The primary cell wall of land plants is composed of the polysaccharides cellulose, hemicelluloses and pectin. The composition of cell walls varies between taxonomic group and species and may depend on cell type and developmental stage. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. Cell walls are absent in many eukaryotes, including animals, but are present in some other ones like fungi, algae and plants, and in most prokaryotes (except mollicute bacteria). It provides the cell with both structural support and protection, and also acts as a filtering mechanism. It can be tough, flexible, and sometimes rigid.
CytoskeletonĪ cell wall is a structural layer surrounding some types of cells, just outside the cell membrane.
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