Nitrogen is the major component of earth’s atmosphere. It enters the food chain by means of nitrogen fixing bacteria and algae in the soil. This nitrogen which has been “fixed” is now available for plants to absorb. These types of bacteria form a symbiotic relationship with legumes – these types of plants are very useful because the nitrogen fixation enriches the soil and acts as a “natural” fertilizer. The nitrogen – fixing bacteria form nitrates out of the atmospheric nitrogen which can be taken up and dissolved in soil water by the roots of plants. Then, the nitrates are incorporated by the plants to form proteins, which can then be spread through the food chain. When organisms excrete wastes, nitrogen is released into the environment. When ever an organism dies, decomposers break down the corpse into nitrogen. Nitrogen can be used again by nitrifying bacteria to fix nitrogen for the plants.