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
Sucrose is actively transported into phloem cells
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Answer
The transport of carbohydrates, primarily in the form of sucrose, occurs through active transport mechanisms. Sucrose is actively loaded into the phloem by companion cells, which use ATP to move sucrose against its concentration gradient, facilitating a higher concentration within the phloem.
Step 2
Effect on water potential
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Answer
The loading of sucrose into the phloem lowers the water potential of the phloem cells. This results in water entering the phloem from the xylem via osmosis, increasing the turgor pressure within the phloem.
Step 3
Pressure flow hypothesis
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The increased turgor pressure creates a pressure gradient that drives the flow of the phloem sap toward areas of lower pressure, such as sinks (e.g., roots, buds, or non-photosynthetic tissues). This process is explained by the pressure flow hypothesis.
Step 4
Transport mechanisms
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Transport through the phloem is facilitated by the sieve elements that allow for rapid movement of the sap filled with carbohydrates. This transport is efficient and enables quick distribution to various parts of the plant.
Step 5
Unloading at sink tissues
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Answer
At sink tissues, sucrose is unloaded from the phloem. This can occur through passive or active transport methods, allowing for the carbohydrates to be utilized for energy, growth, or storage.
