes, scrotum, sperm ducts,
prostate gland, urethra and penis, and state the functions of these parts
Part
Function
Testes
Scrotum
produce sperm and testosterone
a sac that keeps testes cool (outside body); keeping
them cooler than body temperature
Muscular tube which links the testis to the urethra
to allow the passage of semen containing sperm
Adds fluid and nutrients to sperm, to form semen
To pass semen containing sperm through the penis,
also carries urine from the bladder at different times
become firm, inserted into vagina during sexual
intercourse  transfer sperm
Sperm Ducts
Prostate Glands
Urethra
Penis
≥ Identify and name on diagrams of the female reproductive system: the ovaries, oviducts, uterus, cervix
and vagina, and state the functions of these parts
Part
Ovary
Oviduct
Uterus
Cervix
Vagina
77
Function
contains follicles, produce and
stores eggs, produce oestrogen
Carries an ovum to the uterus,
with propulsion provided by tiny
cilia in the wall; Fallopian tubes
= site of fertilisation
where fetus develops
a ring of muscles that separate
the vagina from the uterus
receives sperm from erect penis
during intercourse; sperm are
deposited here
≥ Describe fertilisation as the fusion of the nuclei from a male gamete (sperm) and a female gamete (egg
cell/ovum)
 Sexual intercourse involves inserting the erect penis into the vagina.
 When stimulated, spongy tissue in the penis filled with blood and
becomes erect.
 At the climax, semen is ejaculated from the penis into the neck of
the vagina.
 Muscles in the wall of the sperm duct help to propel the semen
forward
 The sperms with their tails swim from the vagina, through the cervix
and uterus, into an oviduct.
 Ovum/egg pass down in oviduct
 A single sperm penetrates the membrane of ovum by secreting a protease enzyme; only the head of the
sperm goes in, the tail is left outside.
 The sperm nucleus and the egg nucleus fuse to form a diploid zygote = fertilization
 Sperm can remain active in the oviduct for at least 2 days and the ovum may take a day to pass from the
ovary to the uterus, so there is a fertile period of 3 to 4 days around ovulation when fertilization can
happen.
≥ Explain the adaptive features of sperm, limited to flagellum, mitochondria and enzymes in the acrosome
 Tail (for motility) which propels it through the cervix, uterus and fallopian tube towards the egg.
 Each sperm has many mitochondria (where respiration occurs) to release the energy needed for its
journey.
 Acrosomes allow them to break through the cell membrane of the egg.
≥ Explain the adaptive features of egg cells, limited to energy stores and the jelly coat that changes at
fertilization
 It has a large cytoplasm which contains the nutrients and mitochondria needed for mitosis (cell division)
after fertilisation.
 Each egg has a special cell membrane which only allows one sperm to fertilise it.
≥ State that in early development, the zygote forms an embryo which is a ball of cells that implants into the
wall of the uterus
When the sperm and egg nucleus fuse together, they form a zygote. The zygote continues to move slowly
down the oviduct. As it goes, it
divides by mitosis. After several
hours, it has formed a ball of cells
called embryo. It takes several hours
for the embryo to reach the uterus
and by this time it will be a ball of 16
or 32 cells. The uterus has thing,
spongy lining, and the embryo sinks
into it. This is called implantation.
78
≥ State the functions of the umbilical cord, placenta, amniotic sac and amniotic fluid
Part
Functions

Umbilical cord
umbilical cord transports nutrients / excretory
products
 attaches the placenta to the fetus
Placenta
 Prevention of maternal and fetal blood mixing
 Protection against mother’s immune system
 Supply of oxygen (to fetus)
 Loss of carbon dioxide (from fetus)
 Loss of urea / waste
 Protection against pathogens
 Transfer of antibodies (from mother)
 Supply of nutrients
 Supply / removes water
 Secretes hormone
Amniotic sac
 membrane from embryo cells: encloses fetus
 prevents entry of pathogens
 secretes the amniotic fluid
Amniotic fluid
 supports fetus
 protects against damage
 provides constant temperature
 allows fetus to move
 needed for bone / muscle growth / development
 helps lungs / gut develop
 collects fetal urine / waste
 provides sterile environment
≥ Describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients,
gases and excretory products and providing a barrier to toxins and pathogens (structural details are not
required)
 The placenta brings the blood supply of the fetus close to that of the mother, but prevents mixing;
 This is important because the fetus and mother may have different blood groups and any mixing can result
in blood clotting;
 Also the mother’s blood pressure is higher compared to the fetus which might damage the fetal organs;
 Blood from fetus passes through the umbilical cord in the umbilical artery to the placenta.
 Substances that diffuse across the placenta are as follows:
Type of substance
Respiratory gases
Soluble nutrients
Disease‐preventing substances
Nitrogenous excretory
substances
Potentially harmful substances
To fetus from mother
Oxygen
Amino acids, glucose, fatty acids,
glycerol, vitamins, minerals, water
Antibodies, antibiotics
To mother from fetus
Carbon dioxide
Urea
Alcohol, nicotine and other drugs,
viruses, bacteria
Some toxins, e.g. nicotine, and pathogens, e.g. rubella virus, can pass across the placenta and affect the fetus
79
≥ Outline the growth and development of the fetus in terms of increasing complexity in the early stages and
increasing size towards the end of pregnancy
Ovary




Pituitary gland

a follicle develops
secretes oestrogen
↑↑ oestrogen in the blood.
lining of the uterus grows thick, spongy
secretes LH, FSH

stimulates follicle to secrete
oestrogen.
When the follicle is fully developed ‐‐‐> LH ↑↑↑↑ and FSH ↑↑

follicles rupture and release fully developed ovarian
cells (ovulation)

empty follicle stops secreting oestrogen

becomes a corpus luteum

secretes progesterone
uterus lining thick, spongy, well supplied with blood in

case an egg is fertilised.


If the egg is fertilized
corpus luteum does not degenerate so quickly
secretes progesterone until the embryo sinks into
uterus wall and a placenta develops

Placenta secretes progesterone through pregnancy
it maintains the uterus lining so that the
menstruation does not happen during pregnancy
80

↓↓ LH, FSH



If the egg is not fertilized
corpus luteum gradually disappears
no more progesterone secreted
uterus lining breaks down

Menstruation
a new follicle develops
81
≥ Discuss the advantages and disadvantages of breast‐feeding compared with bottle‐feeding using formula
milk
Advantages
 provides most suitable food
 easy to digest
 less risk of allergies / child less likely to develop diabetes
 provides passive immunity / provides protection against pathogens / diseases / microorganisms
(antibodies)
 always available
 less risk of infection (sterile)
 bonding with mother
 is at body temperature
 it’s free
Disadvantages
 time consuming
 transfer of viruses / HIV / hepatitis B
 painful / sore nipples / mastitis
 stressful / may be embarrassing




