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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
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, one would first establish a systematic method for sampling. This can be done by using randomly selected quadrats placed along the sand dune. The steps include:
- Selection of Quadrats: Randomly determine the position of quadrats using random numbers or a random number generator to avoid bias.
- Sampling Area: Use a sufficient number of quadrats to ensure accurate representation, typically at least 20 or more.
- Percentage Calculation: For each quadrat, estimate the percentage cover of beach grass and then compute the total percentage cover across all quadrats. Finally, divide this total by the number of quadrats sampled to reach the mean percentage cover.
Step 2
The scientists concluded that the results shown in Figure 5 were due to succession taking place.
Answer
The results shown in Figure 5 indicate a clear pattern of succession as the age of the sand dunes increases. Initially, beach grass, being a pioneer species, establishes itself, leading to increased percentage cover. Over time, as the dune ages (from 0 to around 150 years), the percentage cover of beach grass rises significantly. Following this, other plant species, such as conifer trees and hardwood trees, emerge and establish themselves, which corresponds with changes in the environment, such as improved soil quality and increased shade. This shift in plant diversity and the introduction of these later-stage species indicates a successful ecological succession process.
Step 3
Use Figure 5 to explain the results in Figure 6.
Answer
Figure 6 shows a comparison of the net primary productivity (NPP) associated with the sand dunes aging over time. Based on the data presented in Figure 5, it can be inferred that as the dunes age, the habitat becomes more complex and diverse, leading to increased productivity. The presence of larger plants such as hardwood trees typically results in higher NPP due to their large leaf surface area, meaning more sunlight can be captured for photosynthesis. This aligns with the trend seen in Figure 5, where increased age correlates with increased productivity.
Step 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?
Answer
From Figure 6, we can conclude that the net primary productivity (NPP) in sand dunes older than 1000 years remains relatively constant or may even show a slight decline. This could be attributed to the saturation of the ecosystem, where growth is balanced between photosynthesis and respiration. As the ecosystem stabilizes, the presence of mature trees may reduce light availability for younger plants below them, leading to a more stable but lower productivity rate. Additionally, nutrient cycling may also stabilize over time, contributing to this observation.