Describe the transport of carbohydrate in plants.
- AQA - A-Level Biology - Question 9 - 2022 - Paper 1
Question 9
Describe the transport of carbohydrate in plants.
Worked Solution & Example Answer:Describe the transport of carbohydrate in plants.
- AQA - A-Level Biology - Question 9 - 2022 - Paper 1
Step 1
Describe the active transport of sucrose
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Answer
Sucrose is actively transported into the phloem cells from the source tissues such as leaves. This process requires energy, typically in the form of ATP, as it moves against the concentration gradient.
Step 2
Explain the role of companion cells
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Answer
Companion cells play a vital role in the transport of sucrose by assisting the phloem cells. They are involved in loading the sucrose into the phloem and facilitating the movement of substances between the sieve tubes and the adjacent cells.
Step 3
Discuss the water potential and its effect
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Answer
The influx of sucrose lowers the water potential in the phloem. This causes water to enter from the xylem by osmosis, generating hydrostatic pressure that drives the flow of sap through the phloem.
Step 4
Identify the pressure flow mechanism
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The pressure flow mechanism suggests that the movement of carbohydrates is driven by differences in pressure between the source (high pressure) and the sink (low pressure) regions.
Step 5
State the final transport pathway
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Answer
Finally, the carbohydrates are transported to various sink tissues such as roots, fruits, or storage organs via the phloem channels.
