Only a Tenth of the Energy Survives Each Step Up a Food Chain
See what makes an ecosystem, sort organisms into trophic levels, apply the ten per cent law to find the energy left at each step, and understand why food chains are short and why harmful chemicals concentrate at the top.
Why can a food chain never have twenty links in it?
Because energy leaks away at every step, and after four or five steps there is almost nothing left to support another level.
Start with the energy a field of grass captures from sunlight. Only about a tenth of it reaches the deer that eat the grass. Only a tenth of that reaches the tiger that eats the deer. Two steps, and ninety-nine parts in a hundred are gone. A fifth or a sixth level would have so little energy available that no population could survive on it.
So the shortness of food chains is not an accident of who eats whom. It is a direct consequence of how energy behaves, and that is the central idea of this chapter.
What the chapter builds on that.
- An ecosystem is all the organisms of an area together with the non-living surroundings they interact with
- Trophic levels sort every organism by how many steps of eating separate it from the sun
- The ten per cent law tells you how much energy survives each step
- Energy flows in one direction only — it never returns from a tiger to the grass
- A food web is the honest picture, because most organisms eat at more than one level
And one consequence is worth naming at the start, because it is examined every year. Energy decreases as you go up the chain, but certain harmful chemicals increase, and they reach their maximum concentration in exactly the organisms at the top. That is biomagnification, and it is the reason environmental chemistry matters to human health.
This page covers the first part of the CBSE Class 10 Science chapter on our environment: ecosystem components, food chains and webs, trophic levels, energy flow and biomagnification.
Start with the energy a field of grass captures from sunlight. Only about a tenth of it reaches the deer that eat the grass. Only a tenth of that reaches the tiger that eats the deer. Two steps, and ninety-nine parts in a hundred are gone. A fifth or a sixth level would have so little energy available that no population could survive on it.
So the shortness of food chains is not an accident of who eats whom. It is a direct consequence of how energy behaves, and that is the central idea of this chapter.
What the chapter builds on that.
- An ecosystem is all the organisms of an area together with the non-living surroundings they interact with
- Trophic levels sort every organism by how many steps of eating separate it from the sun
- The ten per cent law tells you how much energy survives each step
- Energy flows in one direction only — it never returns from a tiger to the grass
- A food web is the honest picture, because most organisms eat at more than one level
And one consequence is worth naming at the start, because it is examined every year. Energy decreases as you go up the chain, but certain harmful chemicals increase, and they reach their maximum concentration in exactly the organisms at the top. That is biomagnification, and it is the reason environmental chemistry matters to human health.
This page covers the first part of the CBSE Class 10 Science chapter on our environment: ecosystem components, food chains and webs, trophic levels, energy flow and biomagnification.
What are the components of an ecosystem?
Two broad components: the biotic, meaning all the living organisms, and the abiotic, meaning the non-living physical and chemical surroundings.
The abiotic components include air, water, soil, temperature, sunlight, humidity and the minerals dissolved in the soil. They set the limits on what can live where, which is why a desert ecosystem and a pond ecosystem support entirely different organisms.
The biotic components are divided by how the organism obtains its food, and this three-way split is the one to know precisely.
- Producers, or autotrophs — green plants and blue-green algae, which make their own food from carbon dioxide and water using sunlight. They are the entry point for all the energy in the ecosystem, because nothing else can capture sunlight
- Consumers, or heterotrophs — organisms that depend directly or indirectly on producers for food
- Decomposers, or saprophytes — bacteria and fungi that break down the dead remains of plants and animals
Consumers are themselves classified, and the classification is by diet:
- Herbivores eat plants — deer, goat, cow, grasshopper
- Carnivores eat other animals — lion, snake, frog
- Omnivores eat both plants and animals — bear, crow, human being
- Parasites live on or in another organism and take food from it — Cuscuta, ticks, lice
Why decomposers matter more than their size suggests. They break down complex organic matter in dead bodies and waste into simple inorganic substances, which then return to the soil and the air for producers to use again. Three things follow:
- Nutrients are recycled, so the ecosystem does not run out of minerals
- Dead matter does not pile up, so the environment is cleaned
- Without decomposers the cycle would break — nutrients would stay locked inside dead bodies and plants would starve even in a world full of dead material
Natural and artificial ecosystems. Forests, ponds, lakes and grasslands are natural; gardens, crop fields and aquariums are artificial, created and maintained by human beings. An aquarium needs cleaning and feeding precisely because it is incomplete — it lacks the full set of decomposers and the self-balancing scale of a natural pond.
