The cell wall is a thick rigid protective layer surrounding all plant cells except gametes and zoospores. Beside plants, it occurs in fungi, bacteria, blue-green algae etc but it is completely absent in an animal cell.
fig:Structure of Plant cell wall
It consists of following important parts;
It is present in all growing living plant cell. But only this wall layer is present in a certain plant cell. eg; Parenchyma. It is thin, elastic and lies inner to the middle lamella. Its thickness may range to 1-3µm (micron). It is chemically composed of cellulose, hemicellulose, and pectin. It consists of loosely arranged cellulose microfibrils which remain embedded in the matrix of hemicellulose, pectin, and water.
It is present or formed only in certain mature non-dividing or dead cells. Eg; cork cells, sclerenchyma, tracheids, vessels. It lies inner to the primary wall and is thick and inelastic in nature. Its thickness may range from 5-10µ. The chemical composition of a secondary wall is cellulose, hemicellulose, pectin and extra chemical compound like lignin. It consists of closely arranged cellulose microfibrils in the matrix.
It lies in between the primary walls of two adjoining cell. It is also called cementing layer which joins the cell together. It is chemically composed of calcium and magnesium pectates.
Plasmodesmata are cytoplasmic connections or bridges present between two adjoining cells. These connections are present in small pores across the cell wall. They help to transfer the substances across the cell and also give cytoplasmic continuity to the cells.