Humans and biodiversity

7. Ecology

Biodiversity is the variety of different species of organisms, and a high level of it keeps ecosystems stable. A growing human population that also wants a higher standard of living takes more resources, makes more waste and takes up more land, and all three of those reduce biodiversity.

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215 questions6 subtopicsFoundation tier

What humans and biodiversity covers

Every subtopic below has its own questions, mark schemes and notes.

4.7.3.1-4.7.3.3Biodiversity, waste and land use

4.7.3.4-4.7.3.5Deforestation and global warming

Cutting down forests on a large scale releases carbon dioxide and reduces how much is taken back out of the air, while destroying habitats. Rising carbon dioxide and methane levels trap more energy in the atmosphere, warming the Earth and changing where species can live.

4.7.3.6Maintaining biodiversity

Scientists, governments and ordinary citizens have set up programmes to reduce the damage humans do to ecosystems. None of them is free, and each has to be weighed against pressures such as cost, jobs, food supply and the demand for land.

4.7.4.1-4.7.4.3Trophic levels and biomass

A food chain can be split into numbered trophic levels, from producers at level 1 upwards. Biomass is the mass of living material, and only about a tenth of it makes it from one level to the next, which is why food chains are short and why pyramids of biomass narrow towards the top.

4.7.5.1-4.7.5.3Food security and farming

Food security means having enough food to feed a population, and several pressures threaten it. Fishing and farming can both be made more productive, but the methods raise questions about sustainability and about how animals are treated.

4.7.5.4Biotechnology

Biotechnology means manipulating living things and biological processes to make something useful. Microorganisms are grown industrially to make food such as mycoprotein, bacteria are genetically engineered to make human insulin, and crops are genetically modified to raise yields or improve nutrition.

Key terms

The definitions examiners expect, in the wording that earns the mark.

Biodiversity — The variety of different species of organisms on Earth or within an ecosystem.

Pollution — Harmful substances released into water, land or air, which kill organisms and reduce biodiversity.

Peat — Partly decayed plant material that builds up in acidic, waterlogged ground and stores carbon.

Landfill — A site where household and other solid waste is buried in the ground.

Deforestation — The large-scale cutting down of forests.

Greenhouse gas — An atmospheric gas, such as carbon dioxide or methane, that absorbs and re-radiates energy that would otherwise leave the Earth.

Global warming — The gradual increase in the Earth's temperature caused by rising levels of greenhouse gases.

Climate change — A long-term change in weather patterns; global warming is one type and causes others, such as changed rainfall.

Breeding programme — A scheme in which endangered animals are bred in captivity to stop the species becoming extinct.

Field margin — A strip of land at the edge of a field where wild flowers and grasses are left to grow.

Hedgerow — A line of shrubs and trees at a field boundary that provides a habitat for many species.

Subsidy — Money paid by a government to encourage someone to do something, such as restoring hedgerows.

Trophic level — A stage of a food chain, occupied by organisms with the same role in it.

Producer — An organism at trophic level 1 that makes its own food by photosynthesis.

Apex predator — A carnivore with no predators of its own, at the top of a food chain.

Biomass — The mass of living material.

Decomposer — A bacterium or fungus that breaks down dead material by secreting enzymes onto it.

Egestion — The release of food that was eaten but never absorbed, as faeces.

Food security — Having enough food to feed a population.

Sustainable food production — Producing enough food now without using resources faster than they can be renewed, so food can still be produced in the future.

Fishing quota — A limit on the number and size of fish that may be caught in a particular area.

Overfishing — Catching fish faster than the population can replace itself, so stocks fall.

Biotechnology — Manipulating living things and biological processes to produce a useful product.

Mycoprotein — A high-protein food made from fungal biomass and used as a meat substitute.

Restriction enzyme — An enzyme that cuts DNA at a specific sequence, leaving sticky ends.

Plasmid — A small circular loop of DNA found in bacteria, used as a vector in genetic engineering.

Recombinant DNA — DNA made by joining together pieces of DNA from two different sources.

Ligase — The enzyme used to join sticky ends of DNA together.

Where marks get lost

The mistakes that come up again and again in this topic.

Biodiversity is the variety of different species, not the number of individual organisms - a field with a million grass plants of one species has very low biodiversity.
If a question asks why peat destruction adds carbon dioxide to the air, you need both routes: microorganisms respiring as the drained peat decays, and burning peat as a fuel.
Say which of water, land or air a named pollutant affects - a general answer of 'it causes pollution' will not score.
Deforestation has two separate carbon effects and questions usually want both: less carbon dioxide taken in by photosynthesis, and more released by burning and by microorganisms respiring.
The greenhouse effect itself is not a bad thing - it is the increase in it that causes global warming. Do not write that greenhouse gases are pollutants that should all be removed.
Sea level rise has two causes: melting ice and the expansion of seawater as it warms. Only giving melting ice throws away a mark.
'Changes in distribution' means where species are found, not how many there are. Say whether the range gets wider or narrower and why.
'Evaluate' means give both sides and then reach a conclusion. A list of advantages alone will not reach the top marks.
Field margins and hedgerows work because they add habitat variety to a field of a single crop - say that, rather than just naming them.
Recycling helps biodiversity through land, not just through resources: less landfill means less habitat taken over.
Trophic level 1 is the producer, so a food chain with three animals in it has four levels, not three. Count the plant.
Egestion and excretion are not the same: faeces is food that was never absorbed, urine contains waste made inside the body.
The one per cent figure is for light energy reaching producers; the ten per cent figure is for biomass passing between levels. Do not swap them.
In the efficiency formula the divisor is the biomass at the previous level, not the level you have arrived at - dividing the wrong way round gives an answer above 100%.
A pyramid of biomass is not a pyramid of numbers. Do not explain its shape by saying there are fewer organisms.
Explain why a threat is a threat rather than just naming it - 'conflict' scores little, 'conflict disrupts the supply of food and water to an area' scores.
Bigger mesh size helps in two distinct ways: unwanted species escape, and young fish survive to breed. Name the one the question asks about.
Restricting movement works by reducing energy transferred to the environment so more goes into growth. Saying 'so the animal gets fatter' does not explain anything.
Sustainable does not simply mean 'good for the environment' - it means the resource is not used faster than it renews.
The order matters: cut with a restriction enzyme, join with ligase. Naming the wrong enzyme for the wrong job is a common error.
Both the human gene and the plasmid must be cut with the same restriction enzyme, otherwise the sticky ends do not match.
Fusarium is grown aerobically, so a fermenter needs an air supply - do not describe mycoprotein production as fermentation without oxygen.
Golden rice does not contain vitamin A itself; it makes a chemical the body converts into vitamin A.

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