13.3 Nutrient cycles

• What are the two nutrient cycles mentioned in the study material?

  Nitrogen cycle and phosphorus cycle
• Why must nitrogen be recycled in ecosystems?


  Because there is a finite amount of nitrogen on Earth
• What is the role of bacteria in the nitrogen cycle?


  Bacteria recycle nitrogen from dead organisms and waste products
• What are the four stages of the nitrogen cycle?


  1. Ammonification
  2. Nitrification
  3. Denitrification
  4. Nitrogen fixation
• What occurs during ammonification in the nitrogen cycle?


  Microbes break down organic matter to ammonia
• What enzymes are involved in the ammonification process?


  Extracellular protease and deaminase enzymes
• What is the intermediate product formed during nitrification?


  Nitrite ion, NO2^-
• How do most plants take in nitrate ions?


  Through their roots
• What is the outcome of denitrification in the nitrogen cycle?


  Nitrate ions are converted to nitrogen gas
• How can denitrification be prevented?


  By ensuring soil is well drained and aerated
• What is nitrogen fixation?


  The process of converting nitrogen gas into ammonia
• Where do nitrogen-fixing bacteria typically live?


  In root nodules of leguminous plants
• What type of relationship exists between nitrogen-fixing bacteria and leguminous plants?


  A mutualistic relationship
• What is the role of phosphate ions in the phosphorus cycle?


  They are taken in by plants from the soil
• How is phosphate released from sedimentary rocks?


  Through weathering
• What contributes to the release of phosphate from bones and shells?


  The decay of bones, shells, and excreta of some birds
• What is the function of mycorrhizae in plants?


  They facilitate the uptake of water and inorganic ions
• How do mycorrhizae benefit plants?


  By increasing surface area and holding water and minerals
• What is the impact of nitrogen fertilizers on crop yields?


  They greatly increase crop yields
• What are some negative effects of nitrogen fertilizers on the environment?


  They can reduce biodiversity, cause leaching, and lead to eutrophication
• What are the key processes involved in the nitrogen cycle?


  • Ammonification
  • Nitrification
  • Denitrification
  • Nitrogen fixation
• What are the key components of the phosphorus cycle?


  • Uptake of phosphate ions by plants
  • Release of phosphate from sedimentary rocks through weathering
  • Decay of bones, shells, and bird excreta
  • Role of mycorrhizae in nutrient uptake