Part 6 — Vascular Tissue Details: Xylem/Phloem Elements, Companion Cells, Rays (Questions 126–150)

Q126. Vessel element perforation plates function to:

A) Connect sieve tubes only
B) Allow unobstructed water flow between vessel elements; perforation may be simple or scalariform, reducing resistance across elements
C) Store starch only
D) Form stomata
Answer: B
Explanation:

B) Correct — perforation plates enable water flow; types vary.
A/C/D) Incorrect.

Q127. Tracheids differ from vessel elements in that tracheids:

A) Are present only in angiosperms
B) Are elongated, dead at maturity, with tapered ends and bordered pits for water movement and are main conducting cells in gymnosperms
C) Conduct sugars actively
D) Have companion cells
Answer: B
Explanation:

B) Correct — tracheids common in gymnosperms and some angiosperms; vessels are angiosperm feature.
A/C/D) False.

Q128. Sieve plates are found in:

A) Xylem vessels only
B) Sieve tube elements of phloem facilitating flow of phloem sap between sieve elements; pores lined by callose during injury
C) Epidermis only
D) Root cap only
Answer: B
Explanation:

B) Correct — sieve plates connect sieve elements.
A/C/D) Not correct.

Q129. Companion cells support sieve tube elements because they:

A) Are dead at maturity
B) Supply metabolic support, loading/unloading of sugars, since sieve tube elements lack nucleus & many organelles
C) Only provide mechanical strength
D) Replace xylem conduction
Answer: B
Explanation:

B) Correct — companion cells assist in phloem function.
A/C/D) False.

Q130. Bordered pits in tracheids are important for:

A) Wood color only
B) Water movement between tracheids while minimizing air-seeding (cavitation prevention); pit membranes regulate flow and provide safety
C) Sugar transport only
D) Light absorption
Answer: B
Explanation:

B) Correct.
A/C/D) Not true.

Q131. Phloem fibres (sclerenchyma) function primarily as:

A) Conducting cells for water
B) Mechanical support for vascular bundles and stem; they are dead at maturity with lignified walls
C) Synthesis of sugars
D) Gas exchange cells
Answer: B
Explanation:

B) Correct.
A/C/D) Incorrect.

Q132. Which of the following statements is true?

A) Xylem parenchyma in trees is abundant in ring porous species only
B) Xylem parenchyma stores food, assists in radial transport, and may form tyloses with aging; amount varies by species
C) Xylem lacks any living cells in all plants
D) Xylem always transports sugars
Answer: B
Explanation:

B) Correct — xylem parenchyma living cells play storage/transport roles.
A/C/D) Wrong.

Q133. Sieve tube elements in angiosperms are characterized by:

A) Presence of dense nucleus at maturity
B) Lack nucleus at maturity, presence of sieve plates, and associated companion cells maintain function
C) Lignified secondary walls only
D) Photosynthetic activity mainly
Answer: B
Explanation:

B) Correct.
A/C/D) False.

Q134. Phloem loading involves:

A) Only passive diffusion in all plants
B) Active transport (apoplastic or symplastic routes) loading of sucrose into companion cells/sieve elements often via proton-sucrose symporters for source-to-sink translocation
C) Xylem conduction only
D) Guard cell opening exclusively
Answer: B
Explanation:

B) Correct — phloem loading can be active or passive depending on species.
A/C/D) Incorrect.

Q135. Ray parenchyma in wood is primarily for:

A) Longitudinal conduction only
B) Radial conduction and storage, and contributing to heartwood/sapwood transitions via parenchyma metabolic activity
C) Forming cambium only
D) Leaf formation
Answer: B
Explanation:

B) Correct.
A/C/D) Not true.

Q136. Apoplastic loading into phloem refers to:

A) Symplastic movement through plasmodesmata only
B) Movement of sugars through cell walls/extracellular spaces to companion cells requiring active transport into sieve elements often via membrane transporters
C) Transport via xylem vessels only
D) Movement only in roots
Answer: B
Explanation:

B) Correct — apoplastic loading uses membrane transport proteins.
A/C/D) Not apoplastic.

Q137. Which xylem elements are primarily responsible for conduction in angiosperms?

A) Vessel elements more efficient in axial water transport, tracheids also present but less efficient — angiosperms typically have vessels
B) Phloem only
C) Parenchyma only
D) Epidermal cells
Answer: A
Explanation:

A) Correct.
B/C/D) False.

Q138. Compartmentalization of xylem and phloem into bundles is critical because:

A) Ensures coordinated conduction of water & nutrients while allowing mechanical support and isolating damage
B) Only for aesthetic reasons
C) Prevents any transport between root and shoot
D) Eliminates need for cambium
Answer: A
Explanation:

A) Correct — vascular architecture optimizes function.
B/C/D) Wrong.

