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Scientists investigated the effect of a heat treatment on mass transport in barley plants - AQA - A-Level Biology - Question 8 - 2018 - Paper 1
Question 8
Scientists investigated the effect of a heat treatment on mass transport in barley plants. They applied steam to the short section of a leaf of the heat-treated pla... show full transcript
Worked Solution & Example Answer:Scientists investigated the effect of a heat treatment on mass transport in barley plants - AQA - A-Level Biology - Question 8 - 2018 - Paper 1
Step 1
Explain how the results in Figure 9 support this conclusion.
Answer
The results in Figure 9 indicate that the distribution of radioactively labelled carbon is significantly higher in the heat-treated plant compared to the control. This suggests that the heat treatment has damaged the ability of the phloem to transport substances effectively in the heat-treated plant, as the movement of carbon compounds is not uniform across the plant. The areas where carbon is allocated in the heat-treated plant indicate disrupted transport pathways, supporting the conclusion that the phloem is damaged.
Step 2
Explain how the results in Table 4 support this conclusion.
Answer
Table 4 shows that the water content in the heat-treated plant (84.6%) is significantly lower than that of the control plant (92.8%). This difference implies that the xylem, responsible for water transport, remains functional despite the heat treatment. If the xylem was damaged, we would expect the water content to be similarly low in both plants, thus supporting the conclusion that the xylem is unaffected.
Step 3
What can you conclude about the movement of Fe²⁺ in barley plants? Use all the information provided.
Answer
The results in Figure 10 indicate that heat treatment has a more pronounced effect on the young leaves compared to the old leaves. The higher ratio of Fe²⁺ concentration in the top half of the leaves of the untreated young leaf suggests that Fe²⁺ is moving up effectively through the plant. However, in the treated young leaves, this ratio is significantly lower, indicating hindered movement due to possible damage to the xylem. Therefore, it can be concluded that heat treatment negatively affects the transport of nutrients like Fe²⁺ in young leaves, likely due to damage to the xylem while still allowing some transport in old leaves.