Cell size. Some cells are very small and visible only with a microscope. Smallest cell is of bacterium, PPLO. An ostrich egg is the largest animal cell. In plants an alga, Acetabularia has a single cell of about 10 cm in length.
Cell shapes are very diverse. Some cells like those of Amoeba and white blood cells continuously change their shape. Most cells, however, maintain their constant shape. The shape of the cell is related to its function.