Energy and ecosystems Flashcards
Principles (autotrophs and heterotrophs)
In any ecosystem there are producers (autotrophs)
Photoautotrophs use light energy to synthesise their own food, while chemoautotrophs use inorganic molecules
Through photosynthesis, plants synthesise organic compounds (e.g. glucose) from (atmospheric or aquatic) carbon dioxide
Most sugars synthesised are used as respiratory substrates and the rest are used to make other groups of biological molecules e.g. cellulose -> form plant biomass
Heterotrophs (e.g. animals) cannot synthesise their own energy, but must obtain it from autotrophs or other heterotrophs; they act as consumers in food webs
Biomass and its stored energy are transferred through trophic levels in a food web (inefficiently)
Measuring biomass (mass of carbon or dry mass of tissue per given area)
Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area
1) Sample is dried in an oven set to a low temperature (low temperature to avoid combustion, where biomass would be lost)
2) Sample reweighed at regular intervals e.g. every day
3) All water removed when mass remains constant
4) Mass of carbon taken to be 50% of dry mass
Dry mass is more representative because water content of samples vary
Measuring biomass (calorimetry)
The chemical energy stored in dry biomass can be estimated using calorimetry.
Sample of dry biomass is burnt
Energy released is used to heat a known volume of water
Change in temperature of water used to calculate the chemical energy
Gross primary production (GPP)
Chemical energy store in plant biomass, in a given area/volume, in a given time i.e. the total energy resulting from photosynthesis
Net primary production (NPP)
Chemical energy store in plant biomass after respiratory losses (R) to the environment have been taken into account
NPP = GPP - R
The NPP is available for plant growth and reproduction
The NPP is also available to other trophic levels in the ecosystem, such as herbivores and decomposers
Net production of consumers
To work out the net production of consumers (N), the formula below can be used:
N = I – (F + R)
I = the chemical energy store in ingested food
F = the chemical energy lost to the environment in faeces and urine
R = respiratory losses to the environment
Rates of productivity units
Rates of productivity are recorded using the units: kJ ha-1 year-1
kJ: a unit for energy
Per unit area (e.g. ha): different environments vary in size; standardises results so environments can be compared
Per year: more representative as takes into account the effect of seasonal variation (temperature etc.) on biomass so environments can be compared
Energy transfer between trophic levels is inefficient (sun to producer)
Wrong wavelength of light
Light strikes non-photosynthetic
region e.g. bark
Light reflected
Lost as heat
Energy transfer between trophic levels is inefficient (Producer to primary consumer to secondary consumer etc)
Respiratory loss – energy used for
metabolism e.g. active transport
Lost as heat
Not all plant/animal eaten e.g. bones
Some food not digested ( faeces)
Farming practices to increase energy transfer efficiency (crops)
Simplifying food webs to reduce energy/biomass losses to non-human food chains
e.g. Herbicides kill weeds less competition more energy to create biomass
e.g. Fungicides reduce fungal infections more energy to create biomass
e.g. Pesticides reduce loss of biomass from crops
Fertilisers e.g. nitrates to prevent poor growth due to lack of nutrients
Livestock
Reducing respiratory losses within a human food chain (so more energy to create biomass) e.g. restrict movement and keep warm (especially in winter)
Slaughter animal while still growing/young, when most of their energy is used for growth
Selective breeding to produce breeds with higher growth rates
Treated with antibiotics to prevent loss of energy due to pathogens
