Year 8 Science · Unit 1 · Lesson 17
Challenge Worksheet
Learning Goals
Case study: banksias dying beside a bush track
Rangers noticed that banksias in one bushland reserve were turning yellow, wilting and dying, even after heavy rain. They suspected Phytophthora cinnamomi, a microscopic water mould that lives in soil. It infects the roots of many Australian native plants, including banksias, and makes them rot. It spreads when infected soil or water moves, for example in mud on boots, bike tyres and cars.
The rangers marked out five plots in the reserve, each with 40 banksias. They tested the soil in each plot and counted the living and dead banksias. All five plots had the same rainfall.
| Plot | Distance from track (m) | Phytophthora in soil? | Alive | Dead | Dead (%) |
|---|---|---|---|---|---|
| A | 2 | yes | 12 | 28 | |
| B | 10 | yes | 24 | 16 | |
| C | 50 | no | 37 | 3 | |
| D | 150 (beside a creek) | yes | 18 | 22 | |
| E | 200 | no | 38 | 2 |
Source: a made-up plot survey for this case study.
1. The rangers’ description above is a case study, and Table 1 is a table of results. State what each of these types of evidence is best at showing.
2. Complete the last column of Table 1. Then calculate the average percentage of dead banksias for the plots with Phytophthora and for the plots without it.
Answer % (with; without)
Find the errors
Jess’s answer to “Why are the banksias dying?”
Claim: Walking tracks kill banksias.
Evidence: Plot A had 28 banksias.
Reasoning: Roots make the plant’s food, so when the roots rot the plant starves.
Conclusion: This proves that Phytophthora will kill every plant in Australia.
3. Each part of Jess’s answer has one error. Complete the table.
| Part | What is wrong | A better version |
|---|---|---|
| Claim | ||
| Evidence | ||
| Reasoning | ||
| Conclusion |
Evaluate the claim
4. A visitor says: “The banksias are dying because people trample the ground near the track. The water mould has nothing to do with it.” Use two plots from Table 1 to test this claim, and state how far the data support it.
5. Infected banksias wilt and die even after heavy rain. Write an evidence-based explanation of why. Include a claim, evidence using your answers to Question 2, reasoning that follows the structure → role → function → effect frame, and one limit of this evidence.
Warm Up
1. Case study: one specific example of a disruption and its effects on the wider system. Table: values that can be compared to find patterns or trends. [2 marks]
Your Turn
2. Dead (%): A 28 ÷ 40 × 100 = 70%; B 40%; C 7.5%; D 55%; E 5%. With Phytophthora: (70 + 40 + 55) ÷ 3 = 55%. Without: (7.5 + 5) ÷ 2 = 6.25% (about 6%). [4 marks: 2 column (1 if one or two wrong), 1 each average]
3. Claim: blames the track, not the cause the data point to; better: “Banksias are dying where Phytophthora is in the soil.” Evidence: 28 is the number dead, not the total, and there is no comparison; better: “55% died in infected plots compared with about 6% in plots without it.” Reasoning: roots do not make food, leaves do; better: “Rotting roots cannot take in water and minerals, so the leaves wilt.” Conclusion: “proves” and “every plant in Australia” go far beyond one survey of banksias; better: “In this reserve, Phytophthora is linked to banksia deaths.” [4 marks: 1 per part, error and fix]
Evaluate the claim
4. Plot D is 150 m from the track, where there is little trampling, yet 55% died, and it has Phytophthora. Plot C is closer (50 m) but has no Phytophthora, and only 7.5% died. So deaths follow the water mould, not closeness to the track, and the claim is not supported. Trampling could still add to the damage in plot A, but the data cannot show that. [3 marks: 1 per plot used correctly, 1 judgement]
Show What You Know
5. Marking guide (points expected): 1 claim (Phytophthora rots the roots, which kills the banksias); 1 evidence (55% compared with about 6%, e.g. plot A 70%); 1 structure and role (roots take in water and minerals); 1 function (water is carried up the stem to the leaves); 1 effect (leaves wilt and cannot make food, so the plant dies; rain does not help because damaged roots cannot take the water in); 1 limit (one reserve, one survey, a link not proof, other causes possible, only banksias studied). [6 marks]
Common error to watch for: in Question 2, averaging all five plots together, or dividing by 5 for each group. Only three plots have Phytophthora and two do not.