Question

despite losing nuclei the mature sieve tube cells remain alive and function how does it happen

Answer 1

Please find the answer below:

Despite losing nuclei the mature sieve tube cells remain alive and function because they actively transport the sugars and thus do not need adenosine triphosphate to do so.

Sieve tube cells transport their substances from high concentration area to low concentration area. Hence, they cant survive without a nucleus.

Answer 2

The mature sieve tube cells remain alive and function to transport sugar from higher concentration to lower concentration as; Permeability is not dependent upon the nucleus.

EXPLANATION:

The main function of sieve tubes is to transport carbohydrates, sugar in the plant from the leaves to the fruit and root .They actively transport sugars and hence, they don't require 'ATP' (adenosine triphosphate).

The sugars move with concentration gradient and also has pre-set destinations. They only have to transport their substances from an area of "high concentration" to an area of "low concentration", and thus don't require any instructions from the nucleus and can survive without one.  Permeability is not dependent upon the nucleus either.