GCSE-ready- Home
- Lessons
- GCSE & IGCSE Biology
- Nitrogen cycle, decomposition and food security
Nitrogen cycle, decomposition and food security
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
Nitrogen is needed for proteins. Bacteria recycle it, and farmers manage it to grow enough food. Separate Biology only.
The nitrogen cycle
Nitrogen-fixing bacteria (in soil and in root nodules of legumes like peas) turn nitrogen gas into compounds plants can use.
Decomposers turn proteins in dead matter into ammonia.
Nitrifying bacteria turn ammonia into nitrates.
Denitrifying bacteria turn nitrates back into nitrogen gas, often in waterlogged soil.
Decomposers turn proteins in dead matter into ammonia.
Nitrifying bacteria turn ammonia into nitrates.
Denitrifying bacteria turn nitrates back into nitrogen gas, often in waterlogged soil.
Decomposition
Decay is fastest when it is warm, moist and has oxygen.
Rate of decay can be found from the change in mass over time.
Rate of decay can be found from the change in mass over time.
Food security
Having enough affordable, nutritious food. Threats include a growing population, climate change, pests, diseases and conflict.
Solutions include crop rotation, fertilisers, pest control, GM crops and reducing waste.
Solutions include crop rotation, fertilisers, pest control, GM crops and reducing waste.
Why do farmers plant legumes like peas in rotation?
- Legumes have nitrogen-fixing bacteria in root nodules.
- These add nitrates to the soil.
- The next crop gets more nitrogen.
Answer: To add nitrates to the soil.
Nitrogen-fixing, nitrifying, decomposing and denitrifying bacteria cycle nitrogen. Decay is fastest when warm, moist and with oxygen. Food security is threatened by population growth, climate and pests.
Check you have got it
Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.