Biodiversity — AQA GCSE Biology
Test yourself on Biodiversity with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
Biodiversity explained
Biodiversity means the variety of life, measured as the number of different species present.
Read the full explanation
It can be considered on a global scale, covering all species on Earth, or on a local scale within one ecosystem such as a pond or woodland. A habitat with many different species has high biodiversity; one dominated by a single species has low biodiversity. Biodiversity also includes the range of genetic variation within a species, because populations with greater genetic variation are more likely to survive changing conditions. When comparing two areas, count or estimate the number of species present rather than simply the total number of organisms, since a large population of one species does not give high biodiversity.
A great biodiversity ensures the stability of ecosystems by reducing the dependence of one species on another for food, shelter and the maintenance of the physical environment.
Stable ecosystems keep functioning when conditions change. High biodiversity contributes to this stability because many species perform similar roles, so the loss of one species has less impact. If a woodland has several plant species providing food and shelter, a disease affecting one tree species does not remove all food and nesting sites. Similarly, several decomposers and pollinators may maintain nutrient cycling and reproduction. Where biodiversity is low, species depend heavily on one another: a single crop species, one pollinator or one decomposer may be essential, so its decline can collapse the whole community. Reducing dependence on any one species for food, shelter and maintaining the physical environment therefore buffers the ecosystem against change.
The future of the human species on Earth relies on us maintaining a good level of biodiversity.
Humans depend on other organisms for survival, so losing biodiversity threatens human populations. We rely on plants and algae for oxygen and on other organisms for food, medicines and raw materials. Ecosystems also provide services such as pollination of crops, pest control, flood protection and nutrient cycling in soil. If biodiversity falls, these services become less reliable: fewer pollinators can reduce crop yields, and soil degradation can lower food production. Genetic diversity in wild species is also a source of traits that plant breeders may need when crops face new diseases or a changing climate. Maintaining biodiversity therefore supports food security, health and a stable environment for future human generations.
Many human activities are reducing biodiversity and only recently have measures been taken to try to stop this reduction.
Biodiversity is the variety of different species living in an ecosystem, and also the genetic variation within those species. Human activities reduce it in several ways. Deforestation removes habitats and the species that depend on them. Pollution of water, air and land damages organisms and food chains. Overfishing and hunting remove species faster than they can reproduce. Building roads, houses and farms fragments habitats so populations become small and isolated. Introduced species may outcompete or eat native organisms. Only recently have people acted to slow this loss, for example by creating nature reserves, protecting endangered species by law, replanting woodland, reducing pollution and recycling resources. These measures aim to maintain the variety of life for future generations.
Your focus
- State that biodiversity is the variety of different species on Earth or within an ecosystem.
- Compare the biodiversity of two described habitats using the number of species present.
- Explain why genetic variation within a species is part of biodiversity.
Show all 12 objectives
- Explain how high biodiversity reduces the dependence of one species on another.
- Describe how reduced dependence on a single species helps an ecosystem remain stable when conditions change.
- Apply the idea of stability to a named low-biodiversity ecosystem and predict the effect of losing one species.
- Explain why human survival depends on maintaining biodiversity.
- Give examples of ecosystem services that support human food production and health.
- Evaluate how a named human activity could reduce biodiversity and affect human populations.
- Define biodiversity as the variety of species and genetic variation within species.
- Describe human activities that reduce biodiversity and explain their effects.
- Describe recent measures taken to stop the reduction in biodiversity.
Biodiversity exam tips
Marking Points
- Biodiversity is the variety of different species, not simply the total number of individual organisms.
- It can be measured globally across the whole Earth or locally within a single ecosystem.
- An ecosystem with many different species has high biodiversity; one with few species has low biodiversity.
- Biodiversity includes genetic variation within a species as well as the number of species.
- Comparing biodiversity between two areas requires identifying and counting the different species present, not just counting individuals.
- High biodiversity makes an ecosystem better able to withstand environmental change because different species respond in different ways.
- High biodiversity means many species are present, so several species can carry out similar roles.
- If one species declines, others can still provide food, shelter or nutrient cycling, so the ecosystem continues to function.
