Q. No.Identify the incorrect statement regarding aquaporins:
1. Water channels are transmembrane proteins made up of eight different types of aquaporins.
2. Water moves most rapidly in tissues that have aquaporin water channels.
3. The presence of water channels increases membrane permeability to water.
4. Aquaporins selectively conduct water molecules in and out of the cell but allow some passage of protons.
1. Water channels are transmembrane proteins made up of eight different types of aquaporins.
2. Water moves most rapidly in tissues that have aquaporin water channels.
3. The presence of water channels increases membrane permeability to water.
4. Aquaporins selectively conduct water molecules in and out of the cell but allow some passage of protons.
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What is incorrect regarding apoplast transport in plants?
1. The apoplast is formed by the continuum of cell walls of adjacent cells as well as the extracellular spaces.
2. Transport velocity is lower in the apoplast than in the symplast.
3. Apoplast transport also accounts for a higher proportion of water transport in plant tissues than does symplastic transport.
4. The apoplastic pathway is also involved in passive exclusion.
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Root pressure is caused by:
1. active distribution of mineral nutrient ions into the root xylem.
2. passive distribution of mineral nutrient ions into the root xylem.
3. a lower water potential in soil than the root cells.
4. transpirational pull.
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Mass flow of liquid water from roots to the leaves is primarily driven by:
1. Root pressure
2. Capillary action
3. Water potential differences
4. Active transport
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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 |
Trace the correct path of water from the soil through the plant to the atmosphere:
| 1. | endodermis- cortex - epidermis - vessel elements - intercellular spaces in mesophyll - stomata. |
| 2. | epidermis - cortex - Casparian strip - endodermis - sieve cells - intercellular spaces in the mesophyll - stomata. |
| 3. | Casparian strip - root hairs - epidermis - cortex - xylem - endodermis - intercellular spaces in mesophyll - stomata. |
| 4. | root hairs - cortex - endodermis - vessel elements - intercellular spaces in mesophyll - stomata. |
The apoplast pathway in plants includes all the following except:
1. the lumen of a xylem vessel
2. the lumen of a sieve tube
3. the lumen of tracheids
4. the cell wall of a root hair
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The Casparian strip in plant roots:
1. is located in the walls of the outermost portion of the cortex.
2. is composed predominantly of lignin and hence is impermeable to water.
3. ensures active uptake of all minerals by the roots.
4. ensures that all water and dissolved substances must pass through a cell membrane before entering the vascular cylinder.
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Translocation in xylem will not be facilitated by:
1. The cohesion of water molecules.
2. A negative water potential.
3. The root parenchyma.
4. The active transport of solutes.
It is a common observation that pine seedlings grown in sterile potting soil grow much slower than seedlings grown in soil from the area where the seeds were collected. The most probable cause for this would be:
| 1. | damage to root hairs during the sterilization process. |
| 2. | the absence of mycorrhizae in the sterilized soil. |
| 3. | lack of essential minerals in a sterilized soil. |
| 4. | non functioning of protein pumps in the sterilized soil. |
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