ENERGY & ECOSYSTEMS

• • Plants and algae are producers – they photosynthesise.
  • Consumers eat other organisms.
  • Primary consumers eat producers.
  • Secondary consumers eat primary consumers...
• Plants are photoautotrophs - This means they can make their own organic compounds using light energy and simple inorganic molecules.
• In any ecosystem, plants synthesise organic compounds from atmospheric, or aquatic, carbon dioxide.
• • Most carbohydrate synthesised by plants is used by the plant as respiratory substrate.
  • A respiratory substrate is simply a chemical that can be respired to produce ATP.
  • The rest is used to make other groups of biological molecules e.g. cellulose. These biological molecules form the biomass of the plants.
• The chemical energy store in dry biomass can be estimated using calorimetry.
• How to calculate the chemical energy stored in dry biomass:

  • Take fresh sample of tissue and heat at 100oC to evaporate off all the water.
  • Weigh and heat until no further change in mass (to make sure all water evaporated off).
  • Put known mass of dried sample in a calorimeter.

  Sample is burnt in pure oxygen within this device
• Calorimetry using a bomb calorimeter

  • The bomb is surrounded by a water bath, and the heat of combustion causes a rise in the temperature of this water. The bomb is made of steel to ensure high heat conduction.
  • Pure oxygen is used to ensure complete combustion.
  • In turn, the water bath is fully surrounded by an insulating layer to reduce heat loss, and has a stirrer to evenly distribute the heat energy.
  • The specific heat capacity of water can be used to calculate the energy released from the dry tissue.
• Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume.
• Net primary production (NPP) is the chemical energy store in plant biomass in a given area or volume, after respiratory losses to the environment have been taken into account.
• NPP = GPP – R
• Secondary production is the chemical energy stored in consumer biomass in a given area or volume 
• The net secondary production of consumers (N), such as animals, can be calculated as:

  N = I – (F + R)
• Productivity: measuring chemical energy stored in biomass that has been produced in a given area in a given time

  kJ ha-1 year-1
• Energy is lost between trophic levels due to respiration, excretion (urine) and faeces. Food chains can’t go on forever.