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Lessons · Teaching · food chains, food webs and what eats what

Arrows point the way the energy goes

A food chain starts with a producer that makes its own food, and each arrow points from the thing eaten to the thing eating it, because the arrow shows where the energy travels. A food web is many chains joined, and decomposers return nutrients to the start.

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In beta. This lesson was written for Hone and has not yet been checked by a state certification officer. Practice material, not professional advice. What that means.

What it is for

The arrow direction is the most commonly drawn-backwards thing in elementary science, including by teachers, and it is not a convention to memorise: it is a claim about energy. Once a class knows the arrow means 'energy goes this way', they stop drawing it backwards.

How to think about it

Start with the producer, which is almost always a plant. Draw each arrow from the eaten to the eater and say the sentence out loud: energy goes this way. Remove one organism and trace what increases and what decreases, because that is the question an examination asks.

Worked example

Grass to rabbit to fox: the arrow always points at the eater
Say 'energy goes this way' with each arrow drawn.
Producers make their own food; consumers eat others; decomposers break down the dead
Three jobs, and the third is the one left off diagrams.
Remove the foxes: rabbits rise, then grass falls, then rabbits fall
The effect travels both up and down the chain, and it arrives late.
Only a fraction of the energy passes at each step, which is why chains are short
Most of it is lost as heat, so there is nothing left for a sixth link.

Your turn

Name what the arrow in a food chain points towards.

The arrow points from the eaten towards the

The trap

Drawing the arrow from the eater to the eaten, as though it meant 'eats'. It means 'energy flows to', and the whole diagram is wrong if it is reversed.

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