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Summary Energy and ecosystems
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Summary of biomass, calorimetry, trophic levels, trophic efficiency, primary and secondary production, and also the nitrogen cycle
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Energy and EcosystemsBIOMASS
Definition: the total mass of living material, measured in a specific area of a certain period of
time
Measuring biomass:
measured using dry mass in any given area
Grams per square metre (gm2)
Grams per cubic metre (gm3)
Calorimetry:
The chemical energy store in dry mass can be estimated using calorimetry
1. A sample of dry material is weighed
2. It is then burnt in pure oxygen within a sealed chamber.
3. This is then surrounded by a water bath and the combustion causes a rise in
the temperature of the water.
4. As we know the specific heat capacity of water (how much energy is needed
to heat 1g by 1°C) we can calculate the energy released by the biomass.
Calorimetry:
It takes 4.2j of energy to heat 1g of water by 1°C
Energy transferred = mass of the water (g) x 4.2 (j/g°C) x temperature increase (°C)
eg. if 0.5g of food is burned, 10 cm3 of water warms up by 20°C
1 cm3 of water has a mass of 1g
Energy transferred to water = 10 x 4.2 x 20 = 840 J
Energy content of the food = 840 ÷ 0.5 = 1680 J/g
, TROPHIC LEVELS
The main trophic levels consist of:
Primary producers (autotrophs)
Primary consumers (Herbivores)
Secondary consumers (Primary Carnivores)
Tertiary consumers (Secondary Carnivores)
FOOD WEB
Definition: a graphical representation of the natural interconnections of food chains. Also
known as a consumer-resource system.
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