A scientist models part of the nitrogen cycle using three containers.
Container 1 contains soil with free-living nitrogen-fixing bacteria and is supplied with nitrogen gas. When the bacteria in container 1 die, their material is transferred to container 2, which contains decomposer bacteria and fungi. Soluble substances from container 2 are then transferred to oxygenated soil in container 3, which contains nitrifying bacteria.
The nitrogen may be present as nitrogen gas, nitrogen-containing compounds in dead material, ammonium compounds or nitrates.
Which sequence explains the changes in the form of nitrogen across the three containers?
Nitrogen-fixing bacteria produce nitrogen-containing compounds; decomposers produce nitrates; nitrifying bacteria convert nitrates into nitrogen gas.
Nitrogen-fixing bacteria produce nitrogen-containing compounds; decomposers release nitrogen gas; nitrifying bacteria convert nitrogen gas into nitrates.
Nitrogen-fixing bacteria produce nitrogen-containing compounds; decomposers produce ammonium compounds; nitrifying bacteria produce nitrates.
Nitrogen-fixing bacteria produce nitrates; decomposers convert nitrates into nitrogen gas; nitrifying bacteria produce ammonium compounds.
101 exam-style questions on Edexcel GCSE Biology 9.3 Material cycles and decomposition, covering 9.3.1 Cycling of materials through ecosystems, 9.3.2 The carbon cycle, 9.3.3 The water cycle, 9.3.4 The nitrogen cycle, 9.3.5 Indicator species and pollution, 9.3.6 Decomposition in preservation and composting, and 9.3.7 Rate changes in decay of biological material. Each one has a worked solution and a mark scheme showing where the marks go.