Q139. Callose deposition in phloem sieve plates occurs:

A) During normal active translocation only
B) Rapidly upon injury to block sieve tubes and prevent loss of phloem contents — reversible by callose degradation when damage removed
C) Only in xylem vessels
D) To create new sieve plates during growth
Answer: B
Explanation:

B) Correct — callose plugs sieve pores under injury.
A/C/D) Not accurate.

Q140. Phloem unloading at sinks (e.g., developing fruit) can occur via:

A) Only apoplastic route requiring membrane transport and invertase activity
B) Only symplastic route via plasmodesmata depending on tissue and developmental stage; both apoplastic and symplastic unloading occur in plants
C) Xylem vessels only
D) Root hairs only
Answer: B
Explanation:

B) Correct — unloading mechanism varies; both routes used.
A/C/D) Incomplete or false.

Q141. Which is a correct statement about vessel perforation types?

A) Simple perforation plate has single large opening, scalariform has ladder-like bars — affects flow resistance
B) All plates identical in all species
C) Perforation plates are only in phloem
D) Only present in roots
Answer: A
Explanation:

A) Correct — types impact hydraulic conductance.
B/C/D) False.

Q142. Companion cells types include:

A) Albuminous cells in gymnosperms equivalent to companion cells in angiosperms; in angiosperms companion cell types vary (ordinary, transfer, etc.) linked to phloem loading strategies
B) Only one universal type everywhere
C) Never associated with sieve tubes
D) Function as xylem only
Answer: A
Explanation:

A) Correct nuance — gymnosperms have albuminous cells; angiosperm companion cell diversity relates to loading.
B/C/D) Wrong.

Q143. Function of phloem parenchyma includes:

A) Only conduction of water in xylem
B) Storage, radial transport and assisting in loading/unloading of solutes; living cells within phloem tissue
C) Dead, lignified support exclusively
D) Forming root cap
Answer: B
Explanation:

B) Correct.
A/C/D) Incorrect.

Q144. Which of the following is true of fibre caps in vascular bundles?

A) They only occur in roots always
B) Provide mechanical strength around the conducting tissues and sometimes form protective caps (e.g., around phloem or xylem)
C) They conduct sugars instead of phloem
D) They are formed by cambium exclusively
Answer: B
Explanation:

B) Correct — fibre caps are supportive sclerenchyma.
A/C/D) Not accurate.

Q145. Pits on the radial walls facilitate:

A) Horizontal (radial) movement of water/nutrients between xylem elements and neighboring parenchyma; pits are thin portions of secondary wall exposing primary wall and pit membrane
B) Vertical water conduction exclusively
C) Photosynthesis only
D) Flower opening
Answer: A
Explanation:

A) Correct — radial transport via pits.
B/C/D) Wrong.

Q146. Anomalous secondary thickening in some dicots (e.g., Boerhaavia) results from:

A) Regular cambial ring only
B) Presence of additional cambia that produce rings of vascular tissues or parenchymatous tissues leading to unique vascular patterns
C) No cambial activity at all
D) Only monocot features
Answer: B
Explanation:

B) Correct — multiple cambia or activity patterns cause anomaly.
A/C/D) Not correct.

Q147. Which of the following provides evidence of secondary growth in stems?

A) Ring of vascular bundles only in monocots
B) Presence of secondary xylem (wood) and secondary phloem and periderm (cork) indicate secondary growth typical in dicots/gymnosperms
C) Only apical meristem activity
D) Presence of root hairs on stem
Answer: B
Explanation:

B) Correct.
A/C/D) Not evidence of secondary growth.

Q148. In woody stems, sugars produced in leaves are mainly transported through:

A) Xylem vessels
B) Phloem sieve tubes from source to sink, pressure-flow mechanism explains bulk flow of phloem sap
C) Epidermis only
D) Lenticels
Answer: B
Explanation:

B) Correct — phloem conducts assimilates.
A/C/D) False.

Q149. Which factor increases vulnerability to cavitation in xylem?

A) Wide vessel diameter increases risk of air-seeding and cavitation during water stress; narrower tracheids less vulnerable
B) Narrow conduits always increase cavitation risk
C) Presence of tyloses always prevents cavitation
D) High humidity causes cavitation
Answer: A
Explanation:

A) Correct — trade-off between conductance and safety.
B/C/D) Not accurate.

Q150. Which is the best description of sieve tube element organelles at maturity?

A) Fully nucleated and metabolically self-sufficient
B) Lost nucleus and reduced organelles; rely on companion cell for metabolic support while having many mitochondria in companion cell for energy-demanding loading/unloading
C) Dead and lignified like tracheids
D) Only store starch and do nothing else
Answer: B
Explanation:

B) Correct.
A/C/D) False.

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Part 6 — Vascular Tissue Details: Xylem/Phloem Elements, Companion Cells, Rays (Questions 126–150)