b4

• give three molecules which are cycled through ecosystems

  • oxgyen
  • carbon dioxide
  • water
• briefly describe how water is cycled through and ecosystem

  1. water evaporates from rivers and lakes and from transpiration
  2. water condenses as clouds
  3. water is returned through precipitation
• briefly describe how carbon dioxide is cycled through an ecosystem

  1. carbon dioxide is fixed through photosynthesis
  2. respiration releases carbon dioxide
  3. decomposition releases carbon dioxide
  4. combustion releases carbon dioxide
• briefly describe how nitrogen is cycled through an ecosystem

  • nitrogen is fixed by lightning, the habor process and bacteria
  • denitrifying bacteria release nitrogen back into the atmosphere
• why is recycling in ecosystems necessary?

  • to create a continuous flow of nutrients
  • to provide fresh water
• how would a decrease in oxygen availability affect the rate of decomposition?

  • lack of oxygen causes microorganisms to respire anaerobically
  • anaerobic decay is slower than aerobic decay
• how would a decrease in water availability affect the rate of decomposition?

  • decomposing microorganisms need water for chemical processes
  • the less water available, the slower the rate of these processes
• how would a change in temperature affect the rate of decomposition?

  • a decrease in temperature slows the rate of the decomposition reactions
  • a large increase in temperature will denature enzymes, slowing or even stopping decomposition
• four abiotic factors that affect communities

  • light intensity
  • temperature
  • moisture levels
  • soil pH
• four biotic factors that affect communities

  • number of predators
  • food availability
  • disease
  • human activity
• three types of interdependence

  • mutualism
  • predation
  • parasitism
• parasitism

  • where one organism live on another and takes nutrients from the other organism
  • beneficial to the parasite but detrimental to the host
• mutualism

  • two organisms depend on each other
  • both organisms benefit from the relationship
• four things animals compete for

  • mates
  • space
  • food
  • water
• four things plants compete for

  • light
  • water
  • minerals
  • space
• producer


  an organism that makes its own food
• primary consumer

  an organism that feeds on producers
• secondary consumer

  an organism that feeds on primary consumers
• biomass


  the dry mass of all the living organisms in an area
• why is dry mass used for biomass?

  the wet mass varies as the amount of water in the organism varies
• equation for the efficiency of biomass transfer

  efficiency = (energy transferred / total energy available) x 100
• why are biomass transfers not 100% efficient?

  energy is lost through:

  • egestion (removal of faeces)
  • excretion (removal of urine)
  • respiration
  • production of inedible bones and shells
• how does the efficiency of biomass transfers affect the number of trophic levels in a biomass pyramid?

  the less efficient the transfers, the fewer trophic levels and the fewer organisms in higher trophic levels