fv5 - nitrogen cycle

AP Environmental Science: Unit 1 – The Living World: Ecosystems

Topic: 1.5 The Nitrogen Cycle

Overview of the Nitrogen Cycle

  • Definition: The nitrogen cycle is the process by which nitrogen is exchanged between the atmosphere, land, and water.

    • Importance: Nitrogen is a macro-nutrient essential for the growth and development of all living organisms, being a key component of proteins, DNA, and other biomolecules.

Key Processes in the Nitrogen Cycle

  • Nitrogen Fixation:

    • Converts nitrogen gas (N2) into usable forms like ammonia (NH3) or nitrate (NO3).

    • Occurs through:

      • Biotic Pathway: Nitrogen-fixing bacteria in plant roots convert N2 to NH3.

      • Abiotic Pathway: Natural events (lightning, fires) and human activities (fossil fuel combustion) convert N2 to NO3.

  • Nitrification:

    • The conversion of ammonia (NH3) into nitrite (NO2) and then into nitrate (NO3).

    • Carried out by bacteria in soil and water.

  • Assimilation:

    • Plants absorb nitrates through their roots and incorporate them into proteins and other biomolecules.

    • Consumers obtain nitrogen by eating plants.

  • Ammonification:

    • The process where decomposers break down organic nitrogen from dead organisms into ammonium (NH4).

  • Denitrification:

    • Specialized bacteria convert nitrates back into nitrogen gas (N2), completing the cycle.

    • Occurs primarily in oxygen-depleted environments.

Human Impacts on the Nitrogen Cycle

  • Fertilizer Use:

    • Human usage of nitrogen fertilizers exceeds natural nitrogen fixation.

    • Overuse can lead to negative consequences, such as:

      • Disruption of ecosystem balances.

      • Decreased species richness as nitrogen-demanding plants outcompete others.

Key Terms to Review

  • Abiotic Pathway: Transfer of energy/materials between non-living components in an ecosystem.

  • Ammonification: Conversion of organic nitrogen into ammonia by decomposer bacteria.

  • Assimilation: Uptake of nutrients by plants and animals for growth.

  • Biotic Pathway: Transfer of energy/materials between living organisms.

  • Denitrification: Conversion of nitrates back into nitrogen gas.

  • Fertilizers: Substances added to soil/plants to provide essential nutrients.

  • Limiting Nutrient: An essential nutrient in short supply that restricts growth.

  • Mineralization: Breakdown of organic matter into inorganic substances.

  • Nitrate (NO3): A nitrogen-oxygen compound essential for plant growth.

  • Nitrification: Conversion of ammonia into nitrite and then nitrate.

Conclusion

Understanding the nitrogen cycle is crucial for recognizing its role in ecosystems and the impact of human activities on this vital process. Focus on the significance of nitrogen in biological systems and the consequences of its disruption rather than memorizing