1. The nitrogen cycle

2. Why is the cycle important and what is nitrogen used for? Not many organisms can use nitrogen directly from the air (78%) Recycling of nitrates allows plants to manufacture proteins for growth. Therefore it is a limiting factor for yield/ dry mass

3. 4 Main stages Ammonification- production of ammonia from organic compounds. Nitrification- Conversion of ammonium ions to nitrate ions. Nitrogen fixing: 1) Free living bacteria- nitrogen gas reduced to ammonia. 2) Mutualistic bacteria- symbiotic relationship with plants. Denitrification- Conversion of ammonium ions to gaseous nitrogen.

4. Non-living/ living stages Nitrogen in the soil is classed as a non-living phase of the cycle. When ions are absorbed or fixed through nodules into producers, consumers and decomposers the ammonium in the macromolecules becomes part of the living phase.

5. Final links/ processes in the cycle Death and excretion- Saprobiotic organisms break down urea or dead organisms into ammonium ions. Absorption- Nitrate ions actively transported through root hair cells. Feeding- Consumers obtain nitrates from digestion.

6. Put it all together Ammonium ions Nitrite ions Nitrate ions Nitrogen in the atmosphere Nitrogen fixing (free living bacteria) Nitrification De-nitrification Ammonium containing molecules (protein) Producers Ammonium containing molecules (protein) Consumers Ammonium containing molecules (protein) Decomposers Absorption Digestion Nitrogen fixation (mutualistic bacteria) Death Death and excretion Ammonification Non-living living

7. Typical questions Where and how does nitrogen entre the living and non-living stages of the nitrogen cycle? How is nitrogen recycled in the nitrogen cycle? Why do farmers achieve a faster rate of crop growth when they plough?