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May 2025 Section II

0/34 marks

2025 · 6 questions · 32 parts · 34 marks

0Correct0Partial0Wrong32Unattempted
1(A)1(B)(i)1(B)(ii)1(B)(iii)1(C)(i)1(C)(ii)1(C)(iii)1(D)(i)1(D)(ii)2(A)2(B)(i)2(B)(ii)2(C)(i)2(C)(ii)2(D)(i)2(D)(ii)3(A)3(B)3(C)3(D)4(A)4(B)4(C)4(D)5(A)5(B)5(C)5(D)6(A)6(B)6(C)6(D)
Context for question 3
Buffelgrass, an invasive grass species in southwestern desert ecosystems, is threatening the saguaro cactus, a keystone species in these ecosystems. Buffelgrass is drought-tolerant and can survive wildfires. However, the dry buffelgrass also acts as fuel for wildfires, causing the fires to be more severe. Older saguaro cacti can survive wildfires; however, many of the young cacti cannot. Scientists conducted an experiment to determine whether they could control the abundance of the buffelgrass population. The scientists identified several native grass species that, when grown with buffelgrass, might reduce the abundance of buffelgrass. They grew buffelgrass in the presence of several different native grass species in greenhouses, in either nondrought (watered every 3 days) or drought (watered every 9 days) conditions. After twelve weeks, they measured the height and dry weight of the buffelgrass in each treatment group.
3(A)Ecosystems, Populations and SuccessionEasy1 mark
Describe the effect that removing a keystone species will have on an ecosystem.
3(B)Ecosystems, Populations and SuccessionEasy1 mark
Identify a control group the scientists should include in their experiment.
3(C)Ecosystems, Populations and SuccessionEasy1 mark
State the null hypothesis of the experiment in which buffelgrass is grown in the presence of native grass species.
3(D)Ecosystems, Populations and SuccessionMedium1 mark
Scientists have found that the population growth rates of native grasses are much slower than the population growth rate of buffelgrass following a wildfire. The scientists claim that wildfires will therefore increase the abundance of buffelgrass plants in the ecosystem. Based on the information given, justify the scientists’ claim.
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