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Cell Membrane

Last Updated : 26 Feb, 2024
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The cell membrane, also known as the plasma membrane, bounds the cell. The cell membrane is composed of proteins and lipids. It is a selectively permeable membrane that binds the cell and separates the cell from the outside environment. In this article, we will study cell membrane structure, function, and composition along with the cell membrane diagram.

What is a Cell Membrane?

Cell Membrane Definition: A cell membrane is a thin semi-permeable membrane that surrounds and encloses a cell’s cytoplasm.

In certain animals, the cell membrane also acts as a basis of attachment for the cytoskeleton, whereas in others, it functions as the cell wall. As a result, it aids in cell support and shape maintenance. The membrane also provides a cell structure and allows it to join with neighboring cells to form tissues.

The cell membrane regulates the passage of substances into and out of cells by being selectively permeable to ions and organic molecules. The cell membrane’s primary role is to separate the interior of the cell from the outside environment.

Cell membrane is made up of lipids (phospholipids and cholesterol) and proteins and is semi-permeable. The primary function of plasma membrane are as follows:

  • Keeping the inside cell’s integrity intact.
  • Providing support and protection to the cell from its surroundings.
  • Helps to regulate cell development by balancing endocytosis and exocytosis.
  • The cell membrane is also involved in cell signaling and communication.
  • It functions as a selectively permeable membrane, admitting only certain chemicals enter the cell.

Cell Membrane Diagram

The labelled diagram of cell membrane is given below:

Cell Membrane

Cell Membrane Structure

The cell membrane is composed of two phospholipid-based layers. The bilayer is generated by arranging phospholipids such that their head regions (which are hydrophilic) face both the exterior and internal cytosolic environments. These phospholipids’ (hydrophobic) tails are facing each other.

Electrostatic, van der Waals, non-covalent interactions, and hydrogen bonding are the forces that drive the development of this bilayer. This unusual configuration of hydrophilic and hydrophobic layers prevents nucleic acids, amino acids, proteins, carbohydrates, and ions from passing through the bilayer. The many components of the cell membrane are listed below.

Integral Membrane Proteins 

Integral Membrane Proteins are structures found on the inside, outside, and all throughout the cell membrane. These proteins may be seen using fluorescence and electron microscopy. These proteins are found on the cell membrane’s entire/complete surface. Cadherins, integrins, clathrinid-coated pits, desmosomes, caveola’s, and other structures are examples of these structures.

Peripheral Membrane Proteins  

These proteins are associated with the membrane’s surface via hydrogen bonds and electrostatic interactions. The hydrophilic phospholipid heads that compose the bilayer create the hydrogen bonds of these peripheral proteins.

Cell Membrane Skeleton 

The cytoskeleton lines the surface of the cell membrane on the cytoplasmic side. The structure, or cytoskeleton, is important in the operations of organelles such as cilia. The cytoskeleton also aids in the attachment of membrane proteins to the cell membrane.

Composition of Cell Membrane

Proteins and lipids are major components of the cell membrane. Different processes are responsible for incorporating and removing materials into  and out of the membrane. The fusing of the cell membrane with intracellular vesicles leads to the expulsion of the contents of the vesicles.


Phospholipids are an important component of cell membranes. Phospholipids naturally arrange their hydrophilic (attracted to water) head portions to face the aqueous cytosol and extracellular fluid, while their hydrophobic (repelled by water) tail areas face away from the cytosol and extracellular fluid. The lipid bilayer is semi-permeable, enabling only specific molecules to pass through.


Carbohydrates, or sugars, are occasionally discovered coupled to proteins or lipids on the exterior of a cell membrane. They can only be found on the extracellular side of a cell membrane. These sugars combine to produce the glycocalyx.


Glycolipids are carbohydrate sugar chains that are linked to cell membrane surfaces. They assist the cell in recognizing other cells in the body.


Another lipid component of animal cell membranes is cholesterol. Cholesterol molecules are spread preferentially between membrane phospholipids. Preventing phospholipids from being too densely packed together, helps to protect cell membranes from becoming rigid. Cholesterol is not present in plant cell membranes.

Cell Membrane Function

A cell membrane shields the cell’s structures. Cell membranes are semipermeable, which means that only specific items may flow through them. Cell membranes also form and sustain the cell’s structure.

