Biodiversity is important for the stability of ecosystems. Explain why a reduction in biodiversity can threaten the survival of species within an ecosystem, and describe one way in which human activities can reduce biodiversity.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Scientists monitoring a tropical rainforest recorded a sharp decline in the number of different plant species over a ten-year period. During the same period, several animal species that depended on those plants also disappeared from the area.
Model answer (5 marks)
Biodiversity is the variety of species in an ecosystem.
1. Species are interdependent; if one species declines, the species that rely on it (e.g. predators, pollinators, herbivores) are also affected.
2. A loss of species reduces the number of alternative food sources and ecological relationships, so the ecosystem becomes less stable and more vulnerable to change.
3. Human activities such as deforestation remove large areas of habitat, directly killing many species and fragmenting populations.
4. Deforestation also reduces habitat connectivity, making it harder for species to find mates, food and shelter, which accelerates further declines.
5. Consequently, the survival of many species is threatened when biodiversity is reduced.
1. Species are interdependent; if one species declines, the species that rely on it (e.g. predators, pollinators, herbivores) are also affected.
2. A loss of species reduces the number of alternative food sources and ecological relationships, so the ecosystem becomes less stable and more vulnerable to change.
3. Human activities such as deforestation remove large areas of habitat, directly killing many species and fragmenting populations.
4. Deforestation also reduces habitat connectivity, making it harder for species to find mates, food and shelter, which accelerates further declines.
5. Consequently, the survival of many species is threatened when biodiversity is reduced.
Examiner tips
- Use the term ‘biodiversity’ early; link species loss to interdependence; explain how fewer alternatives reduce stability; give a specific human activity and its effect; keep answer concise to fit 5 marks.
Common mistakes
- Mixing up ‘biodiversity’ with ‘species richness’; failing to mention interdependence; giving a vague human activity without explaining its impact; writing too long and losing marks for lack of focus.
Mark scheme (5 marks)
- Biodiversity refers to the variety of different species (or organisms) in an ecosystem / habitat
- Species within an ecosystem are interdependent, so if one species declines / disappears, others that depend on it are also affected
- A reduction in biodiversity reduces the stability of an ecosystem because there are fewer alternative food sources / relationships, making it more vulnerable to change
- Correct identification of a human activity that reduces biodiversity — e.g. deforestation / habitat destruction / pollution / over-hunting / introduction of non-native species / monoculture farming
- Explanation of how that human activity reduces biodiversity — linked clearly to the named activity
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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