A cell wall is an outer layer present over the plasma membrane in the plant cells.
It is an important of plant cell parts as it provides shape, strength, and protection.
It is not present in animal cells and protozoa.
However, the bacterial cell walls are made of glycoproteins and glycolipids molecules. While, the plant cell wall is composed of cellulose, non-cellulose polysaccharides and structural proteins.
Further, with age, the organic materials in the cell wall of plants vary. The primary cell wall found in young cells consists of pectin, hemicellulose beside the cellulose microfibrils. While the secondary cell wall also has the same composition as an extra layer over the previous one in mature cells.
These walls are in general no porous and are physically dry in nature.
The cell wall being absent in animal cells indicates a special function and role in the plant cells.
So the cell wall functions are worth studying.
What are the Functions of the Cell Wall
The cell wall’s main function is physical support. But the study reveals more points as
1. Exoskeleton: Cell wall acts as an exoskeleton and it provides mechanical support and also balances intracellular osmotic pressure.
2. They give external protection to the cell. That is they prevent any physical damage to the inner cell structures from external forces.
3. Prevent cells from drying: The cell wall helps bacteria to tolerate intense heat of the sun. If not the cell wall, the cell would dry up due to evaporation. So the cell wall prevents from desiccation of cell. Without a cell wall, the cell would dry up leading to plasmolysis.
In animals, this is not needed as they move away to shade or shelter to escape the heat. The cell wall is so hard that bacteria are even resistant to sterilization.
4. They keep the cell clumped: Cell walls are always interlinked in plants and other multi-cellular organisms. This cell wall forms stable joints helping the cell to clump to each other and stay in a fixed position in the whole plant.
In animals, the cells form tissues which are attached to the skeleton system for support. These animal cells are attached to each other by cell membranes and not by a cell wall.
Also, see the difference between the cell wall and cell membrane.
5. They give shape: Cell wall provides fixed shape to the cell. Without a cell wall, the cell would have flexible shape. So the rigid and hard structure of plants is due to a cell wall. Hence because of the cell wall, plants might not be needing an internal skeleton like those found in humans and animals. In animals and humans, the shape is due to the bony skeleton. But due to the cell wall, the cells are clumped together to give a definite shape.
6. Manage waste matter: Many metabolites in plants are excreted by shedding of leaves or other parts. But some of the metabolites are just merged with the cell wall. Hence we can see that cell wall increases in size (width) as the cell ages in plants. As the plant ages, bio-molecules like chitin, lignin are deposited into the cell wall.
This way the waste material is dumped into the cell wall. In humans and animals, the waste matter is carried away by blood to the excretory organs for expulsion from the body.
7. Permeability: Cell wall though is tough and rigid is permeable to small molecules like water and carbon dioxide. This helps the movement of water within the plant without the requirement of blood circulation. Of course, the main transport vessel for the conduction in-plant is xylem and phloem. But cell wall permeability helps inter-cellular transport by diffusion and other processes.
8. Channel for food and water: With age, the cell wall becomes thicker and grows internally replacing the cytoplasm as the cell becomes aged and dies. Due to further addition of material, the cell wall forms into sieve tubes as phloem or localized thickening as xylem.
Xylem helps in the movement of water and dissolved nutrients upwards of the plant. While phloem helps to conduct sugar and other metabolites downward from leaves of the plants.
9. Cytoplasmic bridges: Cell wall also form cytoplasmic bridges which establish continuity between adjacent cells. They pass through the thick pectocellulose membrane. These bridges permit free circulation of fluid which helps to maintain the tonicity of the plant cell.
Further, they allow passage of solutes and macromolecules. So cell walls do not act as complete partitions between cells, but form a large syncytium with skeleton support.
Also besides, in bacteria cell wall provides flagella and pili functions. Flagella help in movement, while pili help in genetic material exchange.
Thus cell wall performs those functions in plants which are absolutely needed due to lack of motion. And also the need to tolerate harsh climate and natural conditions.