Why is that shape of a cheek cell not as well defined as a plant cell

Cheek cells lack a rigid cell wall and due to this their shape is not as well defined as a plant cell.

Explanation:

Cell wall is the outermost structure in plant and bacterial cells. The plant cell wall is made up of cellulose and provide rigidity and shape to the cell. In animal cell, the cell wall is absent and the outermost part of the cell is the cell memrane. This is the reason that most animal cell lack rigidity and shape.