Purpose
Build a physical model of energy loss between trophic levels, and use it to explain why food chains are short.
Materials
- 1 000 dried beans (or beads) per group
- Four containers labelled Producers, Primary, Secondary, Tertiary
Procedure
- Put all 1 000 beans in Producers. Each bean is 10 kJ of stored energy.
- Move 10% of them to Primary. Set the rest aside — that is energy lost as heat, movement, and uneaten material.
- Repeat for Secondary, then Tertiary.
- Record what remains at each level.
Data
| Level | Beans | Energy (kJ) | Percent of original |
|---|---|---|---|
| Producers | 1000 | 10 000 | 100% |
| Primary consumers | |||
| Secondary consumers | |||
| Tertiary consumers |
Analysis
- How many beans would a fifth level receive? What does that predict about ecosystems?
- A farm can grow food for people, or grow feed for cattle that people then eat. Using your model, explain which feeds more people from the same land.
- Real ecosystems transfer between 5% and 20%, not exactly 10%. Redo the last row at 5% and at 20%. How much does the answer change?
The one to think hardest about
Nothing was destroyed in this model — energy is conserved. So where did the beans you set aside actually go, in a real ecosystem?
Hand in
- Completed table
- A labelled pyramid diagram drawn to scale
- Analysis answers
Curriculum connection
B2.2
explain how naturally occurring phenomena, including the cycling of matter and the flow of energy, contribute to the dynamic equilibrium within and between ecosystems
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A1.3
apply an engineering design process and associated skills to design, build, and test devices, models, structures, and/or systems
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