Cell Wall and Cell Membrane

Cell membrane, also known as plasma membrane, is a thin membrane that surrounds every live cell and serves as a barrier between the cell and the surrounding environment. The cell’s components, which are frequently large, water-soluble, highly charged molecules such as proteins, nucleic acids, carbohydrates, and chemicals involved in cellular metabolism, are contained within this cell membrane (also known as the plasma membrane) and are protected from the environment. Aside from the cell itself, in the surrounding water-based environment, there are ions, acids, and alkalis that can be harmful to the cell, as well as nutrients that the cell needs in order to survive and thrive. Consequently, the cell membrane performs two functions: first, it serves as a barrier, keeping essential nutrients and waste products in while keeping unwanted substances out; and second, it serves as a gate, allowing waste products to be transported into the cell and nutrients to be transported out of the cell.

Cell Wall

A cell wall is an external layer that surrounds specific cells outside of the cell membrane. Cell membranes are found in all cells, although only plants, fungus, algae, most bacteria, and archaea have cell walls. The cell wall gives the cell strength and structural support, and it may determine what types and concentrations of chemicals enter and leave the cell to some extent. Depending on the type of organism, the materials that make up the cell wall differ. Different kinds of creatures have evolved the cell wall at different times.

Cell Wall Functions

Since the plasma membrane is a delicate layer that cannot provide identical protection against varied external conditions, the major role of a cell wall is to give protection to the cell’s internal structures. Furthermore, cell walls are crucial for giving cells their particular forms. The cell wall stops the cell from expanding and rupturing when the internal pressure inside the cell rises owing to the entry of water. The cell wall regulates molecule passage throughout the cell, allowing only tiny metabolic molecules to pass, safeguarding the cell from poisons and drugs. Cell walls help in cell adhesion and give cells a distinct shape in multicellular creatures with cell walls.

Cell Wall Structure

Plant Cell Walls

Cellulose, a carbohydrate that forms long fibres and provides the cell wall its rigidity, is the most important component of the plant cell wall. Microfibrils are formed when cellulose fibres are bundled together. The cell wall is made up of a network of carbohydrates and structural proteins. Primary cell walls, which are thin, are present in plant cells that are in the process of growing. Secondary cell walls form once the cells have reached complete maturity. On the interior of the primary cell wall, a thick layer called the secondary cell wall forms.   The intermediate lamella, which is pectin-rich and helps plant cells stick together, is also present between plant cells.

Algae Cell Walls

Algae are a diversified group, and their cell walls reflect that variety. Some algae, such as green algae, have cell walls that resemble plant cell walls in structure. Brown and red algae, for example, have cellulose as well as other polysaccharides or fibrils. The cell walls of diatoms are composed of silicic acid. Mannans, xylans, and alginic acid are other significant compounds found in algal cell walls.

Fungi Cell Walls

Fungi have chitin in their cell walls, which is a glucose derivative with a structure similar to cellulose. Chitin layers are extremely tough; chitin is the same chemical that is found in the rigid exoskeletons of insects and crustaceans. Along with lipids and proteins, the fungal cell wall contains glucans, which are additional glucose polymers. Hydrophobins are proteins found in the cell walls of fungi. Hydrophobins are exclusively found in fungus, and they provide cell strength, assist them to stick to surfaces, and control the flow of water into the cells. The cell wall surrounds the cell membrane in fungi and is the most exterior layer.

Bacteria and Archaea Cell Walls

Bacterial cell walls often include the porous polysaccharide peptidoglycan, which allows tiny molecules to pass through. The cell envelope is made up of the cell membrane and the cell wall. For many bacteria, the cell wall is critical to their survival. It gives bacteria, which are single-celled, mechanical structure and protects them from internal turgor pressure. Bacteria have a larger concentration of molecules like proteins within them than in their surroundings, therefore the cell wall prevents water from entering the cell. Gram staining is also possible due to differences in cell wall thickness. Gram staining is a method for identifying bacteria in general; bacteria with thick cell walls are gram-positive, whereas bacteria with thinner cell walls are gram-negative.

CELL MEMBRANE DEFINITION

A cell’s cytoplasm is surrounded by a thin semi-permeable membrane called the cell membrane. Its aim is to protect the cell’s interior integrity by admitting some chemicals into the cell while preventing others from entering. In certain species, it also functions as a basis of attachment for the cytoskeleton, whereas in others, it serves as a foundation of attachment for the cell wall. As a result, the cell membrane also helps to support and maintain the cell’s structure.​

Cell Membrane Functions

Moving on to the important responsibilities and duties that the cell membrane plays in a cell’s biological functioning, we may deduce the following-

1) Shape & Structure of the cell – The cell membrane serves as an anchor for the cytoskeleton.

2) Barrier and gatekeeper of the cell – The cell membrane guards the cytosol from the external environment.

3) Cellular transport – It controls the movement of molecules across the membrane.

4) Cell communication and recognition – assists tissues work together in unison.

5) Cell signalling – contains receptors and enzymes

CELL MEMBRANE STRUCTURE

Phospholipid Bilayer

A phospholipid bilayer makes up the cell membrane. Phospholipids are lipid molecules with two fatty acid tails and a phosphate group head. Importantly, phospholipid molecules have features that allow them to create a double-layered membrane spontaneously.

A phospholipid’s phosphate group head is hydrophilic, whereas the phospholipid tail is hydrophobic. This means that water attracts the phosphate group, but repels the tail.

Membrane-Associated Factors

The cell membrane also includes lipid compounds, notably glycolipids and sterols, in addition to the phospholipid bilayer. Cholesterol is an essential sterol that controls the fluidity of the cell membrane in animal cells. Membranes become more fluid as cholesterol levels drop, but they also become more porous to chemicals. The quantity of cholesterol in the membrane helps in maintaining its permeability, allowing the appropriate quantity of molecules to enter the cell at any given time.

Many different proteins are also found in the cell membrane. About half of the cell membrane is made up of proteins.

Conclusion

Both the cell wall and the cell membrane are crucial organelles in living organisms. The former, on the other hand, is only present in plants, fungi, and a few bacteria. The Cell Wall is a type of extracellular matrix that surrounds each of a plant’s cells. Many of the features that distinguish plant cells from animal cells are due to the cell wall. Cell Membranes are made up of lipids and proteins and act as a barrier between cells and intracellular organelles. Membranes separate the interior from the outside, allowing only certain molecules to pass through and relaying messages via a sequence of chemical reactions.