BRAINCAKEMicroorganisms in the Nitrogen Cycle
Nitrogen is needed to make amino acids, proteins and nucleic acids. The air is 78% nitrogen gas (N2), but plants and animals cannot use it directly. Microorganisms carry out the key steps that convert nitrogen between its different forms.
1. Nitrogen fixation: N2 is reduced to ammonia (NH3), which forms ammonium ions (NH4+), by the enzyme nitrogenase.
- Rhizobium bacteria live in the root nodules of legumes such as peas, beans and clover. This is mutualism: the plant receives ammonium, and the bacteria receive carbohydrates.
- Free-living bacteria in the soil, such as Azotobacter, also fix nitrogen.
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More in The Efficiency of Ecosystems
- The Limitations of Efficiency Calculations
- Energy Transfer and Food Chain Length
- Nutrient Recycling
- Conditions for Recycling Nutrients
- Microorganisms in the Carbon Cycle
- Short-term Carbon Sinks
- Long-term Carbon Sinks
- Human Influence
All 20 lessons in The Efficiency of Ecosystems · All Edexcel A-level Biology topics