Learning outcomes:
4.8
describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation
4.9
describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion
4.10
describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of bacteria are not required).
The Water Cycle:
waterc.GIF
Key ideas – Evaporation, Condensation, Precipitation & Transpiration (rather unhelpfully not shown on this diagram)

The Carbon Cycle:
carbc.GIF
Key ideas – Respiration, Photosynthesis, Decomposition & Combustion
The Nitrogen Cycle:
nitrc.GIF

This is not particularly easy to understand. You need to know the roles of all the different bacteria. There are 4;

- Decomposers – turn nitrogen in protein into ammonium (NH4+)
- Denitrifying Bacteria – turn ammonium (NH4+) into N2
- Nitrifying bacteria – turn ammonium (NH4+) into nitrate (NO3-)
- Nitrogen-fixing bacteria – turn N2 into ammonium (NH4+)

Extension - leguminous plants (not technically on syllabus)

All of the above bacteria are naturally present in the soil. The only exception to this is that some Nitrogen-fixing bacteria (e.g. Rhizobium) live in the roots of some plants. These plants are called legumes (e.g. peas, clover etc). They have a symbiotic relationship with the bacteria i.e. both the bacteria and the plant benefit from working together.

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