- 1(current)
Q. No.When a plant undergoes senescence, the nutrients may be
1. Exported
2. Withdrawn
3. Translocated
4. None of the above
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Phloem transport differs from xylem transport as:
| 1. | Xylem transport requires active pumping at stomata, transport in phloem is passive. |
| 2. | Phloem movement is solar powered, xylem movement occurs best in dark. |
| 3. | Phloem carries fluid from the soil to the leaves, while xylem is the reverse. |
| 4. | Phloem can reverse direction, depending on the activity of the "source" and "sink" of its materials but the flow in xylem is essentially unidirectional. |
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What causes the water to flow into the sieve tube at the source?
1. Diffusion of sucrose into the sieve tube, making it hypertonic.
2. Active transport of sucrose into the sieve tube, making it hypertonic.
3. Active pumping of water by the adjacent companion cell.
4. A lower water potential outside the sieve tube.
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In classic experiments on the translocation of organic solutes performed by the Italian anatomist Marcello Malpighi in 1686, the bark of a tree was removed in a ring around the trunk. This experiment, called girdling, was also done by T. G. Mason and E. J. Maskell in 1928. The following were the observations:
I. It has no immediate effect on transpiration.
II. Sugars accumulate above the girdle—that is, on the side toward the leaves—and are depleted below the treated region.
What conclusion/s can be drawn from the above observations?
A: Water moves in the xylem, interior to the bark.
B: Sugar is transported in the bark of the tree and that the sieve elements are the cellular channels of sugar transport.
| 1. Only A | 2. Only B |
| 3. Both A and B | 4. Neither A nor B |
- 1(current)
Q. No.
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