Notice the distinction between energy and matter. Matter — carbon, nitrogen, water, minerals — goes round and round through decomposers. Energy does not cycle at all. It enters once from the sun and leaves as heat, which is why the next two sections treat it separately.
The abiotic components include air, water, soil, temperature, sunlight, humidity and the minerals dissolved in the soil. They set the limits on what can live where, which is why a desert ecosystem and a pond ecosystem support entirely different organisms.
The biotic components are divided by how the organism obtains its food, and this three-way split is the one to know precisely.
- Producers, or autotrophs — green plants and blue-green algae, which make their own food from carbon dioxide and water using sunlight. They are the entry point for all the energy in the ecosystem, because nothing else can capture sunlight
- Consumers, or heterotrophs — organisms that depend directly or indirectly on producers for food
- Decomposers, or saprophytes — bacteria and fungi that break down the dead remains of plants and animals
Consumers are themselves classified, and the classification is by diet:
- Herbivores eat plants — deer, goat, cow, grasshopper
- Carnivores eat other animals — lion, snake, frog
- Omnivores eat both plants and animals — bear, crow, human being
- Parasites live on or in another organism and take food from it — Cuscuta, ticks, lice
Why decomposers matter more than their size suggests. They break down complex organic matter in dead bodies and waste into simple inorganic substances, which then return to the soil and the air for producers to use again. Three things follow:
- Nutrients are recycled, so the ecosystem does not run out of minerals
- Dead matter does not pile up, so the environment is cleaned
- Without decomposers the cycle would break — nutrients would stay locked inside dead bodies and plants would starve even in a world full of dead material
Natural and artificial ecosystems. Forests, ponds, lakes and grasslands are natural; gardens, crop fields and aquariums are artificial, created and maintained by human beings. An aquarium needs cleaning and feeding precisely because it is incomplete — it lacks the full set of decomposers and the self-balancing scale of a natural pond.
Notice the distinction between energy and matter. Matter — carbon, nitrogen, water, minerals — goes round and round through decomposers. Energy does not cycle at all. It enters once from the sun and leaves as heat, which is why the next two sections treat it separately.
Formula
How do you use the ten per cent law to find the energy at each level?
Divide by ten at every step. Only about ten per cent of the energy at one trophic level is transferred to the next, and the remaining ninety per cent is used up or lost.
First, the trophic levels themselves, numbered by the number of eating steps from the sun:
- First trophic level — producers, the green plants
- Second trophic level — herbivores, the primary consumers
- Third trophic level — small carnivores, the secondary consumers
- Fourth trophic level — large carnivores, the tertiary consumers
Worked example 1. Grass captures J of energy from sunlight. Find the energy available at each higher trophic level in the chain grass, deer, tiger.
Producers: J
Deer, the second trophic level:
Tiger, the third trophic level:
If a fourth level existed, it would receive
**Read the sequence once more: , , , . Out of every ten thousand joules the grass captured, the fourth level gets ten. That is one part in a thousand, and it is the whole explanation for why food chains are short.
Worked example 2 — working backwards.** A hawk at the fourth trophic level receives J of energy. How much energy must the producers have captured?
Each step upward divides by ten, so each step downward multiplies by ten. From the fourth level back to the first is three steps:
Five thousand joules of sunlight energy for five joules in a hawk.
