Year 8 Science · Unit 2 · Lesson 21
Challenge Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. Asbestos is still fire-resistant and strong today; what changed was the evidence about its effect on health.
Correct it:
2. Aluminium became cheap because a huge new deposit of aluminium ore was found.
Correct it:
3. Because mesothelioma often appears 20 to 40 years after exposure, the harm from asbestos was easy to argue about while it was happening.
Correct it:
4. The same discovery can lead to helpful and harmful uses: nuclear science gave both medical imaging and weapons.
Correct it:
1. Name two discoveries from the lesson that changed how people live, and give the application area (medicine, electronics or materials) of each.
Scenario: a new wonder fibre
FibreX is a new, cheap insulation fibre that, like asbestos, does not burn. After a 5-year study the company announces: “FibreX is safe. Workers who handle it show no extra lung disease.” Scientists keep following 500 workers who handle it and 500 of similar age who do not (Table 1).
| Years since the study began | Workers who handle FibreX | Workers who never handle FibreX |
|---|---|---|
| 5 | 2 | 2 |
| 10 | 3 | 3 |
| 20 | 9 | 4 |
| 30 | 25 | 5 |
Source: FibreX and all data are invented for this exercise.
2. At 30 years, calculate the percentage of each group with lung disease. How many times as likely are the FibreX workers to have lung disease?
FibreX workers are times as likely
3. Use Table 1 and what you know about asbestos to evaluate the company’s 5-year announcement. Then say how long a study like this should run before a fibre is called safe, and why.
4. Evaluate this claim: “Science always makes substances safer and better. Every discovery is an improvement.” Use at least two real examples from the lesson, and end with a judgement.
True or false
1. True. 2. False: aluminium became cheap because the Hall-Héroult process (1886) made extraction from ore cheap; aluminium was already the most abundant metal in Earth’s crust. 3. True. 4. True.
1. Any two, for example: penicillin (medicine); medical imaging from nuclear science (medicine); silicon semiconductors and computer chips, or the transistor (electronics); lithium-ion batteries (electronics); the Hall-Héroult process for cheap aluminium (materials). [2 marks: 1 per discovery with its correct area]
Your Turn
2. FibreX: 25 ÷ 500 × 100 = 5%. Never handle: 5 ÷ 500 × 100 = 1%. 5% ÷ 1% = 5 times as likely. [3 marks: 1 each percentage, 1 ratio]
Go Deeper
3. The announcement matches the 5-year data (2 and 2), but it is not justified: the difference only appears after 20 years (9 vs 4) and is large by 30 years (25 vs 5). Like mesothelioma from asbestos, lung disease from fibres can take decades to appear, so 5 years is far too short to call the fibre safe. A fair study should follow matched groups for at least 30 to 40 years, because fibre diseases such as mesothelioma can take 20 to 40 years to appear. [4 marks: 1 early data equal, 1 later difference, 1 delay link to asbestos, 1 study length with reason]
Show What You Know
4. Marking guide (points expected): 1 supporting example: the Hall-Héroult process made aluminium cheap for cans, foil and aircraft, or penicillin made deadly infections treatable; 1 how understanding led to that improvement; 1 counter-example: asbestos had excellent properties, but evidence (asbestosis, lung cancer, mesothelioma) showed its fibres cause disease, and Australia banned it in 2003; 1 a second counter-point: nuclear science gave both medical imaging and weapons, or harms can take decades to show; 1 the chain runs both ways: discoveries can make a substance available or take one away; 1 judgement avoiding “always”: science tends to improve how we use substances, partly by revealing harms, but not every discovery is an improvement. [6 marks]
Common error to watch for: treating the asbestos ban as science “failing”. It was scientific evidence that revealed the harm; the point is that discoveries do not only ever make things better.