Energy and ecosystems

• Describe the transfer of energy between organisms

  -Plants make glucose from atmospheric or aquatic carbon dioxide, using sunlight energy

  -Most glucose is used in respiration. The rest is used to produce other biological molecules like cellulose, proteins, lipids and DNA

  -These biological molecules form the biomass of an organism

  -Some of the biomass of an organism can be transferred into consumers in a food chain

  -After death, all biomass is decomposed by microorganisms called saprobionts, which digest organic compounds
• Why does less than 10% of sunlight energy that hits producers transferred to biomass?

  -Light doesn't hit chlorophyll

  -Light is the wrong wavelength and isn't absorbed by chlorophyll, so it is reflected

  -Other limiting factors such as CO2 concentration
• Why does less than 10% of chemical energy in an organism transfer into biomass in its consumer?

  -Not all parts are eaten

  -Some parts can't be digested

  -Energy is lost as faeces and urine

  -Energy is lost as heat during respiration
• Define biomass

  The mass of organic compounds in a population in an area. It can be measured as the mass of carbon in the population
• Why is dry mass used when measuring biomass?

  The volume of water in organisms fluctuates a lot, so dry mass is more accurate than fresh mass
• How is dry mass obtained?

  -Heat the plants to evaporate water

  -Weigh at regular intervals until the mass remains constant
• How is calorimetry used to measure the chemical energy store of dry mass?

  -A sample is burned, and the energy released is conducted by the steel to heat the water

  -Energy released (q) is calculated using q=mc∆T where m is the volume of water, c is the specific heat capacity of water and ∆T is the temperature change
• Why is the method of calorimetry to measure chemical energy store of dry mass unrepresentative?

  Only a small sample is used so normally unrepresentative of the producer population
• How does a calorimeter provide accurate measurements of energy content?

  -The stirrer distributes heat energy

  -It is insulated to reduce heat loss
• Define productivity

  The rate of biomass production

  Measured as the energy per area per time scale
• What is the equation for plant production?

  NPP = GPP - R
• What do the components of the equation for plant production mean?

  NPP = net primary production - the chemical energy in plants after respiration. It is available to use for growth and reproduction and can be passed on to other trophic levels.

  GPP = gross primary production - the chemical energy store in a plant as a result of photosynthesis.

  R = respiratory losses - the heat energy lost during respiration.
• How do farmers simplify food webs to reduce energy losses to non-human food chains?

  Chemical pesticides and biological pest control
• What is the equation for consumer production?

  N = I - (R+F)
• What do the components of the equation for consumer production mean?

  N = net production - the chemical energy store available for growth and reproduction. It can be passed on to other trophic levels.

  I = injested - the chemical energy eaten.

  R = respiratory losses - the heat energy lost during respiration.

  F = faeces - the chemical energy lost in faeces and urine.
• How do farmers reduce respiratory losses in livestock within human food chains?

  -Movement is restricted so less muscle contraction

  -Livestock are kept inside in warm conditions so less energy is needed to maintain body temperature