SL and HL Subtopic 2.2: Energy and biomass in ecosystems. Construct an ecological pyramid by arranging organisms into trophic levels and drawing horizontal bars whose widths are proportional to numbers, biomass, or energy. Interpret its shape by explaining why values usually decrease along the food chain.
Construction Method
- Place producers at the base, followed by primary, secondary, and higher consumers.
- Obtain the value for each level; combine species occupying the same trophic level.
- Use a consistent scale and centred bars proportional to values.
- Label trophic levels, values, and units, and state the pyramid type.
| Pyramid | What bar width represents | Interpretation |
|---|---|---|
| Numbers | Number of organisms, often per unit area | May be upright or inverted. One oak tree can support thousands of insects. |
| Biomass | Dry mass of living material per unit area, such as |
