Human impacts, biodiversity and food security — Edexcel GCSE Biology
Fish farming, non-indigenous species and eutrophication, the benefits of biodiversity and reforestation, and factors affecting food security.
Revision notes
5 short notes, in the order of the specification. Each one in short:
Fish farming is a human interaction with ecosystems that has positive and negative impacts on biodiversity. It provides a reliable food supply and reduces overfishing of wild fish stocks. However, waste and uneaten food can cause eutrophication, disease and parasites can spread to wild fish, and escaped fish may compete or interbreed with wild fish.
A non-indigenous species is one brought, deliberately or accidentally, into an area where it does not naturally live. It may have no natural predators, so its population grows quickly, and it can compete with, eat or spread disease to native species. Biodiversity falls as native species decline, although some are introduced for food or to control pests.
Eutrophication happens when too many nutrients, such as nitrates from fertilisers or sewage, run off into lakes and rivers. Algae grow quickly and block light, so plants and algae lower down die. Decomposer bacteria feed on the dead material and use up the oxygen in the water for aerobic respiration, so fish and other aquatic animals die.
Maintaining biodiversity, locally and globally, keeps ecosystems stable because species depend on each other. Biodiversity provides food, materials and medicines, and supports pollination of crops and cycling of materials. Conservation programmes protect endangered animal species, and reforestation restores habitats, absorbs carbon dioxide by photosynthesis and reduces soil erosion and flooding.
Food security
Triple onlyFood security means having enough food to feed a population. It is threatened by an increasing human population, increasing animal farming and meat and fish consumption, new pests and pathogens, environmental change caused by human activity, and sustainability issues such as growing biofuel crops and the cost of fertilisers, pesticides, fuel and animal feed.
Exam questions
5 exam-style questions (17 marks), each with its mark scheme.
Answer the questionsFlashcards
12 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of ecosystems and material cycles on one page, so you can see where this subtopic fits.
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Quick check questions
Name the three human interactions you must be able to explain for this topic.
Show answer
Fish farming, introduction of non-indigenous species, eutrophication.
Why do fish die in eutrophication?
Show answer
Bacteria feeding on dead plants and algae use up the oxygen in the water.
Give two benefits of reforestation.
Show answer
Any two of: restores habitats, absorbs carbon dioxide, reduces soil erosion.
What is meant by a non-indigenous species?
Show answer
A species introduced to an area where it does not naturally live.
Frequently asked questions
What is eutrophication and what causes it?
Eutrophication is caused by too many nutrients, such as nitrates from fertilisers or sewage, running into lakes and rivers. Algae grow quickly and block light, so plants below die. Decomposer bacteria feed on the dead material and use up the oxygen for aerobic respiration, so fish and other aquatic animals die and biodiversity falls.
Why is biodiversity important to ecosystems?
Biodiversity is important because ecosystems with high biodiversity are more stable. Species depend on each other, so the loss of one is less likely to cause others to fail. Biodiversity also gives humans food, materials and medicines, and species help maintain the conditions we depend on, such as pollination of crops and cycling of materials.
What are the advantages and disadvantages of fish farming?
Fish farming provides a reliable food supply, reduces overfishing of wild stocks, and lets conditions be controlled so fish grow quickly. However, waste and uneaten food pollute water and can cause eutrophication, disease and parasites can spread to wild fish, and escaped fish may compete or interbreed with wild fish, reducing their genetic variety.
How do non-indigenous species affect biodiversity?
Non-indigenous species can reduce biodiversity. With no natural predators in the new area, their population can grow quickly. They compete with native species for food and space, may eat native species, or carry diseases that native species cannot resist. Native species decline or die out, although some introductions provide food or control pests.
What are the threats to food security?
Triple only Food security is threatened by an increasing human population, by more meat and fish consumption, which needs more land because energy is lost at each trophic level, and by new pests and pathogens that destroy crops and farm animals. Environmental change such as climate change, and sustainability issues such as biofuel crops and costly fertilisers, add to the problem.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026