Where the missing ninety per cent goes, and all three destinations should be named:
- Used in the organism's own life processes — respiration, movement, growth and reproduction
- Lost as heat to the surroundings, which is energy that leaves the ecosystem for good
- Left uneaten or undigested — roots, bark and bones are not consumed, and part of what is eaten passes out as waste
Two properties of energy flow that follow, and both are examined as statements.
- The flow is unidirectional. Energy moves from the sun to producers to consumers and never back. A tiger's energy does not return to the grass
- The energy available decreases at every level, which is why the number of organisms and the total mass generally decrease as you go up
The comparison to make. Matter is recycled by decomposers; energy is not recycled at all. It enters once as sunlight and departs as heat, so an ecosystem needs a continuous supply of sunlight in a way that it does not need a continuous supply of carbon.
First, the trophic levels themselves, numbered by the number of eating steps from the sun:
- First trophic level — producers, the green plants
- Second trophic level — herbivores, the primary consumers
- Third trophic level — small carnivores, the secondary consumers
- Fourth trophic level — large carnivores, the tertiary consumers
Worked example 1. Grass captures J of energy from sunlight. Find the energy available at each higher trophic level in the chain grass, deer, tiger.
Producers: J
Deer, the second trophic level:
Tiger, the third trophic level:
If a fourth level existed, it would receive
**Read the sequence once more: , , , . Out of every ten thousand joules the grass captured, the fourth level gets ten. That is one part in a thousand, and it is the whole explanation for why food chains are short.
Worked example 2 — working backwards.** A hawk at the fourth trophic level receives J of energy. How much energy must the producers have captured?
Each step upward divides by ten, so each step downward multiplies by ten. From the fourth level back to the first is three steps:
Five thousand joules of sunlight energy for five joules in a hawk.
Where the missing ninety per cent goes, and all three destinations should be named:
- Used in the organism's own life processes — respiration, movement, growth and reproduction
- Lost as heat to the surroundings, which is energy that leaves the ecosystem for good
- Left uneaten or undigested — roots, bark and bones are not consumed, and part of what is eaten passes out as waste
Two properties of energy flow that follow, and both are examined as statements.
- The flow is unidirectional. Energy moves from the sun to producers to consumers and never back. A tiger's energy does not return to the grass
- The energy available decreases at every level, which is why the number of organisms and the total mass generally decrease as you go up
The comparison to make. Matter is recycled by decomposers; energy is not recycled at all. It enters once as sunlight and departs as heat, so an ecosystem needs a continuous supply of sunlight in a way that it does not need a continuous supply of carbon.
What is the difference between a food chain and a food web?
A food chain is a single straight sequence of who eats whom. A food web is the whole set of interconnected chains in an ecosystem, and it is what really exists.
Two standard food chains to be able to write.
- In a grassland: grass, then grasshopper, then frog, then snake, then hawk
- In a pond: algae, then small aquatic animals, then small fish, then large fish
Each arrow in a food chain means two things at once — it points from the organism being eaten to the organism eating it, and it shows the direction in which energy flows.
Why the food web is the more honest picture. A real organism rarely eats at only one level:
- A frog eats insects but is eaten by both snakes and birds, so it belongs to several chains at once
- A human being eats plants and animals, occupying two trophic levels in the same meal
- A hawk may eat a snake, a rat or a small bird, which sit at different levels
So the chains cross and share members, forming a web. And that interlinking is what gives an ecosystem its stability, which is the reason the distinction matters:
- In a single chain, removing one organism breaks everything above it
- In a web, a predator that loses one prey species can switch to another, so the ecosystem absorbs the loss
Worked reasoning — what happens if all the frogs are removed? Trace both directions from the missing level:
- The level below increases. Insects have lost a predator, so their population rises sharply and they may damage the crops
- The level above decreases. Snakes have lost a food source, so their numbers fall unless they can switch prey
- The effect spreads further. More insects means less grass, and fewer snakes means more rats
That pattern — the level below rises, the level above falls — is the answer to every "what if this organism disappeared" question, and it works for any level you are given.
