Layers and Functions of Plant Cell Wall

Cell wall is a rigid structure which lies outside the plasma membrane. The cell wall is secreted by the cell. Thus the structure, thickness and chemical nature of cell wall varies with the type of cell and its function. This structure consists of three main layers, primary cell wall, middle lamella and secondary cell wall.

 

Primary Cell Wall

Each cell produces a thin primary wall. It is a true wall and develops in newly growing cell, i.e. during cell division.

Plant Cell Wall

Middle lamella

It’s present between adjacent primary walls of the two cells. It is the first layer to be formed; it is formed of sticky gel like magnesium and calcium salts of pectin.

 

Secondary cell wall

It is formed between the primary cell wall and the plasma membrane. It is formed in woody tissues e.g. stem and nuts.

 

Constituents of Plant Cell Wall

The major constituent of the primary cell wall is cellulose with some pectin, hemicelluloses and lignin. Lignin adds to the hardness of the cell wall. Pectin acts to cement cellulose microfibrils. (Glucose molecules of cellulose joined with one another to form microfibrils.) Microfibrils are arranged in crisscross manner (i.e. the fibers of different layers are at different angles to one another). Secondary wall is composed of inorganic salts, waxes and cutins (wax like substance).

 

Functions of the Cell Wall

1. It gives mechanical strength and skeletal support to the individual cell.

2. Cell walls are fairly rigid.

3. It gives particular shape to the cell which is due to orientation of cellulose microfibrils.

4. Cell wall develops coating of waxy cutin, the cuticle on exposed epidermis surface reducing water loss and risk of infections.

5. The cell walls of root endodermal cells are impregnated with suberin that forms a barrier to water minerals.

6. The cell walls have minute pores, forming living connections between the cells.

Now explaining it a little differently, the cell wall is a rigid outer structure that encloses the plasma membrane in plant cells. It is synthesized and secreted by the cell and its composition and characteristics vary based on the cell type and its function. The cell wall comprises three main layers, namely the primary cell wall, middle lamella, and secondary cell wall.

The primary cell wall is a thin, true wall that is produced by each cell during cell division. The middle lamella is the first layer to be formed and is present between the adjacent primary walls of two cells. It is formed of sticky gel-like magnesium and calcium salts of pectin. The secondary cell wall is formed between the primary cell wall and the plasma membrane and is present in woody tissues like stem and nuts.

The major constituent of the primary cell wall is cellulose, with some pectin, hemicelluloses, and lignin. Lignin contributes to the cell wall's hardness, while pectin cements cellulose microfibrils. Microfibrils are arranged in a crisscross manner, and the fibers of different layers are at different angles to each other. The secondary wall comprises inorganic salts, waxes, and cutins, which are wax-like substances.

The cell wall performs several essential functions, including providing mechanical strength and support to individual cells, giving shape to the cell due to the orientation of cellulose microfibrils, and reducing water loss and the risk of infection by developing a coating of waxy cutin or cuticle on exposed epidermis surfaces. The cell walls of root endodermal cells contain suberin, which forms a barrier to water and minerals. Finally, the cell walls have minute pores, forming living connections between the cells.