Trace Energy in a Food Web

Understand the idea

Producers use an energy source, usually sunlight, to make food. Consumers obtain energy by eating other organisms. Decomposers help break down dead matter and return nutrients to the environment. In a food web, arrows conventionally point from the food to the organism receiving its energy. Energy flows through ecosystems, while matter is recycled. Changes can have several effects, so predictions should acknowledge other factors.

Worked example

Build two paths: grass → rabbit → fox, and grass → grasshopper → bird → fox. The arrows show energy transfer from what is eaten to the eater. If grass becomes scarce, both rabbits and grasshoppers may have less food. Foxes could then face changes in prey availability. This is a prediction, not a certainty: alternative foods and other conditions also matter.

Try it yourself

1. What does the arrow from rabbit to fox mean?
2. Add a second consumer of grass to the web.
3. Explain one possible effect of fewer grasshoppers on birds, including a limitation.

Check your reasoning

1. Energy in the rabbit is transferred to the fox when the fox eats it.
2. An appropriate herbivore, such as a deer, with an arrow from grass to that animal.
3. Birds that rely on grasshoppers may have less food; the effect also depends on other prey and environmental conditions.

Make it work for your learner

For support, model the example one step at a time and ask the learner to explain each choice in their own words. Use a sketch, organizer or physical model where helpful. For a challenge, create a new example, test an alternative explanation or describe when the model would not apply.

Exit check

Use arrows to explain energy transfer and predict possible effects in a food web. Explain your reasoning with a specific example before moving on.