TOP

Edexcel Categories Archives: IGCSE

Cloning

5.17 – Describe the process of micropropagation (tissue culture) in which small pieces of
plants (explants) are grown in vitro using nutrient media.
– Explants (small pieces of plant) are grown in vitro in agar jelly as it contains nutrients
(amino acids and glucose).
– Plant hormone and bleach and minerals are added to the plant

– The plant is grown in a sterile environment.
– Light and humidity are controlled.
5.18 – Understand how micropropagation can be used to produce commercial quantities
of identical plants (clones) with desirable characteristics.
– Micropropagation can be used to produce commercial (large) quantities of identical
plants (clones) with desirable characteristics.
5.19 – Describe the stages in the production of cloned mammals involving the
introduction of a diploid nucleus from a mature cell into an enucleated egg cell,
illustrated by Dolly the sheep.
– Egg cell is enucleated (nucleus taken out).
– A somatic cell nucleus is inserted into the enucleated egg cell.
– Electric shock initiates mitosis cell division.
– The cell becomes an embryo and is implanted in a surrogate mother’s uterus.
5.20 – Evaluate the potential for using cloned transgenic animals, for example to
produce commercial quantities of human antibodies or organs for transplantation.
– Transgenic animals are animals that have genes from other animals inserted into
their DNA.
– Animals can be given the gene to make human antibodies.
• These can then be injected into humans to help them face an infection within a short
time.
– Animals could have organs with human cells that could be used for transplantation.
• This would solve organ shortages and moral / ethical issues.
• Animals organs can be genetically-modified to reduce rejection.

Continue Reading

Genetic Modification (Genetic Engineering)

– Vector: (a virus or plasmid) that transfers genetic material into a cell, or from one
bacterium to another.
– Recombinant DNA: Genetic material formed by recombination (by restriction
enzymes and ligase enzymes).
– When a virus or plasmid is inside a host cell, it may pick up DNA and carry it into
another host cell.
5.14 – Understand that large amounts of human insulin can be manufactured from
genetically modified bacteria that are grown in a fermenter.
– The human gene that codes for insulin production is taken.
– Plasmids (a vector) are isolated from a bacteria and are cut by restriction enzymes.
– The gene is cut by the same restriction enzyme and is inserted into the plasmid by
ligase enzymes to create a recombinant plasmid.
– The recombinant plasmid is inserted into a bacteria cell and the bacteria is allowed to
reproduce.
5.15 – Evaluate the potential for using genetically modified plants to improve food
production (illustrated by plants with improved resistance to pests).
– Genetically modified plants are plants with enhanced characteristics.
– More nutritional value.
– More resistance to pesticides / herbicides / disease.
– Observed individual downsides of GM crops include sterility, infant mortality, allergies,
stunted growth.
5.16 – Understand that the term ‘transgenic’ means the transfer of genetic material
from one species to a different species.
– Transgenic: The transfer of genetic material from one species to a different species

Continue Reading

Selective Breeding

5.10 – Understand that plants with desired characteristics can be developed by selective
breeding.
– Plants can be bred selectively by choosing plants with desired characteristics (e.g.
colour, size of fruit) through pollination.
5.11 – Understand that animals with desired characteristics can be developed by
selective breeding.
– Animals can be bred selectively by choosing animals with desired characteristics (e.g.
meat, beauty) through sexual intercourse (with or without human interference).

Continue Reading

Food Production

CROP PLANTS (5.1 – 5.4)
5.1 – Describe how glasshouses and polythene tunnels can be used to increase the yield
of certain crops.
– Conditions in glasshouses and polythene tunnels can be controlled.
– This means that all the limiting factors for plant growth can be set to the optimum
conditions, thus resulting in higher growth and yield.
5.2 – Understand the effects on crop yield of increased carbon dioxide and increased
temperature in glasshouses.

