Year 7 Science · Unit 1 · Lesson 12
Challenge Worksheet
Learning Goals
Design a mini-experiment
A scientist wants to test: "If the primary producer in a food web is removed, which trophic level is affected first and most severely?" Plan the investigation below.
| What I will change (independent variable) | |
| What I will keep the same (controlled variables — list at least 3) | |
| What I will measure (dependent variable) | |
| My prediction — which trophic level will be affected first and why? | |
| How would I know if my prediction is wrong? (falsification condition) | |
| One limitation of this experiment (why it might not reflect a real ecosystem) |
1. Consider the food web: Grass → Grasshopper → Frog → Snake → Wedge-tailed eagle.
(a) Predict what would happen to the populations of each other organism in this web if all frogs were suddenly removed. Work through each trophic level in order.
(b) Now predict what would happen if all wedge-tailed eagles (the apex predator) were removed instead.
(c) Compare the two scenarios: which removal do you think would cause more severe disruption to the whole food web, and why?
2. In 2019–2020 the Black Summer bushfires burned approximately 18.6 million hectares of eastern Australian bushland, destroying vast areas of vegetation (primary producers).
Using your knowledge of trophic levels and food webs, evaluate whether the loss of producers or the loss of apex predators (such as wedge-tailed eagles displaced by the fires) would have had a greater long-term impact on the recovery of the ecosystem. Justify your answer with reference to at least two trophic levels.
Wrap Up
In one sentence, what was the main idea of this lesson?