Question

A mature sieve tube differs from a vessel

• A. In lacking a functional nucleus
• B. Absence of lignified walls
• C. Being nearly dead
• D. Lacking cytoplasm

Answer 1

Answer: (B)

Absence of lignified walls

A mature sieve tube is composed of vertical cells placed one above other with perforated sieve plates at their lateral walls to serve as the main conducting element of phloem. They lack nucleus but retain protoplast during differentiation. Sieve tube cells do not have lignin in their walls.
Vessels the dead water conducting elements of xylem and lack nucleus and cytoplasm. The absence of nucleus in both sieve tube and vessels make them dead cells. Secondary wall of vessels shows annual, spiral or scalariform thickening due to deposition of lignin.

So, the correct answer is option B.