Why the top level has the fewest organisms. Because the energy available at each level is a tenth of the level below, the top carnivores are supported by the smallest energy supply and so are the fewest in number. Drawing the levels as a stack with the widest band at the bottom gives the familiar pyramid shape, and the narrowing is the ten per cent law made visible.
One point of care. A food chain is written starting from the producer, never from the top carnivore, because the arrows follow the energy. Writing a chain backwards is a marked error, even if all the organisms are correct.
Two standard food chains to be able to write.
- In a grassland: grass, then grasshopper, then frog, then snake, then hawk
- In a pond: algae, then small aquatic animals, then small fish, then large fish
Each arrow in a food chain means two things at once — it points from the organism being eaten to the organism eating it, and it shows the direction in which energy flows.
Why the food web is the more honest picture. A real organism rarely eats at only one level:
- A frog eats insects but is eaten by both snakes and birds, so it belongs to several chains at once
- A human being eats plants and animals, occupying two trophic levels in the same meal
- A hawk may eat a snake, a rat or a small bird, which sit at different levels
So the chains cross and share members, forming a web. And that interlinking is what gives an ecosystem its stability, which is the reason the distinction matters:
- In a single chain, removing one organism breaks everything above it
- In a web, a predator that loses one prey species can switch to another, so the ecosystem absorbs the loss
Worked reasoning — what happens if all the frogs are removed? Trace both directions from the missing level:
- The level below increases. Insects have lost a predator, so their population rises sharply and they may damage the crops
- The level above decreases. Snakes have lost a food source, so their numbers fall unless they can switch prey
- The effect spreads further. More insects means less grass, and fewer snakes means more rats
That pattern — the level below rises, the level above falls — is the answer to every "what if this organism disappeared" question, and it works for any level you are given.
Why the top level has the fewest organisms. Because the energy available at each level is a tenth of the level below, the top carnivores are supported by the smallest energy supply and so are the fewest in number. Drawing the levels as a stack with the widest band at the bottom gives the familiar pyramid shape, and the narrowing is the ten per cent law made visible.
One point of care. A food chain is written starting from the producer, never from the top carnivore, because the arrows follow the energy. Writing a chain backwards is a marked error, even if all the organisms are correct.
Exam tip
How should you lay out a trophic-level answer?
Start every chain with a producer, divide by ten at each step, and name the trophic level by number as well as by type. Those three habits cover most of the marks in this topic.
- Write chains left to right from the producer, with each arrow pointing toward the organism that eats
- Divide by ten going up, multiply by ten coming down — and count the steps carefully, since a fourth-level organism is three steps from the producer, not four
- Name both labels: "deer, a herbivore at the second trophic level"
- Give all three destinations of the lost ninety per cent — life processes, heat, and uneaten or undigested material
- Say unidirectional when asked about the direction of energy flow, and give the reason: energy never returns from a consumer to a producer
- Distinguish energy from matter — energy flows through and leaves, matter is recycled by decomposers
- For a "what if removed" question, answer in both directions: the level below increases, the level above decreases
- Do not place human beings at a single trophic level — being omnivores, we occupy more than one
The misconception to name. Decomposers are not a separate branch tacked on at the end of the chain. They act on dead material from every level, which is why they are drawn returning nutrients to the soil rather than sitting above the top carnivore.
A second trap. The ten per cent law applies to energy, not to the number of organisms. A thousand grasshoppers do not become a hundred frogs by counting — the tenth is a tenth of the energy, and the number of organisms depends on how large each one is.