– Glasshouses and polythene tunnels increase the heat in the environment that crops
are growing in.
– Photosynthesis occur faster when there is more heat and carbon dioxide.
– As a result, more glucose is produced, thus more energy and growth, and increased
crop yield.
5.3 – Understand the use of fertiliser to increase crop yield.
– Fertilisers contain minerals (see 2.21) that plants require to grow (e.g. NPK fertiliser).
5.4 – Understand the reasons for pest control and the advantages and disadvantages of
using pesticides and biological control with crop plants.
– Pesticide: A chemical that kills the pest, but not the crop plant.
• Advantages: Fast and accurate, with almost instant results.
• Disadvantages: Bioaccumulation in food chains; harm other organisms; pest may
become immune; may cause eutrophication.
– Biological control: Introducing a predator into the environment to eat the pest but not
the crop plant.
• Advantages: No need for chemical pesticides; cheap and self-regulating.
• Disadvantages: It may not eat the pest and eat useful species; may increase out of
control.
MICRO-ORGANISMS (5.5 – 5.8)
5.5 – Understand the role of yeast in the production of beer.
C6H12O6 → 2C2H5OH + 2CO2
– Yeast converts glucose to ethanol and carbon dioxide during anaerobic respiration in a
fermenter.
5.6 – Describe a simple experiment to investigate carbon dioxide production by yeast, in
different conditions.
– Have a test tube of yeast in glucose solution.
– Put a layer of oil on top of the test tube to keep conditions anaerobic (i.e. prevent
oxygen from entering the tube).
– Put the test tube in a water bath and heat the water to vary the temperature.

– Collect gas coming off in a tube.
5.7 – Understand the role of bacteria (Lactobacillus) in the production of yoghurt.
MAKING YOGHURT
– Heat the milk to 80℃.
• The milk is heated to 80℃ to pasteurise it and kill pathogenic microorganisms.
– Leave the milk to cool down to 46℃.
• To denature enzymes but avoid killing lactobacillus and allow it to work at the
optimum temperature.
– Add lactobacillus bulgaricus to change the milk into yoghurt.
• The lactobacillus respires anaerobically.
– Leave in a warm place for 8 hours.
• Allows lactobacillus to make lactic acid over time, as well as encourage bacterial
reproduction and enzymes to work at an optimum temperature.
• The pH is lowered and this kills lactobacillus as well as denature the enzymes.

5.8 – Interpret and label a diagram of an industrial fermenter and explain the need
to provide suitable conditions in the fermenter, including aseptic precautions,
nutrients, optimum temperature and pH, oxygenation and agitation, for the growth
of micro-organisms.
– The stirring paddles turns the blades and evenly distributes the mixture.
• Temperature / heat, concentration of substance and oxygen are evenly
distributed by stirring paddles.
– The fermenter is cooled by water flowing within the water jacket.
– The temperature and pH are monitored by temperature and pH probes.
• The fermenter can be adjusted to optimum conditions to allow enzymes to work at
a fastest rate.
– The air inlet allows oxygen to enter the fermenter.
• Oxygen is needed for the micro-organisms to respire aerobically.
– An agitator makes the air into very small bubbles; this means they have a larger
surface area and can dissolve easily, so there is better access to oxygen for
microorganisms.
– Aseptic (disinfected) conditions are needed.
• This prevents the contamination of the wanted product, and prevents other
microorganisms from using up nutrients and oxygen.
– Nutrients are needed in the fermenter so the microorganism can grow.
FISH FARMING (5.9)
5.9 – Explain the methods which are used to farm large numbers of fish to provide a
source of protein, including maintenance of water quality, control of intraspecific and
interspecific predation, control of disease, removal of waste products, quality and
frequency of feeding and the use of selective breeding.
– Water is filtered to maintain water quality (removal of microorganisms, faeces etc).
• Also, if the water is cleaned regularly the spread of disease is minimised and the
oxygen levels can maintain the respiration of the fish.
– Intraspecific predation is competition within a species.
• This can be stopped by separating fish of different ages, separating fish of different
genders, giving fish adequate room.

Interspecific predation is competition between species.
• This can be stopped by fencing the area the fish are in, putting nets around the area
the fish are in, keeping the fish in inside tanks.

– To minimise spread of disease, water should be changed regularly and their
surroundings sterilised often.
• Water is sterilised by adding antibiotics, and the spread of disease minimised by
removing dead or infected fish.
– Waste can be removed by changing the water in a tank or changing the nets.
– Fish need to be fed frequently in small amounts, this is so they don’t starve and
ensures that there is no wasted food (which could cause a decrease in water quality).
• It is important to feed fish food with nutrients (proteins) for growth, as well as add
hormones to increase their growth.
– Selective breeding can ensure that farmers produce fish with desired characteristics
by letting only the fish with the desired characteristics breed and pass on the gene.