mother may not be able to produce enough milk
cannot see how much baby has consumed
task cannot be shared with other parent
medications / drugs / alcohol can pass to baby
82
≥ Describe the ante‐natal care of pregnant women, limited to special dietary needs and the harm from
smoking and alcohol consumption
When a woman is pregnant, she should take extra care of her health since it will affect the fetus too. She
should ensure that her diet contains lots of calcium (for fetus bones), extra iron (needed for haemoglobin 
lots of red blood cells needed to carry nutrient), little extra carbohydrate (energy to move her heavier body
around), and extra protein (to help to form her growing fetus’s new cells). Harmful substances travel across
the placenta too. Smoking can cause the baby to grow more slowly and be born smaller than normal. Pregnant
woman should also avoid alcohol consumption.
≥ Outline the processes involved in labour and birth, limited to:
Stage 1
 The muscular walls of the uterus start to contract ‐‐‐> slowly stretch the opening of the cervix.
 The pressure breaks the amniotic sac, releasing the amniotic fluid.
 Contraction gradually become more frequent, pushing the baby down towards the cervix, which
become dilated to allow baby to pass through.
Stage 2
The vagina stretches to allow the baby to be born.
Stage 3
The baby is still attached to the placenta by the umbilical cord, so this is cut and tied. The placenta breaks
away from the wall of the uterus and passed out (afterbirth).
≥ Describe the sites of production of oestrogen and progesterone in the menstrual cycle and in pregnancy
Hormone
Production in menstrual cycle
Production in pregnancy
Oestrogen
Ovary; Follicle; Corpus Leteum
Placenta
Ovary; Remains of Follicle; Corpus Placenta; Corpus luteum / yellow
Progesterone
Leteum
body / ovary
≥ Outline artificial insemination (AI)
1. Semen / sperm is collected from male / donor / sperm bank
2. Inserted into vagina / cervix / uterus / womb / oviduct
3. Near time of ovulation / at fertile time
≥ Outline in vitro fertilisation (IVF)
Egg is fertilised outside the body (in dish) and the resulting embryo is placed into the uterus where they
develop in the usual way
83
≥ Describe the roles of testosterone and oestrogen in the development and regulation of secondary sexual
characteristics during puberty
Oestrogen‐ females
 The beginning of the menstrual cycle
 Body mass increases and redistributed‐ to hips and breasts
 Body hair‐ pubic
 Voice deepens slowly
 Development of sexual organs
Testosterone‐ males
 Production of sperm
 Growth of sexual organs/genitals
 Body hair‐ pubic, arms and face
 Broad shoulders
 Increase in muscles
 Voice breaks (becomes deeper)
 Development of a sexual drive
≥ Explain the role of hormones in controlling the menstrual cycle and pregnancy, limited to FSH, LH,
progesterone and oestrogen
Hormone
Role in menstrual cycle
o
o
o
o
Oestrogen
o
o
o
o
o
o
Progesterone
o
o
o
FSH
o
o
o
LH
o
o
o
Repair of the endometrium / lining of uterus
Thickening / building up of endometrium
Development of blood (vessels) / glands
Prepares (uterus) for implantation of embryo
Release of LH
Inhibits release of FSH (from pituitary)
Stops, production / release of more eggs
Causes change in cervical mucus
Maintains the lining of uterus
Prepares for implantation
Prevents FSH secretion / inhibits LH
Prevents follicle development
FSH stimulates follicle (cells) to grow  to
secrete oestrogen
Causes maturation of egg
Low FSH after ovulation, prevents further
follicle stimulation
Stimulate oestrogen and progesterone
secretion
Stimulate maturation of ovum
Ovulation
Formation of corpus leteum
84
Role in pregnancy
o Develops (lining of) uterus /
endometrium
o Prevent shedding of lining /
menstruation
o Inhibit (release of) FSH by pituitary
gland
o Stops menstrual cycle in pregnancy
o Promotes development / maintains
blood vessels
≥ Outline the following methods of birth control:
Natural:
Abstinence
Avoiding sexual intercourse completely or ensure that they do not have sexual intercourse when the woman
has an egg in her oviducts.
Monitoring Body Temperature
Record of body temperature is needed. Around the time of ovulation, the temperature rises slightly
Cervical Mucus
The woman can check for the mucus in her vagina. This becomes more liquid and slippery around the time of
ovulation
Chemical:
IUD (Intra‐uterine device)
A device that is placed inside the uterus (some contain copper)
IUS
A device that slowly releases hormones that prevent implantation. This interferes with the ability of sperm to
find and fertile the egg, and also prevents the implantation and the development of any egg that does get
fertilised.
Contraceptive pill
The pill contains the female sex hormones oestrogen and progesterone. One pill is taken every day. The
hormones are like those that are made when a woman is pregnant, and stop egg production
Spermicides
Spermicidal cream in the vagina kills sperm
Barrier:
Condom
Placed over erect penis. It traps semen as it is released, stopping it from entering vagina
Femidom
Same as condom but placed in vagina
Diaphragm or caps
It is a circular sheet of rubber, which is placed over the cervix, at the top of the vagina. Spermicidal cream is
first applied around the edges. Sperm deposited in the vagina cannot get past the diaphragm into the uterus
Surgical:
Sterilisation
In a man, the sperm ducts are cut or tied, stopping sperm from travelling from the testes to the penis. In a
woman, the oviducts are cut or tied, stopping eggs from travelling down the oviducts
85
≥ Outline the use of hormones in contraception and fertility treatments
Fertility drugs
FSH / LH / clomiphene / clomid causes the ovaries to produce more eggs which increases the chance of
fertilisation
Female
hCG stimulates follicles to release eggs
Progesterone causes lining of uterus / endometrium to thicken which increases chance of implantation
Male
hCG to stimulate testosterone production
Testosterone stimulates sperm production
Chemical methods of birth control
Oestrogen / progesterone in contraceptive pill prevents FSH release  prevents egg / follicle development 
prevents ovulation / release of eggs
Progesterone only pills inhibit sperm movement through cervix which prevents implantation
Contraceptive pill kills sperm in vagina / cervix and prevents sperm reaching egg / entering oviduct
≥ Discuss the social implications of contraception and fertility treatments
Fertility
o Stress is associated with difficulty having children
o Multiple births might occur
o Problems with unused embryos (when used with IVF)
o Issues with elderly parent(s)
o Religious objections to use of fertility drugs
o Treatment might be expensive
o Increases populations
o Can be used to increase populations (useful in countries where birth rate is low)
Contraception
o It is a widely held belief that the pill revolutionized sex for women as they no longer had to worry about
pregnancy.
o Another social effect is that it allows for population control in a way that did not exist 100 years ago.
o It is also a class/religious/monetary thing: those who can most afford to have and raise children can select
when and how many they have. Those who can least afford to have and raise multiple children (poverty,
3rd world countries) are least likely to have access to contraception and may be the most in need of it.
o STDs are also relevant. AIDS in women has increased greatly because they are more likely to contract it
during sexual intercourse with an infected partner.
o Religion often forbids the use of contraception (catholics are notorious for this) and yet believe they have
no responsibility for the spread of illness.
o If contraception were universally available and acceptable, it could be a great equalizer against poverty
and disease.
86
Sexually transmitted infection is an infection that is transmitted via body fluids through sexual contact
Human immunodeficiency virus (HIV) is an example of an STI
HIV infection may lead to AIDS
≥ Explain how the spread of STIs is controlled
o Use of condom/femidom (during sexual intercourse)
o To abstinence from sexual intercourse
o Screening of blood for transfusions/blood checked for HIV
o Use of sterile needles (for injecting drugs) / don't share needles
o Feed baby with bottled powdered milk (if mom has HIV)
o Use sterilised surgical instruments
≥ Describe the methods of transmission of HIV
o Unprotected sexual intercourse
o Across placenta at birth or in breast milk
o Sharing needles
o Blood for transfusion
≥ Outline how HIV affects the immune system, limited to decreased lymphocyte numbers and reduced
ability to produce antibodies
o HIV infects lymphocytes causing fewer antibodies to be produced
o Infected cells are not killed by immune system
o Phagocytes become less effective
o Increased susceptibility to infectious diseases, cancers and opportunistic diseases
o AIDS will be developed
≥ Discuss the implications to a species of self‐pollination and cross‐pollination in terms of variation, capacity
to respond to changes in the environment and reliance on pollinators
87
1 7 . Inheritance
Inheritance is the transmission of genetic information from generation to generation
Chromosome 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
Allele is a version of a gene
Mitosis is nuclear division giving rise to genetically identical cells
