biology : class11 Polar auxin transport : Functions, Effects, Applications : Auxin MCQ Questions and Answers
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Polar auxin transport
MCQ questions and answers.
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MCQ Questions
1. Which feature most directly distinguishes polar auxin transport from simple diffusion through plant tissues?
A.
It occurs only when auxin concentration is higher in the source tissue
B.
It has a fixed direction determined by the cellular orientation of auxin-efflux carriers
C.
It takes place exclusively through the xylem under transpiration pull
D.
It requires auxin to remain permanently bound to cell-wall proteins
Correct Answer:
It has a fixed direction determined by the cellular orientation of auxin-efflux carriers
Explanation:
Polar auxin transport is directional because auxin-efflux proteins, especially PIN proteins, are positioned asymmetrically on specific sides of cells. This directionality is not explained by simple diffusion.
2. In a typical shoot organ, basipetal polar auxin transport is best described as movement of auxin from the:
A.
Root tip toward the root elongation zone
B.
Shoot apex toward the basal regions of the shoot
C.
Mature leaves toward the shoot apex only through the phloem
D.
Root cap toward the shoot apex through the xylem
Correct Answer:
Shoot apex toward the basal regions of the shoot
Explanation:
Basipetal transport in the shoot proceeds from the apical region toward the base. The direction results from the organized placement of auxin transport proteins in successive cells.
3. If PIN proteins in a file of shoot cells are relocated from the basal membrane to the apical membrane, what is the most immediate consequence for polar auxin transport in that file?
A.
The direction of cell-to-cell auxin transport will reverse
B.
Auxin will become unable to enter the first cell in the file
C.
Auxin transport will become completely independent of membrane proteins
D.
Auxin will be transported only through the apoplast in both directions
Correct Answer:
The direction of cell-to-cell auxin transport will reverse
Explanation:
PIN proteins act as directional auxin-efflux carriers. Changing their polar localization changes the side through which auxin exits each cell and can therefore reverse the direction of transport.
4. Which experimental result would provide the strongest evidence that a compound specifically inhibits polar auxin transport rather than merely reducing auxin synthesis?
A.
The compound lowers auxin concentration uniformly in all tissues
B.
The compound prevents movement of radiolabeled auxin between tissues while externally supplied auxin remains detectable at the source
C.
The compound increases the rate of auxin synthesis in shoot apices
D.
The compound increases the diffusion of auxin across isolated lipid membranes
Correct Answer:
The compound prevents movement of radiolabeled auxin between tissues while externally supplied auxin remains detectable at the source
Explanation:
A transport inhibitor should block directional movement while not necessarily removing auxin from the tissue where it was supplied. Measuring radiolabeled auxin movement directly distinguishes transport inhibition from reduced synthesis.
5. Why can polar auxin transport continue through a chain of living cells even when the overall auxin concentration gradient is unfavorable?
A.
Auxin is transported only through dead xylem vessels
B.
Each cell can use energy-dependent uptake and directional efflux to pass auxin to the next cell
C.
Auxin spontaneously polymerizes and moves through plasmodesmata
D.
The cell wall actively pumps auxin without participation of the plasma membrane
Correct Answer:
Each cell can use energy-dependent uptake and directional efflux to pass auxin to the next cell
Explanation:
Polar auxin transport is a cell-to-cell process involving auxin uptake and efflux systems. Directional efflux through asymmetrically localized carriers allows transport to be maintained even against simple diffusion expectations.
6. A localized auxin source is placed on one side of a stem segment. Which observation most strongly indicates that transport through the segment is polar?
A.
Auxin appears at equal rates on both sides of the segment
B.
Auxin moves efficiently only when the source is placed at one end of the segment, and movement is greatly reduced after the segment is inverted
C.
Auxin remains at the source regardless of the segment's orientation
D.
Auxin movement increases only when the tissue is completely nonliving
Correct Answer:
Auxin moves efficiently only when the source is placed at one end of the segment, and movement is greatly reduced after the segment is inverted
Explanation:
A polar transport system has a preferred direction. Inverting a tissue segment places its cellular transport machinery in the opposite orientation, reducing transport in the original direction.
7. Which statement correctly compares polar auxin transport in shoots and roots?
A.
Both shoots and roots transport auxin only from the apex toward the base
B.
Shoot and root tissues may show different net directions because the orientation of their transport systems differs
C.
Roots lack membrane-based auxin transport and rely exclusively on diffusion
D.
Only roots display polar transport because shoots transport auxin through xylem alone
Correct Answer:
Shoot and root tissues may show different net directions because the orientation of their transport systems differs
Explanation:
The direction of polar auxin transport depends on the orientation of transport proteins within the tissue. Therefore, shoot and root systems can exhibit different characteristic directions of auxin movement.
8. In a tissue in which auxin transport becomes concentrated along a narrow group of neighboring cells, the process is most consistent with:
A.
Loss of all cellular polarity in the tissue
B.
Canalization of auxin transport through coordinated reinforcement of transport pathways
C.
Random diffusion caused by the absence of transport proteins
D.
Permanent immobilization of auxin in the cell wall
Correct Answer:
Canalization of auxin transport through coordinated reinforcement of transport pathways
Explanation:
Canalization refers to the development of focused auxin transport channels. Auxin flow can reinforce the alignment and activity of transport machinery in neighboring cells, concentrating transport into defined paths.
9. A mutation prevents PIN proteins from reaching their proper polarized positions but does not eliminate auxin production. Which outcome is most directly expected?
A.
Auxin synthesis will necessarily stop in every tissue
B.
Directional cell-to-cell auxin transport and its spatial distribution will be disrupted
C.
Auxin will be converted immediately into mineral nutrients
D.
Auxin will move normally because PIN localization does not affect transport direction
Correct Answer:
Directional cell-to-cell auxin transport and its spatial distribution will be disrupted
Explanation:
Correct polar localization of PIN proteins is essential for directional auxin efflux. If PIN positioning is defective, auxin can accumulate abnormally and fail to move through tissues in the normal direction.
10. Why is the cellular polarity of auxin transporters especially important in a continuous file of plant cells?
A.
It ensures that each cell releases auxin toward a consistent neighboring cell, producing tissue-level directional flow
B.
It makes every cell independently synthesize identical amounts of auxin
C.
It prevents auxin from entering any cell in the file
D.
It converts polar transport into unrestricted bidirectional diffusion
Correct Answer:
It ensures that each cell releases auxin toward a consistent neighboring cell, producing tissue-level directional flow
Explanation:
When efflux carriers are similarly oriented across successive cells, auxin exits each cell toward the next cell in the pathway. This coordinated polarity generates net directional transport across the tissue.
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