The Nitrogen Cycle

“The Nitrogen Cycle”

• Nitrogen is a fundamental component of amino acids, proteins, and DNA, and is essential for all living organisms.
• The atmosphere is the principal reservoir for nitrogen, constituting about 78% of the earth’s air. However, plants and animals cannot utilise nitrogen directly from the atmosphere.
• This is where the nitrogen cycle comes in, which describes how nitrogen in the environment is converted into various forms that can be utilised by organisms.

Key Stages of the Nitrogen Cycle:

1. Nitrogen Fixation: Nitrogen gas (N2) from the atmosphere is converted into ammonia (NH3) by nitrogen-fixing bacteria which live in the soil or in the root nodules of leguminous plants. Some is also fixed through lightning strikes.

2. Ammonification: When plants and animals die or when organisms produce waste, the nitrogen in their bodies is converted into ammonium (NH4+) by decomposers.

3. Nitrification: Special types of bacteria in the soil, called nitrifying bacteria, convert the ammonium into nitrites (NO2-) and then into nitrates (NO3-). This form of nitrogen can be used by plants.

4. Assimilation: Plant roots absorb nitrate, which they then use to form amino acids, proteins, and DNA.

5. Denitrification: In the absence of oxygen, other types of bacteria in the soil, called denitrifying bacteria, convert nitrates back into in nitrogen gas, which is released back into the atmosphere.

Potential human impact on the Nitrogen Cycle:

• The excessive use of nitrogen-rich fertilisers can lead to an increase in nitrate content of soil which can contaminate groundwater.
• Burning of fossil fuels releases nitrogen oxides into the atmosphere which can cause air pollution.

Remember, a solid understanding of the nitrogen cycle will also assist in comprehending other nutrient cycles and ecological principles. Diagrams can be a helpful tool when studying the nitrogen cycle. Practice drawing and labelling the cycle to strengthen your comprehension.