Question

Which of the following helps in maintenance of the pressure gradient in sieve tubes?

• A. Albuminous cells
• B. Sieve cells
• C. Phloem parenchyma
• D. Companion cells

Answer 1

The Correct Option is D

The question revolves around understanding the function of different cell types within the phloem tissue of plants. Let us evaluate the role of each option in maintaining the pressure gradient in sieve tubes:

1. Albuminous Cells: These are associated with sieve cells (not sieve tubes) in non-angiosperms. They aid in the functioning of sieve cells but are not directly involved in the active transport processes that establish a pressure gradient in angiosperms.
2. Sieve Cells: These are the main conducting elements in gymnosperms. However, sieve tubes in angiosperms are responsible for transporting sugars and other nutrients. Sieve cells do not independently maintain the pressure gradient.
3. Phloem Parenchyma: These cells are involved in storage and lateral transport within the phloem but do not directly contribute to regulating the pressure gradient in sieve tubes.
4. Companion Cells: These are closely associated with sieve tube elements in angiosperms. They help in loading and unloading of sugars and other solutes in the sieve tubes. The active transport of solutes into the sieve tubes by companion cells results in an osmotic gradient, driving water into the tubes and creating a pressure difference that facilitates the flow of sap.

Therefore, Companion Cells are responsible for maintaining the pressure gradient in sieve tubes in angiosperms through their role in actively transporting solutes, which generates the osmotic potential required for sap flow. The correct answer is Companion Cells.