Question

Which one of the following is an incorrect comparison between tracheids and vessels?

• A. Tracheids - narrow lumen, Vessels - broad lumen
• B. Tracheids - usually have bordered pits, Vessels - usually possess simple pits
• C. Tracheids - end walls of cells are dissolved, Vessels - tapering ends
• D. Tracheids - unicellular, Vessels - multicellular

Answer 1

The correct option is C Tracheids - end walls of cells are dissolved, Vessels - tapering ends

The structural elements of xylem are tracheids, vessels or tracheae, xylem fibres, xylem parenchyma and rays.

Tracheids are primitive conducting elements of xylem. A single tracheid is a unicellular, highly elongated cell with hard, thick and lignified walls and a narrow lumen. The ends of tracheids are tapering or chisel like. The tracheids found one above the other are separated by cross walls which bear bordered pits. The maximum bordered pits are found in the tracheids of gymnosperm plants.

Vessels are an advance conducting element of xylem. It is a long cylindrical, tube like, multicellular structure with lignified walls and, a wide central lumen. The end walls of the cells are completely or partially dissolved due to which vessels work as a pipe line during conduction of water. Vessels contain usually simple pits on their lateral walls. Types of thickening on the walls of vessels is the same as tracheids.

Thus option c is the only incorrect comparison.