The nitrogen cycle

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

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?