Fatty Acid Oxidation
Nitrogen Fixation, Assimilation, Elimination
Just as photosynthesis or chemosynthesis must reduce carbon dioxide in the atmosphere before it can be used in biological reactions, so must biological nitrogen change from elemental N2 to a -3 level, as in ammonia, NH3. In terrestrial and aquatic systems, reduced nitrogen is often a limiting nutrient for plant growth. About half of all global nitrogen fixation occurs industrially in a process that requires a metal catalyst at 500 atmospheres pressure and at 300° Celsius. In contrast, biological nitrogen fixation takes place in a much less extreme environment (about 25° and 1 atmosphere pressure) in the roots of leguminous plants or in bacteria, using enzymatic catalysts. Eventually it returns to the atmosphere as N2. The overall process is referred to as the nitrogen cycle.