Continue Reading

Human Influences on the Environment

4.11 – Understand the biological consequences of pollution of air by sulphur dioxide and
by carbon monoxide.
– Sulphur dioxide reacts with rainwater to form sulphurous acid, which falls as acid rain.
– Carbon monoxide is created as a result of incomplete combustion.
• Carbon monoxide binds to haemoglobin in the bloodstream which reduces the
capacity to carry oxygen.
4.12 – Understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs
are greenhouse gases.
– Greenhouse gas: Gas that contributes to global warming by absorbing long-wave
infrared radiation and trapping heat.
– Water vapour, carbon dioxide, nitrous oxide, methane and CFC (chlorofluorocarbons)
are greenhouse gases.
4.13 – Understand how human activities contribute to greenhouse gases.
– Many human activities contribute to the release of greenhouse gases.
• Combustion releases carbon dioxide.
• Keeping large numbers of livestock releases methane.
4.14 – Understand how an increase in greenhouse gases results in an enhanced
greenhouse effect and that this may lead to global warming and its consequences.
– An increase in greenhouse gases results in an enhanced greenhouse effect.
– This may lead to global warming and its consequences.
• Melting ice caps.
• Extremes of climate.
• Enhanced natural disasters.
• Extinction of species.
4.15 – Understand the biological consequences of pollution of water by sewage,
including increases in the number of micro-organisms causing depletion of oxygen.
– An increase in the number of microorganisms is caused by pollution of water by
sewage.

– Microorganisms respire and use up oxygen, causing the water environment to become
anoxic.
4.16 – Understand that eutrophication can result from leached minerals from fertiliser.
– Eutrophication can result from leached minerals from fertiliser.
• Algae forms as minerals are leached into waterways.
• Algae blooms form and block the sunlight.
• Without sunlight, plants die as there is a lack photosynthesis.
• Bacteria respires by decomposing on dead matter.
• Anoxic conditions causes animals to die.
4.17 – Understand the effects of deforestation, including leaching, soil erosion,
disturbance of the water cycle and of the balance in atmospheric oxygen and carbon
dioxide.
– Leaching: Loss of nutrients from the soil.
– Soil erosion: Weakened soil.
– Water cycle is disturbed.
– Imbalance in atmospheric oxygen and carbon dioxide.

Continue Reading

Cycles Within Ecosystems

4.8 – Describe the stages in the water cycle, including evaporation, transpiration,
condensation and precipitation.
– Evaporation: When water turns into water vapour due to heat.
– Transpiration: When water evaporates from the surface of a plant.
– Condensation: When water vapour turns back into water.
– Precipitation: When water is released from clouds.
4.9 – Describe the stages in the carbon cycle, including respiration, photosynthesis,
decomposition and combustion.
– Respiration: When organisms release carbon dioxide.
– Photosynthesis: When plants take in carbon dioxide.
– Decomposition: When decomposers decay dead matter, releasing carbon dioxide.
– Combustion: When matter is burned, releasing carbon dioxide.
4.10 – Describe the stages in the nitrogen cycle, including the roles of nitrogen
fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria.
– Nitrogen-fixing bacteria: Converts nitrogen gas into ammonia.
– Decomposers: Break down matter and releasing nitrogen back into the air.
– Nitrifying bacteria: Converts nitrogen compounds into nitrites, then into nitrates.
– Denitrifying bacteria: Converts nitrates to nitrogen gas.
– Lightning: Converts nitrogen gas into nitrates and nitrites.

Continue Reading

Feeding Relationships

4.4 – Explain the names given to different trophic levels to include producers, primary,
secondary and tertiary consumers and decomposers.
– Producer: Plants which photosynthesise to provide food.
– Consumer: Animals that eat plants or other animals.
• Primary consumer: Animals that eat the producer and are usually herbivores.
• Secondary consumer: Animals that eat the primary consumer and are carnivores.
• Tertiary consumer: Animals that eat the secondary consumer and are carnivores.
• Quaternary consumer: Animals that eat the tertiary consumer and are carnivores.
– Decomposers: Decay dead material and help to recycle nutrients.
4.5 – Understand the concepts of food chains, food webs, pyramids of number, pyramids
of biomass and pyramids of energy transfer.