  • To keep the cell’s physical integrity that is, to physically surround the contents of the cell and to govern the passage of particles, such as ions or molecules, into and out of the cell.
  • The cell membrane protects the cell’s physical integrity. In the case of animal cells (which lack cell walls), the cell membrane binds the cell together by encapsulating the cytoplasm and organelles inside it.
  • The cell membrane physically divides internal components (eukaryotic cells’ organelles) from the external environment. The cell membrane shields the cell from some of the hazardous substances found in its surroundings.
  • It also prevents the loss of valuable biological macromolecules retained within the cell by the plasma membrane.
  • A cell membrane is composed of proteins and lipids. A cell membrane contains three types of proteins: structural proteins, transport proteins, and glycoproteins. These maintain cell structure and form, transport substances across the membrane, and send messages between cells.
  • Cell membranes frequently include receptor sites for certain biochemicals such as hormones, neurotransmitters, and immunological proteins. This allows the cell to perceive and interpret signals from the extracellular environment.
  • Cell membranes are selectively permeable and enclose cells (within the cell wall in the case of plant cells and prokaryotic cells). That is, the structure of these membranes allows certain particles, such as molecules, but not others, to flow through the membrane and therefore into or out of the cell.
  • The process by which cells ingest molecules by engulfing them is known as endocytosis. The plasma membrane forms a tiny inward distortion termed an invagination, which captures the material to be delivered. Endocytosis is the process by which solid particles (“cell eating” or phagocytosis), tiny molecules and ions (“cell drinking” or pinocytosis), and macromolecules are internalized. Endocytosis is a type of active transport since it requires energy.

Conclusion – Cell Membrane

The cell membrane is the outermost layer in animal cell that separates the interior of the cell from the outside environment. It consists of a lipid bilayer that is semipermeable. The cell membrane functions to regulates the transport of materials entering and exiting the cell.

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FAQ’s – Cell Membrane

What is the Function of the Cell Membrane?

The cell membrane regulates the entry and exit of substances, maintaining the cell’s internal environment and facilitating communication and signaling between cells.

How is the Cell Membrane Structured?

The cell membrane is composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates that provide fluidity, flexibility, and specificity in function.

Can you Explain the Fluid Mosaic Model of the Cell Membrane?

The fluid mosaic model describes the cell membrane as a fluid combination of phospholipids, cholesterol, and proteins that move freely and serve various functions, including transport and signaling.

What Role do Proteins Play in the Cell Membrane?

Membrane proteins function in transport, as receptors for signal transduction, as anchors for cell structure and shape, and in facilitating cell to cell communication.

 How does the Cell Membrane Contribute to Homeostasis?

The cell membrane maintains homeostasis by controlling the substances that enter and leave the cell, ensuring optimal conditions for the cell’s functions.

Where do Chromosomes Reside in a Cell? Explain What they do? 

They are situated in the cell’s nucleus, and each chromosome contains genes that are responsible for some attribute or characteristic. These genes pass these characteristics down from parents to kids.

Which Chemical is Found in Both the Cell Membrane and Space?  

Ethanolamine, present in all Earth’s cell membranes, was also detected in space. It’s vital for genetic and metabolic processes due to its composition of oxygen, nitrogen, hydrogen, carbon, phosphorus, and sulfur.

What is Cytoplasm?

The cytoplasm is the live component of the protoplasm between the plasma membrane and the nucleus.

What is the Boundary called in Each Cell?

The cell membrane, also known as the plasma membrane, is the border of the cell. The cell membrane shields the cell or its inner components from the outside environment. It gives the cell form and a distinct structure.

Is the Cell Membrane Hydrophobic or Hydrophilic?

All cell membrane lipids are amphipathic, with a hydrophilic polar end and a hydrophobic nonpolar end. This dual nature attracts water on the outer layer and repels it on the inner layer.

Why is Cell Membrane Semi-permeable?

The cell membrane is semi permeable as it allows selective entry of solute through the cell.

What is Cell Membrane Structure and Function?

The cell membrane is composed of a phospholipid bilayer with embedded proteins. It regulates the passage of substances in and out of the cell, maintains cell shape and integrity, and facilitates cell communication.

What is the Difference Between Cell Wall and Cell Membrane?

The cell wall offers structural support and protection in plant, fungal, and bacterial cells, while the cell membrane regulates substance passage and maintains cell integrity with its phospholipid bilayer structure.

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