In plant biology, which substance is distinct and not equivalent to xylem?

Xylem is a type of tissue in vascular plants primarily responsible for the transport of water and dissolved minerals from the roots to the rest of the plant, as well as providing structural support. Phloem, on the other hand, is a different type of vascular tissue that transports the products of photosynthesis, such as sugars, from the leaves to other parts of the plant. Although both xylem and phloem are essential components of the vascular system, they have distinct functions and structures, making phloem not equivalent to xylem.

In contrast, substances like starch, chlorophyll, and cellulose have different roles in plant biology. Starch serves as an energy storage molecule, chlorophyll is a pigment involved in photosynthesis, and cellulose provides structural integrity to plant cell walls. Each of these substances serves unique purposes within the plant, but they do not substitute for the transport or structural functions of xylem. Thus, the distinction between xylem and phloem is crucial, as it highlights the specialized roles of different vascular tissues in plants.