Meiosis is reduction division in which the chromosome number is halved from diploid to haploid resulting in
genetically different cells
Haploid nucleus is a nucleus containing a single set of unpaired chromosomes, e.g. in gametes
Diploid nucleus is a nucleus containing two sets of chromosomes, e.g. in body cells
Genotype is the genetic make‐up of an organism in terms of the alleles present (eg. Tt or GG)
Phenotype is the observable features of an organism
Homozygous is having two identical alleles of a particular gene
Heterozygous is having two different alleles of a particular gene
Dominant is an allele that is expressed if it is present
Recessive is an allele that is only expressed when there is no dominant allele of the gene present
Sex‐linked characteristic is 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
In a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs (46
chromosomes)
Role of mitosis in growth, repair of damaged tissues, replacement of cells and asexual reproduction
The exact duplication of chromosomes occurs before mitosis
During mitosis, the copies of chromosomes separate, maintaining the chromosome number (details of stages
of mitosis are not required)
Meiosis is involved in the production of gametes
Two identical homozygous individuals that breed together will be pure‐breeding
Heterozygous individual will not be pure‐breeding
≥ Describe the inheritance of sex in humans with reference to XX and XY chromosomes
o 23 pairs of chromosomes present in each human cell; one pair is the sex chromosome;
o These determine the sex of the individual;
o Males have XY, and females have XX.
88
≥ Explain that 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 (knowledge of the details of nucleotide structure is not required)
DNA has only four bases but proteins have 20 different amino acids. This means that the four DNA ‘letters’
have to be combined to make different ‘words’, each one signifying a particular amino acid.
≥ Explain that DNA controls cell function by controlling the production of proteins (some of which are
enzymes), antibodies and receptors for neurotransmitters
Controls functions in the cell
DNA molecule carries a code that instructs the cell about which kinds of proteins should make. Each
chromosome carries instructions for making many different proteins. A part of DNA molecule coding for one
protein is called a gene. Protein is made up of long chains of amino acids. There are 20 different amino acids.
The sequence of these amino acids in a protein molecule determines the final shape of the molecule and this
shape also affects how the protein works. DNA contains a code that determines exactly what sequence of
amino acids a cell should string together when its making a particular protein. This is how genes affect an
organism’s features. A gene determines what protein will be made, and protein affects a feature of the
organism. Many proteins do this by acting as enzymes. Other proteins have different functions, such as
antibodies and receptors for neurotransmitters.
≥ Explain how a protein is made, limited to: 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 (knowledge of the details of transcription or translation is not required)
DNA is found in the nucleus of protein. Protein
synthesis happens on the ribosomes, in the cytoplasm.
To carry information from the DNA to the ribosome, a
messenger molecule called RNA (mRNA) is used. When
a protein is to be made, an mRNA molecule is made in
the nucleus, copying the base sequence from the
appropriate length of DNA. The mRNA then moves out
from the nucleus into the cytoplasm, and attaches to a
ribosome. If you have a good diet, then the cytoplasm
in your cells will contains plenty of all the 20 different
amino acids. As the long, thin mRNA molecule passes
through it, the ribosome links amino acids together in exactly the right order to make the desired protein,
following the code contained on the mRNA molecule.
≥ Explain how meiosis produces variation by forming new combinations of maternal and paternal
chromosomes (specific details are not required)
Human gametes are formed by the division of cells in the ovaries and testes. The cells divide by a special type
of cell division called meiosis. Meiosis shares out the chromosomes so that each new cell gets just one of each
type. Each pair of homologous chromosome comes from the mother and father. During meiosis, the new cells
get a mixture of these. So a sperm cell could contain a chromosome 1 from the man’s father and a
chromosome 2 from his mother, and so on. There are all sorts of combinations, this is why gametes are
genetically different from the parent cell. Meiosis gives genetic variation.
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≥ Describe stem cells as unspecialised cells that divide by mitosis to produce daughter cells that can become
specialised for specific functions
'Unspecialised' stem cells can develop into any other type of cell.
Stem cells are found in animal zygotes (very young embryos), and in
plants of all ages.
o A zygote is a structure that forms when a sperm fertilises an egg.
o a zygote containing eight identical cells
o Zygote at the eight cell stage
o The zygote then divides many times by mitosis to form an
embryo. The first division of the zygote forms two cells, the next
four, the next eight, and so on.
o Up to the eight‐cell stage, all of the cells are identical. They are
called embryonic stem cells. It is possible for embryonic stem
cells to develop into any other specialised type of cell that the
growing embryo needs ‐ for example, nerve cells, blood cells and
muscle cells. However, once the embryonic stem cells become
specialised, they can't change into any other type of cell.
o The specialised cells can form all the different types of tissue that the embryo needs.
Switching genes on and off
Cells become specialised because the genes that are not required are switched off. Only the genes needed to
make a particular type of cell work are switched on. So muscle cells only have the genes needed to make
muscle cell proteins switched on. All the other genes, such as those needed to make blood cell proteins and
nerve cell proteins, are switched off.
≥ Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic ratios, limited
to 1:1 and 3:1 ratios
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≥ Explain how to use a test cross to identify an unknown genotype
An organism that shows a dominant characteristic could have either of two possible genotypes. It could be
homozygous for the dominant allele, or it could be heterozygous. For example, a grey chinchilla could have the
genotype GG or Gg. We can find out the genotype of an individual with the dominant phenotype for a
particular gene by crossing it with one known to have the homozygous recessive genotype for the same gene
This is called a test cross. For example, if we know that the allele for tallness is dominant to the allele for
dwarfness in a certain species of pea, then the genotype of any tall plant could be determined by crossing it
with a dwarf plant. If any of the offspring are dwarf, then this must mean that the tall parent had an allele for
dwarfness. It must have been heterozygous. Try this out for yourself, using a genetic diagram. If none of the
offspring are dwarf, this almost certainly means that the tall parent was homozygous for the tallness allele.
However, unless there are large numbers of offspring, this could also happen if the tall parent is heterozygous
but, just by chance, none of its gametes carrying the recessive allele were successful in fertilisation.
≥ Explain co‐dominance by reference to the inheritance of ABO blood groups – phenotypes being A, B, AB
and O blood groups and alleles being IA, IB and Io
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. There are three alleles of the gene governing this instead of
two. Allele IA and IB are codominant, but both are dominant to IO. A
person with the genotype IA IB has the blood type AB, in which characteristics
of both A and B antigens are expressed.
≥ Describe colour blindness as an example of sex linkage
Most of the time sex‐linked genes are
carried on the X chromosome. Since females
have two X chromosomes they have two
copies of the sex‐linked gene whereas males
only have one since they only have one X
chromosome. Colour blindness is example of
sex linkage. Genes that are found only on
the non‐homologous parts of the X or Y
chromosomes are called sex‐linkage genes.
One of these sex‐linked genes control the
production of the three different kinds of cone cells in the retina. A recessive allele of this, b, results in only
two types of cone cells being made. A person who is homozygous for this allele cannot tell the difference
between red and green. They are said to be red‐green colour blind.
This condition is much more common men than in woman. Pic
below shows possible genotypes that a woman might have, but only
two possible genotypes for man. When we write genotypes
involving sex‐linked genes, we need to show the chromosomes as
well as the allele. So the five possible genotypes and their
phenotypes for red‐green colour‐blindness are:
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≥ Use Punnett squares in crosses which result in more than one genotype to work out and show the possible
