Energy Transferred In Ecosystems
Overview
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 grain. 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 from end to end. 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 the numbers: tracking one animal's whole yearly ledger from mouthful to growth, building a pyramid of biomass to scale, and reading one you are handed in an exam closely enough to say what it tells you about the ecosystem and what it cannot.
Objectives
- 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.
- The biomass at each stage can be drawn to scale and shown as a pyramid of biomass. Students should be able to interpret pyramids of biomass and construct them from appropriate information.
Mind map
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Energy Transferred In Ecosystems. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Approximately what percentage of the 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
- In a pyramid of biomass the scale used is 1 cm to 300 g/m2. The producers have a biomass of 3000 g/m2. How long should the producer bar be? A. 1 cm B. 3 cm C. 10 cm D. 30 cm Answer: C
- Why do ecologists compare dry mass rather than the mass of the living organisms? A. Dry mass is quicker to measure than wet mass B. Water content varies between organisms, so wet mass is not a fair measure of the material present C. Water stores most of the energy in an organism D. Drying an organism increases the energy it contains Answer: B
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