- Low biodiversity creates heavy dependence on a few species, so the loss of one species can have a large effect on the community.
- Maintenance of the physical environment includes processes such as nutrient cycling, soil formation and water retention carried out by living organisms.
- Stability means the ecosystem can resist or recover from change, such as disease, drought or the arrival of a new predator.
- Reducing dependence between species is the mechanism linking high biodiversity to ecosystem stability.
- Humans depend on other organisms for food, oxygen, medicines and raw materials.
- Ecosystem services such as pollination, pest control, flood protection and nutrient cycling support human life and agriculture.
- Loss of biodiversity can reduce crop yields and food security, for example through loss of pollinators or fertile soil.
- Wild species contain genetic variation that can be used to improve crops and livestock, especially when conditions change.
- Maintaining biodiversity helps ensure resources remain available for future human generations.
- Human activity that reduces biodiversity can therefore harm human populations as well as wildlife.
- Biodiversity means the variety of species in an ecosystem and the genetic variation within each species.
- Human activities such as deforestation, pollution, overfishing, hunting and building reduce biodiversity by destroying or fragmenting habitats.
- Small isolated populations are more vulnerable to extinction because they have less genetic variation.
- Measures taken recently include nature reserves, legal protection of species, replanting trees, reducing pollution and recycling.
- These measures aim to slow or stop the reduction in biodiversity and protect ecosystems for the future.
Examiner Tips
- 💡Define biodiversity in terms of variety of species, and add 'within an ecosystem or on Earth' to show you understand both scales.
- 💡When comparing two habitats, refer to the number of different species present and give a clear conclusion about which has greater biodiversity.
- 💡If a question mentions genetic variation, link it to biodiversity by explaining that variation within a species is part of the variety of life.
- 💡Use the phrase 'reduces dependence on one species' and then give a concrete example such as several pollinators or several decomposers.
- 💡Structure your answer as cause and effect: high biodiversity leads to several species per role, which leads to continued food, shelter and nutrient cycling.
- 💡When asked about a low-biodiversity example such as a wheat field, explain that a single pest or disease could remove the dominant species and disrupt the whole community.
- 💡Link each point about biodiversity to a specific human need, such as food, medicine or clean water, rather than saying 'it is important'.
- 💡Use examples of ecosystem services, such as bees pollinating crops or wetlands reducing flooding, to show applied understanding.
- 💡When discussing the future, refer to future generations and the need to keep resources and ecosystem services available.
- 💡Name at least two specific human activities and explain how each reduces biodiversity.
- 💡When describing measures, link each one to how it protects species or habitats.
- 💡Use the phrase genetic variation when explaining why small populations are at risk.
Common Mistakes
- Confusing biodiversity with population size: a field containing thousands of one grass species has a large population but low biodiversity.
- Thinking biodiversity applies only to the whole planet: it can also describe a single ecosystem, such as a hedgerow or rock pool.
- Ignoring genetic variation: two woodlands with the same species list can differ in biodiversity if one population has much less genetic variation.
- Saying high biodiversity means no species can ever be lost: it means the ecosystem is more likely to keep functioning when a species is lost, not that loss is impossible.
- Treating stability as the same as no change: stable ecosystems still change, but they continue to support a community of organisms.
- Forgetting the physical environment: decomposers and plants maintain soil and nutrient cycles, which is part of the stability described.
- Thinking biodiversity matters only for wildlife: human food security, medicine and oxygen supply all depend on other species.
- Assuming technology removes all dependence on nature: artificial pollination or fertiliser use is costly and cannot replace every ecosystem service.
- Confusing maintaining biodiversity with leaving nature completely untouched: sustainable management, such as protected areas and reduced pollution, can maintain biodiversity while people use resources.
- Thinking biodiversity only means the number of organisms; the correction is that it means the variety of species and the genetic variation within them.
- Assuming all human activity harms biodiversity; the correction is that some recent measures, such as conservation and recycling, help to protect it.
- Confusing habitat destruction with pollution; the correction is that both reduce biodiversity but by different mechanisms, so describe the specific cause.