Cell Wall – Properties, Components and Function

The cell wall was discovered by Robert Hooke in 1665.

Structure:

It is the outermost boundary of the plant cells. Each cell, whether isolated or occurring in tissues, has its cell wall. The chemical composition of the cell walls is different from specie too. E.g., the plant cell wall is composed of Cellulose, Hemicellulose, and pectin.

The cell wall of Fungi is composed of Chitin, the Cell wall of bacteria is composed of Murein, and the cell wall of Algae is composed of Glycoproteins and polysaccharides. Some other compounds, i.e., lignin and cutin, are also found in the cell wall.

6000 Glucose monomers combine to form a cellulose chain. 100 cellulose chains combine to form Micelle. 20-40 micelles combine to form a microfibril, and 250 microfibrils combine to form a microfibril, which is combined to form a cell wall.

Cell walls have three fundamental layers, namely

i) Middle lamella

ii) Primary wall

iii) Secondary wall.

i) Middle Lamella:

The middle lamella is a layer that cements the cell walls of two adjoining plant cells. It is the first formed layer deposited at the time of cytokinesis. The cell plate formed during cell division develops into the middle lamella or labellum.

The middle lamella is made up of calcium and magnesium pectate. In a mature plant cell, it is the outermost layer of the cell wall. It is usually 1 micrometer in thickness.

ii) Primary Wall:

This layer is formed between the middle lamella and plasma membrane in growing plant cells. It primarily comprises cellulose microfibrils within a gel-like matrix of hemicellulose fibers and pectin polysaccharides.

The primary cell wall provides the strength and flexibility needed for cell growth. It is usually 1-3 micrometers in thickness.

ii) Secondary wall:

This layer is formed between the primary cell wall and plasma membrane in some plant cells. Once the primary cell wall has stopped dividing and growing, it may thicken to form a secondary cell wall. This rigid layer strengthens and supports the cell. In addition to cellulose and hemicellulose,

Some secondary cell walls contain lignin. Lignin strengthens the cell wall and aids in water conductivity in plant vascular tissue cells. It is usually 5-10 micrometers thick and consists of three layers S1, S2, and S3.

FUNCTION OF CELL WALL

1) It Provides a definite shape and structure to the cell.

2) It Provides support and protection against infections.

3) It helps transport substances and Communications in the cells.

4) It prevents water loss.

5) It helps in osmotic regulations.

6) It prevents the cell from rupturing due to turgor pressure.

7) It provides mechanical protection from pathogens and insects.

8) The cell wall stores carbohydrates for plant growth, especially in seeds.

9) The cell wall sends signals for the cell to enter the cell cycle to divide and grow.

10) It helps diffuse gases in and out of the cell.

EXPANSION PROTEIN

Expansion Protein is a glycoprotein that causes the cell wall’s loosening and expansion by adding cellulose molecules to the microfibrils. It helps in the formation of cells by removing old microfibrils and adding new microfibrils And also increases the size of the cell.

Why is the Cell wall considered non-living?

Technically  cell wall is not alive, but Biologists generally agree that for something to be
considered “alive,” it must

1) Independently reproduce

2) Use energy and produce waste 3) Grow

If you put a cell wall in a container with food and water, it would never reproduce or do any of the functions associated with life.

A cell wall is a hard sugary coating on the outside of the plant, bacterial and some fungal cells. Its function primarily maintains the cell’s shape and protects it from damage.

The fundamental principle is that the smallest unit of life is the cell. Therefore, tissues are living because they are made of cells, and organs are living because they are made of tissues. But anything that makes up a cell necessarily has not to be alive.

So all the organelles in a cell, like the nucleus, mitochondria, and endoplasmic reticulum, are non-living. It’s only when all of the parts of a cell come together to make a cell that you have a functional living entity.

The cell wall is just one component of the cell that, together with other components, produces the plant. The plant is alive, but not the cell wall.

Why is the cell wall considered living?

Wall was considered dead due to the presence of cellulose. But with the increasing pace in cell biology, we learned that the cell wall has specific proteins known as expansins. These proteins were found to affect increasing or decreasing cell wall size.

External or internal stimuli bring out this change. This property, i.e., the ability to sense a change in the environment and then act correspondingly, is one of the fundamental properties of life. Hence cell wall is living.

FAQs

Key Points

• 🌱 The cell wall is a structural layer surrounding some types of cells just outside the cell membrane.
• 🌱 It provides shape, support, and protection to the cell.
• 🌱 The chemical composition of the cell walls varies depending on the organism.
• 🌱 Plant cell walls are composed of cellulose, hemicellulose, and pectin.
• 🌱 Fungal cell walls comprise chitin, bacterial cell walls of murein, and algal cell walls of glycoproteins and polysaccharides.
• 🌱 The cell wall has three layers: middle lamella, primary wall, and secondary wall.
• 🌱 The middle lamella cements the cell walls of two adjoining plant cells.
• 🌱 The primary wall comprises cellulose microfibrils, hemicellulose fibers, and pectin polysaccharides.
• 🌱 The secondary wall forms in some plant cells and may contain lignin.
• 🌱 The cell wall performs various functions, such as providing support, protection, osmotic regulation, preventing water loss, and mechanical protection.
• 🌱 Expansion protein loosens and expands the cell wall by adding cellulose molecules.
• 🌱 The cell wall is non-living because it does not reproduce independently, use energy, or grow.
• 🌱 The cell wall is considered living due to the presence of expansins, proteins that can sense and respond to environmental changes.
• 🌱 Cell walls are primarily found in plant cells, bacteria, fungi, and some protists.
• 🌱 Animal cells do not have cell walls; they have a flexible cell membrane.
• 🌱 Plant cell walls comprise cellulose, hemicellulose, pectin, proteins, and lignin.
• 🌱 The cell wall contributes to plant growth by providing structural support and directing cell growth orientation.

Read Also:

• Plant Cell – Definition, Structure, Diagram & Function
• Fungi-Mycelium, Cell structure, Reproduction, Nutrition
• Structure and Function of a Typical Bacterial Cell with Diagram
• Cell Membrane – Definition, Function, and Structure | Biology.
• Cell Plate – Structure, Formation, and Function