What argument would you give for the necessity of a cell wall in plants usually fixed in one place versus in animals usually moving from one place to the other?
[Pg. No. 14]

Plants are usually fixed in one place, so their cells need a rigid cell wall for support, protection and maintaining shape. The cell wall, made mainly of cellulose, helps plant cells withstand the pressure of water entering them and provides strength to plant parts. Animal cells lack a cell wall because they need greater flexibility for movement and different body functions; they have only a cell membrane around them.