- Write chains left to right from the producer, with each arrow pointing toward the organism that eats
- Divide by ten going up, multiply by ten coming down — and count the steps carefully, since a fourth-level organism is three steps from the producer, not four
- Name both labels: "deer, a herbivore at the second trophic level"
- Give all three destinations of the lost ninety per cent — life processes, heat, and uneaten or undigested material
- Say unidirectional when asked about the direction of energy flow, and give the reason: energy never returns from a consumer to a producer
- Distinguish energy from matter — energy flows through and leaves, matter is recycled by decomposers
- For a "what if removed" question, answer in both directions: the level below increases, the level above decreases
- Do not place human beings at a single trophic level — being omnivores, we occupy more than one
The misconception to name. Decomposers are not a separate branch tacked on at the end of the chain. They act on dead material from every level, which is why they are drawn returning nutrients to the soil rather than sitting above the top carnivore.
A second trap. The ten per cent law applies to energy, not to the number of organisms. A thousand grasshoppers do not become a hundred frogs by counting — the tenth is a tenth of the energy, and the number of organisms depends on how large each one is.
Did you know
Why are the worst chemical concentrations found at the top of the chain?
Because energy shrinks as you go up but certain chemicals do not — they stay in the body of whatever eats them, and each level accumulates everything its food carried.
Think about the two quantities moving up together. A deer eats a great deal of grass over its life and keeps only a tenth of the energy. But if each mouthful of grass carried a chemical the deer cannot break down or excrete, the deer keeps nearly all of it — the whole amount from every mouthful. The tiger that eats several deer inherits all of theirs. Energy divides at each step while the chemical adds up.
This is biomagnification, and it means the concentration of such a substance is:
- Lowest in the producers, where it first enters from soil or water
- Higher in the herbivores, which eat large amounts of producers
- Higher still in the carnivores, and highest in the top carnivores
Which chemicals behave this way. Ones that are not easily broken down and not easily excreted — many pesticides and certain heavy metals. Sprayed on a crop, washed into the soil, absorbed by plants, they begin the climb.
And the reason this appears in a science syllabus rather than only in a chemistry one. Human beings eat at more than one trophic level, and often near the top of aquatic chains. A chemical that is harmless in the water can be dangerous in a large fish — not because the chemical changed, but because the chain concentrated it.
Two practical consequences, both examinable.
- Washing vegetables and fruits before eating them removes part of the residue on the surface, which is why it is advised
- Reducing the use of persistent chemicals in farming is the only measure that addresses the cause, since once such a substance is in a food web it stays there
A related idea about waste, which the next part develops. Substances that decomposers can break down are biodegradable; those they cannot are non-biodegradable. Biomagnification is what non-biodegradable substances do when they get into a food chain instead of a landfill — they do not disappear, they travel, and they gather.
One last observation that ties the chapter together. The ten per cent law and biomagnification are the same fact seen from two sides. Energy is used up as it is passed on; matter that cannot be used up is not. The first makes food chains short; the second makes the top of a short chain a risky place to be.
Think about the two quantities moving up together. A deer eats a great deal of grass over its life and keeps only a tenth of the energy. But if each mouthful of grass carried a chemical the deer cannot break down or excrete, the deer keeps nearly all of it — the whole amount from every mouthful. The tiger that eats several deer inherits all of theirs. Energy divides at each step while the chemical adds up.
This is biomagnification, and it means the concentration of such a substance is:
- Lowest in the producers, where it first enters from soil or water
- Higher in the herbivores, which eat large amounts of producers
- Higher still in the carnivores, and highest in the top carnivores
Which chemicals behave this way. Ones that are not easily broken down and not easily excreted — many pesticides and certain heavy metals. Sprayed on a crop, washed into the soil, absorbed by plants, they begin the climb.
And the reason this appears in a science syllabus rather than only in a chemistry one. Human beings eat at more than one trophic level, and often near the top of aquatic chains. A chemical that is harmless in the water can be dangerous in a large fish — not because the chemical changed, but because the chain concentrated it.
Two practical consequences, both examinable.
