Cycling and human impact on ecosystems

• Trophic levels 


  the position of organisms in the food chain
• Biomass is lost in

  • faeces
  • indigestible parts of organisms
  • urine
  • heat to surroundings
  • energy to move
  • respiration
• 1% of light energy is used for photosynthesis
• the energy transfer between organisms is only 10-20% efficient so biomass is lost
• atmospheric carbon

  carbon bonded with oxygen in the air (0.04%)
• carbon in plants

  • plants remove carbon from the atmosphere when they use carbon dioxide for photosynthesis
  • they use carbon to form organic molecules (glucose, cellulose)
  • they put carbon back into the atmosphere during respiration
• primary consumers


  herbivore and omnivore animals consume plants and ingest their carbon molecules
• carbon passes between consumers in the foodchain
• carbon in decay

  • dead organisms contain carbon and are broken down by decomposers
  • decomposers are micro-organisms that respire releasing carbon dioxide into the atmosphere
• carbon in respiration

  • all living organisms respire releasing energy from glucose and producing carbon dioxide as a waste product
• carbon in power stations

  • fossil fuels are burnt releasing carbon
  • combustion releases carbon dioxide
• decomposition


  the breakdown of biomass by micro-organisms
• factors affecting decay

  • temperature
  • oxygen supply
  • moisture
  • pH levels
• extrapolate


  extend graph
• exponential


  an extremely rapid growth
• pollution


  the addition of substances to the environment that may be harmful to living organisms
• reasons for deforestation

  • housing
  • farming
  • build roads
  • palm oil
  • increase tourism
  • infsdtructure
• effects of deforestation

  • less photosynthesis
  • more carbon dioxide
  • destroying habitats
  • biodiversity is decreased
  • expensive
  • plants for medicines won't be found
• peat bogs

  • store lots of carbon in the ground
  • preserve artefacts
  • important for biodiversity
• the greenhouse effect


  energy from the sun reaches the earth warming it up and lots of it gets reflected back into space but is absorbed by greenhouse gases in the atmosphere
• fertilisers


  provide a source of nutrients to help a plant grow
• herbicide 


  kills any weeds in the area so the plant can grow without competing for water
• pesticide/insecticide 


  kills insects that might be feeding on the plant or damage it's growth and appearance
• algal bloom


  a thick layer of algae formed on top of the water