different genotypes
≥ Explain that all body cells in an organism contain the same genes, but many genes in a particular cell are
not expressed because the cell only makes the specific proteins it needs
Every cell in a multi‐cellular organism contains a complete set of chromosomes with every gene needed to
make every protein that that organism will ever make.
However, in any particular cell, only a very small fraction of these genes are ever expressed.
Each cell is specialised to carry out a certain task and will only need to express certain genes.
Gene expression is the process by which specific genes are activated to produce a required protein.
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1 8 . Variation & Selection
Variation is differences between individuals of the same species
Mutation is genetic change
Gene mutation is a change in the base sequence of DNA
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
Process of adaptation is the process, resulting from natural selection, by which populations become more
suited to their environment over many generations
Continuous variation results in a range of phenotypes between two extremes, e.g. height in humans
Discontinuous variation results in a limited number of phenotypes with no intermediates, e.g. tongue rolling
Mutation is the way in which new alleles are formed
Ionising radiation and some chemicals increase the rate of mutation
Phenotypic variation is caused by both genetic and environmental factors
Discontinuous variation is mostly caused by genes alone, e.g. A, B, AB and O blood groups in humans
People who are heterozygous (HbS HbA) for the sickle‐cell allele have a resistance to malaria
≥ Distinguish between phenotypic variation and genetic variation
Our genetic make‐up, the sum total of our genes, is called a genotype, but the characteristics which show up
in our appearance are called a phenotype. Genetic variation gives rise to differences between individuals that
are inherited. For example, our eye colour is inherited from our parents. But our phenotype is also affected by
environmental variation such as:
o Climate, diet, physical accidents, culture, lifestyle
Many kinds of variation are influenced by both environmental and genetic factors, because although our
genes decide what characteristics we inherit, our environment affects how these inherited characteristics
develop. For example:
o a person might inherit a tendency to be tall, but a poor diet during childhood will cause poor growth
o plants may have the potential for strong growth, but if they do not receive sufficient mineral resources
from the soil, they may hardly grow at all
Identical twins are a good example of the interaction between inheritance and environment, as such twins are
genetically the same. Any differences you may see between them – for example in personality, tastes and
particular aptitudes – are due to differences in their experience or environment.
≥ Describe the symptoms of sickle‐cell anaemia
o Feeling tired / fatigue
o Short of breath (Hb doesn’t deliver oxygen to their cells efficiently)
≥ Explain how a change in the base sequence of the gene for haemoglobin results in abnormal haemoglobin
and sickle‐shaped red blood cells
Some people have a mutation in the gene that codes for the production of Hb. The mutant allele that
produces a faulty type of Hb has a tiny difference in the DNA sequence between normal Hb. This changes the
amino acids sequence in the Hb, preventing the Hb working as it should. This faulty Hv has a tendency to
produce fibres inside red blood cells when oxygen concen. is low. The red blood cells get pulled into a ‘sickle’
shape and get stuck in blood capillaries
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≥ Use genetic diagrams to show how sickle‐cell anaemia is inherited
≥ Explain the distribution of the sickle‐cell allele in human populations with reference to the distribution of
malaria
The possible genotypes are:
o HNHN normal haemoglobin, no anaemia
o HNHn some abnormal haemoglobin, sickle cells trait (not life‐threatening)
o HnHn abnormal haemoglobin, sickle cells anaemia (life‐threatening)
Malaria is a life‐threatening disease caused by a parasite that invades red blood cells. The parasite is carried
by some species of mosquito.
o A person who is heterozygous (HNHn) for sickle cell anaemia has protection from malaria, because the
malaria parasite is unable to invade an reproduce in the sickle cells.
o A person who is homozygous for sickle cell anaemia (HnHn) also has protection, but is at high risk of dying
form sickle cell anaemia.
o A person with normal haemoglobin (HNHN) in a malarial country is at high risk of contracting malaria.
When the distributions of malaria and sickle cell anaemia are shown on a map of the work, it is found that the
two coincide in tropical areas because of the selective advantage of the Hn allele in providing protection
against malaria.
≥ Record and present the results of investigations into continuous and discontinuous variation
1. Make a survey of at least 30 people, to find out whether or not they can roll their tongue. Record your
results on a table
2. Measure the length of the third finger of the left hand of 30 people. Take the measurement from the
knuckle to the fingertip, no including the nail.
3. Divide the finger lengths into suitable categories, and record the numbers in each
category, like this:
4. Draw a histogram of your results
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≥ Interpret images or other information about a species to describe its adaptive features
Xerophytes:
Hydrophytes
≥ Differences between natural and artificial selection
Natural selection is the process by which favorable heritable traits become more common in successive
generations of a population of reproducing organisms, and unfavorable heritable traits become less common,
due to differential reproduction of genotypes. Artificial selection is the intentional breeding for certain traits,
or combinations of traits, over others, and is synonymous with "Selective breeding"
≥ Outline how selective breeding by artificial selection is carried out over many generations to improve crop
plants and domesticated animals
Only the organisms with the advantageous (best) features breed and the ones that are disadvantageous don’t.
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≥ Explain the adaptive features of hydrophytes and xerophytes to their environments
Xerophytes: Plants that live in deserts
Adaptation
Closing stomata
Waxy Cuticle
Hairy Leaves
Stomata on underside of leaves
Cutting down on the surface area
Deep/Spreading roots
Description
Plants lose most of their water from their stomata. If
the stomata are closed, then the transpiration rate
will slow right down. However, if the stomata are
closed, the plant can’t photosynthesise (CO2 cannot
diffuse out) so the stomata close when it is too hot
and dry, or when they could not
Desert plants often covered with waxy cuticle (from
epidermis). The wax makes the leaf waterproof
Some plants have hairs on their leaves. These hairs
trap layer of moist air next to the leaf
The lower surface of stomata is usually cooler than
the upper one, so less water will evaporate. In
desert plants, there may be fewer stomata than
usual, and they may be sunk into deep pits in the
leaf.
The smaller the surface area, the less water will
evaporate from it. Small surface area helps to
conserve water but this slows down photosynthesis
(less light, and carbon dioxide is absorbed too)
To search for water deep down
Hydrophytes: Plants that live in wet places or in water
Adaptation
Large air spaces / large spongy mesophyll
Leaves float
Stomata in upper surface
Thin cuticle
Description
To float
Efficient at absorbing light
Diffusion of gas from the air
No need to reduce water loss by transpiration
≥ Describe natural selection with reference to:
Variation within populations:
Most populations of organisms contain individuals which vary slightly different from one another. Some slight
variations may better adapt some organisms to their environment than others.
Production of many offspring:
Most organisms produce lots of offspring so they can survive to adulthood
Competition for survival
The population doesn’t generally increase in size so there must therefore be considerable competition for
survival between the organisms
Struggle for survival
Best adapted organisms most likely to survive
Reproduction by individuals that are better adapted to the environment than others
Well‐adapted organisms that survive and reproduce  pass on their alleles
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≥ Describe selective breeding with reference to:
Natural selection is the process by which plants and animals that can adapt to changes in their environment
are able to survive and reproduce while those that cannot adapt do not survive. It gives the greater chance of
passing on of genes by the best adapted organisms.
Example for Plants:
1. Choose plants with desired features
2. Cross / breed plants
3. Collect seeds
4. Grow seeds and check plants for features
5. Cross plants showing features with original variety
6. Keep crossing and selecting until you get what feature you wanted
Example for Dogs:
1. Choose suitable feature to improve (eg: ears)
2. Select individuals for breeding (with the one you want the ears of)
