organisation of an ecosystem

• define population

  a species that occupy the same habitat
• define habitat 


  the place in which an organism lives
• define community

  populations of different species interacting
• define ecosystem

  the interaction between the biotic and abiotic factors in an area
• what do food chains show

  food chains show the feeding relationships of different organisms and the flow of energy between the organisms
• define biomass

  the total mass of living material
• what are trophic levels

  the stages in a food chain
• what do arrows in a food chain represent

  the direction of biomass transfer
• describe a simple food chain

  producer -> primary consumer -> secondary consumer-> tertiary consumer
• whats a producer

  an organism that makes its own food
• what types of organisms are primary producers

  photosynthetic organisms like green plants and algae that trap energy from the sun
• what is a primary consumer

  an organism that feeds on producers
• what is a secondary consumer

  an organism that feeds on primary consumers
• whats tertiary consumer

  an organism that feeds on secondary consumers
• what is a predator

  a consumer that kills and eats other animals
• what is prey

  an animal that is killed and eaten by another animal
• describe the pattern of predators and prey in a stable community

  the numbers of predators and prey rise and fall in cycle
• why are producers the first trophic level

  • producers provide all biomass for the food chain (production of glucose via photosynthesis )
  • the rest of the food chain involves the transfer of this biomass
• what piece of apparatus is used to measure the abundance and distribution of organisms in an area

  quadrat
• what piece of apparatus is used to study the distribution of organisms across a gradient

  belt transect
• when considering the abundance of organisms, what is meant by the term mean

  the average number of organisms
• how is the arithmetic mean calculated

  sum of each number of each organism / the total number of each type of organism
• when considering the abundance of different organisms, what is meant by the term mode

  the most populous organism
• when considering the abundance of organisms, what is meant by the term median

  the organism that represents the middle value when the numbers of each organism are arranged from lowest to highest
• describe how materials cycle through the living and non-living components of an ecosystem

  • organisms take in elements from their surroundings e.g. soil, air
  • elements converted to complex molecules which become biomass
  • elements transferred along food chains
  • elements returned to environment during excretion and decomposition of dead organisms
• give three molecules which are cycled through ecosystems

  • oxygen
  • carbon dioxide
  • water
• describe the carbon cycle

  • plants fix carbon dioxide into organic molecules during photosynthesis
  • the organic carbon-containing molecules are passed onto organisms that eat the plants
  • carbon dioxide is released back into the atmosphere by respiration from animals and plants
  • burning fossil fuels also releases carbon dioxide into the atmosphere
• why is the carbon cycle important

  carbon-containing molecules such as glucose are important for living organisms to grow and provide energy for vital functions within cells
• describe the water cycle

  • water from lakes an ocean evaporates
  • the evaporated water condenses into clouds and returns to earth as precipitation
  • the water from precipitation is useful for life on land
  • the water then returns to rivers and oceans through surface run off
• whys the water cycle important

  living organisms require water and the water cycle provides organisms on land with a continuous supply of water
• what is meant by decomposition

  the break down of dead materials into simpler organic matter
• why are microorganisms important for the cycling of materials through an ecosystem

  microorganisms( bacteria and fungi) return carbon to the environment by releasing carbon dioxide through respiration while they decompose dead matter. the decomposition of dead matter in soil returns mineral ions to the environment for the other organisms to use e.g. plants use mineral ions for growth
• how do decomposers break down dead matter

  they release enzymes which catalyse the breakdown of dead material into smaller molecules
• what are the two types of decomposition

  • aerobic decomposition (with oxygen)
  • anaerobic decomposition (without oxygen)
• what factors affect the rate of decomposition

  • oxygen availability
  • temperature
  • water content
• whys oxygen required for decomposition

  most decomposers require oxygen for aerobic respiration
• how does the availability of oxygen affect the rate of decomposition

  • as oxygen level increase, the rate of decomposition increases
  • as oxygen levels decrease, the rate of decomposition decreases
• why can decomposition still occur in the absence of oxygen

  some decomposers respire anaerobically

  (however the rate of decomposition is slower as anaerobic respiration produces less energy)
• how does soil water content affect the rate of decomposition

  decomposers require water to survive

  • in moist conditions the rate of decomposition is high
  • in waterlogged soils there is little oxygen for respiration so the rate of decomposition decreases
• why does decomposition require water


  water is required for the excretion of enzymes and absorption of dissolved molecules