4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria

Nitrogen fixing bacteria turn nitrogen from N2 into ammonia.
Decomposers break down dead animals, urea and egested materials which releases nitrogen into the soil as ammonia.
Nitrifying bacteria convert nitrates into nitrogen.
Denitrifying bacteria break down nitrates into nitrogen which is then released into the atmosphere.

Here is a diagram to help explain:

commons.wikimedia

This animation is very helpful:
https://www.classzone.com/books/ml_science_share/vis_sim/em05_pg20_nitrogen/em05_pg20_nitrogen.swf

4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

Respiration is carried out by animals and plants to release energy from glucose, the equation is:
C₆H₁₂O₆ + 6O₂    →    6CO₂ + 6H₂O . This means carbon is produced.

Photosynthesis is what plants do to create glucose the equation is:
6 CO₂ + 12 H₂O → C₆H₁₂O₆ + 6 O₂ + 6 H₂O. This means carbon is used.

Decomposition is happens when an animal dies, it is then eaten by a decomposer which releases the carbon in it back into the atmosphere.

Combustion is burning, if something with carbon is burnt it will release it into the atmosphere, e.g. a tree, fossil fuel.

This is one of many useful diagrams:

frankswebspace

4.8 describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation

Evaporation is when water turns into steam due to being heated
Transpiration is when water is evaporated from leaves
Condensation is when water vapour turns into water due to being cooled, this forms clouds
Precipitation is when water is released from a cloud, e.g. rain, snow, hail

The best way to understand this is with a diagram:

cleanwatercampaign