A conservation organisation is working to protect a rainforest ecosystem that contains a large number of different species. Explain why maintaining a high level of biodiversity in this ecosystem is important, and suggest two human activities that could reduce biodiversity in this area.

Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 2.5 Biodiversity · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Rainforests cover less than 6% of the Earth's surface but are estimated to contain more than half of the world's plant and animal species. Rates of deforestation in tropical rainforests have increased significantly over the past 50 years.

Model answer (5 marks)

Maintaining a high level of biodiversity ensures a more stable ecosystem because if one species is lost others can often fulfil the same ecological role, preventing a collapse of the food web.

High biodiversity also reduces the likelihood that the loss of a single species will trigger a cascade of extinctions, so the overall ecosystem remains resilient.

For humans, diverse species are a source of potential medicines, food and raw materials; loss of biodiversity could mean the loss of these future resources.

Deforestation for agriculture or urban development removes habitat and directly reduces species numbers.

Pollution, such as chemical runoff, can also reduce biodiversity by killing or impairing organisms and altering habitats.

Examiner tips

  • Use the exact phrases from the mark scheme – ‘stable ecosystems’, ‘food webs’, ‘cascade of extinctions’, ‘human welfare’, ‘potential new medicines’.
  • Show two distinct human activities – e.g. deforestation and pollution – and explain how each reduces biodiversity.
  • Keep each point concise and directly linked to the marks.

Common mistakes

  • Mixing up ‘biodiversity’ with ‘species richness’ without explaining the difference.
  • Listing activities that do not directly reduce biodiversity, e.g. tourism, without showing the mechanism.

Mark scheme (5 marks)

  1. A greater variety of species / higher biodiversity provides more stable ecosystems / food webs because if one species is lost others can fill its role
  2. Loss of one species is less likely to cause the collapse / extinction of other species when biodiversity is high
  3. High biodiversity is important for human welfare, e.g. potential new medicines / food sources / raw materials could be lost
  4. One human activity that reduces biodiversity, e.g. deforestation / land clearance for agriculture / urbanisation
  5. A second, different human activity that reduces biodiversity, e.g. pollution / hunting / introduction of invasive species / monoculture farming

Key terms in this question

biodiversity · ecosystem

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