What is the Function of Companion Cells

Question

What is the function of companion cells?  
A) These cells provide metabolic support to vessel elements.
B) These cells provide metabolic support to sieve elements.
C) These cells provide metabolic support to tracheids.
D) These cells prevent water from entering the endodermis.
E) These cells control the opening and closing of stomata.

Accepted Answer

Companion cells are specialized parenchyma cells that are associated with sieve elements in the phloem. Their main function is to provide metabolic support to sieve elements, which are responsible for transporting sugars and other organic molecules throughout the plant. The companion cells do this by producing and maintaining the energy and nutrients that are required by the sieve elements to carry out their function. In addition, companion cells also help to regulate the movement of molecules in and out of the sieve elements through plasmodesmata.