Energy Transfers and Nutrient Cycles Flashcards
Biomass
mass of carbon or dry mass of tissue per unit area
Suggest how to determine the chemical energy store in dry biomass
- calorimetry
- burn in pure oxygen and heat water until no further change in mass
Suggest limitations of biomass measurements
- accurate measurement involves removes all water from an organism which kills it
- estimations based on samples can be unrepresentative
Give reasons why only 1% of light energy is captured by plants
- reflected by water vapour and particulates in atmosphere
- wrong wavelength of light so not absorbed
- light misses chloroplasts
Gross Primary Production
- chemical energy stored in plant biomass in a given AREA
- production = kJm^-2 and productivity kJm^-2year^-1
Suggest how sugars and other organic compounds synthesised by plants are used
- respiratory substrates
- stored as biomass
Net Primary Production
- chemical energy stored in plant biomass for a given AREA after respiratory losses to the environment have been taken
into account - NPP = GPP - R
Suggest what net primary production is available for
- plant growth
- plant reproduction
- available to consumers at other trophic levels
Net Primary Production of consumers
N = I - (F + R)
where I = chemical energy store in ingested food, F
= chemical energy lost to the environment in faeces and
urine and R = respiratory losses to the environment
Explain why most food chains only reach four or five trophic levels at most
- energy lost at each stage of food chain
- insufficient energy to support a large enough breeding population
How to increase GPP and NPP of plants
GPP
- high light intensity via open field/artificial light of correct wavelength
- warm temperature via warm climate/heaters
- plentiful water supply via rainfall/irrigation
- rich mineral supply via fertilisers
NPP
- selectively bred
Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer
- some light energy fails to strike chloroplast/is reflected/not of appropriate wavelength
- efficiency of photosynthesis in plants is low/approximately 2% efficient
- respiratory loss / excretion / faeces / not eaten
- loss as heat
- efficiency of transfer to consumers greater than transfer to producers/approximately 10%
- efficiency lower in older animals/herbivores/ primary consumers/warm blooded animals
- carnivores use more of their food than herbivores
Explain briefly how to improve efficiency of energy transfer in human food chains
- simplify food webs by removing competitors and pests
- reduce respiratory losses
- keep food chains short
Intensive Farming
- optimal conditions
- reduce respiratory losses
- high efficiency of energy transfer hence net production
- maximise profits
Explain how intensive rearing of livestock increases net productivity
- keep in enclosed spaces to limit movement/warm so more energy for growth
- controlled diet with high nutrient concentration
- protect from predators
- selectively breed
- slaughter before fully grown
