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Scientists investigated the process of succession on sand dunes - AQA - A-Level Biology - Question 4 - 2018 - Paper 1
Question 4
Scientists investigated the process of succession on sand dunes. They measured the percentage cover of different species of plants on sand dunes of different ages. S... show full transcript
Worked Solution & Example Answer:Scientists investigated the process of succession on sand dunes - AQA - A-Level Biology - Question 4 - 2018 - Paper 1
Step 1
1. Describe how you would determine the mean percentage cover for beach grass on a sand dune.
Answer
To determine the mean percentage cover for beach grass on a sand dune, I would employ the following steps:
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Random Sampling: Select random quadrats on the sand dune using a method such as random number generation or a table of random numbers. This ensures a diverse representation of the area.
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Quadrat Size: Use multiple quadrats of equal size to accurately estimate the percentage cover. A standard practice often involves using a square meter as the size of each quadrat.
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Percentage Calculation: After recording the percentage cover of beach grass in each quadrat, I would calculate the mean by summing all the percentage values and dividing by the number of quadrats sampled.
Step 2
2. The scientists concluded that the results shown in Figure 5 were due to succession taking place. Use Figure 5 to explain why the scientists reached this conclusion.
Answer
The scientists concluded that succession was taking place based on the observed changes in the percentage cover of different plant species as the age of the sand dune increased.
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Pioneer Species Dynamics: Beach grass, identified as a pioneering species, shows a high percentage cover at younger ages, indicating its role in the initial stabilization of the sand dune. As time progresses, its percentage cover decreases.
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Replacement by Other Species: The increase in shrub-bunchgrass and conifer trees as the dune ages indicates that these species are replacing beach grass, suggesting a shift in the ecosystem. This is a hallmark of ecological succession where one community is replaced by another.
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Climax Community Formation: The gradual increase in hardwood trees in the later stages suggests the arrival of a climax community, which supports the idea of succession.
These changes confirm that as sand dunes mature, the species composition and vegetation structure evolve, supporting the conclusion of succession.
Step 3
3. Use Figure 5 to explain the results in Figure 6.
Answer
Figure 5 shows the mean percentage cover of different plant species over time. However, specific information regarding Figure 6 is needed for this answer. Assuming Figure 6 depicts further changes or results related to NPP in older dunes, it could indicate the carryover effects of the dominance of certain species observed in Figure 5.
Step 4
4. Using evidence from Figure 6, what can you conclude about the net primary productivity (NPP) in the sand dunes that are older than 1000 years? Explain your answer.
Answer
From Figure 6, we can conclude that in sand dunes older than 1000 years, the net primary productivity (NPP) remains relatively constant. This conclusion is supported by:
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Species Composition Stability: As older dunes reach a stable climax community, the ratio of photosynthesis to respiration stabilizes, causing NPP to remain constant over time.
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Environmental Conditions: Stability in the biotic and abiotic conditions over time suggests a balance in plant growth and energy production.