Nitrogen Cycle

key notes:–

Introduction to Nitrogen Cycle

  • The nitrogen cycle describes how nitrogen is converted into different chemical forms as it circulates between the atmosphere, terrestrial, and marine ecosystems.
  • Nitrogen is essential for all living organisms because it is a key component of proteins and DNA.

Nitrogen in the Atmosphere

  • About 78% of Earth’s atmosphere is made up of nitrogen gas (N₂), but most organisms cannot use nitrogen directly in this form.

Key Processes of the Nitrogen Cycle

a. Nitrogen Fixation

  • Nitrogen-fixing bacteria in the soil or in the roots of legumes (such as peas and beans) convert nitrogen gas (N₂) from the atmosphere into ammonia (NH₃) or ammonium (NH₄⁺).
  • This process makes nitrogen available for plants to use.

b. Nitrification

  • Nitrifying bacteria convert ammonia (NH₃) into nitrates (NO₃⁻), which plants can take up and use for growth.
    1. Ammonia is first converted into nitrites (NO₂⁻) by Nitrosomonas bacteria.
    2. Nitrites are then converted into nitrates (NO₃⁻) by Nitrobacter bacteria.

c. Assimilation

  • Plants absorb nitrates (NO₃⁻) from the soil through their roots.
  • These nitrates are used to produce proteins, amino acids, and other essential compounds.
  • Animals eat the plants and obtain nitrogen by consuming plant proteins.

d. Ammonification (Decomposition)

  • When plants and animals die or excrete waste, decomposers (such as fungi and bacteria) break down nitrogen-containing compounds.
  • This process converts nitrogen in dead matter into ammonia (NH₃) or ammonium (NH₄⁺), which can be reused by plants or further converted.

e. Denitrification

  • Denitrifying bacteria in the soil convert nitrates (NO₃⁻) back into nitrogen gas (N₂), releasing it into the atmosphere.
  • This process closes the nitrogen cycle, returning nitrogen back into the air.

Importance of the Nitrogen Cycle

  • Soil Fertility: The nitrogen cycle ensures that nitrogen is available in forms that plants can use, which is crucial for plant growth.
  • Ecosystem Balance: It helps in the cycling of nutrients, making nitrogen available to various organisms and maintaining the balance of ecosystems.
  • Agriculture: Understanding the nitrogen cycle is vital for managing fertilizers and improving crop yields.

Human Impact on the Nitrogen Cycle

  • Use of Fertilizers: Excessive use of synthetic fertilizers can lead to nitrate pollution in water bodies, causing eutrophication, which harms aquatic ecosystems.
  • Burning of Fossil Fuels: It can increase the amount of nitrogen oxides (NOx) in the atmosphere, contributing to acid rain and air pollution.

Conclusion

  • The nitrogen cycle is a vital process for sustaining life on Earth.
  • It ensures the continuous availability of nitrogen in different forms, which is essential for plant and animal growth.

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