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.
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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.
Guide students to analyze what each level of the pyramid represents and how it relates to energy flow in the ecosystem. Encourage them to consider why certain levels might look unusual (like a large producer or many small consumers) and discuss real-world examples to deepen understanding.
Prompt students to question why some pyramids are not perfectly shaped. Discuss factors such as organism size, reproductive rates, and energy loss that affect the pyramid structure.
Present a simple food web and have students predict how adding or removing an organism would change the pyramid. This helps reinforce how interconnected ecosystems are and the impact on energy flow.
Organize small groups to compare their pyramids and reasoning. Encourage students to explain their thinking and respectfully challenge one another’s interpretations for deeper insight.
Ask students to research or observe a food chain in your schoolyard or community. Have them create a pyramid of numbers and biomass based on real observations, making the lesson more relevant and memorable.
A pyramid of numbers shows the count of organisms at each trophic level, while a pyramid of biomass displays the total mass of living organisms at each level. Biomass pyramids typically narrow at higher levels, reflecting energy loss, while number pyramids may not always have this shape due to varying organism sizes.
To draw a pyramid of numbers, list each organism in the food chain as a level and use rectangles to represent their population size. The base is the producer, and each step up represents the next consumer. The rectangle width reflects the number of organisms at that level.
Pyramids of biomass get narrower because energy is lost at every trophic level through respiration, movement, and waste. As a result, less living material is available to support the next level up.
For the food chain Oak → Aphid → Ladybug → Sparrow, the pyramid of numbers might show one oak tree at the base, many aphids feeding on it, fewer ladybugs eating the aphids, and even fewer sparrows preying on the ladybugs.
Pyramids help students visually understand energy flow and population structure in ecosystems. They make it easier to see how energy and biomass decrease at each trophic level and identify trends in food chains.