A cell wall is defined as the non-living component, covering the outmost layer of a cell. Its composition varies according to the organism and is permeable in nature. The cell wall separates the interior contents of the cell from the exterior environment. It also provides shape, support, and protection to the cell and its organelles. However, this cellular component is present exclusively in eukaryotic plants, fungi, and a few prokaryotic organisms.
Functions of Cell Wall
The main functions of the cell wall are:
Protecting the cell against physical damage and invading pathogens.
Cell wall controls and regulates the direction of cell growth.
Providing the strength, structural support and maintaining the shape of the cell.
Functions as a storage unit by storing carbohydrates for use in plant growth, especially in seeds.
It allows entry of smaller molecules through it freely.
Structure of Cell Wall
The cell wall is the outer covering of a cell, present adjacent to the cell membrane, which is also called the plasma membrane. As mentioned earlier, the cell wall is present in all plant cells, fungi, bacteria, algae, and some archaea. An animal cell is irregular in its shape and this is mainly due to the lack of cell wall. The compositions of the cell wall usually vary along with organisms.
The plant cell wall is generally arranged in 3 layers and composed of carbohydrates, like pectin, cellulose, hemicellulose and other smaller amounts of minerals, which form a network along with structural proteins to form the cell wall. The three major layers are:
Primary Cell Wall
The Middle Lamella
The Secondary Cell Wall
Primary Cell Wall
The primary cell is situated closest to the inside of the cell and is the first-formed cell wall. It is mainly made up of cellulose, allowing the wall to stretch for the purpose of growth. Several primary cells contain pectic polysaccharides and structural proteins. It is also comparatively permeable and thinner than the other layers.
The middle lamella is also the outermost layer and it acts as an interface between the other neighbouring cells and glues them together. This layer primarily consists of pectins. However, other substances such as lignin and proteins can also be found.
Secondary Cell Wall
The secondary cell wall is formed inside the primary cell wall once the cell is completely grown. Some types of cells (especially the cells of xylem tissues) consist of cellulose and lignin and these provide additional rigidity and waterproofing. Also, this layer provides the characteristic rectangular or square shape to a cell. It is also the thickest layer and permits permeability.
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By Team Learning Mantras