Biology
Ecology and biological evidence
- 1.
Explain why random quadrat placement is preferable to choosing visually species-rich patches when estimating mean plant density.
[3 marks] · no calculator - 2.
Explain why decomposers matter for nutrient cycling but do not recycle energy back to producers.
[3 marks] · no calculator - 3.
Five 0.50 m^2 quadrats contain 4, 6, 5, 3 and 7 plants. Estimate mean density per m^2 and total plants in a uniform 200 m^2 habitat.
[3 marks] - 4.
Producers have net production 12000 kJ m^-2 year^-1 and herbivores 900 kJ m^-2 year^-1. Calculate transfer efficiency and explain two routes accounting for energy not entering herbivore production.
[3 marks] - 5.
A mark-release-recapture study captures 40 animals, marks and releases them, then captures 50 animals including 10 marked. Estimate population size and explain three assumptions whose violation could invalidate the estimate.
[4 marks] - 6.
River sites with high nitrate also have low dissolved oxygen. Evaluate a eutrophication explanation and design evidence that distinguishes it from a temperature confound.
[4 marks] · no calculator
Marking points are indicative, not an official mark scheme. Accept equivalent valid methods and supported interpretations that address the task; award each mark once without requiring the model wording.