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First teaching 2015

Last exams 2025

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Pyramid of Biomass (DP IB Environmental Systems & Societies (ESS)) : Revision Note

Alistair Marjot

Written by: Alistair Marjot

Reviewed by: Bridgette Barrett

Updated on

Pyramids of Biomass

  • A pyramid of biomass measures the amount of biomass present at each trophic level at a specific point in time and represents the standing stock of each trophic level

    • Biomass can be measured in grams of biomass per square metre (g m–2) or units of energy, such as joules per square metre (J m–2)

  • As per the second law of thermodynamics, the quantities of biomass generally decrease along food chains, so the pyramids become narrower towards the top

  • This means that pyramids of biomass are usually pyramid-shaped but can occasionally be inverted and show higher quantities at higher trophic levels

    • Pyramids of biomass are snapshots of the ecosystem and may not indicate productivity over time

    • A fertile intensively grazed pasture may have a lower standing crop biomass of grass but higher productivity than a less fertile ungrazed pasture because biomass is constantly removed by herbivores, resulting in an inverted pyramid of biomass

  • Inverted pyramids sometimes occur due to marked seasonal variations

    • For example, in some marine ecosystems, the standing crop of phytoplankton, the major producers, is lower than the mass of the primary consumers, such as zooplankton

    • This is because the phytoplankton reproduce very quickly and are constantly being consumed by the primary consumers, which leads to a lower standing crop but higher productivity

    • This can occur because phytoplankton can vary greatly in productivity (and therefore biomass) depending on sunlight intensity

A8wkWry9_2-2-4-pyramid-of-biomass

Constructing a Pyramid of Biomass

  • Being able to construct accurate pyramids of biomass from appropriate data is an important skill

Worked Example

Figure 1 shows:

  • A food chain with four trophic levels

  • The total mass of organisms at each trophic level

Figure 1

 

Clover →

Snail   →

Thrush    →

Sparrowhawk

  Biomass in kg

    80

  30

   10

       2

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

worked-example-constructing-a-pyramid-of-biomass-2
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Alistair Marjot

Author: Alistair Marjot

Expertise: Biology & Environmental Systems and Societies Content Creator

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

Bridgette Barrett

Reviewer: Bridgette Barrett

Expertise: Geography Lead

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.

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