Question

Sieve tubes and companion cells are components of

Answer 1

Hint: Sieve tubes and companion cells combine together to form a sieve element-companion cell complex. Sieve tubes do not have membranes or a nucleus and they need companion cells to undertake the function of transporting molecules. They are part of the vascular tissues in plants.

Complete answer:
To answer this question we need to know about the vascular bundles in plants. It comprises the xylem which is associated with the ascent of sap. It comprises tracheids, vessels, xylem parenchyma and fibres.
Phloem is a kind of transporting vascular tissue which acts as a mode of transport of sugars from source tissues to sink tissues. Phloem also helps in the transportation of various proteins like mRNA and other proteins.

The four main elements of Phloem are sieve tubes, companion cells, phloem fibres and phloem parenchyma cells. This indicates that sieve tubes and companion cells form components of Phloem.
-Sieve tubes seem to belong, narrow and pointed tubes which are present in the Phloem part of angiosperms while companion cells are attached to sieve tubes as they assist the sieve tube in the transportation of food.
-Companion cells transport ATP (Adenosine Triphosphate), proteins and many other nutrients to sieve tubes. The companion cells ensure the movement of nutrients in the Phloem. There are no pores in the transverse wall of companion cells.

Note: The companion cells do not have any exact function. They regulate the activity of adjacent sieve elements and also contribute to the loading and unloading of sugar into the sieve element. Companion cells have small vacuoles and these cells contain nuclei. On the other hand, sieve tubes are relatively large cells that have larger vacuoles.