- Washing vegetables and fruits before eating them removes part of the residue on the surface, which is why it is advised
- Reducing the use of persistent chemicals in farming is the only measure that addresses the cause, since once such a substance is in a food web it stays there
A related idea about waste, which the next part develops. Substances that decomposers can break down are biodegradable; those they cannot are non-biodegradable. Biomagnification is what non-biodegradable substances do when they get into a food chain instead of a landfill — they do not disappear, they travel, and they gather.
One last observation that ties the chapter together. The ten per cent law and biomagnification are the same fact seen from two sides. Energy is used up as it is passed on; matter that cannot be used up is not. The first makes food chains short; the second makes the top of a short chain a risky place to be.
Exam relevance
How does ecology at this level prepare you for NEET?
This is foundation work for Class 12 Ecosystem and Environmental Issues, examined heavily in NEET and in the CBSE Class 12 Biology paper.
Where the trophic-level idea leads. Class 12 formalises it with ecological pyramids — pyramids of number, of biomass and of energy — and asks which of them can be inverted and which cannot. The pyramid of energy is always upright, and the reason is exactly the ten per cent law you use here. A pyramid of number can be inverted, as with a single large tree supporting many insects, and that contrast is a favourite NEET item.
Where the ten per cent law leads. Class 12 adds primary productivity, gross and net, along with the standing crop and standing state, and the same tenth-at-each-step arithmetic runs through the numericals. The law does not change — what grows is the vocabulary around it.
Where the decomposer idea leads. Class 12 breaks decomposition into its named steps — fragmentation, leaching, catabolism, humification and mineralisation — and then builds the nutrient cycles, carbon and phosphorus, on top of them. Your sentence about nutrients returning to the soil is what those cycles describe in detail.
Where the food-web idea leads. Class 12 treats ecosystem stability, keystone species and the effects of species loss. The two-directional reasoning you practise here — the level below rises, the level above falls — is the beginning of that analysis.
Where biomagnification leads. Class 12 covers it directly under environmental issues, along with eutrophication, biochemical oxygen demand and the effects of persistent pollutants. The concept is taught again with the same name, so what you learn here is used unchanged.
Question types to expect. At this level: energy at a given trophic level, naming producers and consumers, writing a food chain, and the effects of removing an organism. In NEET: pyramid comparisons, productivity numericals, decomposition steps, and assertion-reason items on unidirectional energy flow.
The single trap that costs marks. Counting trophic levels wrongly and applying the ten per cent law one time too many or too few. Count the arrows, not the organisms — a chain with four organisms has three transfers.
A second trap. Saying energy is recycled in an ecosystem. Matter is recycled; energy is not. NEET sets assertion-reason questions on exactly that distinction, and the phrase to hold on to is that energy flow is unidirectional.
Board versus competitive emphasis. The CBSE paper marks the definitions, the chain and the stepwise energy calculation; NEET marks the comparison — which pyramid inverts, which cycle is sedimentary, where a pollutant concentrates. The transferable habit is asking at every step whether the quantity is being used up or merely moved, because energy is used up and matter is only moved, and almost every question in this topic turns on that difference.
Where the trophic-level idea leads. Class 12 formalises it with ecological pyramids — pyramids of number, of biomass and of energy — and asks which of them can be inverted and which cannot. The pyramid of energy is always upright, and the reason is exactly the ten per cent law you use here. A pyramid of number can be inverted, as with a single large tree supporting many insects, and that contrast is a favourite NEET item.
Where the ten per cent law leads. Class 12 adds primary productivity, gross and net, along with the standing crop and standing state, and the same tenth-at-each-step arithmetic runs through the numericals. The law does not change — what grows is the vocabulary around it.
Where the decomposer idea leads. Class 12 breaks decomposition into its named steps — fragmentation, leaching, catabolism, humification and mineralisation — and then builds the nutrient cycles, carbon and phosphorus, on top of them. Your sentence about nutrients returning to the soil is what those cycles describe in detail.