3. Select offspring that show improvement
4. Use these for future breeding
Example for Cows (Milk):
1. Choose or select the cows in your herd that produce the most milk
2. Let only these cows reproduce
3. Select the offspring that produce the most milk
4. Let only these offspring reproduce
5. Keep repeating the process of selection and breeding until you achieve your goal.
≥ Describe evolution as the change in adaptive features of a population over time as the result of natural
selection
In this way (natural selection), over a period of time, the population will lose all the poorly adapted individuals
making the population better adapted to its environment. This theory is often called the theory of natural
selection because it suggests that the best‐adapted organisms are selected to pass on their characteristics to
the next generation.
≥ Describe the development of strains of antibiotic resistant bacteria as an example of evolution by natural
selection
o Bacteria reproduce rapidly‐ a new generation can be produced every 20 minutes;
o Antibiotics (is a chemical that kills bacteria by preventing bacterial cell wall formation) are used to treat
bacterial infections;
o Mutations occur during reproduction, which produce some variation in the population of bacteria;
o Individual bacteria with the most favourable features are most likely to survive and reproduce;
o A mutation may occur that enables a bacterium to resist being killed by antibiotic treatment, while the rest
of the population is killed when treated;
o This bacterium would survive the treatment and breed, passing on the antibiotic‐resistant gene to its
offspring;
o Future treatment of this population of bacteria using the antibiotic would be ineffective.
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1 9 . Organisms & their Environment
≥ Describe the flow of energy through living organisms including light energy from the sun and chemical
energy in organisms and its eventual transfer to the environment
 The Earth receives two main types of energy from the sun: light (solar) and heat
 Photosynthetic plants and some bacteria can trap light energy and convert it into chemical energy
 Heterotrophic organisms obtain their energy by eating plants or animals that have eaten plants
 So all organisms, directly or indirectly, get their energy from the sun
 This energy is passed from one organism to another in a food chain
 This energy does not return in a cycle but is lost to the environment
Food chain is showing the transfer of energy from one organism to the next, beginning with a producer
Trophic level is the position of an organism in a food chain, food web, pyramid of numbers or pyramid of
biomass
Food web as a network of interconnected food chains
Producer as an organism that makes its own organic nutrients, usually using energy from sunlight, through
photosynthesis
Consumer as an organism that gets its energy by feeding on other organisms
Herbivore as an animal that gets its energy by eating plants
Carnivore as an animal that gets its energy by eating other animals
Decomposer as an organism that gets its energy from dead or waste organic material
≥ Describe how energy is transferred between trophic levels
 Energy is lost at each trophic level (90% is lost, and only 10% passed)
 Energy lost through respiration
 Energy lost in excretion
 Some of the material in the organism being eaten is not used by the consumer e.g. a locust (insect) does
not eat the roots of the maize, and some of the parts eaten are not digestible
≥ Construct simple food chains
N. diversicolor is a filter feeder. It filters plankton from sea water. Annelids like N. diversicolor form an
important part of the ecosystems of estuaries. Fish feed on annelids when the sea covers the mud in the
estuary. When the tide is out wading birds are the main predators of annelids. Birds of prey are the main
predators of the wading birds
Plankton  annelid  wading birds
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≥ Explain why food chains usually have fewer than five trophic levels
 Most energy from Sun not available
 Some materials are inedible or indigestible
 As energy is passed along the chain, each organism uses some of it in;
 On an average, about 90% of the energy is lost and 10% is passed at each level in a food chain;
 So the further along the chain you go, the less energy there is;
 There is plenty of energy available for producers, so there are usually a lot of them;
 There is less energy for primary consumers, and least in secondary consumers;
 Thus towards the end of food chain the organisms get fewer in number.
 Only small total percentage reaching fourth trophic level
 Not enough energy in fourth trophic level to support another level
≥ Identify producers, primary consumers, secondary consumers, tertiary consumers and quaternary
consumers as the trophic levels in food webs, food chains, pyramids of numbers and pyramids of biomass
Pyramid of biomass
Pyramid of Numbers
99
Food web
≥ Explain why the transfer of energy from one trophic level to another is inefficient
Energy transfer is inefficient because energy is lost while moving from one trophic level to another. This is
because
 Not the entire organism is consumed or digested. Parts such as root, woody stems, bones, scales, feathers
etc aren't eaten, and some materials that are such as cellulose cannot be digested.
 Energy is used up by organisms in each trophic level for movement and transport inside their bodies.
 Energy is used in respiration and is released from the body of the organism as heat.
 Energy becomes lost in excretion.
≥ Explain why there is a greater efficiency in supplying plants as human food, and that there is a relative
inefficiency in feeding crop plants to livestock that will be used as food
When we eat meat, eggs or cheese, or drink milk, we are feeling further along the food chain. There is less
energy available for us from the original source. It will be more efficient to eat grass in field rather than letting
cattle eating it. (More energy in plants than livestock  lower tropic level than livestock)
≥ Discuss the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent a
food chain
A pyramid of biomass is better than a pyramid of numbers because when you compare masses it gives us a
better idea of the amount of energy that is available at each trophic level. In a pyramid of biomass, it shows
the amount of energy that is lost through each step. this is the amount each trophic level decreases in
comparison to the previous.
≥ Use food chains and food webs to describe the impacts humans have through over‐harvesting of food
species and through introducing foreign species to a habitat
100
≥ Describe the carbon cycle, limited to photosynthesis, respiration, feeding, decomposition, fossilisation and
combustion
1.
2.
3.
4.
5.
6.
7.
Carbon moves into and out of the atmosphere mainly in the form of carbon dioxide;
Plants take carbon dioxide out of the air by photosynthesis;
Plants convert carbon dioxide into organic materials (carbohydrates, fats and proteins);
Herbivores obtain carbon compounds by eating plants;
Carnivores gain carbon compounds by eating other animals;
Animals (respire) and plants release carbon dioxide back into the air through respiration;
When organisms die they usually rot
(decompose);
8. Decomposers breakdown the organic molecules
through the process of respiration to release
energy. Thus decomposers also release carbon
dioxide;
9. If a dead organism does not decompose, the
carbon compounds are trapped in its body. Over
a long period, this can form fossil fuels;
10. Combustion of fossil fuels releases carbon
dioxide back into the air.
≥ Discuss the effects of the combustion of fossil fuels and the cutting down of forests on the carbon dioxide
concentrations in the atmosphere
 Photosynthesis takes carbon dioxide out of the atmosphere and replaces it with oxygen;
 Respiration and combustion use up oxygen from the atmosphere and replace it with carbon dioxide;
 When fossil fuels are burnt, the carbon in them combines with oxygen from the air, and forms carbon
dioxide. This process is called combustion;
 Combustion of fossil fuels is thought to be having an effect on the balance of carbon dioxide;
 The extra carbon dioxide may be causing the percentage of carbon dioxide in the air to increase;
 The loss of the trees may reduce the amount of photosynthesis taking place;
 As a result the concentration of carbon dioxide increases and oxygen decreases in the atmosphere;
 The rise in the levels of carbon dioxide levels in the atmosphere could be dangerous as it may cause global
warming.
101
≥ Describe the water cycle, limited to evaporation, transpiration, condensation and precipitation
Energy from the Sun heats the surface of the Earth.
Plants release water vapour into the air through transpiration.
Water evaporates from oceans, rivers, lakes and soil.
The warm, moist air rises because it is less dense.
Water vapour condenses into water droplets as it cools down, forming clouds.
Water droplets get bigger and heavier they begin to fall as rain, snow and sleet (precipitation), draining
into streams, rivers, lakes and sea.
 Plant root take up water by osmosis.
 In addition, animals lose water to the environment through exhaling and sweating, and in urine and
faeces.






