AP Environmental Science / Unit 1: The Living World: Ecosystems
1.5 The Nitrogen Cycle
Notes
Most nitrogen is $\mathrm{N_2}$ gas, which most organisms can't use.
- Nitrogen fixation: bacteria (or lightning) turn $\mathrm{N_2}$ into ammonia.
- Nitrification: ammonia → nitrite → nitrate.
- Assimilation: plants take up nitrates/ammonium.
- Ammonification: decomposers return ammonia. Denitrification: nitrate → $\mathrm{N_2}$.
Practice
Bacteria converting $\mathrm{N_2}$ to ammonia:
Making nitrogen usable.
Denitrification returns nitrogen to:
Closes the cycle.
Legumes host nitrogen-fixing bacteria in their:
Mutualism.
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