Home / IB DP Biology- B4.2 Ecological niches – IB Style Questions For SL Paper 2

IB DP Biology- B4.2 Ecological niches - IB Style Questions For SL Paper 2 - FA 2025

IBDP Biology Paper 2 - All Chapters

Question

Gersmehl diagrams for two ecosystems are shown.

a. Identify the processes represented by the arrows labelled A and B in both diagrams.

b. Deduce, with a reason, which ecosystem is representative of a tropical rainforest.

▶️ Answer/Explanation

 a.

  • A: Decomposition (Decay) — Transfer of nutrients from litter to soil.

  • B: Leaching (or erosion/run-off/weathering) — Loss of nutrients from soil, typically due to water movement.

b.

  • Ecosystem I is representative of a tropical rainforest.

Reason:

  • Small litter store due to rapid decomposition (warm, moist conditions promote decay).
  • Large biomass store reflects high primary productivity.
  • High leaching from the soil is consistent with heavy rainfall in tropical regions.

Markscheme:

a.
Process A: decomposition/decay
Process B: leaching/erosion/run-off/weathering

b.
Ecosystem I
Low levels of litter due to high rates of decomposition OR high amounts of biomass related to high rates of productivity OR weathering/leaching due to high rates of precipitation

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