Year 4 Science: Longer food chains and the effects of change
Part of the Year 4 Science habitats, change and food chains chapter. Chapter overview · whole chapter on one page
Longer food chains and the effects of change
A food chain shows how each living thing depends on the one before it. If one link is removed, the living things after it lose their food. If the producer disappears, the whole chain is affected.
To count the arrows, take one away from the number of living things: a chain with five living things has four arrows.
Key ideas
- A chain with five living things has four arrows.
- If a producer dies, every living thing above it in the chain is affected.
- Removing one link changes the living things that depend on it.
- Every food chain starts with a plant.
Method. Count the names in the chain.
- Read the chain. The chain has grass, grasshopper, frog and grass snake.four names
- Count them. So there are four living things in the chain.4
- Write the answer. 4
Check. Four living things have three arrows. ✓
Method. Count the arrows.
- Count the gaps. Four living things have three gaps between them.three gaps
- Write the number. So the chain has three arrows.3
- Write the answer. 3
Check. One fewer arrow than living things. ✓
Method. Think about what eats the grass.
- Look at the chain. The grasshopper eats the grass, so it is the first living thing to lose its food.grasshopper
- Name the living thing. So the grasshopper loses its food first.Grasshopper
- Write the answer. Grasshopper
Check. The grasshopper is the first eater after the grass. ✓
Watch out
Watch out: a chain with four living things has three arrows, not four. Count the gaps between the living things, not the names.
Try it at home or school (with a grown-up). Draw a short food chain of three living things from a garden, with a grown-up. Then cover one living thing with a piece of paper, and say what would happen to the others.
Exam tip
Grown-up tip. Ask: “If this one was gone, who would lose their food?” Let your child count the arrows, and then the living things.
Exercise 4E Longer food chains and the effects of change
Method. Count the names.
- Read the chain. Grass, mouse and owl are the three names.three names
- Write the answer. 3
Check. Three names have two arrows. ✓
Method. Count the gaps between the names.
- Count the gaps. Three living things have two gaps between them.two gaps
- Write the answer. 2
Check. Two arrows join three living things. ✓
Method. Look at the last name in the chain.
- Read the end of the chain. The last living thing in the chain is the grass snake.grass snake
- Write the answer. Grass snake
Check. The grass snake is the top predator in this chain. ✓
Method. Find the plant in the chain.
- Read the start of the chain. Grass is the plant at the start.grass
- Write the answer. Grass
Check. Every chain starts with a producer. ✓
Method. Think about what eats grass.
- Read the chain. The grasshopper eats the grass.eats the grass
- Write the answer. Grasshopper
Check. The grasshopper is the first to lose its food. ✓
Method. Subtract one from the number of living things.
- Count the living things. There are five living things.five
- Subtract one. Five living things have four gaps between them, so four arrows.5 - 1 = 4
- Write the answer. 4
Check. Check: four arrows join five living things. ✓
Method. Find the animals that hunt other animals.
- Look at each link. The mouse eats grass, so it is not a predator. The owl eats the mouse.owl eats mouse
- Count the predators. There is one predator, the owl.1
- Write the answer. 1
Check. Only the owl hunts another animal in this chain. ✓
Method. Count the arrows before and after.
- Before. The long chain has three arrows.three arrows
- After. With no grass snake, the chain has two arrows.two arrows
- Decide. The number of arrows changes, so the answer is yes.yes
- Write the answer. yes
Check. Removing a link removes an arrow. ✓
Method. Think about what happens to the grass snake.
- Read the chain. The grass snake is the last living thing, so nothing in the chain eats it.last living thing
- Decide. So the grass snake is not prey in this chain, and the answer is no.no
- Write the answer. no
Check. The last living thing in a chain is not eaten by anything in that chain. ✓
Method. Think about what the frog eats.
- Think about the frog. Frogs eat grasshoppers, so frogs need grasshoppers to eat.frogs eat grasshoppers
- Write the prediction. If grasshoppers disappear, the frogs have less food, so fewer frogs should survive.fewer frogs
- Write the answer. Accept any prediction with a reason, such as: the frogs would have less food, so fewer frogs would survive.
Check. Each link depends on the one before it. ✓
Method. Follow the chain from the grass.
- Follow the chain. Grass feeds the grasshopper, which feeds the frog, which feeds the grass snake.feeds
- Write the effect. So a change to the grass affects every link above it.every link
- Write the answer. Accept any sentence that says if the grass is harmed, the grasshoppers, frogs and grass snake lose their food, one link at a time.
Check. A change at the start of a chain reaches the end of it. ✓