Difference between the cell wall and the cell membrane is primarily due to the differences in three factors like composition, function and permeability.
Composition: The composition of cell wall mainly comprises of proteins and carbohydrates, whereas a cell or plasma membrane comprises of lipids, proteins and some amount of carbohydrate.
Function: The functional role of the cell wall is to provide protection and rigidity. In contrast, a cell membrane protects the protoplasm and mediates the exchange of materials between a cell and environment.
Permeability: A cell wall shows complete permeability towards small molecules, whereas the plasma membrane shows semi permeability that allows water, specific molecules or ions to enter inside or outside a cell.
Both cell wall and cell membrane are somewhat similar in a way that they are involved in maintaining the cellular physiology of an organism.
Content: Cell Wall Vs Cell Membrane
|Properties||Cell wall||Cell membrane|
|Existence||It surrounds the cell membrane||It surrounds the inner protoplasm|
|Thickness||Comparatively thicker than the cell membrane (4-20 µm wide)||Thin (5-10 µm wide)|
|Distribution||Found in bacteria, plant and fungal cell||Found in all cells|
|Composition||Composed of proteins and carbohydrates||Composed of lipids, proteins and carbohydrates|
|Permeability||Completely permeable to small protein molecules||Semipermeable to ions and organic molecules|
|Metabolic activity||It is metabolically inactive and non-living in nature||It is metabolically active and living in nature|
|Flexibility||It is rigid and having fixed shape||It is highly flexible|
|Cell receptors||It lacks the presence of cell receptors||It contains the cell surface receptors|
|Visibility||Visible under the light microscope||Visible under the electron microscope|
|Functional role||It is protective in function||It mediates the exchange of materials or ions inside and outside the cell|
It is the outermost covering of most of the bacterial, fungal and plant cell. A plant cell wall primarily forms of cellulose (a most copious polysaccharide found in nature). The cell-wall of bacteria comprises a murein peptidoglycan layer, formed by the combination of carbohydrates and amino acids. Among bacteria, Mycoplasma is an exception that lacks the cell-wall. A fungal cell primarily contains chitin (a nitrogenous polysaccharide).
The plant cell-wall mainly comprises the following elements like:
Primary wall: It incorporates cellulose, hemicellulose and pectin.
Middle lamella: It primarily contains pectin (a sticky substance), binding the cell wall to the cell membrane.
Secondary lamella: Exists in woody plants by the deposition of cellulose, hemicellulose, pectin and lignin.
Plasmodesmata: These can consider as the tiny orifices or channels that allow the conduction of materials within the cell.
The cell-wall functions to provide structural integrity, cell protection (against turgor pressure and osmotic lysis), storage and communication.
The plasma membrane, cytoplasmic membrane or plasmalemma are the alternative names for the cell membrane. It is common in all living cells, or we can say it is imperative to sustain life. Singer and Nicolson were the two scientists who gave the 3D model and studied the structure of the plasma membrane through electron microscopy. Composition of cell membrane consists of 60-80% of proteins, 20-40% of lipids and 2-10% of carbohydrates.
It consists of a phospholipid bilayer membrane that comprises of 50% phospholipid, 2% glycolipids and the remaining sterol. The phospholipids and glycolipids generally consist of 16-18 carbon-atoms fatty acid chain, which can be saturated or unsaturated. A lipid bilayer membrane also comprises carbohydrates (predominantly glycoproteins), which helps in cell-cell recognition. The structure of the plasma membrane contains two significant elements, such as polar or hydrophilic head and two hydrophobic tail.
The cholesterol chains embedded within the fatty-acid tails and help in providing the membrane fluidity. Plasmalemma also contains a group of three proteins like integral, peripheral and lipid-anchored proteins. A plasma membrane performs a vital role in water or ionic conduction, cell signalling and adhesion.
Key Differences Between Cell wall and Cell membrane
- A cell wall exists as an envelope surrounding the plasma membrane, whereas a cell membrane exists as a protective layer surrounding the inner protoplasm.
- The cell wall consists thickness of 4-20 µm or comparatively thicker and shows complete permeability. Oppositely, a plasmalemma comprises a thickness of 5-10 µm and shows semi permeability.
- A cell wall is found in the bacterial, plant and fungal cell, whereas the presence of plasma membrane is typical in all the cell types.
- The cell wall acts like a non-living and metabolically inactive cell, oppositely a plasma membrane functions as a living and metabolically active cell.
- Plasma membrane shows a flexibility that was proved by the fluid mosaic model, where the molecules can contract or move. In contrast, cell wall shows rigidity and fixed shape.
- One of the distinguishing features is the presence of cell surface receptors, which lacks in the cell wall.
Despite many differences, both the cell wall and plasma membrane are the outer coverings, protecting the inner cytoplasm and internal cell organelles against physical and chemical damage. These can consider as a shell that protects the inner body from extreme environmental conditions.