exam questions

• explain why the value for GPP is lower than the light energy available to the ecosystem(3)

  • not all of the light falls on the leaves/plant
  • some of the light is reflected from the surface of the leaf
  • some of the light misses the chloroplasts and passes through the leaf
  • some of the light is the wrong wavelength thus not absorbed by the chlorophyll
• explain why respiration affects the production of biomass(3)

  • GPP-R=NPP
  • organic molecules/glucose are used in respiration to provide energy
  • because some organic molecules/glucose are used in respiration, the less is available for the production of biomass
• Succession


  The gradual changes in an ecosystem over time as new species arrive and others decline
• Primary Succession


  1. Pioneer species colonise bare land

  2. Pioneers change environment by forming soil/humus

  3. Pioneer species germinate easily and withstand harsh conditions

  4. Environment becomes less hostile for other/new species

  5. Decomposition of pioneers helps form soil

  6. Arrival of grasses and small plants adapted to shallow/nutrient-poor soils

  7. Roots of small plants help hold soil in place

  8. Environment becomes more suitable for other/new species

  9. Soil becomes deeper/more nutrient-rich to support larger shrubs/trees

  10. Change/increase in diversity/biodiversity

  11. Final species becomes the dominant climax community
• Succession occurs in a range of natural ecosystems
• explain why net production of consumers is less than the net production from producers(4)

  • not all of the energy available from the producer is taken up
  • Some parts of the grass are not eaten
  • Some parts of the grass is not digestible by the deer (so the energy it contains is not passed on to the deer)
  • Some energy is lost to the environment as respiratory losses
  • Some energy is lost due to excretion from consumer
• explain why it is rare to find a natural food chain which has more than 5 trophic levels(4)

  • Energy is lost (from organisms) at each trophic level
  • There is insufficient energy remaining to support further trophic levels
  • (Approximately) 90% of energy is lost at each tropic level
• explain why 2 species occupying different niches is an advantage(3)

  • Reduced competition for a resources/food/shelter
  • Ensures both species survive and can reproduce