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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The Casparian strip ensures that only selective substances may pass through the:
1. root hairs.
2. root cortex.
3. ground tissue.
4. endodermis.
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Advantages of transpiration to the plants include:
I. evaporative cooling.
II. mineral transport.
III. increased turgor.
1. I and II only
2. I and III only
3. II and III only
4. I, II and III
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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 happens to the tensile strength of fluid column with a decrease in the diameter of a tracheid?
1. It increases.
2. It decreases.
3. It approaches zero.
4. It approaches infinity.
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Substances travelling via the symplast move from cell-to-cell through:
1. membrane proteins.
2. phospholipid channels.
3. tonoplast.
4. plasmodesmata.
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Advantages of tracheids over vessels for long-distance transport to great heights include:
I. Adhesive forces are proportionally greater in narrower cylinders than in wider cylinders.
II. The smaller the diameter of the xylem, the more likely cavitation will occur.
III. Cohesive forces are greater in narrow tubes than in wide tubes of the same height.
1. Only I and II
2. Only I and III
3. Only II and III
4. I, II and III
The flow of water through the xylem is regulated by:
1. passive transport of mineral ions by the root endodermis.
2.the number of nuclei in the companion cells in the phloem.
3. the evaporation of water from the leaves.
4. active transport by tracheid and vessel elements.
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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. |
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.