CB9.2 — Human impact and conservation (Edexcel 1SC0)

Threats to biodiversity

• Habitat destruction: deforestation for agriculture, urban development; draining wetlands.
• Pollution: air (SO₂, NOₓ from burning fossil fuels → acid rain); water (eutrophication from fertiliser run-off); land (pesticides, plastic).
• Overexploitation: overfishing; poaching of endangered species.
• Invasive species: introduced species outcompete native species.
• Climate change: habitat shifts; ocean acidification; extreme weather.

Eutrophication

1. Fertiliser (nitrates/phosphates) washes from fields into rivers/lakes.
2. Nitrates stimulate rapid algal growth (algal bloom) → blocks light.
3. Plants below surface die (no photosynthesis).
4. Decomposers bacteria break down dead plants → multiply → use up dissolved oxygen.
5. Fish and other aquatic animals die from lack of oxygen (deoxygenation).

Conservation strategies

• In situ: conserving organisms in their natural habitat — national parks, marine reserves, seed banks.
• Ex situ: conserving organisms outside their natural habitat — zoos, botanical gardens, frozen zoos (genetic material stored).
• International agreements: CITES (controls trade in endangered species); climate agreements.
• Reforestation: planting trees to restore habitats and absorb CO₂.