Launching your learning experience…
Detailed notes on Organisms and their Environment for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Diagrams of who eats whom. Food chains are simple lines; food webs are interconnected networks.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Linear: producer → consumer → consumer → consumer. Arrows show energy flow.
Definition. A food chain shows the sequence of feeding relationships in a single line.
Standard format:
Grass → rabbit → fox → hawk
Arrows. Always point FROM food TO eater. The arrow shows the direction of ENERGY FLOW.
Components:
Trophic levels.
Worked qualitative. Construct a food chain for a marine ecosystem with phytoplankton, krill, mackerel, tuna.
Cambridge tip. ALWAYS check arrow direction. Eaten → eater (the energy flows that way).
Most organisms eat (and are eaten by) many species. Food webs show this.
Why webs? Real ecosystems aren't simple chains. A fox might eat rabbits, mice, birds, fruit. Hawks might eat rabbits, mice, foxes.
A FOOD WEB shows MULTIPLE chains overlapping in one diagram:
hawk
/ | \
fox owl shrew
| | | |
rabbit mouse
| | |
grass
Reading a food web:
Why webs matter:
Worked qualitative. Why do islands often have simpler ecosystems and more vulnerable species?
Cambridge tip. When given a food web, count arrows IN and OUT to identify predators and prey.
Remove a species → ripple effects through the whole web.
Direct effects.
Indirect effects (cascade).
Worked qualitative. In Yellowstone, wolves were exterminated by 1920 then reintroduced in 1995. What happened?
After wolf reintroduction:
The lesson. Top predators often have outsized effects on entire ecosystems. Removing them can collapse the system.
Cambridge tip. When asked predict effects of removing a species, trace at LEAST TWO levels of consequences (direct + indirect). Cambridge marks this depth.
Verbatim phrases and definitions Cambridge mark schemes credit.
Food chains/webs appear Paper 4 (5-7 marks: construct, label, predict effects). Examiner reports flag students drawing arrows the wrong way and missing cascade effects.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (19.2); 0610/42 May/Jun 2024 — Q23 (food webs); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on food chains and food webs, written exactly the way a tutor would explain them at the board.
Question
Using grass, fox, rabbit and hawk, construct a food chain and identify the trophic level of each organism.
Step-by-step solution
Step 1
grass → rabbit → fox → hawk — the arrows point in the direction of energy flow (from the food to the feeder).
Step 2
Grass is the producer (trophic level 1); rabbit is the primary consumer (level 2).
Step 3
Fox is the secondary consumer (level 3); hawk is the tertiary consumer (level 4).
Answer
grass → rabbit → fox → hawk. Producer (1) → primary consumer (2) → secondary consumer (3) → tertiary consumer (4).
Examiner tip
Arrows point from the organism eaten to the organism that eats it (the direction of energy flow), NOT the other way.
Question
In the food chain algae → small fish → large fish → heron, name (a) the producer, (b) a primary consumer and (c) a tertiary consumer.
Step-by-step solution
Step 1
(a) The producer is the algae (it photosynthesises).
Step 2
(b) The primary consumer is the small fish (it eats the producer).
Step 3
(c) The tertiary consumer is the heron (it is the fourth organism, eating the large fish).
Answer
(a) Algae; (b) small fish; (c) heron.
Examiner tip
Count along the chain: producer, primary consumer, secondary consumer, tertiary consumer.
Question
Explain the difference between a food chain and a food web.
Step-by-step solution
Step 1
A food chain shows a single line of feeding relationships — one organism eating the next.
Step 2
A food web is a network of interconnected food chains in an ecosystem.
Step 3
A food web shows that most organisms eat — and are eaten by — more than one species.
Step 4
So a food web is more realistic; a food chain is a simplified part of it.
Answer
A food chain is a single line of who-eats-whom; a food web is a network of interlinked food chains, showing that most organisms have several food sources and predators.
Question
Explain why a pyramid of numbers is sometimes inverted, using the food chain oak tree → caterpillars → birds.
Step-by-step solution
Step 1
A pyramid of numbers shows the number of organisms at each trophic level.
Step 2
Here, there is only one large oak tree (the producer), but it feeds many caterpillars (primary consumers).
Step 3
So the producer bar (1 tree) is narrower than the primary consumer bar (many caterpillars), making the pyramid look inverted at the bottom.
Step 4
This happens because pyramids of numbers do not take size into account — one big tree provides food for many small animals.
Answer
A single large producer (one oak tree) can feed many small consumers (caterpillars), so the producer bar is narrower than the bar above it and the pyramid of numbers is inverted.
Examiner tip
Pyramids of numbers ignore size, so they can be inverted. A pyramid of biomass or energy is always upright.
Question
In a food web, foxes eat rabbits, and rabbits eat grass. Explain what is likely to happen to the rabbit and grass populations if all the foxes are removed.
Step-by-step solution
Step 1
With the foxes (a predator) removed, fewer rabbits are eaten.
Step 2
So the rabbit population increases.
Step 3
The larger number of rabbits eats more grass, so the grass population decreases.
Step 4
Eventually, if the grass becomes scarce, there is not enough food for all the rabbits, so the rabbit population may fall again, until a new balance is reached.
Answer
Removing the foxes lets the rabbit population rise (fewer eaten); the extra rabbits eat more grass, so the grass falls; eventually a shortage of grass limits the rabbits again.
