Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).
Assertion (A): Plant cells undergo cytokinesis by a different mechanism than animals cells.
Reason (R): Plant cells are enclosed by a relatively inextensible cell wall.
In light of the above statements, choose the correct answer from the options given below. 

Assertion is correct. In animal cells, cytokinesis typically involves cell furrow method whereas in plant cell the cytokinesis involves cell plate method.
Reason is correct. The cell wall of plant cells provides structural support and rigidity to the cell. Unlike animal cells, which lack a cell wall, the presence of the cell wall in plant cells affects the process of cytokinesis. The rigid cell wall constrains the movement of the plasma membrane during cell division, necessitating a different mechanism (cell plate formation) for cytokinesis in plant cells.

Therefore, Reason (R) provides a valid explanation for why Assertion (A) is true. The presence of the relatively inextensible cell wall in plant cells indeed leads to a different mechanism of cytokinesis compared to animal cells.