Practice important
Cambial activation
MCQ questions and answers.
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MCQ Questions
1. A ring of bark is removed from a woody stem while the vascular cambium remains intact. If auxin transport from young leaves is experimentally blocked, which cambial response is most directly expected?
A.
Increased production of secondary xylem above the ring
B.
Reduced cambial cell division and secondary vascular formation
C.
Immediate conversion of the cambium into cork tissue
D.
Uncontrolled division of mature xylem vessels
Correct Answer:
Reduced cambial cell division and secondary vascular formation
Explanation:
Auxin produced in young expanding leaves is transported toward the stem and stimulates vascular cambial activity. Blocking this supply reduces cambial division and the formation of secondary vascular tissues.
2. In an isolated woody stem segment, which treatment would most specifically restore cambial activation when the normal auxin source has been removed?
A.
Applying auxin to the upper cut surface
B.
Applying abscisic acid to the lower cut surface
C.
Applying cytokinin only to mature xylem vessels
D.
Removing the remaining secondary phloem
Correct Answer:
Applying auxin to the upper cut surface
Explanation:
Auxin moves basipetally from young shoot tissues and promotes vascular cambial activity. Applying auxin to the upper surface of a stem segment can substitute for the missing shoot-derived auxin signal.
3. Which observation provides the strongest evidence that auxin has activated the vascular cambium rather than merely enlarging pre-existing xylem cells?
A.
An increase in the length of mature vessel elements
B.
A wider zone of actively dividing cambial initials and their derivatives
C.
A decrease in the diameter of the stem
D.
Expansion of epidermal cells without vascular changes
Correct Answer:
A wider zone of actively dividing cambial initials and their derivatives
Explanation:
Cambial activation is demonstrated by renewed or enhanced division of cambial initials and production of new secondary vascular cells, not simply by enlargement of already mature cells.
4. A stem receives auxin on one side in a narrow vertical band. Which cambial effect is most likely to appear first in that region?
A.
Localized increase in secondary vascular tissue production
B.
Complete disappearance of the vascular cambium throughout the stem
C.
Uniform inhibition of cambial division on the opposite side
D.
Immediate replacement of all xylem by primary phloem
Correct Answer:
Localized increase in secondary vascular tissue production
Explanation:
Auxin can activate the cambium locally. A localized auxin supply is therefore expected to enhance cambial division and secondary vascular production near the treated region.
5. Why does girdling a woody stem often lead to abnormal thickening near the upper edge of the girdle, provided the cambium is not removed?
A.
Auxin arriving from the shoot accumulates above the interruption and stimulates nearby cambial activity
B.
Auxin is synthesized only in the exposed xylem and moves upward into the bark
C.
The girdle converts mature phloem directly into vascular cambium
D.
Water accumulation alone activates cambial initials independently of hormones
Correct Answer:
Auxin arriving from the shoot accumulates above the interruption and stimulates nearby cambial activity
Explanation:
Shoot-derived auxin normally moves downward through the stem. Girdling can interrupt the transport pathway, causing auxin accumulation above the girdle and enhanced cambial activity in that region if the cambium remains intact.
6. Which combination would most strongly indicate that auxin is promoting secondary growth through cambial activation in a young woody shoot?
A.
Increased cambial cell division followed by greater production of secondary xylem and phloem
B.
Reduced cambial division accompanied by only epidermal cell expansion
C.
Increased elongation of root hairs without additional vascular tissue
D.
Premature loss of all living cells in the vascular cambium
Correct Answer:
Increased cambial cell division followed by greater production of secondary xylem and phloem
Explanation:
Auxin-mediated cambial activation involves increased division of cambial initials and the subsequent formation of secondary xylem inwardly and secondary phloem outwardly.
7. In a stem culture, auxin is supplied continuously at a very high concentration. After an initial increase, cambial activity declines. Which interpretation is most appropriate?
A.
Cambial cells may require an appropriate auxin concentration, and excessive auxin can inhibit normal cambial function
B.
The decline proves that auxin is unrelated to cambial activation
C.
High auxin necessarily causes all cambial cells to become mature xylem immediately
D.
Cambial activity can continue indefinitely without living cambial initials
Correct Answer:
Cambial cells may require an appropriate auxin concentration, and excessive auxin can inhibit normal cambial function
Explanation:
Auxin promotes cambial activity within a suitable concentration range. Excessive concentrations may disturb normal regulation and suppress the division response after an initial stimulation.
8. A researcher removes young leaves from one branch but leaves the leaves on a comparable branch intact. Which result most directly supports a role for leaf-derived auxin in cambial activation?
A.
The defoliated branch shows less cambial division and reduced secondary vascular production
B.
The defoliated branch produces more secondary xylem because auxin is no longer used by leaves
C.
Both branches lose their cambium immediately, regardless of leaf removal
D.
Only the epidermis of the defoliated branch divides more rapidly
Correct Answer:
The defoliated branch shows less cambial division and reduced secondary vascular production
Explanation:
Young leaves are important sources of auxin. Their removal decreases the auxin signal reaching the stem and can consequently reduce vascular cambial activation and secondary growth.
9. Which experimental comparison best distinguishes auxin-dependent cambial activation from a nonspecific effect of applying a solution to a woody stem?
A.
Applying auxin to one stem and an equivalent solvent without auxin to another comparable stem
B.
Applying auxin to one stem and water to a leaf blade of the same stem
C.
Applying two different auxin concentrations without an untreated control
D.
Measuring only stem color after treatment
Correct Answer:
Applying auxin to one stem and an equivalent solvent without auxin to another comparable stem
Explanation:
A matched solvent control isolates the effect of auxin itself. Greater cambial division or secondary vascular production in the auxin-treated stem would support auxin-dependent cambial activation.
10. If auxin transport from the shoot is restored to only one side of a previously auxin-deprived woody stem, what pattern of secondary growth is most consistent with cambial activation by auxin?
A.
Greater secondary tissue production adjacent to the restored transport pathway
B.
Identical secondary tissue production on every side despite unequal auxin supply
C.
Complete cessation of cambial division on the side receiving auxin
D.
Formation of secondary tissues only in the epidermis
Correct Answer:
Greater secondary tissue production adjacent to the restored transport pathway
Explanation:
The vascular cambium responds spatially to auxin supply. Restoring auxin transport on one side should preferentially stimulate cambial division and secondary vascular production in nearby cambial regions.
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