Question

Plant cells responsible for the transport of water are dead when they are mature enough to act as water transport tissues. These cells include which of the following cell types?
I. Tracheids
II. Vessel elements
III. Sieve tube members
IV. Companion cells

• A. I only
• B. I and II only
• C. I,II, and III only
• D. I,II, III, and IV
• E. II and III only

Answer 1

The correct option is B I and II only

I. Tracheids are elongated tube like cells having tapering ends and lack perforations. At maturity tracheids become dead as the walls become lignified but they continue to transport water.

II. Vessels are composed of row of cells placed one above the other. Vessels are also dead elements but help in conduction of water.

Tracheids and vessels both are called tracheary elements because their main function is conduction of sap.

III. Sieve tube members or elements are slender, elongated cells. Nucleus is present in younger sieve elements but it disappears at maturity.

IV. Companion cells are present between the sieve tubes in the phloem of angiosperms. These are living cells with large nucleus that controls the activity of non-nucleated sieve tubes.

Hence, tracheids and vessel elements are the plant cells responsible for the transport of water are dead when they are mature enough to act as water transport tissues.

So, the correct answer is 'I and II only'.