The cell wall, cellulosic wall or cellulosic skeletal membrane, is a resistant and flexible cellulose structure that delimits cell organelles in a plant cell.
Remember that plant cells form plant tissues. In turn, animal cells lack cell walls, chloroplasts and vacuoles.
Functions
The main functions of the cell wall is to provide support, resistance and protection against external pathogens. Therefore, it collaborates with the absorption, transport and secretion of substances.
In addition, the cell wall acts as a filter for plant cells, as it allows the exchange of substances between other neighboring cells.
It also protects against excessive water entry, thus preventing osmotic lysis, that is, cell rupture. Another important function is that the cell wall shapes the various plant cells.
Structure
The cell wall is a very resistant structure composed of microfibrils of the polysaccharide called cellulose .
It surrounds the plasma membrane and in its structure has pores that act as filters in relation to the external environment.
Classification
The cell wall can be primary and secondary:
- Primary Cell Wall : they are basically formed from cellulose, hemicellulose and pectins. Although thin, it is resistant and flexible, thus allowing cell growth. It has a high water content, with about 70%. On primary walls, hydrogen bridges provide greater elasticity to the structure.
- Secondary Cell Wall : they are basically formed from cellulose and hemicellulose. Not all plant organisms have this type of structure. It is thicker than the primary, in addition to being very resistant since it is composed of lignin. It has a water content lower than the primary, that is, 20%. Secondary walls limit space and provide greater rigidity.
In addition to the primary and secondary wall, the middle lamella is a thin layer outside the walls that has the function of connecting the cell with others that are nearby.
Types
The cell wall is present in plants, algae, fungi and some bacteria. Thus, they differ slightly in their structure and composition.
- Plant Cell Wall : formed by cellulose microfibrils, the plant cell wall generally has a primary and a secondary wall.
- Cell Wall of Algae : formed by different types of cellulose such as the walls of glycoproteins and polysaccharides.
- Cell Wall of Fungi : formed by chitin , and in some cases by cellulose, the cell wall of fungi protects these organisms against invaders.
- Bacterial Cell Wall : formed by peptidoglycan (sugars linked to amino acids), the bacterial cell wall is classified into Gram Positive and Gram Negative.