Energy Transferred In Ecosystems
Overzicht
Stand in a wheat field on a bright afternoon and an enormous amount of energy is pouring onto every square metre around you. Almost none of it ends up in the bread you will eat. Ninety nine parts in a hundred bounce off, slip past or warm the soil, and of the fraction the crop does capture, most is spent again before anything reaches a cow, a sparrow or you. Ecosystems are not efficient machines. They leak at every joint.
This lesson follows that leak. You will find out why plants and algae hold on to only about one per cent of the light that reaches them, why roughly nine tenths of the biomass at any feeding level never makes it to the level above, and where the missing nine tenths actually goes. Then you will use those two numbers on real figures: reading a set of measurements along a feeding sequence, working out the percentage that survives each step, and explaining why the answer is nearly always small.
Doelstellingen
- Radiation from the Sun is the source of energy for most communities of living organisms. Plants and algae transfer about 1 % of the incident energy from light for photosynthesis. This energy is stored in the substances that make up the cells of the plants.
- Only approximately 10 % of the biomass from each trophic level is transferred to the level above it because: some materials and energy are always lost in the organisms’ waste materials; respiration supplies all the energy needs for living processes, including movement. Much of this energy is eventually transferred to the surroundings. Construction of food webs and chains, and of pyramids of numbers, is not required. An understanding of pyramids of numbers is not required.
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- Approximately what percentage of the incident light energy reaching plants and algae is transferred for photosynthesis? A. 1% B. 10% C. 50% D. 90% Answer: A
- Approximately what percentage of the biomass at one trophic level is transferred to the trophic level above it? A. 1% B. 10% C. 50% D. 90% Answer: B
- Which process does NOT cause biomass to be lost between one trophic level and the next? A. Egestion of undigested food in faeces B. Excretion of urea in urine C. Respiration to supply energy for movement D. Absorption of digested food into the blood Answer: D
- Producers in a habitat store 45 000 kJ/m2 per year. The primary consumers store 3600 kJ/m2 per year. What percentage of the energy is transferred? A. 0.8% B. 8% C. 12.5% D. 80% Answer: B
- Carbon atoms are used again and again in an ecosystem, but energy has to be supplied continuously by the Sun. Why? A. Producers cannot store energy in their cells B. Much of the energy is eventually transferred to the surroundings and cannot be recaptured by organisms C. Energy is destroyed by respiration D. Decomposers use all the energy in dead material Answer: B
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