3.5.3 Energy in Ecosystems Flashcards
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 (e.g. a pond) is being sampled: gm-3
How can the chemical energy store in dry mass be estimated?
Using calorimetry
Energy released = specific heat capacity of water x volume of water (cm3) 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 (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 e.g. kJ/ha/year
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.
energy converted to a useful form (J) x 100 / total energy supplied (J)
