What is the primary role of saprotrophic decomposers (bacteria and fungi) in a terrestrial ecosystem?

Answer and explanation

Correct answer: A. To break down complex organic matter from dead organisms and return bioavailable inorganic mineral nutrients to the soil

  1. Step 1: If dead plants, leaf litter, and animal carcasses accumulated without biological recycling, nutrient cycles would rapidly stall.
  2. Step 2: Saprotrophic bacteria and fungi secrete extracellular digestive enzymes that decompose complex macromolecules (lignin, cellulose, proteins) into simple inorganic compounds (nitrates, phosphates, carbon dioxide), replenishing the soil for plant uptake.
Answer
To break down complex organic matter from dead organisms and return bioavailable inorganic mineral nutrients to the soil
Why not the others: 'To synthesize glucose from sunlight to feed primary consumers directly' This is the primary production role of autotrophic plants and algae, not heterotrophic decomposers; 'To control herbivore population sizes through apex predatory hunting' Apex carnivores regulate herbivores, whereas decomposers feed exclusively on dead organic matter; 'To fix atmospheric oxygen into liquid water during rainfall events' Decomposers consume dissolved oxygen during aerobic cellular respiration; they do not fix atmospheric oxygen.

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