# Describe how nitrogen from a dead animal is returned to the atmosphere as nitrogen gas.

> Cambridge International IGCSE Biology (0610) — 19.3 Nutrient cycles · Describe · 4 marks

## Mark scheme (4 marks)

1. Decomposers (bacteria/fungi) break down protein in the dead animal, producing ammonium ions
2. Nitrifying bacteria convert ammonium ions into nitrites, then nitrates
3. Denitrifying bacteria convert nitrate ions to nitrogen gas
4. Denitrification occurs in anaerobic conditions (without oxygen)

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