AP BIOLOGY

Detailed explanation-1: -sieve element, in vascular plants, elongated living cells of the phloem, the nuclei of which have fragmented and disappeared and the transverse end walls of which are pierced by sievelike groups of pores (sieve plates). They are the conduits of food (mostly sugar) transport from the leaves to the rest of the plant.

Detailed explanation-2: -The structural elements of phloem include sieve tubes, companion cells, phloem parenchyma and secretory cells. The sieve tube is the conducting element of the phloem. It is formed from a vertical series of elongated cells, interconnected by perforations in their walls in areas known as sieve plates.

Detailed explanation-3: -Phloem consists of living cells. The cells that make up the phloem are adapted to their function: Sieve tubes – specialised for transport and have no nuclei .

Detailed explanation-4: -Sieve tubes are considered living cells without a nucleus because the nucleus of companion cells controls their functional activities. Companion cells, which unite with sieve tubes to form the sieve element-companion cell complex, are related to sieve-tube members.

Detailed explanation-5: -A matured sieve cell or sieve tube element lack nucleus. Thus these are enucleated living cells.