Which plant cells are living, specialized parenchymatous cells intimately connected to sieve tube elements via plasmodesmatal pit fields to regulate phloem transport?

Answer and explanation

Correct answer: A. Companion cells

  1. Step 1: Mature sieve tube elements lack a cell nucleus, ribosomes, and large vacuoles, possessing only a peripheral thin layer of cytoplasm.
  2. Step 2: Companion cells are specialized living parenchymatous cells derived from the same mother meristematic cell as the sieve element.
  3. Step 3: They possess a prominent nucleus, dense cytoplasm, and numerous mitochondria, maintaining the hydrostatic pressure gradient and metabolic functions of the enucleate sieve tube.
Answer
Companion cells
Why not the others: 'Phloem fibers (bast fibers)' are dead, thick-walled sclerenchyma providing mechanical support; 'Albuminous cells in pteridophytes' is taxonomically inaccurate because albuminous (Strasburger) cells occur in gymnosperms, while pteridophytes have ordinary parenchyma; 'Xylem tracheids' are dead water-conducting tracheary elements.

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