question_answer

From evolutionary point of view tracheids and sieve cells are more primitive than vessels and sieve tube respectively. The angiosperms have which of the following attributes of xylem?

A) vessel and sieve tube only

B) tracheids, vessels and sieve tube

C) vessel, sieve cells and sieve tube

D) tracheids, vessel and sieve cells

Correct Answer: B

Solution :

Tracheids are elongated or tube like cells with thick and lignified walls and tapering ends. These are dead and are without protoplasm. Vessel is a long cylindrical tube-like structure made up of many cells called vessel members, each with lignified walls and a large central cavity. Sieve tube elements are also long, tube-like structures, arranged longitudinally and are associated with the companion cells. Their end walls are perforated in a sieve-like manner to form the sieve plates.