Q.48 Parenchyma cells associated with sieve tube members are called
(A) Albuminous cells (B) Companion cells (C) Bulliform cells (D) Subsidiary cells

Parenchyma Cells Sieve Tube Members

In plant anatomy, parenchyma cells sieve tube members play a key role in phloem transport, especially for exams testing vascular tissue structure. Question 48 asks: “Parenchyma cells associated with sieve tube members are called (A) Albuminous cells (B) Companion cells (C) Bulliform cells (D) Subsidiary cells.”

This MCQ focuses on phloem components in flowering plants, crucial for understanding sugar translocation in molecular biology and botany.

Correct Answer: (B) Companion Cells

Companion cells are specialized parenchyma cells directly associated with sieve tube members in the phloem of angiosperms. They provide metabolic support to the enucleate sieve tubes, loading sugars via plasmodesmata and maintaining pressure flow.

These cells are connected by numerous pit fields and share a common origin from the same mother cell, ensuring efficient phloem function.

Explanation of All Options

Companion Cells (Correct Choice)

• Specialized parenchyma derived from the same cambium cell as sieve tubes.

• Nucleated, dense cytoplasm; regulate ATP-dependent sucrose loading/unloading.

• Absent in gymnosperms; essential for mass flow in phloem sap transport.

Albuminous Cells (Option A)

• Parenchyma-like cells associated with sieve cells in gymnosperms (not sieve tubes).

• Provide structural support but less metabolically active than companion cells.

• Found in non-flowering plants like pines; not typical in angiosperm phloem.

Bulliform Cells (Option C)

• Large, fan-shaped parenchyma in leaf epidermis of grasses (e.g., rice, wheat).

• Facilitate leaf rolling/unrolling in response to water stress via turgor changes.

• Unrelated to phloem; involved in transpiration control, not transport.

Subsidiary Cells (Option D)

• Parenchyma cells flanking stomatal guard cells in leaf epidermis.

• Aid in potassium ion regulation for stomatal opening/closing.

• Function in gas exchange; no association with vascular sieve elements.

Exam Relevance for Biology Students

Grasping parenchyma cells sieve tube members is vital for topics like phloem transport, plant physiology, and biotech applications in crop improvement. Companion cells often appear in NEET/GATE questions alongside xylem elements.

This knowledge aids bioinformatics analysis of plant genomes, where phloem genes are studied for yield enhancement.