Energy and Ecosystems

• How do plants use the sugars from photosynthesis?

  • primarily as respiratory substrates
  • to synthesise other biological molecules e.g cellulose
• What is biomass?

  Total dry mass of tissue or mass of carbon measured over a given time in a specific area
• Suggest the units for biomass

  • when an area is being sampled: gm-2
  • when a volume is being sampled:gm-3
• How can the chemical energy store in dry biomass be estimated?

  • using calorimetry
  • energy released = 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
• Equation between GPP and NPP

  NPP = GPP - R

  R represents respiratory losses
• Why is most of the suns 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 (urine) & faeces
  • 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
• Give a general equation for % efficiency

  $\frac{energy\ converted\ to\ a\ useful\ form\ \left(J\right)\ }{total\ energy\ \sup plied\ }\ X\ 100$
• 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