KS3 · Biology

Food chains

Here's a claim that sounds wrong: more foxes in a field can mean more grass. By the end of this lesson, you'll be able to explain why.

Food chains

Follow the food

View: 1 · Follow the food. Showing 2 layers: Garden chain, Arrows

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tap a box or an arrow ↑

Start where the food starts: the cabbage. Now follow the arrows. Each one points to the organism that GETS the food, so read it as 'is food for': the cabbage is food for the caterpillar, and the caterpillar is food for the blue tit.

Switch the views to build the chain up. Then turn the level names off and see if you can still name every level.

Biology · Producers and consumers

Maker or eater?

Does it make its own food, or does it have to eat other organisms to get food?

Still to sort

Producer (0)

Makes its own food.

Where the line is: The only question that matters: can it make its own food? Plants do it by photosynthesis, using light and chemicals from their surroundings.

Consumer (0)

Can't make its own food — eats other organisms.

Where the line is: Being eaten doesn't decide it, and neither does eating plants. A consumer is anything that has to eat other organisms because it can't make food itself.

8 of 8 still to sort.

Every organism in a food chain is one or the other. Sort them, then read why.

Why food matters

Reason it through

Why does a fox need to eat rabbits at all?

Link 1 of 4

First link · your turn

Before it can do anything else, what does the fox have to get?

Locked — reveal the link above first

Reading a food chain

What is this diagram really telling you?

Here's the garden chain again: cabbage → caterpillar → blue tit.

Which is closest to what you think right now?

The arrow means 'eats', so it should point from the eater to its food: blue tit → caterpillar.Each box is one animal — one caterpillar gets eaten by one blue tit.It shows there are more cabbages than caterpillars, and more caterpillars than blue tits.Each box is a whole population, and each arrow shows which way the food passes.

How sure are you?

I'm sureI think soI'm guessing

The arrow means 'eats', so it should point from the eater to its food: blue tit → caterpillar.

This is a common misconception

That's the most common slip, and it flips every arrow in the chain. The arrow shows where the food GOES, so it points to the organism that gets it: caterpillar → blue tit, read as 'the caterpillar is food for the blue tit'.

Each box is one animal — one caterpillar gets eaten by one blue tit.

This is a common misconception

Each level stands for a whole population: all the caterpillars living in that place, not just one. The chain is about types of organism feeding on other types.

It shows there are more cabbages than caterpillars, and more caterpillars than blue tits.

This is a common misconception

A food chain diagram doesn't show numbers at all. It tells you who is food for whom — it can't tell you how many individuals are in each population.

Each box is a whole population, and each arrow shows which way the food passes.

This matches the evidence

Exactly right. Three boxes, three populations; two arrows, two feeding links. And because each box is a population, you can ask what happens when one of them changes size.

Arrows show where the food goes. Boxes are populations. The diagram shows no numbers.

Populations

What changes a population?

View: What makes it grow. Showing 2 layers: Population, Adds individuals

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Two things add rabbits to this field's population: new rabbits being born (reproduction), and rabbits moving in from somewhere else (migration into the area).

Switch views to see what adds individuals and what takes them away, then tap an arrow.

Use the chain to predict

Here's where the chain earns its keep. Commit to an answer before you look.

In the field chain grass → rabbit → fox, the fox population increases. What happens next?

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What you need to know

Organisms depend on one another for food. A food chain shows these feeding relationships, and food chains can be combined into food webs.
Producers (plants and some microorganisms) make their own food. Consumers, including humans and other animals, can't — they eat other organisms.
Every arrow points to the organism that gets the food. Read it as 'is food for'.
Each level in a food chain is a population, and a change in one population affects the others in the chain.

The big picture

A food chain is a model of who is food for whom. It starts with a producer, its arrows show which way the food passes, each level is a whole population, and you can use it to predict how a change in one population spreads along the chain.

Key points

1Nutrition is how an organism gets food. Food is the fuel for cellular respiration, which provides the energy for life processes such as movement.

2Every food chain starts with a producer, followed by the primary, secondary and then tertiary consumer.

3All animal food, including meat, links back to plants.

4A population is the number of individuals of one type of organism in a specific place. Its size changes through reproduction, death and migration into or out of the area.

5A food chain diagram shows who is food for whom — not how many individuals there are.

6If a top consumer increases, its prey decreases and the prey's food increases.

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Worked example

Problem

In a garden, the food chain is cabbage → caterpillar → blue tit. The cabbage population falls. Predict what happens to the caterpillars, and what happens after that.

⚠ Watch out

Drawing the arrows backwards, from the eater to its food. The arrow points to whoever GETS the food: grass → rabbit, never rabbit → grass.

🧠

Memory hook

Arrow = 'is food for'. Follow the food from the producer, then follow the knock-on: more foxes → fewer rabbits → more grass.

✓

Check yourself

Cover the page. Write the field chain with its arrows, label every level, and then say in one sentence what the arrow between the first two organisms means.

Flashcards

(15)

What is a producer?

An organism that makes its own food — plants and some microorganisms.

How do plants make their food?

By photosynthesis, using light and chemicals from their surroundings.

What is a consumer?

An organism that can't make its own food, so it gets food by eating other organisms. Humans and other animals are consumers.

What does an arrow in a food chain mean?

'Is food for'. It shows a transfer of biomass and points to the organism that gets the food.

What must every food chain start with?

A producer.

What is a primary consumer?

The first consumer in a food chain — the one that eats the producer.

What is a secondary consumer?

The consumer that eats the primary consumer.

What is a tertiary consumer?

A third consumer — one that eats the secondary consumer.

What is nutrition?

The life process by which organisms get the food they need.

What do all organisms use food for?

As fuel for cellular respiration, which provides the energy for life processes such as movement.

Meat comes from animals. So why does all animal food link back to plants?

Consumers can't make food, so every animal's food comes from eating other organisms — and following that food back always reaches a plant.

What is a population?

The number of individuals of one type of organism in a specific place.

Name the ways a population's size can change.

Reproduction, death, and migration into or out of the area.

What does one box in a food chain stand for — and what doesn't the diagram show?

A whole population of that organism, not one individual. The diagram doesn't show how many individuals there are.

A top consumer's population increases. What happens to its prey, and to the prey's food?

The prey decreases, so the prey's food increases.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Maker or eater?

What is this diagram really telling you?

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