Nitrogen fixation

• Nitrogen fixation is the process by which nitrogen gas is converted into nitrogen-containing compounds. It can be carried out industrially and also occurs naturally when lightning passes through the atmosphere.
• There are two main types of nitrogen-fixing bacteria: free-living nitrogen-fixing bacteria and mutualistic nitrogen-fixing bacteria.
• Free-living nitrogen-fixing bacteria reduce gaseous nitrogen to ammonia, which they then use to manufacture amino acids. Nitrogen-rich compounds are released from them when they die and decay.
• Mutualistic nitrogen-fixing bacteria live in nodules on the roots of plants such as peas and beans. They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.