Cells that are specialized for the transport of sugar between apoplast and symplast are __________ cells.

• A. mesophyll
• B. guard
• C. bundle sheath
• D. aquaporin
• E. companion

Answer: (E)

Verified step by step guidance

1. Understand the terms 'apoplast' and 'symplast'. The apoplast refers to the network of cell walls and intercellular spaces through which water and solutes can move freely. The symplast is the inner side of the plasma membrane where water and solutes can move via plasmodesmata.
2. Recognize the role of companion cells. Companion cells are specialized cells in the phloem of plants that assist in the transport of sugars and other nutrients between the apoplast and symplast.
3. Identify the function of companion cells in relation to the sieve tube elements. Companion cells are closely associated with sieve tube elements and help in loading and unloading sugars into the phloem.
4. Consider the other options provided: mesophyll cells are involved in photosynthesis, guard cells regulate the opening and closing of stomata, bundle sheath cells are involved in the Calvin cycle in C4 plants, and aquaporins are water channel proteins.
5. Conclude that companion cells are the correct answer because they are specifically adapted for the transport of sugars between the apoplast and symplast, supporting the function of sieve tube elements in the phloem.