Year 8 Science · Unit 4 · Lesson 19
Challenge Worksheet
Learning Goals
From model to theory, in order
These are the stages by which the ulcer model became accepted. Number them 1 to 5.
| Order (1-5) | Stage |
|---|---|
| Other laboratories repeated the work and patients were cured with antibiotics. | |
| Warren observed curved bacteria in samples of inflamed stomach lining. | |
| Marshall drank a culture of the bacteria and became ill with gastritis. | |
| The explanation was accepted worldwide and the two shared a Nobel Prize. | |
| Warren and Marshall proposed that the bacterium inflames the lining and causes ulcers. |
1. Outline how the ulcer model became a workable theory. Refer to the first observation, the proposed mechanism, the test that could have failed, and what other scientists did.
2. Before Warren and Marshall's work, the accepted explanation for ulcers was stress and excess acid. Explain why it was reasonable for other doctors to be unconvinced at first, and what changed their minds.
3. The particle model began as a way to explain why gases can be squashed. Explain what had to happen for it to count as a theory rather than a one-off model.
4. A newspaper headline reads: 'Evolution is only a theory.' Using the scientific meaning of the word, explain what is wrong with the way 'only' is used here.
5. Design a test case for this model: 'The school hall is colder than the classrooms because it has a concrete floor and no carpet.' State the prediction, and state the result that would disprove the mechanism.
Wrap Up
In two sentences, explain why a theory staying open to new evidence is a strength rather than a weakness.