Companion cells' essential features support sieve tube function in phloem

Steps:

• Recall companion cells provide metabolic support and symplastic connections to sieve tube elements for sugar transport.
• Identify feature 1: dense cytoplasm with numerous mitochondria enables active loading of sugars via ATP.
• Identify feature 2: presence of chloroplasts aids photosynthesis but is not required for phloem loading.
• Identify feature 3: abundant plasmodesmata allow solute exchange with sieve tubes, essential for transport.

Why C is correct:

• Features 1 and 3 align with the definition of companion cells as metabolically active cells connected symplastically to enucleate sieve tubes for phloem function.

Why the others are wrong:

• A includes non-essential feature 2, overstating requirements.
• B omits critical feature 3 for solute transfer.
• D excludes feature 1, ignoring metabolic support needs.

Final answer: C