This guide covers IGCSE Biology topic 21: human influences on ecosystems. You will revise pollution (air, water, land), deforestation (causes and effects), conservation (why and how), and sustainable use of resources.

Key concepts to revise

• Pollution – Air (e.g. CO₂, sulfur dioxide; greenhouse effect, acid rain); water (e.g. sewage, fertiliser; eutrophication); land (e.g. pesticides, plastic).
• Deforestation – Removal of trees; causes: farming, logging, roads. Effects: loss of habitat, CO₂ increase (less absorption, burning), soil erosion, flooding.
• Conservation – Protecting species and habitats; reasons: biodiversity, resources, ethics. Methods: protected areas, breeding programmes, seed banks, laws.
• Sustainable use – Using resources so they are not used up; e.g. sustainable fishing (quotas, mesh size), replanting trees.

Exam tips and command words

• State – One cause of deforestation; one effect of pollution (e.g. eutrophication).
• Describe – The greenhouse effect (CO₂ and others trap heat); eutrophication (excess nutrients → algal bloom → oxygen depletion).
• Explain – Why deforestation increases CO₂ (fewer trees to absorb; burning releases CO₂); why conservation is important (biodiversity, future resources).
• Suggest – One way to reduce pollution or to use resources sustainably.

Common mistakes

• Confusing greenhouse effect (natural; keeps Earth warm) with enhanced greenhouse effect (extra CO₂ from human activity; global warming).
• Saying “pollution causes global warming” without naming CO₂ (or other greenhouse gases).
• Not stating that conservation can include sustainable use (use but do not destroy).

Revision checklist

• State one cause and one effect of deforestation.
• Describe the greenhouse effect and link CO₂ to global warming.
• Describe eutrophication (excess nutrients → algae → oxygen depletion).
• State one method of conservation and one way to use a resource sustainably.

Next steps

Book a free trial with an IGCSE Biology tutor to practise human impact and conservation questions, or explore Tutopiya’s learning portal for more revision resources.