– →: is eaten by
– Food chain: The simplest way of showing feeling relationships within an ecosystem.
– Food webs: A more complex demonstration of feeding relationships and how each
food chain in an ecosystem is related to each other

– Pyramids of number: Represent the numbers of organisms in each trophic level in a
food chain, irrespective of their mass.

– Pyramids of biomass: Show the total mass of the organisms in each trophic level,
irrespective of their numbers.

– Pyramids of energy transfer: Shows the transfer of energy through a food chain

4.6 – Understand the transfer of substances and of energy along a food chain.
– Substances are transferred along a food chain.
PRODUCER → PRIMARY CONSUMER → SECONDARY CONSUMER …
4.7 – Explain why only about 10% of energy is transferred from one trophic level to the
next.
– Only 10% of energy is transferred from one tropic level to the next.
– All the other 90% of energy is used for life processes.

Continue Reading

The Organism in the Environment

4.1 – Understand the terms population, community, habitat and ecosystem.
– Population: All the organisms of a particular species found in an ecosystem at any
one time.
– Community: The populations of all species found in a particular ecosystem at any
one time.
– Habitat: Places where specific organisms live in an ecosystem.

– Ecosystem: A distinct, self-supporting system of organisms interacting with each
other and with a physical environment.
4.2 – Explain how quadrats can be used to estimate the population size of an organism
in two different areas.
– A quadrat is a square with dimensions of one metre.
– Place random quadrats at a numbered grid corresponding to the habitat.
• The numbers are generated randomly using the random number function on a
calculator.
– The number of each species is counted within the quadrat.
– The number of species in the quadrat (1m2) is multiplied to obtain the number of
species in the area (A m2).
4.3 – Explain how quadrats can be used to sample the distribution of organisms in their
habitats.
– Quadrats can be used to estimate the distribution of organisms, a sample.
• Animals that do not move much (e.g. snails) or plants are sampled.
– The sample size must be sufficient and representative (i.e. able to represent the whole
area), multiple samples may be necessary.

Continue Reading

Inheritance

3.13 – Understand that the nucleus of a cell contains chromosomes on which genes are
located.
– The nucleus of a cell contains chromosomes on which genes are located.
3.14 – Understand that a gene is a section of a molecule of DNA and that a gene codes
for a specific protein.
– Gene: A section of a molecule of DNA that codes for a specific protein.
3.15 – Describe a DNA molecule as two strands coiled to form a double helix, the strands
being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C)
with guanine (G).
– A DNA molecule consists of two coiled strands to form a double helix.
– The strands consists of paired bases:

• Adenine (A) – Thymine (T)
• Cytosine (C) – Guanine (G)
3.16 – Understand that genes exist in alternative forms called alleles which give rise to
differences in inherited characteristics.
– Allele: Alternate form of a gene.
– Alleles give rise to differences in inherited characteristics.
3.17 – Understand the meaning of the terms: dominant, recessive, homozygous,
heterozygous, phenotype, genotype and codominance.
– Dominant: Gene allele that expresses over another allele.
• Present in both homozygous pairs and heterozygous pairs.
• Represented by a capital letter.
– Recessive: Gene allele that is only expressed when paired with another recessive
allele.
• Present in homozygous recessive pairs only. In heterozygous pairs, the dominant
allele is expressed over the recessive allele.
• Represented by a lowercase letter.
– Homozygous: Same pair of genes.
• Homozygous dominant: Two dominant gene alleles.
• Homozygous recessive: Two recessive gene alleles.
– Heterozygous: Different pair of genes (i.e. one dominant and recessive gene).
– Phenotype: The characteristic that the gene displays.
– Genotype: The actual nature of the gene.
– Codominance: When both alleles are expressed in a heterozygous pair.
3.18 – Describe patterns of monohybrid inheritance using a genetic diagram.
– Monohybrid inheritance: The inheritance of one gene (see 3.20).
3.19 – Understand how to interpret family pedigrees.

