Page 22 - Curriculum Visions Dynamic Book

Nitrogen cycle
Nitrogen is continually transferred between the land, animals, plants and the atmosphere in a never-ending cycle. This nitrogen cycle is one of the most important cycles for life on Earth. Here are the main stages summarised from the detail provided on the previous pages:
 The cycle begins when lightning flashes provide the energy for atmospheric nitrogen and oxygen to combine to form dilute
nitric acid.
 Several species of bacteria, fungi, and blue–green algae can convert nitrogen
into nitrogen-containing compounds such as nitrates. These compounds are then used in photosynthesis to make new sources of energy for the growth of plant tissue.
 Along the food chain, animals use the nitrogen locked up in plant and animal tissues as a way of getting the nitrogen they need
to build new cells. The nitrogen is obtained during the process of digestion.
 All animals produce waste nitrogen in the form of a nitrogen-containing compound called urea. This is removed from the body during excretion. It will either evaporate or be broken down by bacteria. Nitrogen-containing compounds are very soluble and rainwater may wash them into rivers, where they may cause pollution problems.
 Bacteria involved in decomposing waste and dead material release nitrogen from its compounds, forming gas that can escape to the atmosphere, thus completing the cycle.
Nitrogen is fixed in the atmosphere during lightning.
Nitrogen is dissolved in rainwater to form dilute nitric acid, natural acid rain that provides some of the nitrogen fertiliser requirements of plants.
Bacteria in the nodules of leguminous plants produce ammonia and soluble nitrates.
Nitrates are released to the soil in the form of anions (negative ions). There are no natural anion attractors in the soil, so they cannot be stored there. Instead they are washed through the soil to rivers. Thus, a constant supply of nitrates is required throughout the growing season.
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