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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 show that there is a significant presence of radioactively-labelled carbon in the heat-treated plant after 4 hours. This indicates that mass flow of substances in the phloem, which is responsible for transporting photosynthates, is compromised due to the heat treatment, as seen in the absence or lesser degree of radioactivity in control plants. Therefore, this concludes that the heat treatment has damaged the phloem.
Step 2
Explain how the results in Table 4 support this conclusion.
Answer
The results in Table 4 show that the heat-treated plant has a significantly lower water content (8.4%) compared to the control plant (92.8%). This suggests that the xylem, responsible for water transport, is unaffected, as water content in the control remains high. Thus, the heat treatment seems to have primarily affected the phloem and did not impair the xylem functionality.
Step 3
What can you conclude about the movement of Fe²⁺ in barley plants?
Answer
The data from Figure 10 indicates that the heat-treated young leaves show a higher concentration of Fe²⁺ in the top half versus the lower half, suggesting active transport is occurring, where Fe²⁺ moves upwards in the plant. Conversely, for old leaves, the concentration is more uniform, indicating reduced movement of Fe²⁺, possibly due to damage in the xylem. Overall, the movement of Fe²⁺ is more efficient in the younger leaves, suggesting they are less affected by the heat treatment.