Organisms & their environment ( 2 )

• Carbon cycle


  Shows how carbon atoms transfer between the atmosphere and living organisms
• Carbon cycle


  1. Plants take in carbon dioxide from the atmosphere during photosynthesis

  2. Feeding animals obtain carbon by consuming plants and other organisms

  3. Carbon dioxide is released back into the atmosphere through respiration by plants, animals and microorganisms

  4. Decomposition of dead organisms releases carbon dioxide into the atmosphere

  5. Formation of fossil fuels under certain conditions

  6. Burning fossil fuels releases carbon dioxide into the atmosphere
• Deforestation reduces the number of plants available to absorb carbon dioxide through photosynthesis
• Deforestation occurs for land purposes and when trees are burned, additional carbon dioxide is released into the atmosphere
• Nitrogen cycle


  Nitrogen is essential for life and is involved in the synthesis of amino acids, DNA and ATP
• Nitrogen cycle


  1. Nitrogen gas (N2) in the atmosphere is converted into usable forms through nitrogen fixation by nitrogen-fixing bacteria

  2. Nitrifying bacteria convert ammonia into nitrites and then nitrates, making them absorbable by plants

  3. Plants absorb nitrate ions and use them to produce amino acids and proteins

  4. Animals get nitrogen by consuming plants or other animals and digesting their proteins

  5. Decomposers break down dead organic matter into ammonium ions, which are then converted into nitrates by nitrifying bacteria

  6. Denitrifying bacteria convert nitrates back into gaseous nitrogen (N2) in oxygen-limited environments
• Population


  A group of organisms of one species living in the same area at the same time
• Community


  All of the populations of different species in an ecosystem
• Ecosystem


  A unit containing the community of organisms and their environment interacting together
• Factors affecting population growth rate

  • Food supply
  • Competition
  • Predation
  • Disease
• Sigmoid population growth curve

  • Lag phase
  • Exponential or log phase
  • Stationary phase
  • Death phase