Companion cells' essential features for phloem support

Steps:

• Recall companion cells metabolically support enucleate sieve tube elements in phloem transport.
• Evaluate feature 1: dense cytoplasm with nucleus and ribosomes enables protein synthesis and regulation, essential for function.
• Evaluate feature 2: abundant chloroplasts is incorrect as companion cells lack them, relying on mitochondria instead.
• Evaluate feature 3: numerous plasmodesmata allow symplastic solute loading/unloading to sieve tubes, essential for transport.

Why B is correct:

• Features 1 and 3 align with the definition of companion cells providing metabolic aid and direct connectivity per phloem physiology.

Why the others are wrong:

• A includes non-essential feature 2, which companion cells do not possess.
• C omits critical connectivity of feature 3.
• D excludes vital metabolic support of feature 1.

Final answer: B