AP BIOLOGY

Detailed explanation-1: -It is made up of living cells except for phloem fibres . It has four elements that are companion cells, sieve tubes, phloem parenchyma, and phloem fibres. It is a pathway to signalling molecules and also has a structural function in the plant body.

Detailed explanation-2: -The main functions of sieve tube members include maintaining cells and transporting necessary molecules with the help of companion cells. The sieve tube members are living cells (which do not contain a nucleus) that are responsible for transporting carbohydrates throughout the plant.

Detailed explanation-3: -Sieve elements are thin-walled cells that are alive at maturity, although the protoplast is greatly changed, and they generally lack nuclei. Sieve elements are elongated and function as the basic photosynthate-conducting cell type in the phloem of vascular plants.

Detailed explanation-4: -Companion cells are found along with sieve tube elements in the phloem. The main function of companion cells is to maintain pressure gradient in the sieve tube elements.

Detailed explanation-5: -The main difference between sieve tubes and companion cells is that sieve tubes are the long, narrow, pointed tubes present in the phloem of angiosperms whereas companion cells are attached to the sieve tubes, regulating the activity of sieve tubes.