Key Facts Table: The Four Types of Bacteria
Part of The Nitrogen Cycle · GCSE GCSE Biology revision
This key facts covers Key Facts Table: The Four Types of Bacteria within The Nitrogen Cycle for GCSE Biology. The nitrogen cycle: nitrogen-fixing, nitrifying, denitrifying bacteria, ammonification, and the role of legumes It is section 8 of 14 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 8 of 14
Practice
15 questions
Recall
15 flashcards
📋 Key Facts Table: The Four Types of Bacteria
| Bacteria Type | What They Do | Conditions Needed | Example |
|---|---|---|---|
| Nitrogen-fixing | N₂ → ammonia (NH₃) | In root nodules or free in soil | Rhizobium |
| Nitrifying | Ammonia → nitrites → nitrates | Aerobic (need oxygen) | Nitrosomonas, Nitrobacter |
| Decomposers | Proteins/nucleic acids → ammonia (ammonification) | Warm, moist, aerobic conditions | Various bacteria and fungi |
| Denitrifying | Nitrates → N₂ (back to atmosphere) | Anaerobic (no oxygen, waterlogged soils) | Pseudomonas |
Key additional facts:
- Atmospheric nitrogen = 78% N₂, but plants cannot use N₂ directly
- Plants absorb nitrates via active transport (against concentration gradient, requires energy)
- Nitrogen is essential for making amino acids, proteins, DNA, and chlorophyll
- Legume crop rotation enriches soil with nitrogen naturally
- Lightning can fix nitrogen but contributes only a tiny fraction
Quick Check: A farmer grows peas (a legume) one year, then wheat the next. The wheat crop after the peas grows much better than wheat grown on land that has never had peas. Explain why the pea crop improves the growth of the following wheat crop.
Pea plants are legumes that have mutualistic nitrogen-fixing bacteria (Rhizobium) living in root nodules on their roots. These bacteria convert atmospheric nitrogen gas into ammonia, which is then converted to nitrates in the soil. When the pea crop is ploughed in after harvesting, the nitrogen-rich root nodules and plant material decompose. Decomposers (bacteria and fungi) break down the proteins, releasing ammonia through ammonification. Nitrifying bacteria then convert this ammonia to nitrates. This raises the nitrate concentration in the soil significantly, giving the following wheat crop a much better supply of nitrogen for making amino acids and proteins, leading to faster growth and higher yield.