Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).
Assertion (A): The layer of cells in the dicotyledonous root that controls water movement is made of tightly packed, barrel-shaped cells.
Reason (R): These cells have a special waxy coating called suberin in certain areas, which prevents water from passing through freely.  
In light of the above statements, choose the correct answer from the options given below.

The assertion is accurate. The layer of cells responsible for controlling water movement in dicotyledonous roots is called the endodermis. The endodermis is characterized by having tightly packed, barrel-shaped cells with impermeable casparian strips in their radial walls. These casparian strips act as barriers, controlling the movement of water and ions into the vascular tissue of the root.

The reason is correct and supports Assertion (A). The suberin present in the radial walls of the endodermal cells forms the casparian strips. This waxy coating is impermeable to water and prevents water from passing freely between adjacent cells. Instead, water must pass through the selectively permeable plasma membranes of the endodermal cells, allowing for controlled movement of water into the vascular tissue.

Therefore, both Assertion (A) and Reason (R) are accurate, and Reason (R) explains why the cells of the endodermis control water movement effectively.