<P> Cell walls serve similar purposes in those organisms that possess them . They may give cells rigidity and strength, offering protection against mechanical stress . In multicellular organisms, they permit the organism to build and hold a definite shape (morphogenesis). Cell walls also limit the entry of large molecules that may be toxic to the cell . They further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water . Their composition, properties, and form may change during the cell cycle and depend on growth conditions . </P> <P> In most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength . The apparent rigidity of primary plant tissues is enabled by cell walls, but is not due to the walls' stiffness . Hydraulic turgor pressure creates this rigidity, along with the wall structure . The flexibility of the cell walls is seen when plants wilt, so that the stems and leaves begin to droop, or in seaweeds that bend in water currents . As John Howland explains </P> <P> Think of the cell wall as a wicker basket in which a balloon has been inflated so that it exerts pressure from the inside . Such a basket is very rigid and resistant to mechanical damage . Thus does the prokaryote cell (and eukaryotic cell that possesses a cell wall) gain strength from a flexible plasma membrane pressing against a rigid cell wall . </P> <P> The apparent rigidity of the cell wall thus results from inflation of the cell contained within . This inflation is a result of the passive uptake of water . </P>

Function of the cell wall of a plant cell