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Learn5090Paper 1 · Multiple ChoiceRelationships of organisms with one another and with the environmentPollution and conservation
Relationships of organisms with one another and with the environment · Subtopic 4 of 5

Pollution and Conservation

Humans destroy habitats for farming, building, mining and logging. Deforestation reduces biodiversity, increases CO₂ (less photosynthesis, burning), causes soil erosion and flooding. Eutrophication: fertilisers or sewage add nutrients → algal bloom → algae block light, plants die → decomposers respire and use up oxygen → fish die. Greenhouse gases (CO₂, methane) cause climate change. Plastics don't biodegrade and harm wildlife. Conservation protects species and habitats with reserves, laws, seed banks, captive breeding and education; sustainable use includes fishing quotas, net mesh sizes and replanting forests.

Cambridge 5090 Paper 1Cambridge 5090 Paper 2Cambridge 0610 Papers 2, 4Cambridge 0610 Papers 1, 3Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 45 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Describe the causes and effects of habitat destruction and deforestation.
  • Explain eutrophication step by step.
  • Describe effects of other pollutants.
  • Describe conservation methods and sustainable resource use.
Pause and think

Why can a river be full of green algae yet have dead fish floating in it?

Section 2 of 14

Core idea

Start hereA crowded planet

Humans now use over a third of Earth's land for farming. Our activities affect every ecosystem on the planet.

The big idea

Habitat destruction and pollution reduce biodiversity. Conservation and sustainable use protect species and resources for the future.

1. Eutrophication

Eutrophication step by step

It's the decomposers that use up the oxygen.

Worked exampleDeforestation

A rainforest is cleared for cattle ranching.

Goal
Three consequences.
Strategy
Biodiversity, carbon, soil.
  1. habitat loss\text{habitat loss}
    Species lost; biodiversity falls.
  2. ↑CO2\uparrow\mathrm{CO_2}
    Less photosynthesis; burning releases carbon.
  3. soil erosion and flooding\text{soil erosion and flooding}
    No roots to hold soil or absorb water.
AnswerLoss of species, more greenhouse gas, damaged soil.
✓ CheckCattle also release methane ✓.
Key takeawaySustainability Fishing quotas, larger net mesh, replanting forests, protected areas, seed banks and captive breeding.
Pause and think

Why are seed banks important even for common crops?

Summary

  • Habitat loss and deforestation.
  • Eutrophication via decomposers.
  • Conservation and sustainable use.
Key words
Biodiversity
Variety of species in an area.
Eutrophication
Excess nutrients leading to oxygen loss in water.
Sustainable
Meeting present needs without harming future supply.
HistorySilent Spring. Rachel Carson's 1962 book Silent Spring revealed how the pesticide DDT built up in food chains and harmed birds, launching the modern environmental movement.
Fun factFrozen seeds. The Svalbard Global Seed Vault, buried in an Arctic mountain, stores over a million seed samples as a backup for the world's crops.
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