Question

What is nitrogen fixation? Give some examples of nitrogen fixation.

Short answer

Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into biologically available forms like ammonia (NH₃), nitrate (NO₃⁻), or nitrogen-containing compounds, which are essential for the growth and development of living organisms. Examples of nitrogen fixation processes include biological nitrogen fixation, such as the symbiotic relationship between Rhizobium bacteria and legume plants; atmospheric nitrogen fixation, which occurs during lightning strikes when nitrogen and oxygen react to form nitrogen oxides and eventually dissolve in rainwater as nitrate; and industrial nitrogen fixation, like the energy-intensive Haber-Bosch process that manufactures ammonia for nitrogen-containing fertilizers.

Step-by-step solution

Definition of Nitrogen Fixation

Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into biologically available forms like ammonia (NH₃), nitrate (NO₃⁻), or nitrogen-containing compounds. This process is crucial because nitrogen is an essential element for the growth and development of living organisms, including plants.

Example 1: Biological Nitrogen Fixation

Biological nitrogen fixation is carried out by certain bacteria and archaea, known as nitrogen-fixing organisms or diazotrophs. These organisms can convert atmospheric nitrogen into ammonia (NH₃) through an enzyme called nitrogenase. A well-known example of biological nitrogen fixation occurs in the root nodules of legume plants, where Rhizobium bacteria form a symbiotic relationship with the plants. The bacteria fix nitrogen for the plants, and in return, the plants provide the bacteria with carbohydrates as an energy source.

Example 2: Atmospheric Nitrogen Fixation

Atmospheric nitrogen fixation occurs when nitrogen is combined with other elements in the atmosphere due to natural phenomena such as lightning. During a lightning strike, the high temperatures and pressure cause nitrogen (N₂) and oxygen (O₂) to react, forming nitrogen oxides (NOx). These nitrogen compounds can then dissolve in rainwater, forming nitric acid (HNO₃) and eventually reaching the soil as nitrate (NO₃⁻) and becoming accessible to plants.

Example 3: Industrial Nitrogen Fixation

The most common method of industrial nitrogen fixation is the Haber-Bosch process, which manufactures ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂) gases. The ammonia produced can then be used to create nitrogen-containing fertilizers. The Haber-Bosch process has played a significant role in increasing crop yields and global food production since its development in the early 20th century. However, it also consumes a lot of energy and contributes to greenhouse gas emissions. Each of these examples demonstrates the different processes through which nitrogen fixation can occur, making nitrogen accessible to plants and other organisms and allowing life to flourish on Earth.