Measuring biomass
Biomass shows how much energy is stored at a trophic level.
- Measured as dry mass to remove water
- Water does not contain usable energy
- Units are usually g m⁻²
Always mention dry mass in exams when describing biomass.
Ecological pyramids
Ecological pyramids always place producers at the base.
They help visualise how energy and matter decrease as you move up a food chain.
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Pyramid of numbers
A pyramid of numbers counts individuals, not energy.
- Often pyramid-shaped
- Can be inverted (e.g. insects feeding on one tree)
- Does not show energy transfer
Pyramid of biomass
A pyramid of biomass represents stored energy more accurately than numbers.
- Measured in g m⁻²
- Usually pyramid-shaped on land
- Can be inverted in aquatic ecosystems
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Pyramid of energy
A pyramid of energy is the most accurate pyramid.
- Always pyramid-shaped
- Measured in kJ m⁻² yr⁻¹
- Shows real energy losses
Pyramids of energy can never be inverted.