Nitrogen cycle - SS2 Biology Lesson Note
The nitrogen cycle is a natural process that involves the transformation and circulation of nitrogen in various forms through the biosphere. Nitrogen is an essential element for living organisms, particularly for the formation of proteins, DNA, and other vital molecules.
The nitrogen cycle consists of several key steps:
1. Nitrogen Fixation: Nitrogen gas (N2) from the atmosphere is converted into a more usable form by certain bacteria called nitrogen-fixing bacteria. These bacteria can be free-living in the soil or form symbiotic relationships with plants, such as legumes. They convert atmospheric nitrogen into ammonium (NH4+), which can be used by plants.
2. Nitrification: Ammonium ions released from nitrogen fixation or from the decomposition of organic matter are converted into nitrite ions (NO2-) and then further into nitrate ions (NO3-) by nitrifying bacteria. This process is called nitrification and usually occurs in soil.
3. Assimilation: Plants and other primary producers take up nitrate ions from the soil and assimilate nitrogen into organic compounds, such as amino acids and proteins. Animals obtain nitrogen by consuming plants or other animals.
4. Ammonification: When plants and animals die or produce waste, the organic nitrogen compounds in their bodies are broken down by decomposers, such as bacteria and fungi. This decomposition process releases ammonium ions back into the soil.
5. Denitrification: Some bacteria called denitrifying bacteria convert nitrate ions back into nitrogen gas, completing the nitrogen cycle. Denitrification occurs in oxygen-deprived environments, such as waterlogged soils or sediments, and it returns nitrogen to the atmosphere, closing the cycle.
Human activities have significantly impacted the nitrogen cycle, primarily through the excessive use of synthetic fertilizers, industrial processes, and combustion of fossil fuels. These activities have led to an overabundance of reactive nitrogen in the environment, causing problems like eutrophication of water bodies and contributing to air pollution.
Understanding and managing the nitrogen cycle is crucial for sustainable agriculture and environmental conservation. Efforts are being made to improve nitrogen use efficiency, reduce fertilizer runoff, promote responsible waste management, and develop more efficient methods of nitrogen fixation to minimize the negative impacts on ecosystems.