3.20 – Predict probabilities of outcomes from monohybrid crosses.
– Probabilities (where A is the dominant allele and a is the recessive allele):
• 25% AA • 50% Aa • 25% aa
3.21 – Understand that the sex of a person is controlled by one pair of chromosomes, XX
in a female and XY in a male.
– The sex of a person is controlled by one pair of chromosomes.
– XX in a female, XY in a male.
3.22 – Describe the determination of the sex of offspring at fertilisation, using a genetic
diagram.
– The sperm contains the XY chromosome.
– The ovum contains the XX chromosome.

3.23 – Understand that division of a diploid cell by mitosis produces two cells which
contain identical sets of chromosomes.
– Division of a diploid cell by mitosis produces two cells which contain identical sets of
chromosomes.
3.24 – Understand that mitosis occurs during growth, repair, cloning and asexual
reproduction.
– Mitosis occurs during growth, repair, cloning and asexual reproduction.
3.25 – Understand that division of a cell by meiosis produces four cells, each with half
the number of chromosomes, and that this results in the formation of genetically different
haploid gametes.
– Division of a cell by meiosis produces four cells, each with half the number of
chromosomes.
– This results in the formation of genetically-different haploid gametes.
3.26 – Understand that random fertilisation produces genetic variation of offspring.
– Random fertilisation produces genetic variation of offspring.
3.27 – Know that in human cells the diploid number of chromosomes is 46 and the
haploid number is 23.
– In human cells, the diploid number of chromosomes is 46.
– In human cells, the haploid number of chromosomes is 23.
3.28 – Understand that variation within a species can be genetic, environmental, or a
combination of both.
– Variation within a species can be genetic, environmental, or a combination of both.
3.29 – Understand that mutation is a rare, random change in genetic material that can be
inherited.
– Mutation: A rare, random change in genetic material that can be inherited.
3.30 – Describe the process of evolution by means of natural selection.
– Variation within a species is caused by a rare, random mutation.

– The mutation of a gene means that the animal survives and is not killed.
– The survived animals reproduce and pass on the gene.
– This is repeated over time and many generations.
3.31 – Understand that many mutations are harmful but some are neutral and a few are
beneficial.
– Many mutations are harmful.
– Some mutations are neutral.
– Few mutations are beneficial.
3.32 – Understand that resistance to antibiotics can increase in bacterial populations,
and appreciate how such an increase can lead to infections being difficult to control.
– Resistance to antibiotics can increase in bacterial populations.
– The increase of resistance to antibiotics can lead to bacterial infections being difficult
to control.
3.33 – Understand that the incidence of mutations can be increased by exposure to
ionising radiation (for example gamma rays, X-rays and ultraviolet rays) and some
chemical mutagens (for example chemicals in tobacco).
– The incidence of mutations can be increased by exposure to ionising radiation.
• E.g. Gamma rays, X-rays and ultraviolet rays.
– The incidence of mutations can be increased by some chemical mutagens.
• E.g. Chemicals in tobacco

Continue Reading

Reproduction

3.1 – Understand the differences between sexual and asexual reproduction.
– Sexual reproduction: Two parents create non-identical offspring who inherits
characteristics from both parents.
– Asexual reproduction: A single parent creates an identical offspring.
3.2 – Understand that fertilisation involves the fusion of a male and female gamete to
produce a zygote that undergoes cell division and develops into an embryo.
– Gamete: A sex cell.

Gamete Human Flowering Plant
Male Sperm Pollen Grain
Female Ovum Ovum

Fertilisation: The fusion of two gametes.
• This involves the fusion of a male and female gamete.
• This produces a zygote that undergoes cell division and develops into an embryo.
FLOWERING PLANTS (3.3 – 3.7)
3.3 – Describe the structures of an insect-pollinated and a wind-pollinated flower and
explain how each is adapted for pollination.
3.4 – Understand that the growth of the pollen tube followed by fertilisation leads to seed
and fruit formation.
Gamete Human Flowering Plant
Male Sperm Pollen Grain
Female Ovum Ovum
Feature Insect Pollinated Wind Pollinated
Petal Large and bright. Unattractive and not bright.
Pollen Larger and stickier with barbs to
cling on insects. Lighter and smaller.
Smell / Nectary Nectary present; sweet-smelling
flower.
No nectary present and no
attracting smell.
Anther In the flower. Exposed so it is easier to catch
pollen or for insects to pollinate.

