Question

The sieve tubes differ from the sieve cells in what characteristics?
(a)Being shorter
(b)Being dead
(c)Lacking nuclei
(d)Having sieve pores at end walls

Answer 1

Hint: Sieve cells are less-skilled phloem sieve components. Sieve tubes are highly specialized phloem sieve elements. Long and narrow cells with tapering end walls are sieve cells. Without any structural developments, the sieve region in the sieve cells is plain and primitive.

Complete answer:
Phloem is a tissue in the vascular system. The conduct of assimilates and food is its key role. It consists of the sieve elements, which can be differentiated by two types, sieve cells and members of the sieve tube. Sieve cells are elongated cells with tapering end walls where vertical cells are positioned one above the other as sieve tubes forming long tubes connected by sieve pores at the end walls. The absence of sieve plates in sieve cells is the main difference between sieve cells and sieve-tube members. In most seedless vascular plants and gymnosperms, their narrow pores are important in their work, which lacks members of the sieve tube and has only sieve cells to transport molecules.
Let’s learn a little bit more about sieve cells and tubes.

Additional Information:
Sieve tube- Elongated living cells (sieve-tube elements) of the phloem in flowering plants, the nuclei of which have broken and vanished, and the transverse end walls of which are pierced by pores (sieve plates) of sieve-like groups. These are the means of transporting food (mostly sugar).
Sieve cells- Sieve components are specialized cells that are necessary for phloem function, a highly structured tissue that carries organic compounds formed during photosynthesis. Sieve elements are the phloem's main conducting cells.
So, the correct answer is ‘having sieve pores at end walls’.

Note: Members of sieve tubes do not have ribosomes or a nucleus and therefore require companion cells to help them act as molecules of transport. In order to help them move molecules between various parts of the plant, companion cells provide Sieve tube members with proteins essential for signaling and ATP.