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Loading of phloem is related
Loading of phloem is related
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Solution
The correct option is A Increase of sugar in phloem
In contrast to xylem transport, the mass flow mode of phloem transport requires that the plasma membrane remain intact. At the source end of the phloem, sugars are moved into the phloem sieve elements. This increase in solute decreases the water potential of the cell and causes water to flow in from surrounding areas by osmosis. The increase in the volume of water in the cell causes an increase in pressure which forces the sugar or water or amino acid solution to move toward the sink tissue.
At the sink tissue, the sugars are off-loaded which increases the water potential and causes water to flow out of the phloem by osmosis. The sieve elements must remain at least partially alive and keep a functioning plasma membrane in order to help control the flow of sugars into and out of the sieve element.
Two distinct methods can be employed by plants to move sugars into the phloem. Symplastic loading involves the movement of sugars through the plasmodesmata from one cell to another. Apoplastic loading involves the movement of sugars from the apoplast (the extracellular cell wall space) across the plasma membrane and into the cell. This movement of sugar against a concentration gradient is accomplished by sugar transporters in the plasma membrane such as SUC2.
So, loading of phloem is related to increase of sugar in phloem and not elongation of phloem cell, separation of phloem parenchyma or strengthening of phloem fiber.
Thus, the correct answer is option A.
In contrast to xylem transport, the mass flow mode of phloem transport requires that the plasma membrane remain intact. At the source end of the phloem, sugars are moved into the phloem sieve elements. This increase in solute decreases the water potential of the cell and causes water to flow in from surrounding areas by osmosis. The increase in the volume of water in the cell causes an increase in pressure which forces the sugar or water or amino acid solution to move toward the sink tissue.
At the sink tissue, the sugars are off-loaded which increases the water potential and causes water to flow out of the phloem by osmosis. The sieve elements must remain at least partially alive and keep a functioning plasma membrane in order to help control the flow of sugars into and out of the sieve element.
Two distinct methods can be employed by plants to move sugars into the phloem. Symplastic loading involves the movement of sugars through the plasmodesmata from one cell to another. Apoplastic loading involves the movement of sugars from the apoplast (the extracellular cell wall space) across the plasma membrane and into the cell. This movement of sugar against a concentration gradient is accomplished by sugar transporters in the plasma membrane such as SUC2.
So, loading of phloem is related to increase of sugar in phloem and not elongation of phloem cell, separation of phloem parenchyma or strengthening of phloem fiber.
Thus, the correct answer is option A.
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