**The Cell Wall**

The layer that is present outside the plasma membrane in plant cells is called the cell wall. It is a rigid, protective structure that provides support and shape to the cell. The cell wall is found in all plant cells and some other organisms like fungi and bacteria, but it is absent in animal cells.

**Composition and Structure:**
1. **Cellulose:** The primary component of the cell wall is cellulose, which is a complex carbohydrate made up of long chains of glucose molecules. Cellulose provides strength and rigidity to the cell wall.
2. **Other Polysaccharides:** Besides cellulose, the cell wall also contains other polysaccharides such as hemicellulose, pectin, and lignin. These polysaccharides contribute to the overall strength and flexibility of the cell wall.
3. **Proteins:** The cell wall also contains various proteins that play a role in cell wall formation, modification, and signaling processes.
4. **Other Components:** In addition to cellulose, polysaccharides, and proteins, the cell wall may also contain other substances like lipids, minerals, and phenolic compounds.

**Functions of the Cell Wall:**
1. **Structural Support:** The primary function of the cell wall is to provide structural support and rigidity to the plant cell. It prevents the cell from bursting or collapsing under osmotic pressure and gives shape to the cell.
2. **Protection:** The cell wall acts as a protective barrier, shielding the cell from mechanical damage and pathogens. It serves as the first line of defense against external threats.
3. **Water Regulation:** The cell wall helps regulate water balance in plant cells. It allows water to pass through it, but its rigidity prevents excessive water uptake, preventing the cell from bursting.
4. **Cell-to-Cell Communication:** The cell wall facilitates communication between neighboring cells. Plasmodesmata, small channels that traverse the cell wall, allow the exchange of molecules and information between adjacent cells.
5. **Support for the Plant Organism:** The cell wall provides support to the entire plant organism by maintaining the structural integrity of tissues and organs. It enables plants to grow upright and withstand environmental stresses.

In conclusion, the cell wall is a critical component of plant cells, providing structural support, protection, water regulation, and facilitating communication between cells. Its composition of cellulose, polysaccharides, proteins, and other components contributes to its strength and functionality.