AP 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 nucleus is considered as the controlling center of the cells. It is present mostly in all eukaryotic except a few. In plant cells, the nucleus is absent in the sieve tubes. Sieve tubes cells are conducting cells of the phloem and do not contain nucleus and ribosomes.

Detailed explanation-3: -A matured sieve cell or sieve tube element lack nucleus. Thus these are enucleated living cells. Q. I transport food in plants and am made of dead enucleated sieve tubes and living multinucleated companion cells.

Detailed explanation-4: -Answer : The cells of phloem are called sieve tubes. These are living cells which contain cytoplasm but no nucleus.

Detailed explanation-5: -Sieve tube members do not have ribosomes or a nucleus and thus need companion cells to help them function as transport molecules.