NEET BIOLOGY

Detailed explanation-1: -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-2: -The sieve tube member is a mature phloem cell involved with long distance movement of food material. They are living cells, but lack a nucleus.

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: -Sieve tubes are elongated tubular conducting channels of phloem. Each sieve tube is formed of several cells called sieve tube members, sieve tube cells or sieve elements. Sieve tube members are placed end to end. Their end walls have many small pores or sieve pits.

Detailed explanation-5: -Nucleus is absent in sieve tubes and Mammalian RBCs.