Students should be able to construct accurate pyramids of biomass from…

The idea

Constructing a pyramid of biomass means drawing a stacked bar chart in which each bar represents one trophic level and the bar width is proportional to the biomass at that level. To do this accurately, first identify the trophic levels and their biomass values from the data, then choose a suitable scale so the largest value fits the space available. Draw horizontal bars with widths calculated from the scale, stack them with trophic level 1 at the bottom, and label each level with its organisms and biomass value, including units such as g/m². A ruler and sharp pencil help produce neat, proportional bars. Accuracy is assessed by whether the bar widths correctly represent the data and whether the pyramid is clearly and correctly labelled.

What earns the marks

• Identify the biomass value for each trophic level from the data.
• Choose a suitable scale that allows all bars to fit and remain proportional.
• Draw each bar with a width proportional to its biomass value.
• Stack the bars with trophic level 1 at the bottom and higher levels above.
• Label each trophic level with the organism type and biomass value, including units.
• Use a ruler and pencil to produce neat, accurate, proportional bars.

Common mistakes and how to put them right

• Drawing bars of equal width regardless of the biomass values.

  Put it right: Each width must be proportional to the data.

• Forgetting to include units such as g/m² when labelling biomass values.

• Placing trophic level 1 at the top.

  Put it right: The producers must be at the bottom.

Exam tips

• Show your scale clearly, for example 1 cm represents 10 g/m², so the examiner can check proportionality.
• Use a ruler for every bar and keep the bars horizontal and evenly spaced.
• Label each level with both the organism and the biomass value to make the pyramid fully accurate.