Balancing the Food Chain

It often helps students to understand a concept better if they can visualise or manipulate.

One way to illustrate the concept of a food chain or web is to build a pyramid to illustrate it.

You will need something that is stackable - at least 10 blocks that can be stacked at least three layers high to represent the food pyramid.

Many classrooms have large wooden Base 10 cubes. These are perfect for creating a representative food pyramid. Alternatively use milk cartons or other stackable boxes to create the pyramid.

Paste or draw a sun on 4 blocks. Decorate 3 blocks to represent plants, grass or seeds. Decorate 2 blocks with pictures of minibeasts and one block with a picture of a bird.

Get the students to build the pyramid with the four sun blocks at the bottom, three plant blocks on top of them, then the two minibeast blocks as the next layer and one bird block at top.

Ask why do we build it this way? Relate it to the food pyramid.

Remove one of the sun blocks. What happens? (the upper blocks should fall thus illustrating the necessity of balance in the food chain)

Remove one or two of the minibeast blocks. The blocks may not fall but now the pyramid won’t be a pyramid.

You could also place pictures on the different sides of the blocks to illustrate different examples of food chains with perhaps minibeasts on the bottom, birds, then rabbits, then foxes.

The Food Chain Tag Game:

There will be lots of running around with this activity so choose a big open space.To achieve the representation of a balanced system, you will need about 5 students to be frogs, 7 to 10 to beinsects. The remainder will be algae. Ensure that the numbers represent a balanced system where algae is more plentifulthan insects, insects are more plentiful than frogs. Since children will need to be identified as something different when they are tagged they will need to have some hand signal or a sound that represents what they are. Perhaps frogs croak, insects buzz, algae hums.

The frogs, being the most dominant in this chain try to tag (eat) the insects who try to tag (eat) the algae. Since frogs decompose when they die and become fertilizer, the algae try to tagthe frogs. Once you are tagged, you turn into whatever tagged you.

After a period of time, stop the game and see how many algae, insectsand frogs are left. Play should resume but should be stopped a few timesbefore the end to determine what has happened and why.

Play a few rounds of the game and then introduce a human who can tag anyone but nobody can tag the human. Ask the children why this would be the case.

Each time the human tags someone,they become another human. See how long it takes before all children havebeen changed into humans.

At the completion of the game talk with the children about what the game illustrates. How does it demonstrate what happens when the balance of the food pyramid changes?

Some questionsfor discussion might include:

What happens to the algae and insects if lots of the frogs have been caught?

What happens to the insects if manyof them have been caught?

What happens when humans dominate thefood chain? How can we keep that from happening?

Anne Baird, Deirdre McKenzie and Tanya Chalmers attended an Intel Teach Program Essentials Course and provided the idea for this portfolio.

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