3.5.3 energy and systems

• Question

  Answer
• What do plants use to synthesis organic compounds

  Atmospheric/ aquatic carbon dioxide
• What are most of the sugars synthesised by a plant used for

  Respiratory substrates
• What’s biomass

  The total mass of living material in a specific area at a given time
• How can biomass be measured

  dry mass of tissue per given area Mass of carbon in tissue per given area (dry mass x 0.5)
• How to measure the chemical energy store in dry biomass

  Calorimetry
• What’s GPP (gross primary production)

  Chemical energy store in plant biomass in a given area/volume
• What’s NPP (net primary production)

  Chemical energy store in plant biomass after respiratory losses to the environment have been taken into account
• Equation to calculate NPP

  NPP= GPP - R GPP, gross production R, respiratory losses to the environment
• What’s NPP used for

  Available for plant growth and reproduction If the plant is consumed it can be available to herbivores/decomposes
• Equation to calculate the net production of consumers (N)

  N= I - (F+R) I, chemical energy store of ingested food F, chemical energy lost to environment in faeces R, respiratory losses to the environment
• How much energy is transfered from the sun to a producer and how is energy lost

  1-3% Incorrect wavelength of light, not all can be absorbed and used for photosynthesis (always use this in exam) Reflected back into space Light may be transmitted through the leaf without making contact with chlorophyll
• How much energy is transferred from producers to primary consumers and reasons for energy loss

  5-10% Not all of the plant is eaten such as roots, so primary consumers energy isn’t the NPP Egestion, much of plant contains cellulose and is indigestible, lost in faeces Excretion of urine and respiration cause heat loss Energy is used for metabolic processes eg active transport, muscle contraction
• How much energy is transferred from primary consumer to secondary consumer and explain losses

  20% Not all of animal is eaten eg bones/fur so energy consumed by the secondary consumer is not NPP Animal tissue is digestible however some energy is lost in faeces through egestion Respiration and excretion of urine loses heat Energy is used for metabolic processes eg active transport, muscle contraction, cell division
• Units for the rate of productivity

  Kj/ha/year Kj- unit of energy ha- unit for area, allows for comparison from different size environments Year- accounts for impact of different seasons, provides an annual average PEAT Productivity, energy, area, time
• Example of a farming practice which increases the efficiency of energy transfer

  Factory farming Animals kept in small confined spaces, movement is restricted less energy used for muscle contraction, warm environment reduced heat loss, predators are excluded so no loss to other organisms in food web
• How can energy losses to non human food chains be reduced

  Simplifying food webs, mono culture of crops (grow lots of the same crop) Use insecticides, kills insects, they can’t eat crop, increases yield Herbicides, kills weeds, reduces interspecific competition for nitrates, light intensity
• Additional practises to increase the efficiency of energy transfer (not on spec)

  Hormones, increase growth rate Selective breeding, higher growth rates Antibiotics, stop disease spreading in confined areas