Edexcel Biology Carbon & Nitrogen CyclesWatch
Driven by the Sun's thermal energy, water from lakes, streams and oceans evaporate and form gaseous water vapour in the atomosphere. Transpiration of plants and respiration of both plants and animals contribute to this water vapour in the atmosphere. When these clouds of water vapour pass over high ground they cool, condense and a precipitation of rain falls to the ground, rivers and oceans, and the process is reset.
Some leguminous plants have nitrogen fixing bacteria present in their root nodules which can convert atmospheric nitrogen to form nitrate and ammonium ions which can be assimilated by the plant.
Detritus, dead and decaying matter are broken down by decomposers which break down the material to release ammonium ions into the soil. These are then converted by nitrifying bacteria to form nitrate ions which also assimilated.
Denitrifying bacteria turns any nitrate ions present in the soil to nitrogen which is then evolved to the atmosphere.