Question

__________ consists of perforated walls.
A. Companion cells
B. Sieve tubes
C. Xylem parenchyma
D. Phloem parenchyma

Answer 1

Hint: The xylem vessels and the phloem sieve tubes are connected end to end to transport the water and the food respectively to long distances in a plant. Their end plates are perforated to allow the easy passage of substances from one vessel and the sieve tubes.

Complete step by step answer: The sieve tubes are a cylindrical tube-like structure made up of cells placed end to the end. The transverse partition wall between the two cells is perforated with the pores. The sieve tubes are the part of phloem with the perforated walls. Therefore, it appears like a sieve and it is named as a sieve plate. The sieve cells are also associated with gymnosperms because they lack in the companion cell. The narrow pores present are necessary for their function in most seedless vascular plants and gymnosperms which lack the sieve tube members and only have sieve cells to transport the molecules.
Therefore, the correct answer is option B.

Additional information: The sieve elements are specialized cells that are important for the function of the phloem; which is a highly organized tissue that transports organic compounds made during photosynthesis. The sieve elements are the major conducting cells in the phloem. The sieve cells are the primitive sugar-conducting cells and are found in all non flowering vascular plants. The sieve-tube members were evolutionarily modified from the sieve cells and are found only in the flowering plants.

Note: The advantage of having perforated walls is that it allows the rapid conduction of water from one vessel element to the next. The xylem and the phloem are known as the complex issues as they are made up of more than one type of cells.