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.