Pyramids of Numbers & Biomass (WJEC GCSE Biology: Combined Science)

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

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

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