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≥ Describe the nitrogen cycle in terms of:
Although the air is full of nitrogen, the plants and animals cant use at all. It must be changed into more
reactive form  ammonia (NH3) or nitrates (NO3‐). Changing nitrogen gas into more reactive form is called
nitrogen fixation. Here are several ways it can be done:
1‐Lightning:
Lightning makes some of the nitrogen gas in the air combine with oxygen, forming nitrogen oxides. It dissolves
in rain and washed into the soil forming nitrates
2‐Aritifical fertilisers:
The addition of artificial fertilizers, compost (decaying plant material) and manure (decaying animal waste –
urine and faeces)
3‐Nitrogen‐fixing bacteria:
These bacteria live in the soil, or in root nodules on plants like peas, beans or clover. They use the nitrogen gas
from the air spaces in soil, and combine it with other substances to make ammonium ions and other
compounds.
Once the nitrogen has been fixed, it can be used to make proteins. Animals eat the plants, so animals get their
nitrogen in the form of proteins. When an animal or plant dies, bacteria and fungi decompose the body. The
protein, containing nitrogen, is broken down to ammonium ions and this is released. Another group of
bacteria, called nitrifying bacteria, turn these ions into nitrates, which plants can use again. Nitrogen is also
returned to the soil when animals excrete nitrogenous waste material, which they have produced by
deamination of excess amino acids. It may be in the form of ammonia or urea. Again, nitrifying bacteria will
convert it to nitrates. A third group of bacteria complete the nitrogen cycle. They are called denitrifying
bacteria, because they undo the work done by nitrifying bacteria. They turn nitrates and ammonia in the soil
into nitrogen gas, which goes into the atmosphere.
103
≥ State the roles of microorganisms in the nitrogen cycle, limited to decomposition, nitrification, nitrogen
fixation and denitrification (generic names of individual bacteria, e.g. Rhizobium, are not required)
 Nitrogen fixation
 Decomposition
 Denitrification
 Nitrification
Population as a group of organisms of one species, living in the same area, at the same time
Community as all of the populations of different species in an ecosystem
Ecosystem as a unit containing the community of organisms and their environment, interacting together, e.g.
a decomposing log, or a lake
≥ Identify the lag, exponential (log), stationary and death phases in the sigmoid population growth curve for
a population growing in an environment with limited resources
Lag phase – the new population takes time to settle and mature before breeding begins. When this happens,
a doubling of small numbers does not have a big impact on the total populations size, so the line of the graph
rises only slowly with time.
Log (exponential) phase – there are no limiting factors. Rapid breeding in an increasing population causes a
significant in numbers. A steady doubling in numbers per unit of time produces a straight line.
Stationary phase – limiting factors, such as shortage of food, cause the rate of reproduction to slow down
and there are more deaths in the population. When the birth rate and death rate are equal, the line of the
graph becomes horizontal.
Death phase ‐ as food runs out, more organisms die than are born, so the number in the population drops.
≥ Identify and state the factors affecting the rate of population growth for a population of an organism,
limited to food supply, predation and disease
 Food
 Water
 Space
 Protection: disease, predator, weather
 Birth rate, death rate, immigration, emigration will determine the population in the area
104
≥ Explain the factors that lead to each phase in the sigmoid curve of population growth, making reference,
where appropriate, to the role of limiting factors
≥ Discuss the increase in human population size over the past 250 years and its social and environmental
implications
If there are no limiting factors, there will be no stationary or death phase – the log phase will continue
upwards, instead of the line leveling off. This has happened with human population growth. Human
population size has increased exponentially because of improvements on food supply and the development of
medicine to control diseases. Infant mortality has decreased, while lifer expectancy has increased.
Social/Environmental implications:
 increase demand for basic resources (food, water, space, medical care, fossil fuels).
 increase pressures on the environment (more land needed for housing, growing crops, road buildings,
more wood for fuel and housing) and more pollution.
 larger population of young people ‐‐> greater demands on education.
 more old people ‐‐> greater demands on healthcare.
≥ Interpret graphs and diagrams of human population growth
105
2 0 . Biotechnology & Genetic Engineering
Bacteria are useful in biotechnology and genetic engineering due to their rapid reproduction rate and their
ability to make complex molecules
≥ Discuss why bacteria are useful in biotechnology and genetic engineering, limited to:
 No one minds what is done to bacteria and fungi. There are no ethical issues like those that might arise if
we used animals
 Although bacterial cells are very different from animal and plant cells, in fact we all share the same kind of
genetic material; DNA. The genetic code is the same for bacteria as it is for humans and all other
organisms. So we can take a gene from a human cell and place it into a bacterial cell, and it will work to
produce the human protein
 Bacteria also have loops of DNA called plasmids. These are quite east to transfer from one cell to another.
We can use plasmids for moving genes from one organism’s cell to another.
≥ Describe the role of anaerobic respiration in yeast during production of ethanol for biofuels
 To make beer, yeast is dissolved in a warm liquid containing the sugar maltose;
 The yeast respires anaerobically by a process called fermentation;
 This process produces ethyl alcohol (ethanol) making the drink alcoholic;
 and carbon dioxide which makes the drink fizzy.
≥ Describe the role of anaerobic respiration in yeast during bread‐making
 Yeast is mixed with water and sugar to activate it;
 The mixture is added to flour to make dough, and left in a warm place;
 The dough rises as the yeast respires and releases carbon dioxide, which gets trapped in the dough;
 When the dough is cooked, the high temperature kills the yeast and evaporates any alcohol formed;
 Air spaces are left where the carbon dioxide was trapped, which gives the bread a light texture.
≥ Investigate and describe the use of pectinase in fruit juice production
Use:
 Extracts more juice / speeds up
juice extraction
 Pectin converted to sugars so juice
is sweeter
 Cell wall material is removed from
juice so the juice is clearer
106
≥ Investigate and describe the use of biological washing powders that contain enzymes
Biological washing powders contain protease and lipase to remove protein stains and fat/grease from clothes.
The enzymes break down proteins or fats on the fabric, forming water‐soluble substances that can be washed
away. This makes the washing powder more effective than detergent alone, especially at lower temperatures.
This save energy (no need to boil water), but if the temperature is too high, the enzyme will be denatured.
≥ Investigate and explain the use of lactase to
produce lactose‐free milk
Lactose is the sugar found in milk. It can be
broken down by the enzyme lactase into
glucose and galactose. However, some people
lack this enzyme and so cannot break down
lactose leading to lactose intolerance. Lactose
intolerant people need to drink milk that has
been lactose reduced. Lactose‐free milk can be
made in two ways. The first involves adding the
enzyme lactase to the milk so that the milk
contains the enzyme. The second way involves
immobilizing the enzyme on a surface or in
beads of a porous material. The milk is then
allowed to flow past the beads or surface with
the immobilized lactase. This method avoids
having lactase in the milk.
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≥ Describe the role of the fungus Penicillium in the production of the antibiotic penicillin
Antibiotics are substances that kill bacteria without harming human cells. Penicillin is made by growing the
