Which is a characteristic of companion cells in the phloem?

Companion cells in the phloem play a crucial role in the transport of nutrients and the conduction of food, primarily carbohydrates produced during photosynthesis. These specialized cells are living cells that support the function of sieve tube elements by providing the necessary energy and help in loading and unloading the sugars into the phloem.

Unlike sieve tube elements that are largely devoid of organelles, companion cells retain their nucleus and cytoplasm, which allows them to perform metabolic activities needed for the maintenance of both their own function and the function of the adjacent sieve tube elements. This unique relationship is essential for the effective transport of nutrients through the plant.

The other choices describe characteristics that do not apply to companion cells, as they are very much alive at maturity, contain cytoplasm and organelles, and do not contribute to the formation of cork tissues.