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.