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In plant anatomy, sieve tube elements, also called sieve tube members, are highly specialised type of elongated cell in the phloem tissue of flowering plants. Unlike the water-conducting xylem vessel elements that are dead when mature, sieve elements are living cells. They are unique in lacking a nucleus at maturity.
Thereof, why are sieve tubes considered living cells?
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.
Additionally, are sieve tube elements alive?
sieve-tube element. An elongated, food-conducting cell in phloem in angiosperms. Unlike the tracheary elements of xylem, sieve elements have living protoplasts when mature, but they lack a nucleus and are dependent upon companion cells for certain functions.
Companion cell is a living cell found within the phloem of angiosperms (flowering plants). Each companion cell is usually closely associated with a sieve tube cell. It regulates the activities of a sieve cell. Sieve cells lack nucleus and are therefore dependent on adjacent companion cells.