Examiner tip
Trace the knock-on effects: removing a predator → prey increases → its food decreases → prey may then fall.
Question
In a food web, owls eat both mice and small birds; mice and small birds both eat seeds. A disease kills most of the mice. Suggest and explain what happens to the small birds.
Step-by-step solution
Step 1
With most of the mice gone, the owls have less food, so they will eat more small birds instead.
Step 2
This increased predation tends to reduce the number of small birds.
Step 3
However, with fewer mice, there is less competition for seeds, so more food (seeds) is available to the small birds.
Step 4
So there are two opposing effects — more predation but more food — and the actual change in the small bird population depends on which effect is stronger.
Answer
Owls eat more small birds (less other prey), which reduces them; but with fewer mice there is less competition for seeds, which helps them. The result depends on which effect is greater.
Examiner tip
A good food-web answer considers BOTH the predator effect and the competition effect, rather than assuming a single outcome.
High-scoring sample answers for food chains and food webs on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State what the arrows in a food chain represent. (1 mark)
Model answer
The arrows represent the direction of energy flow (from the organism eaten to the organism that eats it).
Why this scores
One mark for 'direction of energy flow / the flow of energy'.
In the food chain lettuce → slug → frog → snake, name the producer and the secondary consumer. (2 marks)
Model answer
The producer is the lettuce; the secondary consumer is the frog.
Why this scores
One mark each: lettuce (producer); frog (secondary consumer / third organism).
Explain the difference between a food chain and a food web. (3 marks)
Model answer
A food chain shows a single sequence of organisms, each feeding on the one before it. A food web is a network of many interconnected food chains in an ecosystem. A food web shows that most organisms feed on, and are eaten by, more than one type of organism, so it is a more realistic picture of feeding relationships.
Why this scores
Three marks: food chain = single line; food web = network of interlinked chains; web shows organisms with several food sources/predators.
Explain why a pyramid of numbers for the food chain oak tree → caterpillars → birds is inverted at the bottom. (4 marks)
Model answer
A pyramid of numbers shows the number of organisms at each trophic level. In this food chain there is only one large oak tree acting as the producer, but it provides food for many caterpillars. So the bar for the producer (1 tree) is narrower than the bar for the primary consumers (many caterpillars), which makes the pyramid inverted at the base. This happens because a pyramid of numbers does not take the size of the organisms into account — one very large producer can feed a great many small consumers.
Why this scores
Four marks: pyramid shows numbers; one large producer feeds many consumers; producer bar narrower than the one above; numbers ignore size of organisms.
In a food web, hawks eat snakes, and snakes eat mice. Predict and explain what would happen to the snake and mouse populations if all the hawks were removed. (5 marks)
Model answer
If the hawks (the snakes' predator) are removed, fewer snakes are eaten, so the snake population increases. With more snakes present, more mice are eaten, so the mouse population decreases. As the mice become scarce, there is less food for the snakes, so eventually the snake population may fall again, and the populations settle towards a new balance. So removing the hawks first increases the snakes and decreases the mice, with knock-on effects until a new equilibrium is reached.
Why this scores
Five marks: hawks removed → fewer snakes eaten → snakes increase; more snakes → more mice eaten → mice decrease; mice scarce → less food for snakes → snakes may fall / new balance.
In a food web, foxes eat both rabbits and voles; rabbits and voles both eat grass. A new disease greatly reduces the rabbit population. Discuss the effects this could have on the rest of the food web. (6 marks)
Model answer
If the disease greatly reduces the rabbit population, the foxes lose one of their main food sources, so they will tend to eat more voles instead. This increased predation could reduce the vole population. However, with fewer rabbits eating the grass, there is now less competition for grass, so more grass is available to the voles, which could allow the vole population to increase. The actual effect on the voles depends on whether the increased predation by foxes or the reduced competition for food has the greater effect. The grass population is likely to increase at first, because there are fewer rabbits eating it. If the foxes cannot find enough food overall (fewer rabbits, and only so many voles), the fox population may also fall. This shows how a change to one species in a food web can have knock-on effects on several others, through both feeding relationships and competition.
Why this scores
Up to 6 marks: foxes eat more voles (predation) → voles may fall; fewer rabbits → less competition for grass → voles may rise; the net effect depends on which is greater; grass increases; foxes may decline if food is short; overall knock-on effects through the web.
Definitions to memorise and the exact keywords mark schemes credit for food chains and food webs answers — sharpened from recent examiner reports for the 2026 0610 sitting.
A diagram showing the flow of energy from one organism to the next, beginning with a producer.
A network of interconnected food chains, showing all the feeding relationships in an ecosystem.
A diagram showing the number of organisms at each trophic level. Can be inverted, because it ignores the size of the organisms.
A feeding position in a food chain: producers are level 1, primary consumers level 2, and so on.
The traps other students keep falling into on food chains and food webs questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
It sounds like 'the fox eats the rabbit'.
How to avoid it
Arrows show the flow of ENERGY, from the food to the feeder: grass → rabbit means the rabbit eats the grass.
Why it happens
The web seems robust.
How to avoid it
Food webs are interconnected, so removing one species has knock-on effects: its predators lose food, and its prey may increase.
Why it happens
Students confuse it with a pyramid of energy.
How to avoid it
A pyramid of numbers CAN be inverted (e.g. one tree feeding many insects). A pyramid of energy is always upright.
The things students keep getting wrong in this sub-topic, answered.