Food Chains: Following the Energy

≈ 18 min

A food chain is a diagram that shows the path food and energy take as one living thing is eaten by the next.

\text{grass} \rightarrow \text{zebra} \rightarrow \text{lion}

Two rules make a food chain correct:

Rule 1 — start with a producer. The energy has to enter the ecosystem somewhere, and the only door is a green plant catching sunlight. So every food chain begins with a producer.

Rule 2 — the arrow means "is eaten by". It points in the direction the food and energy travel. Grass $\rightarrow$ zebra is read as "grass is eaten by the zebra", or "energy flows from the grass into the zebra".

Worked example — a Highveld wetland.

\text{pondweed} \rightarrow \text{tadpole} \rightarrow \text{dragonfly larva} \rightarrow \text{small fish} \rightarrow \text{heron}

Check it against both rules. It starts with pondweed, a green producer. ✓ And every arrow points at the eater: the tadpole eats pondweed, the dragonfly larva eats the tadpole, and so on up to the heron. ✓

This chain has $5$ links. Chains rarely run much longer, because at every step most of the energy is used up for moving, growing and keeping warm — there is simply less left for the next eater.

In the food chain grass → zebra → lion, what does the first arrow tell you?

The grass eats the zebra

The zebra eats the grass

The grass and the zebra eat the same food

The zebra slowly turns into grass

Every food chain must begin with a ______.

Which food chain is written correctly?

lion → zebra → grass

grass → zebra → lion

zebra → grass → lion

lion → grass → zebra

How many links (living things) are there in this food chain?

\text{pondweed} \rightarrow \text{tadpole} \rightarrow \text{dragonfly larva} \rightarrow \text{small fish} \rightarrow \text{heron}