Energy Flow Through Ecosystems
Introduced| English | Meaning |
|---|---|
| producer/prəˈdjuːsə/ | An organism that makes organic molecules from inorganic materials using light or chemical energy. |
| consumer/kənˈsuːmə/ | Organisms that obtain organic matter and energy by feeding on other organisms or their products. |
| food chain/fuːd tʃeɪn/ | A sequence showing how energy and matter pass through feeding relationships from one organism to another. |
| trophic level/ˈtrəʊfɪk ˈlevl/ | A feeding level in an ecosystem: producer or primary/secondary/tertiary consumer. |
| autotroph/ˌɔːtəʊˈtrɒf/ | autotroph |
| heterotroph/ˈhetrətrɒf/ | heterotroph |
| endotherm/ˈendəʊθɜːm/ | endotherm |
| ectotherm/ˈektəðɜːm/ | ectotherm |
How can a food web survive in the dark?
- A deep-sea vent receives no sunlight, but chemosynthetic producers 生产者 capture energy from chemical reactions. Consumers 消费者 obtain that stored energy by feeding.
- Compare this with a sunlit food web. Energy sources can differ, yet each organism still needs an energy budget and each feeding transfer is incomplete.
Producers capture the energy
- A producer makes organic food using light or chemical energy.
- Producers form the base of every food chain 食物链.
- They store the Sun's energy as chemical energy in sugar.
- Everything else in the ecosystem depends on this stored energy.
Where does the energy in most ecosystems originally come from?
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Sunlight is captured by producers (plants) through photosynthesis, feeding the whole ecosystem.
A producer in an ecosystem is an organism that…
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A producer makes its own food (photosynthesis); consumers eat other organisms.
Consumers and trophic levels 营养级
- A consumer eats other organisms to get energy.
- Each feeding step is a trophic level: producer, then primary consumer, then secondary, and so on.
- Energy passes up a food chain from level to level.
- But only a fraction of it makes it to the next step.
Build the pyramid of energy
Drag the energy the plants capture and watch only a tenth pass up each level - so the top predator is left with almost nothing.
Assume transfer efficiency is 10% in this example. From 10,000 units, how many reach the next trophic level?
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Under the supplied 10% assumption, 10,000 × 0.1 = 1,000. Real transfer efficiencies vary.
Each feeding step in a food chain — producer, then consumer — is a ____ level.
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A trophic level is one feeding step; energy falls at each higher level.
Transfer is incomplete
- An illustrative transfer efficiency is 10%; measured efficiencies vary.
- The rest is lost, mostly as heat from respiration.
- So each higher level holds far less energy than the one below.
- This is why food chains are short and top predators are rare.
Select all true statements about energy flow.
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Energy enters through producers and transfers incompletely. It ultimately disperses as heat, rather than cycling endlessly through the food web.
Sunlight is not the only entry point
- An autotroph 自养生物 builds organic molecules using an external energy source. Photosynthetic organisms capture light; chemosynthetic organisms capture energy from reactions involving inorganic chemicals, such as those available near some deep-sea vents.
- A heterotroph 异养生物 obtains organic matter from other organisms and metabolizes carbohydrates, lipids or proteins. Decomposers and scavengers are heterotrophs too, not a separate source of new energy.
A producer near a dark vent uses energy from inorganic chemical reactions. It is…
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Autotrophs can use chemical energy as well as light.
Energy budgets affect survival and reproduction
- An endotherm 内温动物 generates substantial metabolic heat to regulate body temperature. An ectotherm 外温动物 relies more on environmental heat and can move into sun or shade; both still use energy for cellular work.
- Energy gained minus maintenance costs is available for growth, storage and reproduction. If costs exceed intake, body reserves and reproductive output can fall. Seasonal breeding or switching reproductive strategies can reflect changing energy availability.
A sustained energy intake below maintenance costs can reduce reproductive output.
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Less energy remains for growth or reproduction, and stored reserves may be consumed.
Worked example: use measured transfer efficiency
- Producer production is 20,000 kJ over a stated area and time; primary-consumer production is 2,400 kJ over the same area and time. Transfer efficiency = 2,400 ÷ 20,000 × 100 = 12%.
- If secondary-consumer production is 240 kJ, the next transfer is 10%. Efficiencies differ; do not impose a universal 10% rule. Lower producer production can support less consumer production unless another resource compensates.
Producer production is 20,000 kJ and consumer production is 2,400 kJ. What is the percentage transfer efficiency?
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2400 ÷ 20000 × 100 = 12%.
Energy flows; atoms cycle
- Energy changes form and ultimately disperses as heat; it is not destroyed or recycled back into sunlight. New energy input sustains the ecosystem. Matter moves between living organisms and nonliving reservoirs.
- Follow water, carbon, nitrogen and phosphorus in Matter cycling through ecosystems. Distinguish a reservoir, where matter is stored, from a process that moves it.
Respiration destroys energy so it no longer exists in any form.
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Energy is conserved but becomes dispersed heat that is unavailable for the next trophic transfer.
Energy is not recycled through a food chain — it is steadily lost. Some energy is dispersed as heat; uneaten or undigested organic matter can enter detrital pathways. A 10% transfer is a useful example, not a fixed law. Unlike nutrients, energy makes a one-way trip and requires continuing input from sunlight or chemical sources.
Following 10,000 units of energy:
- Plants capture 10,000 units of the Sun's energy.
- The primary consumers that eat them get about 1,000 (10%).
- The secondary consumers get about 100 — so little is left that a fourth or fifth level can barely be fed.
Energy enters an ecosystem as sunlight, captured by producers. It flows up a food chain through consumers, one trophic level at a time. Transfer is incomplete and variable; much energy ultimately disperses as heat — so food chains are short and top predators are few.
Write from 500 kilojoules at the next level
- Producers store 5000 kilojoules.
- Transfer efficiency in this example is 10 percent. The lesson's 10000 units give 1000, and 2400 of 20000 is 12 percent.
How many kilojoules reach the next trophic level?
A 10 percent transfer leaves one tenth of the producer energy.
How much of 5000 kilojoules reaches the next level at 10 percent?
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One tenth of 5000 is 500. Other options — 1000 (the other example); 12 (the other efficiency percent).