Pyramid of Numbers and Pyramid of Biomass

Pyramids of numbers and biomass are also used to study food chains in more detail. Biomass is the amount of living material at each trophic level. You would expect that to reduce at each stage as energy is lost between each stage. You would expect the bars of a pyramid of biomass to get narrower at each stage. The bars on a pyramid of number may not get narrower at each stage, as the bars are representing the number of organisms at each stage. A tree, for example, is very big and has a large biomass, but it is only a single living organism.

Using charts to describe food chains can have many benefits in understanding the transfers in energy between each trophic level. In this activity, have your students draw a pyramid of numbers and a pyramid of biomass for different food chains.

This activity looks at the general trends in the pyramids shapes and is not designed to get students drawing the graphs accurately. Have students find data online and draw the charts out more accurately using graph paper.

Student Instructions

Create a storyboard to show how we can represent certain food chains with charts. The two charts we are going to use are called a pyramid of numbers and a pyramid of biomass.

1. Look at the food chains in the first column. They are Oak → Aphid → Ladybug → Sparrow and Grass → Caterpillar → Bluebird.
2. Use this information to create a pyramid of numbers and a pyramid of biomass. You should do this by using rectangles.
3. You don’t need to make the bands of the pyramid exactly the right size.
4. To make this easier, turn on "grid lines" by clicking advanced options at the bottom of the page.