Key Questions

• What do all plants in ecosystems do?


  They synthesise glucose (an organic compound) from carbon dioxide taken from the atmosphere or water around them.
• How do we know that photosynthesis produces an organic compound?

  It takes six carbon molecules to produce one 6-carbon glucose molecule.
• What happens to most of the sugars produced by plants?


  They are used as respiratory substrates.
• What happens to the sugars that aren't respired?


  They are used to make other molecules which build the plant biomass.
• What molecules are the sugars converted to?


  Starch, cellulose, lipids (all contain C, H, and O), also amino acids and molecules such as DNA nucleotides.
• What is biomass?


  The mass of living tissue in an organism. It can be measured wet or dry and dry mass is more useful as it allows for comparisons to be made between different organisms.
• What are appropriate units for biomass?


  The mass of carbon or the dry mass (grams) in a tissue in a given area (metres squared), so g m^2.
• How can we measure the chemical energy store in dry biomass?


  Using a calorimeter (measuring the temperature rise when the dry mass is burned).
• What is Gross Primary Production (GPP) ? 


  The total chemical energy store in plant biomass as a result of photosynthesis (in a given area or volume).
• What is Net Primary Production (NPP) ?


  The chemical energy store in plant biomass after respiratory losses (R) have been taken into account.
• What is the equation for calculating NPP?


  NPP = GPP - R
• What is a plant able to do with the NPP?

  Grow (increase their biomass) and reproduce.
• What can happen to a plant during its lifetime?

  It could grow, mature, and die, or it could be eaten by a primary consumer. The biomass would be available for either herbivores or decomposers.
• How do we calculate net production for consumers?


  N = I - (F + R)
• What does I represent in N = I - (F + R) ?


  The chemical energy store in the ingested food.
• What does F represent in N = I - (F + R) ?


  The chemical energy that is lost to the environment as either faeces or urine.
• What is the difference between excrete and egest?


  Wastes produced by an organism are excreted (urine is produced by the kidneys so is excreted). Wastes that couldn't be digested are egested (faeces are the indigestible material that was ingested, so faeces are egested).
• What is primary productivity?


  The rate of production in producers (mostly green plants). It can be measured in biomass or kJ in a given area in a given time.
• What is secondary productivity?


  The rate of production in consumers. It can be measured in biomass or kJ in a given area in a given time.
• What are appropriate units for productivity?


  If biomass, then g or kg. If energy, then kJ. Areas and time scales are large so hectares (ha) and years would usually be best.
• How can we reduce energy losses in farming food chains?


  Shorter food chains have fewer respiratory losses. Also animals can be farmed to reduce respiratory losses, e.g. keeping them enclosed to reduce movement and keep them warm, feed high protein and easily digestible food; reduce the chance of illness or predation and slaughter before they reach reproductive age so energy isn't transferred to gamete production.