fungus Penincillium in a large fermenter.
≥ Explain how fermenters are used in the production of penicillin
The fungus is grown in a culture medium containing carbohydrates and amino acid. This looks like watery
porridge and is stirred continuously to:
 Keep the fungus in contact with fresh supplies if nutrients.
 Mix O2 into the culture
 Roll the fungus up into little pellets (this facilitates the separating of the liquid part containing penicillin
from the fungus lately).
For first 15‐24 h, the fungus just grows. After that it
begins to secret penicillin. Rate of production depends
on how much sugar is available:
 A lot of sugar  not much penicillin
 No sugar  no penicillin
So small amount of sugar have to be fed all the time
that the fungus is producing penicillin.
The culture is kept going until the rate of production is
so slow that is not worth waiting more (often after a
week). Then it is filtered, and the liquid is treated
to concentrate the penicillin in it.
Water jacket
 maintain optimum / constant temperature
 to prevent enzymes denaturing because as fungus respires releases heat so temperature in the fermenter
increases which would kill fungus therefore no product / no penicillin
Addition of acids and alkalis
 maintains pH / keeps pH constant
 enzymes need optimum pH to give maximum enzyme activity to give maximum yield
108
Genetic engineering as changing the genetic material of an organism by removing, changing or inserting
individual genes
≥ State 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
– the insertion of genes into crop plants to confer resistance to insect pests
– the insertion of genes into crop plants to provide additional vitamins
≥ Outline genetic engineering using bacterial production of a human protein as an example, limited to:
1. Extraction of the gene for insulin from human cells, this is done using enzymes called restriction enzymes.
They leave short lengths of unpaired bases at their end of the cut DNA, called stick ends.
2. The particular length of DNA is identified and extracted from the other DNA
3. We use plasmid to insert DNA into a bacterium (Plasmid  ring of DNA in bacteria)
4. First the ring of DNA in plasmid is cut, using the restriction enzyme (so it will leave complimentary sticky
ends to the ones on the human DNA)
5. The human insulin gene and cut plasmids are now mixed together.
6. The sticky ends (unpaired bases) on the insulin gene pair up with the sticky ends on the plasmids.
7. Enzyme called DNA ligase links the two strands firmly together
8. Now we have plasmids that contains human insulin gene called recombinant plasmids.
9. Plasmid is now inserted into the bacteria and some of them take these plasmids into their cells
10. These bacteria are put in fermenters to reproduce asexually to form a larger population
≥ Discuss the advantages and disadvantages of genetically modifying crops, such as soya, maize and rice
Advantages:
 Resistant to herbicides when they are sprayed on them. Meaning that farmers can spray on these plants
and only the weed is killed. This also reduces the need of spraying herbicides on their crops. This also
reduces the damage to other plants that are growing nearby. Herbicide resistant crops increase yield.
Reduces labour costs which means cheaper food.
 GM cotton plants contain Bt that is toxic to insects. When pests (like cotton ball weevil) eat the cotton
plants, they die. Bt toxin is specific and harms only herbivores that eat the plant.
 GM rice produce more vitamin A than normal rice. Lack of vitamin A is big problem for children in some
countries since it can cause blindness and more than million people die each year
Disadvantages:
 But farmers have to pay a premium to buy the seeds which the end costs don’t fall by much.
 Herbicide resistant gene might spread to plants growing nearby producing weeds that can’t be killed with
herbicides no more.
 Some pests are evolving to become resistant to Bt toxin.
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2 1 . Human Influences on Ecosystems
≥ State how modern technology has resulted in increased food production in terms of:
– agricultural machinery to use larger areas of land and improve efficiency
– chemical fertilisers to improve yields
– insecticides to improve quality and yield
– herbicides to reduce competition with weeds
– selective breeding to improve production by crop plants and livestock, e.g. cattle, fish and poultry
≥ Explain the undesirable effects of deforestation on the environment
Species extinction through habitat loss:
Reduction of habitats or food sources for animals can result in their extinction;
Loss of forest habitat also reduces plant & animal diversity & disrupts the food chains.
Loss of soil by soil erosion:
Removal of trees means there are no roots to hold soil, thus the thin top layer of soil is washed away during
rain;
This causes soil erosion and leaching of minerals;
Desertification can eventually result.
Flooding;
Soil from erosion is washed into rivers, silting it and causing flooding;
When forest is removed there are no plant roots to take up rainwater, which instead flows into streams and
rivers, causing further flooding.
Carbon dioxide build up:
Forests have high rates of photosynthesis so absorb large amounts of carbon dioxide from the atmosphere;
Removal of forests therefore contributes to increases in atmospheric carbon dioxide
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Increase in flooding
Desertification
Soil erosion
Loss of habitat
Disruption to food chain
Extinction of species or loss of biodiversity
Decreased rainfall
Silting of rivers
Loss of (plant) nutrients
Loss of habitat
Forests have high rates of photosynthesis so absorb large amounts of carbon dioxide from the
atmosphere; Removal of forests therefore contributes to increases in atmospheric carbon dioxide
State that through altering food webs and food chains, humans can have a negative impact on habitats
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≥ Describe the negative impacts to an ecosystem of intensive livestock production
 Welfare issues with the crowded conditions
 Disease can spread easily
 Increased risk of resistant bacteria when livestock are given antibiotic
 Waste pollute land and waterways
≥ Discuss the problems which contribute to, famine including unequal distribution of food, drought and
flooding, increasing population and poverty
Famine occurs for many different reasons and the main cause is weather. If the area suffers drought for
several years, then it becomes impossible to grow crops and their animals die too. Sometimes it happens
cause of too much rain that causes flooding which prevents crops from growing. Sometimes human
population might grow to the extend where the area they live in cannot provide enough food for them.
Sometimes when there is war or crisis in the country, people cannot afford food or there is no food to buy.
≥ Describe the reasons for habitat destruction, limited to:
 Cutting down of native vegetation to make land available for growing crops, for farming livestock, for
building houses and factories and building roads.
 Mine for natural resources like metal ores or fossil fuels
 Add pollutants to land and water which can kill plants that normally live there and so change the habitat
≥ Describe the negative impacts to an ecosystem of large‐scale monocultures of crop plants
 Low biodiversity
 Increased population of pests of the crop
 Pests transfer viruses to crops which can cause disease in plants
 Insecticides kill other harmless insects
 Pests becoming resistant to insecticides
 Loss of soil nutrients
State the sources and effects of pollution of land and water, e.g. rivers, lakes and the sea, by insecticides,
herbicides and by nuclear fall‐out
State the sources and effects of pollution of water (rivers, lakes and the sea) by chemical waste, discarded
rubbish, untreated sewage and fertilisers
State the sources and effects of pollution of the air by methane and carbon dioxide, limited to the enhanced
greenhouse effect and climate change
State that some resources can be maintained, limited to forests and fish stocks
State that products can be reused or recycled, limited to paper, glass, plastic and metal
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≥ Discuss the effects of non‐biodegradable plastics in the environment, in both aquatic and terrestrial
ecosystems
