BYA5 SECTION 14.7Energy is transferred through food chains and food webs in a community |
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Ecological pyramids |
| Pyramids of numbers |
- Total number of organisms in a food chain at each trophic level
- Highest number at the bottom (usually producers, then consumers)
- Pyramid will be inverted if lots of small animals are feeding off one large plant
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Pyramids of biomass |
- Total biomass of organisms in a food chain at each trophic level
- Organisms multiplying rapidly may have biomass less than primary consumers
- Dry mass is measured / H2O stores no energy and varies in different organisms
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Pyramid of energy |
- Amount of energy transferred to each level of a food chain in an ecosystem
- Always pyramid-shaped / no energy loss
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Transfer of energy between trophic levels |
| Food chains and food webs |
- Energy is used to produce new cells / remains fixed in that organism
- Energy is passed on to the next trophic level through feeding
- Producers are photoautotrophs (plants)
- Transduce light energy into chemical P.E. by forming new tissues and storing organic compounds
(starch, glucose, lipids, proteins)
- Consumers are herbivores, carnivores and omnivores
- Decomposers are detritivores and saprophytes
- Break down dead complex organic molecules into simple inorganic molecules
- Food chains are feeding relationships and linked with each other to form complex food webs
- Some organisms feed on different trophic levels / leaves and insects
- Some organisms feed on different foods when they are larvae (leaves) and when they are adult (nectar produced by different flowers)
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Energy transfer and efficiency |
- 2% of light energy is converted to chemical P.E. by photosynthesis
- Rest is lost reflection from leaves / heat loss / not all wavelengths are utilised / light strikes non-photosynthetic structures
- 10% of that are passed on along trophic levels
- Rest is lost in respiration / as heat/faeces/urine
- Chemical P.E. / generates heat / stores energy by forming organic matter (new cells)
- Mammals are homeothermic / must maintain constant body temp
- Warm environment / less energy maintains body temp / more organic matter stored / more transferred to consumer
- Small organisms / large surface area:volume ratio / lose high amounts of energy
- Carnivores fix organic matter more efficiently than herbivores
- Herbivores feed on plants
- \ Take up cellulose and lignin / difficult to digest
- \ More food passes through gut and is lost as faeces
- Trout fix organic matter most efficiently, they are
- Poikilotherms → must NOT maintain constant body temp
- More energy is used to fix organic matter
- Carnivores are harvested while they are still young and grow rapidly
- Trout transfer most energy to consumer (human) in terms of food
- [EXAM] Number of food chains is limited
- Due to energy losses (at each trophic level)
- In respiration/egestion/excretion/movement/as heat
- (Too) little energy is left to sustain higher trophic levels/to be passed on
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References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]
