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Year 8

In an ecosystem, there are varying amounts of a particular type of animal and plants.

What you may see is a ‘pyramid of numbers’. This represents the number of organisms of a species in an ecosystem

More often then not, you will see a pyramid like the one to your right.

Notice how the bars at the bottom are thicker and they gradually get smaller as you go further up the food chain.

The thickness represents how many of the organism there are in the ecosystem.

The reason for this is energy. The amount of energy passed on from the flowers to the snails and all the way up to the fox, decreases the higher we go.

This means, at the very top you can only have a few animals or else there wouldn’t be enough energy to sustain them.

The important thing to remember about the ‘pyramid of numbers’ is that its all about the quantity of the organism.

That being said, sometimes the pyramid wont look like a pyramid at all.

Observe the image to the left. Notice how thin the bar is, representing the tree.

Although there may only be one or two trees, since they are so large they can support a huge amount of insect life.

To the right is another one. Since the fleas are so small compared to the rabbit, you can fit a large quantity of them on the rabbit.

Pyramid Of Numbers


1. Construct a pyramid of numbers for the following organisms

       a. Grass - snail - grasshopper - cat

       b. Grass - Rabbit - Ticks

c. Rosebush  Greenfly  Ladybirds

        There is one rosebush, 100 greenfly and 2 ladybirds.

2. Explain why one rosebush can support 100 greenfly

3. Define the term Biomass