– The growth of the pollen tube followed by fertilisation leads to seed and fruit formation.
• The zygote is known as a seed.
• The ovary becomes the fruit.
3.5 – Understand the conditions needed for seed germination.
– Water: Activates enzymes.
– Warm temperatures: Optimum temperature for enzymes to break down starch into
maltose for food.
– Oxygen: For respiration.
3.6 – Understand how germinating seeds utilise food reserves until the seedling
can carry out photosynthesis.
– Germinating seeds utilise food reserves until the seedling can carry out
photosynthesis.
– Food reserves are in the cotyledons (first leaves).
• Light is not needed because the seed does not photosynthesise.
• The process of germination stops once the seed is able to photosynthesise.
3.7 – Understand that plants can reproduce asexually by natural methods (illustrated by
runners) and by artificial methods (illustrated by cuttings).
– Plants can reproduce asexually by natural methods, e.g. runners.
– Plants can reproduce sexually by artificial methods, e.g. cuttings.
HUMANS (3.8 – 3.12)
3.8 – Describe the structure and explain the function of the male and female reproductive
systems.
Male Organ Function
Testicles Produces sperm and the hormone testosterone.
Penis Delivers sperm through the urethra. Consists of two parts, the shaft (main part)
and glans (tip).
Scrotum (Scrotal sac) Hangs under the penis and contains the testicles and epididymis.
Vas Deferens (Ductus deferens) Thin muscular tube that transports sperm from the epididymis
to the urethra.

Seminal Vesicle Secretes a thick fluid that nourishes the sperm. Located at the base of the
bladder.
Epididymis Next to each testicle, a light-coloured tube where sperm is stored. From here,
sperm is transported to the vas deferens.
Prostate Gland Surrounds a portion of the urethra and produces some of the fluid in semen.
Bladder The muscular sac that stores urine until it is released through the urethra.
Urethra Tube that carries semen and urine out of the penis.
Female Organ Function
Ovary There are two ovaries, one on each side of the uterus. Produces eggs and
hormones (progesterone and oestrogen).
Fallopian tube Connects the ovaries with the uterus and allows the egg to travel through during
ovulation.
Uterus Hollow organ with a muscular wall, where the foetus grows.
Vagina Connects the uterus to the outside of the body. The opening of the vagina is on the
outside, known as the vaginal opening.
Cervix The lower part of the uterus that opens during childbirth.

3.9 – Understand the roles of oestrogen and progesterone in the menstrual cycle.
– Oestrogen and progesterone both affect the menstrual cycle.
– Oestrogen: Produced in the ovaries, thickens the womb lining and prompts the
release of LH (luteinising hormone).

– Progesterone: Produced in the ovary (corpus luteum) and maintains the lining of the
womb.
3.10 – Describe the role of the placenta in the nutrition of the developing embryo.
– Digested food molecules and oxygen from the mother’s blood travel via the umbilical
cord to the embryo.
– Waste products from the embryo (e.g. water, carbon dioxide) are excreted by the
mother.
– Particles travel by diffusion from a high concentration to low concentration.

– The placenta has a large surface area.
3.11 – Understand how the developing embryo is protected by amniotic fluid.
– The amniotic fluid protects the embryo by absorbing the shock and force of impact.
3.12 – Understand the roles of oestrogen and testosterone in the development of
secondary sexual characteristics.
– Oestrogen develops the secondary sexual characteristics of girls.
– Testosterone develops the secondary sexual characteristics of boys.

Male Female
Sperm production starts. The menstrual cycle begins, and eggs are released
by ovaries every month.
Growth and development of male sexual organs. Growth and development of female sexual organs.
Growth of armpit and pubic hair, and chest and
facial hair (beard). Growth of armpit and pubic hair.
Increase in body mass; growth of muscles (e.g.
chest).
Increase in body mass; development of ‘rounded’
shape to hips.
Voice breaks. Voice deepens without sudden ‘breaking’.
Sexual ‘drive’ develops. Sexual ‘drive’ develops.
Breasts develop

Continue Reading