Cambridge IGCSE Biology 0610 · Topic 20
Human Influences on Ecosystems
Every human activity in this chapter does the same two things at once: it gets people something they need — food, timber, fish, living space — and it changes an ecosystem somewhere else as a side effect. Once you can hold both halves of that trade-off in view at the same time, most of Topic 20 stops being a list of unrelated facts and starts being one recurring argument applied to four different situations.
Cambridge organises this as four linked sections. Food supply covers how humans increase agricultural production, and the real advantages and disadvantages that come with farming at scale. Habitat destruction and deforestation cover what happens when land is cleared or changed to make that production, or housing, possible. Pollution covers what sewage, excess fertiliser, plastics, methane and carbon dioxide actually do once they enter an ecosystem — not as a vague “pollution is bad” statement, but as specific, traceable mechanisms. And conservation closes the loop: how species, forests and fish stocks can be used without being used up.
Most of the marks lost in this topic are not biology mistakes — they are precision mistakes. “Fertiliser gets washed into rivers and kills fish” states something true, but it skips the actual mechanism a mark scheme is looking for: decomposer respiration using up dissolved oxygen. “Deforestation causes climate change” is true but incomplete without naming which gas, and why removing trees changes its concentration. The pages below are built around exactly this kind of gap — not more content, but the specific causal chain Cambridge rewards.
What’s in this chapter
| Page | Level | What it covers |
|---|---|---|
| Increasing food production | Core | Machinery, fertilisers, insecticides, herbicides and selective breeding — and the causal chain connecting each one to a bigger crop or a bigger herd. |
| Monoculture and intensive livestock production | Core | Why large-scale farming systems cut both ways, and the specific advantages and disadvantages Cambridge expects for each. |
| Biodiversity and habitat destruction | Core | What biodiversity actually measures, the six reasons humans destroy habitats, and how one lost species can move through a whole food web. |
| Deforestation | Core | One cause, four separate consequences — biodiversity loss, soil loss, flooding and rising atmospheric carbon dioxide — each with its own mechanism. |
| Water pollution: sewage, fertiliser and plastics | Core | Why sewage and excess fertiliser both end up killing fish through the same route, and how non-biodegradable plastic does something completely different. |
| Air pollution and the enhanced greenhouse effect | Core | Methane and carbon dioxide, the mechanism that lets them warm the planet, and why the greenhouse effect itself is not the villain of this story. |
| Eutrophication | Supplement | The full eight-step sequence from excess nitrate to dead fish, and why it is oxygen depletion, not poisoning, that does the damage. |
| Sustainable resources and endangered species | Core | What makes a resource sustainable rather than merely renewable, and the six reasons a species slides toward endangerment or extinction. |
| Conserving endangered species | Core + Supplement | Monitoring, captive breeding and seed banks, plus the Supplement extension into artificial insemination, IVF and the genetic risks of a small population. |
| Sustainable forests and fish stocks | Supplement | Education, protected areas, quotas and monitoring — the same sustainability logic applied to two very different resources. |
Core or Supplement?
Six of these pages are Core, so every candidate needs them regardless of tier: increasing food production, monoculture and intensive livestock, biodiversity and habitat destruction, deforestation, water pollution, and the enhanced greenhouse effect. Sustainable resources and endangered species is also Core. Eutrophication is Supplement only — Core candidates should understand that excess fertiliser lowers dissolved oxygen, but the full nitrate-to-decomposer-respiration sequence is examined only at Supplement level. Conserving endangered species is mostly Core, with artificial insemination, IVF and reduced genetic variation added as Supplement extensions on the same page. Sustainable forests and fish stocks is Supplement throughout. If you’re not sure which tier you’re sitting, that’s worth checking before you spend time on the Supplement-only pages.