Aquatic:
 When swallowed it cannot be digested which gets trapped and choke and suffocate and kill fish
 Plastic blocks light for photosynthesis
 May contain and release oil‐soluble toxins
 Large pieces of plastic may block flow of water in a river that reduce concentration of dissolved oxygen
 Loss of organism at a trophic level affects the food chain
Terrestrial:
 Get trapped inside plastic container
 Get plastic cords or bags wrapped around them
≥ Explain the process of eutrophication of water in terms of: – increased availability of nitrate and other ions, –
increased growth of producers, – increased decomposition after death of producers, – increased aerobic respiration by
decomposers, – reduction in dissolved oxygen, – death of organisms requiring dissolved oxygen in water
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Nitrate fertilizers will be washed into streams and rivers
Fast growth of algae when they are supplied with extra nitrates
Light blocked by algae
No more photosynthesis so algae and water plants die
There is no oxygen released by plants
Algae and plants fed on decomposed by bacteria
Bacteria multiply and produce toxins which cause fish to die
Aerobic respiration occurs causing low levels of oxygen which cause death / suffocation / migration of fish
/ animals / invertebrates / (aquatic) creatures / organisms / consumers
≥ Discuss the causes and effects on the environment of acid rain
Causes
 SO2 (Burning of fossil fuels)
 Oxides of nitrogen (Combustion of petrol in car engines)
Effects
 Leaves/plants get damaged
 Trees more likely to get diseased
 Bark gets damaged
 Roots get killed
 Soil pH decreases and becomes acidic
 Release of aluminium from the soil into lakes that are toxic to fish
 Nutrients are leached
 Increased risk of asthma attacks and bronchitis in humans
 Food chains / food webs disrupted
 Animal shells damaged and fail to reproduce
 Loss of habitat and extinction
 Sensitive species of lichens killed
 Corrosion of stonework on buildings
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≥ State the measures that are taken to reduce sulfur dioxide pollution and reduce the impact of acid rain
 Use renewable sources of energy like nuclear power, wind power, wave power, solar power, hydrogen
power
 Use low sulfur fuels
 Reduce use of coal
 Use scrubbers
 Use catalytic converters
 Use more public transport
 Share cars or use hydrid cars
 Use biofuels
 Walking / cycling
 Reduce food miles
 Desulfurisation of coal
≥ Explain how increases in carbon dioxide and methane concentrations in the atmosphere cause an
enhanced greenhouse effect that leads to climate change
 Carbon dioxide is produced by burning of fossil fuels
 Methane is produced from the decay of organic matter and as a waste gas from digestive processes in
cattle
 Carbon dioxide and methane are greenhouse gases
 They are called greenhouse gases as they trap heat in the earth’s atmosphere in the same way a
greenhouse traps heat
 As the concentration of these gases increase in the atmosphere more heat is trapped, making the
atmosphere warmer. This is called enhanced greenhouse effect
 It is causing global warming –Earth’s average temperature is rising
≥ Describe the negative impacts of female contraceptive hormones in water courses, limited to reduced
sperm count in men and feminisation of aquatic organisms
 Prevent the male hormones, testosterone, working effectively
 Cause production of fewer sperm
 Make male fish change sex and become female (feminization)
Sustainable resource as one which is produced as rapidly as it is removed from the environment so that it
does not run out
Sustainable development as development providing for the needs of an mincreasing human population
without harming the environment
≥ Explain the need to conserve non‐renewable resources, limited to fossil fuels
 Fossil fuels are non‐renewable
 Conserve for future generations
 There might be more efficient ways of using them in the future
 Alternatives are expensive
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≥ Explain how forests and fish stocks can be sustained using education, legal quotas and re‐stocking
Education:
Education can help people to understand how important to conserve forests is. In some areas they use trees
as fuel for cooking and education can help them to change it to renewable energy.
Legal quotas:
Imposing quotas can help to sustain number of fish since you are only allowed to catch certain amount of fish.
Most quota systems specify different amounts of different species. (Eg: fishermen are allowed to catch large
amount of fish that aren’t threatened and low quotas or none at all for those with low populations.)
Inspectors visit boats and check the catches. They check if they have caught the fish that are not endangered
and make sure they are in the quota. If over quota or endangered, fish is thrown back in to the sea.
Re‐stocking:
Breeding them in fish hatcheries and releasing them is called re‐stocking.
≥ Explain that sustainable development requires:
As our population increases, we need to build more houses, roads and industries, and to produce more food.
Achieving this without damaging the environment is called sustainable development. Sustainable
development requires the cooperation of many different people and organisations. In most countries, new
developments such as housing, roads or industrial complexes, have to be submitted for approval by planning
authorities. These authorities should take into account the needs of the environment, as well as the business
interests of the developers.
≥ Explain why organisms become endangered or extinct, limited to climate change, habitat destruction,
hunting, pollution and introduced species
 Mass extinction is caused by climate change (eg: volcanoes)
 Species cannot survive without a habitat and we are destroying them
 Animals are hunted for food but sometimes it can destroy the entire species.
 Addition of extra carbon dioxide and methane to the atmosphere causes temperature rise which causes
organisms no longer well adapted to the change. (Eg: Some species require cold conditions, but as
temperature rises, the ice caps melt leaving them without habitats.)
 Introduced species can threaten the existence of native species.
≥ Describe how endangered species can be conserved, limited to monitoring and protecting species and
habitats, education, captive breeding programmes and seed banks
 Monitoring and protecting the species in its natural habitat
 Using captive breeding programmes
 Educating local people about the importance of conservation, and what they can do to help
 Building up seed banks can survive for many years in a dormant state, and germinate in right conditions so
it can be kept in captivity or reintroduced to its natural habitat later on.
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≥ Explain reasons for conservation programmes, to include:
 No right to make species extinct as we live in the same world and keep them for future generations
 Damaging ecosystems harm ourselves too. (Eg: cutting down trees can reduce water vapour that goes back
in the air which can reduce rainfall; people who depend on wood for fuel can no longer cook or heat their
homes). Taking care of our environment can help us make our own living conditions more pleasant and
safe.
 Losing a specie from an ecosystem can have wide‐reaching effects since it might have been a food for a
consumer which can disrupt the food chain/web.
 Many plant species contain chemicals that can be used as drugs. Losing them might cause losing potential
of new medicines
 Wild relative of our crops contain different allele of genes that could be useful in future breeding
programmes
≥ Explain the risks to a species if the population size drops, reducing variation (knowledge of genetic drift is
not required)
If there is variation between individuals, then the population as a whole has a better chance of surviving if
they are threatened by a pathogen, or their habitat changes in some way. At least some of the individuals may
have variations that allow them survive and reproduce, even if others get killed. When the numbers of species
drop to very low levels, so that only a few individuals survive, then much of this genetic variation is lost. This
makes the species much more likely to become extinct.
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