The cell wall is a rigid non-living layer that is found outside the cell membrane and surrounds the cell. Plants, bacteria and fungi all have cell walls. In plants, the wall is comprised of cellulose. It consists of three layers that help support the plant. These layers include the middle lamella, the primary cell wall and the secondary cell wall.
Middle lamella: separates one cell from another. It is a thin membranous layer on the outside of the cell and is made of a sticky substance called pectin.
Primary cell wall: is on the inside of the middle lamella and is mainly composed of cellulose.
Secondary cell wall: lies alongside the cell membrane. It is is made up of a thick and tough layer of cellulose which is held together by a hard, waterproof substance called lignin. It is only found in cells which provide mechanical support in plants.
The human body cannot break down the cellulose in cell walls because we do not produce the enzyme cellulase.
Functions of the Cell Wall
- The main function of the wall is to protect the inner parts of the plant cell, it gives plant cells a more uniform and regular shape and provides support for the plant body.
- The cell wall is completely permeable to water and mineral salts which allows distribution of nutrients throughout the plant.
- The openings in the cell wall are called plasmodesmata which contain strands of cytoplasm that connect adjacent cells. This allows cells to interact with one another, allowing molecules to travel between plant cells.