Pyramids of Numbers & Biomass (WJEC GCSE Biology)

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Naomi H

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Naomi H

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Pyramids of Numbers & Biomass

Pyramids of numbers

  • Pyramids of numbers are diagrams used to visually represent the number of individual organisms present at each stage of a food chain
  • Pyramids of numbers can vary in shape depending on the food chain in question
    • Small individuals will be many in number
    • Large individuals will be few in number
  • Pyramids of numbers should have the following features:
    • Name labels for each trophic level
    • Labels to indicate the number of individuals at each trophic level
  • Some pyramids of numbers may be drawn to scale, meaning that the size of the bar is proportional to the number of individuals
    • An exam question in which a grid has been provided will require any pyramids to be drawn to scale; see below for an example

Pyramid of numbers diagram

~wuTcsHr_pyramid-of-numbers-labelled

Pyramids of numbers show the number of individuals at each stage of a food chain; they should be labelled with the name of each level and the number of individuals represented by each bar

Pyramids of biomass

  • Pyramids of biomass show the mass of living tissue present at each stage of the food chain
  • Pyramids of biomass are always pyramid-shaped, meaning that the bars decrease in size from the base to the top of the pyramid
    • This is because of the energy losses at each stage of a food chain; there is less energy available for the production of new biomass at higher trophic levels
  • Just as with pyramids of numbers, pyramids of biomass should always be clearly labelled to indicate the trophic level and the biomass represented by each bar
  • If a grid is provided then the pyramid should be drawn to scale

Pyramid of biomass diagram

pyramid-of-biomass-labelled

Pyramids of biomass represent the mass of living material at each stage of a food chain; they are always pyramid shaped due to losses at each trophic level

Worked example

Fig. 1 shows a food chain with four trophic levels. Biomass for each organism is shown below in kg.

  Fig. 1

Clover Snail Thrush Sparrowhawk
80   30   10   2

 

Draw a pyramid of biomass for the food chain shown in Fig. 1

worked example constructing a pyramid of biomass

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Naomi H

Author: Naomi H

Expertise: Biology

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.