Year 8 Science · Unit 1 · Lesson 23
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. A species can face several threats at once; the koala faces land clearing, disease, car strikes and dog attacks.
Correct it:
2. Keeping pet cats indoors at night helps protect native wildlife.
Correct it:
3. Once a species is endangered, nothing can stop it becoming extinct.
Correct it:
4. When roads and farms break habitat into pieces, animal populations can become isolated from each other.
Correct it:
Find the errors
This report contains exactly four errors. Underline each one and write the corrections below.
A student’s species report
The numbat is a small marsupial that feeds mainly on gum leaves. It was once widespread, but it survived only in small parts of Western Australia. Its main predators, foxes and cats, have lived alongside numbats in Australia for millions of years, so numbats have had plenty of time to adapt to them. The numbat is endangered, which means it no longer survives anywhere in the wild. The best long-term plan is to move every numbat into zoos, because animals in zoos can be kept safe forever and released whenever needed.
1. Write the four corrections.
Judge the claims
2. For each claim, write whether it is supported, partly supported or not supported, and give one piece of evidence from the lesson. (a) “Introduced species are the only threat to Australian animals.” (b) “One disaster can worsen the threats a species already faces.” (c) “Losing one species cannot harm an ecosystem.”
Gliders after a fire
Scenario: greater gliders
Greater gliders are gliding marsupials that shelter by day in hollows inside large, old trees. A hollow takes many decades to form. After a bushfire, a survey team counted greater gliders at four forest sites and compared them with counts from the year before the fire.
| Site | Hollow-bearing trees lost in the fire (%) | Gliders before | Gliders after |
|---|---|---|---|
| A | 20 | 40 | 34 |
| B | 55 | 36 | 18 |
| C | 5 | 50 | 45 |
| D | 90 | 30 | 6 |
Source: sample survey counts.
3. Calculate the percentage decrease in gliders at Site B and at Site D.
Site B % Site D %
4. A report concludes: “The flames killed the gliders, so fire is the only threat that matters for this species.” Describe the pattern in Table 1, then give two reasons why this conclusion goes too far.
5. A council has money for ONE project to help its greater gliders. Project 1: a zoo breeding centre that could raise 50 gliders a year. Project 2: buying and protecting old forest next to a national park, with community planting days to link patches of bush. Evaluate which project would do more long-term good for the gliders.
True or false
1. True. 2. True. 3. False: an endangered species is still alive, so reducing threats can help it recover (as for the numbat). 4. True.
Find the errors
1. (i) Numbats eat termites, not gum leaves. (ii) Foxes and cats are introduced: they arrived with European settlers, so numbats had no defences. (iii) Endangered means the species is still alive but at serious risk. (iv) Zoos help, but released animals need safe habitat; habitat protection is the best long-term strategy. [4 marks: 1 per correction]
Judge the claims
2. (a) Partly: introduced species such as foxes and cats are a major threat, but habitat loss and climate change are also major threats. (b) Supported: the 2019–20 bushfires pushed some koala populations, already hit by land clearing and disease, close to local extinction. (c) Not supported: species are linked in food webs, and biodiversity makes ecosystems more stable and able to recover. [3 marks: 1 per verdict with evidence]
Gliders after a fire
3. Site B: 36 − 18 = 18; 18 ÷ 36 × 100 = 50%. Site D: 30 − 6 = 24; 24 ÷ 30 × 100 = 80%. [3 marks: 1 working, 1 per percentage]
4. Pattern: the more hollow-bearing trees lost, the bigger the fall in gliders (Site C 10%, A 15%, B 50%, D 80%). Any two: the data point to habitat loss (hollows), not only flames; only four sites and one fire; other threats such as land clearing or extreme heat were not measured. [3 marks: 1 pattern, 1 per reason]
Show What You Know
5. Marking guide (points expected): 1 Project 1 strength: more gliders and an insurance population; 1 Project 1 limit: released gliders need hollow trees, so without safe habitat they cannot survive; 1 Project 2 strength: protects old hollow trees, food and shelter now, and linked patches stop populations becoming isolated; 1 Project 2 limit: planted trees take decades to form hollows; 1 Table 1: gliders fell most where hollow trees were lost; 1 justified choice (usually Project 2: habitat protection is the most effective long-term strategy; accept Project 1 only if it says where gliders could be released safely). [6 marks]
Common error to watch for: in Q3, dividing the drop by the count after the fire instead of the count before it.