Where the food-web idea leads. Class 12 treats ecosystem stability, keystone species and the effects of species loss. The two-directional reasoning you practise here — the level below rises, the level above falls — is the beginning of that analysis.
Where biomagnification leads. Class 12 covers it directly under environmental issues, along with eutrophication, biochemical oxygen demand and the effects of persistent pollutants. The concept is taught again with the same name, so what you learn here is used unchanged.
Question types to expect. At this level: energy at a given trophic level, naming producers and consumers, writing a food chain, and the effects of removing an organism. In NEET: pyramid comparisons, productivity numericals, decomposition steps, and assertion-reason items on unidirectional energy flow.
The single trap that costs marks. Counting trophic levels wrongly and applying the ten per cent law one time too many or too few. Count the arrows, not the organisms — a chain with four organisms has three transfers.
A second trap. Saying energy is recycled in an ecosystem. Matter is recycled; energy is not. NEET sets assertion-reason questions on exactly that distinction, and the phrase to hold on to is that energy flow is unidirectional.
Board versus competitive emphasis. The CBSE paper marks the definitions, the chain and the stepwise energy calculation; NEET marks the comparison — which pyramid inverts, which cycle is sedimentary, where a pollutant concentrates. The transferable habit is asking at every step whether the quantity is being used up or merely moved, because energy is used up and matter is only moved, and almost every question in this topic turns on that difference.
Key takeaways
What should you carry into the second part of this chapter?
One law, four levels and one direction.
- An ecosystem has biotic components — producers, consumers, decomposers — and abiotic components such as air, water, soil, temperature and sunlight
- Producers are the only entry point for energy, since nothing else can capture sunlight
- Consumers are herbivores, carnivores, omnivores or parasites, classified by what they eat
- Decomposers break dead matter into simple substances, recycling nutrients and cleaning the environment
- Trophic levels: producers first, herbivores second, small carnivores third, large carnivores fourth
- The ten per cent law: only about a tenth of the energy passes to the next level, so J at the producers leaves , then , then J
- The other ninety per cent goes into life processes, escapes as heat, or is never eaten or digested
- Energy flow is unidirectional and decreases at every level — which is why food chains have only four or five links
- Matter is recycled, energy is not
- A food web is the interconnected set of chains, and its cross-links give an ecosystem its stability
- Remove an organism and the level below increases while the level above decreases
- Biomagnification: non-biodegradable chemicals become more concentrated at each higher level, so the top carnivores carry the most
The sharpest self-test is a chain and a calculator. Write down grass, grasshopper, frog, snake, hawk, start the grass with J, and work out what reaches the hawk — then check whether your answer really is one part in ten thousand.
- An ecosystem has biotic components — producers, consumers, decomposers — and abiotic components such as air, water, soil, temperature and sunlight
- Producers are the only entry point for energy, since nothing else can capture sunlight
- Consumers are herbivores, carnivores, omnivores or parasites, classified by what they eat
- Decomposers break dead matter into simple substances, recycling nutrients and cleaning the environment
- Trophic levels: producers first, herbivores second, small carnivores third, large carnivores fourth
- The ten per cent law: only about a tenth of the energy passes to the next level, so J at the producers leaves , then , then J
- The other ninety per cent goes into life processes, escapes as heat, or is never eaten or digested
- Energy flow is unidirectional and decreases at every level — which is why food chains have only four or five links
- Matter is recycled, energy is not
- A food web is the interconnected set of chains, and its cross-links give an ecosystem its stability
- Remove an organism and the level below increases while the level above decreases
- Biomagnification: non-biodegradable chemicals become more concentrated at each higher level, so the top carnivores carry the most
The sharpest self-test is a chain and a calculator. Write down grass, grasshopper, frog, snake, hawk, start the grass with J, and work out what reaches the hawk — then check whether your answer really is one part in ten thousand.