Nutrient Cycles and Decomposition

Carbon Cycle

  • Main Processes:
    • Photosynthesis: Plants absorb carbon dioxide (CO₂) from the atmosphere and convert it into glucose.
    • Respiration: Organisms release carbon dioxide (CO₂) back into the atmosphere.
    • Decomposition: Bacteria and fungi break down dead organic matter, releasing carbon dioxide (CO₂).
    • Combustion: Burning fossil fuels releases carbon dioxide (CO₂) into the atmosphere.
  • Human Impact:
    • Deforestation: Reduces the absorption of carbon dioxide (CO₂) by plants.
    • Burning Fossil Fuels: Increases the concentration of atmospheric carbon dioxide (CO₂), contributing to global warming.

Water Cycle

  • The water cycle involves the movement of water through different states.
    • Evaporation: The sun heats water from oceans and lakes, converting it into water vapor.
    • Condensation: Water vapor cools and forms clouds.
    • Precipitation: Water falls back to earth as rain, snow, or hail.
    • Run-off & Infiltration: Water flows back into rivers and lakes or soaks into the ground.
    • Transpiration: Plants release water vapor from their leaves.
  • Importance:
    • Distributes fresh water across the planet.
    • Essential for drinking water, agriculture, and supporting ecosystems.

Nitrogen Cycle

  • Nitrogen Fixation:
    • Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃).
  • Nitrification:
    • Nitrifying bacteria convert ammonia (NH₃) into nitrites (NO₂⁻) and then into nitrates (NO₃⁻).
  • Assimilation:
    • Plants absorb nitrates (NO₃⁻) and use them to synthesize proteins.
    • Animals obtain nitrogen by consuming plants.
  • Decomposition & Ammonification:
    • Decomposers break down dead organisms and waste materials, releasing ammonia (NH₃).
  • Denitrification:
    • Denitrifying bacteria convert nitrates (NO₃⁻) back into nitrogen gas (N₂), which is released into the atmosphere.

Nitrogen Cycle: Decomposition of Proteins

  • Proteins from dead organisms and waste materials (e.g., urea) are broken down into amino acids by decomposers via the release of protease.
  • The amino acids undergo deamination, where the nitrogen-containing amino group (-NH₂) is removed and converted into ammonia (NH₃).
  • Ammonia (NH₃) dissolves in soil water, forming ammonium ions (NH₄⁺).
  • Nitrifying bacteria, such as Nitrosomonas and Nitrobacter, convert ammonium ions (NH₄⁺) into nitrites (NO₂⁻) and then into nitrates (NO₃⁻).
  • The nitrates (NO₃⁻) are absorbed by plants for protein synthesis, thus continuing the nitrogen cycle.
  • In anaerobic conditions, denitrifying bacteria convert nitrates (NO₃⁻) back into nitrogen gas (N₂), which is released into the atmosphere.

Nitrogen Cycle: Decomposition of Proteins Summary

  • Proteins → Amino Acids → Ammonia (NH₃) → Ammonium (NH₄⁺) → Nitrites (NO₂⁻) → Nitrates (NO₃⁻) → Absorbed by Plants
  • Some nitrates may be lost as nitrogen gas via denitrification.