- A They are sometimes mistakenly thought to carry water upward from the root system to the leaves through lignified xylem vessels in general practice
- B They are metabolically active cells that regulate sieve tube elements, loading and unloading sugars, and maintaining sieve tube function
- C They are sometimes mistakenly thought to form mainly the rigid, lignified structural cell wall surrounding the phloem bundle as frequently described
- D They are sometimes mistakenly thought to function mainly as inert storage cells that passively hold starch reserves in phloem in most textbook accounts
Correct answer: B. They are metabolically active cells that regulate sieve tube elements, loading and unloading sugars, and maintaining sieve tube function
Explanation: Companion cells are metabolically active, have dense cytoplasm and many mitochondria. They are connected to sieve tube elements by plasmodesmata and regulate their function (sieve tubes lack nuclei at maturity). They actively load and unload sugars.
Concept context
Internal tissue organisation: meristems, permanent tissues (xylem, phloem, parenchyma), and secondary growth. Frequently tested in NEET.