nucleus is absent in..............and why?

(a)sieve tube

(b) companion cell

(c ) collenchyma

(d)mesophyll

Sieve tube,nuclei is fragmented and disappeared.these are cells which lost their nucleus ribosomes at maturity

Sieve tube loses its nucleus at maturity becauseits mainfunction is to transport sugars and other important molecules necessary for plants. It would thus require a lot of space to manage the transport. It is still alive due to companion cell. They are formed from the same mother cells as sieve tubes and these supply the sieve tubes with ATP and other energy rich molecules require for survival.

Your answer will be sieve tube but nucleus is present in sieve tube but it degenerates at maturity as it requires enough space for transport of sugars and other substances.Its all functions is controlled by companion cells and hence it`s name