B17

• what can feeding relationships within a community be represented by?

  food chains.
• what do all food chains begin with?

  a producer such as a green plant or alga which makes glucose via photosynthesis
• what are producers eaten by?

  primary consumers, which are then eaten by secondary, and tertiary consumers
• what are consumers that kill and eat animals called?

  predators
• why is there usually a 'lag' in predator-prey cycles?

  because it takes time for populations to reproduce and grow
• describe how carbon is cycled through ecosystems

  • carbon dioxide is diffused through plants to be used in photosynthesis to produce glucose.

  • glucose is then used to make carbon compounds which are stored in plants and eaten by a consumer.

  • the consumer breaks down the carbon compounds and traps them in their body when they die.

  • microorganisms decompose dead animals and plants, releasing carbon dioxide via respiration.

  • dead organisms also contain trapped carbon which forms fossil fuels over millions of years.

  • the burning of these fossil fuels releases CO2 back into the air.
• describe how water is cycled through ecosystems

  • energy from the sun causes water to evaporate and turn into water vapour.

  • water vapour also evaporates from plants via the transpiration stream.

  • this water vapour cools as it rises in the atmosphere and condenses to form clouds.

  • the precipitation from these clouds provides water for plants and animals and is absorbed into the soil.

  • water that is not absorbed by the soil runs into streams and rivers and then drains into the sea.

  • some water is absorbed via percolation into rocks underground.
• what is 'decay'?


  the process whereby decomposers break down dead plant and animal matter by secreting enzymes into the environment.
• state some examples of microorganisms that are responsible for decay

  bacteria and fungi
• explain how different factors (temperature, water, oxygen) affect the rate of decay of biological material?

  • temperature: as the temperature increases, decomposers become more active and the rate increases.

  • water: as the amount of water increases, decomposers can do more reactions using enzymes, so the rate increases.

  • oxygen: as the amount of oxygen increases, decomposers have more oxygen for respiration, allowing them to decay matter more quickly, so the rate increases.
• what is compost?


  decomposed organic matter that is used as a natural fertiliser for crops and garden plants
• why do gardeners and farmers try to provide optimum conditions for rapid decay of waste biological material?

  to produce compost
• what does anaerobic decay produce?

  methane gas, which can be burnt as fuel
• describe how biogas generators produce fuel

  biogas generators contain plant and animal waste with microorganisms that decay in anaerobic conditions to produce methane
• what are the trophic levels (level 1 --> 4)?

  level 1: plants and algae that make their own food and are called producers.

  level 2: herbivores eat plants/algae and are called primary consumers.

  level 3: carnivores that eat herbivores are called secondary consumers.

  level 4: carnivores that eat other carnivores are called tertiary consumers.
• what is an 'apex predator'?

  carnivores with no predators who survive at the top of the food chain
• what can pyramids of biomass represent?

  the relative amount of biomass in each level of a food chain
• what are producers of biomass?

  plants and algae that transfer 1% of the incident energy from light for photosynthesis
• how much biomass from each trophic level is transferred to the level above it?

  10%
• state some reasons for the loss in biomass

  not all the ingested material is absorbed, some is egested as faeces, some absorbed material is lost as waste, such as carbon dioxide and water in respiration and water and urea in urine.