ABSTRACT
This chapter examines some of the mechanisms that cells use to control their external shape. It deals with cells encased in rigid cell walls, such as plants and fungi, which change their shape by controlling synthesis and breakdown of their wall in selected regions. Although animal cells lack a rigid cell wall, they often secrete a tough 'exoskeleton' that can have a major influence on the form of the cell. The chapter shows that both plant and animal cells use their actin cortex to control local expansion of the cell surface. All eucaryotic cells employ arrays of microtubules, positioned by microtubule-organizing centers, to give an overall polarity to the cell and control local differentiation of its cortex. The shape of bacteria is dominated by their rigid cell wall, which in turn reflects their very high internal pressure. Cells in the human body vary enormously in size and shape, often reflecting in their form the function they perform.
