Nitrogen cycle

Definition

The nitrogen cycle is a biogeochemical process that describes the movement and transformation of nitrogen through the atmosphere, lithosphere, hydrosphere, and biosphere. This cycle is vital for life on Earth as it converts atmospheric nitrogen into forms that living organisms can utilize, maintaining ecosystem balance and supporting the growth of plants and animals.

5 Must Know Facts For Your Next Test

1. The nitrogen cycle involves several key processes: nitrogen fixation, ammonification, nitrification, and denitrification, which together facilitate the transformation of nitrogen into usable forms.
2. Nitrogen-fixing bacteria play a crucial role in converting atmospheric nitrogen into ammonia, which can then be used by plants to synthesize proteins and nucleic acids.
3. Human activities, such as the use of synthetic fertilizers and fossil fuel combustion, have significantly altered the nitrogen cycle, leading to issues like nutrient runoff and air pollution.
4. Nitrification is the process where ammonia is oxidized to nitrites (NO₂) and then to nitrates (NO₃), making nitrogen accessible to plants.
5. The balance of the nitrogen cycle is essential for maintaining healthy ecosystems, as disruptions can lead to problems like algal blooms in aquatic systems due to excess nutrients.

Review Questions

• How do the processes of nitrogen fixation and denitrification contribute to the overall functioning of the nitrogen cycle?
  • Nitrogen fixation converts atmospheric nitrogen into ammonia, making it accessible for plant uptake. Denitrification, on the other hand, completes the cycle by converting nitrates back into nitrogen gas, releasing it back into the atmosphere. Together, these processes ensure a continuous supply of usable nitrogen for organisms while maintaining the atmospheric balance of nitrogen.
• Evaluate how human activities impact the natural nitrogen cycle and what consequences this may have on ecosystems.
  • Human activities such as excessive fertilizer application and fossil fuel burning disrupt the natural nitrogen cycle by introducing an excess of reactive nitrogen into ecosystems. This can lead to nutrient overloads in water bodies, resulting in harmful algal blooms that deplete oxygen levels and harm aquatic life. Additionally, increased emissions of nitrogen oxides contribute to air pollution and can cause respiratory issues in humans.
• Synthesize information on how the interactions between Earth's spheres are influenced by changes in the nitrogen cycle.
  • Changes in the nitrogen cycle can significantly influence interactions among Earth's spheres. For instance, when excess fertilizers run off into waterways (hydrosphere), it alters nutrient levels leading to eutrophication. This impacts aquatic ecosystems (biosphere), decreases biodiversity, and creates hypoxic conditions. Furthermore, increased emissions from agricultural practices affect air quality (atmosphere) and contribute to climate change. Thus, understanding these interactions is crucial for managing environmental health.

Related terms

Nitrogen Fixation: The process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds in soil, primarily by certain bacteria.

Denitrification:

The microbial process of reducing nitrates (NO₃) to nitrogen gas (N₂), returning nitrogen to the atmosphere and completing the nitrogen cycle.

Ammonification: The conversion of organic nitrogen from dead organisms and waste products into ammonia by decomposer organisms, making it available for uptake by plants.