Question 2
A sieve tube cell is alive but has no nucleus. How is it controlled?
The right answer is the one marked above.
By the nucleus of the companion cell beside it. The sieve tube cell gives up its nucleus, which clears the tube for the food moving through it, and borrows the control it still needs from next door.
Two cells working as one unit is why phloem has to be a complex tissue. Phloem fibres are dead, so they have no nucleus to lend.