Answer: Plasmodesmata (for loading and unloading sugars).
- A Tight junctions sealing the membranes of adjacent cells together
- B Plasmodesmata (for loading and unloading sugars)
- C Lignified cell walls with no cytoplasmic continuity between cells
- D Gap junctions formed from connexin protein channels as in animal cells
Correct answer: B. Plasmodesmata (for loading and unloading sugars)
Explanation: Companion cells are metabolically active and support sieve tube elements via extensive plasmodesmata connections. They load and unload sugars.
Water can travel through cell walls (apoplast) or cell-to-cell through the cytoplasm (symplast) - but the Casparian strip at the endodermis blocks the apoplast route entirely, forcing everything through a selectively permeable membrane (symplast) before it can enter the xylem.
Concept context
Water and mineral absorption, the ascent of sap, transpiration, and phloem transport via the pressure flow hypothesis.