Food Chains and Energy Transfer 2 Food Chains

Food Chains and Energy Transfer (2)

Food Chains and Energy Transfer

Where does energy come from? • Organisms in food chains rely on energy to carry out activities • Ultimate source of energy for almost all organisms in sunlight • Plant use sunlight to make organic compounds • These compounds are used as respiratory substrate or to build biomass

Key definitions • Organisms put into three groups depending on how they get their energy and nutrients • Producers: photosynthetic organisms • Consumers: feed or consume other organisms e. g. animals (primary, secondary and tertiary) • Saprobionts: decomposers, e. g. fungi and bacteria, that break down material in dead organisms and release minerals into soil

Key definitions • Food chains – describe feeding relationships • Trophic levels – the stages in a food chain • Food web – different food chains connected together • Biomass – total mass of living material in a specific area at a given time

Biomass • Varying water content of organisms makes measuring biomass unreliable • Measuring dry mass overcomes this problem but means that animal has to be killed • Only done on a small sample – may not be representative • Measured in g m-2 on land or g m-3 in water

Calorimetry • Energy stored dry mass can be estimated using bomb calorimetry • Sample od dry material is weighed, burnt in pure oxygen in sealed container • This is surrounded by a water bath – we know how much energy is required raise temp of 1 g water by 1°C • We can calculate energy released in k. J kg-1

Building Food Webs • Use the sheets to build a food web 3 D model • Label examples of the following on your model (there may be more than one example of each): -producer -primary consumer -secondary consumer -herbivore -carnivore -omnivore Think about… • How does energy enter the food web? • Is energy lost? How? • Is energy recycled? How?