Cell Wall

The cell wall is a non-living, rigid layer that surrounds the plasma membrane and forms the outermost covering of the cells of fungi and plants. Because it is not a living part of the cell, it is manufactured by the cell but exists as a firm supporting structure rather than an active, metabolising component.

What the cell wall does

The wall carries out several important roles at once:

• It gives the cell its definite shape.
• It protects the cell from mechanical injury and from infection.
• It supports communication between neighbouring cells, allowing cell-to-cell interaction.
• It acts as a barrier, keeping out unwanted large molecules that could harm the cell.

What the wall is made of

The composition of the wall differs between algae and other plants:

• In algae, the wall is built from cellulose along with galactans and mannans, and it also contains minerals such as calcium carbonate.
• In other plants, the wall is made up of cellulose, hemicellulose, pectins and proteins.

Layers of the plant cell wall

As a plant cell develops, its wall is organised into distinct layers:

• Primary wall — the wall of a young, growing plant cell. It is able to grow and increase in extent, but this capacity for growth gradually reduces as the cell matures.
• Secondary wall — formed later, once the cell has matured. It is laid down on the inner side of the wall, that is, on the side facing the plasma membrane.
• Middle lamella — a layer found between adjacent cells, composed mainly of calcium pectate. It works like a glue, holding and cementing neighbouring cells together. …