Cell walls are the feature of almost all plant cells. The cell wall surrounds the cell on the outside and is the secretory product of the cytoplasm. The cell wall is permeable to water.
Structure
Young plant cells are surrounded by a primary wall which is 90% polysaccharide and 10% protein. The polysaccharide is mainly cellulose which is embedded in a matrix of other molecules called pectin and hemicellulose. The primary wall is relatively thin and elastic to allow for growth. When cell growth stops a secondary wall is formed inside the primary wall. The secondary wall is thick and rigid being composed of parallel layers of cellulose microfibrils. The secondary wall is often strengthened by lignin. The primary walls of adjacent cells are "cemented" together by a common layer, the middle lamella, which consists of pectin, a complex carbohydrate and some protein. Small openings or pores exist between the primary wall and middle lamella and are called plasmo- desmata.
Functions