Energy and ecosystems

• How do plants use the sugars from photosynthesis

  ~Primarily as respiratory substrates

  ~To synthesise other biological molecules
• What is biomass

  Total dry mass of tissue or mass of carbon measured over a given time in a specific area
• How can the chemical energy store in dry biomass be estimated

  ~Using calorimetry

  ~Energy releases = specific heat capacity of water x volume of water x temperature increase of water
• Why is bomb calorimetry preferable to simple calorimetry

  Reduces heat loss to surroundings
• How could a student ensure that all water had been removed from a sample before weighing

  Heat the sample and reweigh it until the mass reading is constant
• Define gross primary production (GPP)

  Total chemical energy in plant biomass within a given volume or area
• Define net primary productivity (NPP)

  Total chemical energy available for plant growth, plant reproduction and energy transfer to other trophic levels after respiratory losses
• Give the mathematical relationship between GPP and NPP

  ~NPP = GPP - R

  ~Where R represents respiratory losses
• Why is most of the sun's energy not converted to organic matter

  ~Most solar energy is absorbed by atmosphere or reflected by clouds

  ~Photosynthetic pigments cannot absorb some wavelengths of light

  ~Not all light falls directly on a chlorophyll molecule

  ~Energy lost as heat during respiration/photosynthesis
• How can the net production of consumers be calculated

  ~N = I - (F+R)

  ~I = chemical energy from ingested food

  ~F = energy lost as faeces and urine

  ~R = respiratory losses
• Why does biomass decrease along a food chain

  ~Energy lost in nitrogenous waste

  ~Some of the organism is not consumed

  ~Energy lost to surroundings as heat
• Define primary and secondary productivity

  ~Rate of primary or secondary production

  ~Biomass in a specific area over a given time period
• Outline some common farming practices used to increase the efficiency of energy transfer

  ~Exclusion of predators = no energy lost to other organisms in food web

  ~Artificial heating = reduce energy lost to maintain constant body temperature

  ~Restriction of movement

  ~Feeding is controlled at the optimum
• Explain why the length of food chains is limited

  ~Energy is lost at each trophic level

  ~So there is insufficient energy to support a higher trophic level
• What is a pyramid of biomass

  Diagram that shows the biomass at each trophic level
• Why is a pyramid of biomass preferable to a pyramid of numbers

  Shape of pyramid of numbers may be skewed since a small number of producers can support many consumers