- 1(current)
Q. No.Identify the correct statements regarding bulk flow in plants:
I. Driven primarily by pressure potential.
II. More effective than diffusion over greater distances.
III. Depends on the difference in pressure potential at the source and sink.
IV. Depends on the force of gravity on a column of water.
V. May be due to either positive or negative pressure potential.
1. I, II and III only
2. II, III and V only
3. II, III, IV and V only
4. I, II, III and V only.
Assertion: The concentration of free sugar in the sink is always lower than in the sieve tube.
Reason: The unloaded sugar is consumed during growth or metabolism or converted to insoluble polymers such as starch.
1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.
- If both the assertion and the reason are true and the reason is a correct explanation of the assertion
- If both the assertion and reason are true but the reason is not a correct explanation of the assertion
- If the assertion is true but the reason is false
- If both the assertion and reason are false
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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 Withdrawn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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I. Sugars are loaded into the sieve tubes of the phloem at the sugar source (leaf). The osmotic pressure of the sieve tubes is decreased; water is taken up from the surrounding tissue, which results in an increase in turgor pressure at the source.
II. Unloading of sugars from the sieve tubes at the sinks (stem and roots) increases the sieve tube osmotic pressure, water escapes to surrounding tissue, and turgor pressure is reduced.
III. The turgor pressure gradient between the source and the sink is the driving force for phloem transport.
IV. Phloem function is linked to xylem transport as water circulates between the two tissues. Phloem takes up water from the xylem along the whole transport pathway unless sugar unloading is locally very large. The transpiration stream in the leaves can also pass apoplastically along the cell walls without crossing the membrane of cells.
1. I, II and III only
2. I, II and IV only
3. I, III and IV only
4. I, II, III and IV
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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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