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Plasma Membrane – Definition, Structure, Components, Functions

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The plasma membrane acts as a protective barrier made of a lipid bilayer with embedded proteins that separates the interior of the cell from its external environment. The plasma membrane, also known as the cell membrane, is a vital component of the living organism that regulates the movement of substances into and out of the cell. It also participates in cell signaling and adhesion and contributes to the overall functionality and integrity of the cell which maintains a stable internal environment. 

What is a Plasma Membrane?

The plasma membrane, also referred to as the cell’s outermost envelopes or structure, encircles both the cell and its organelles. This double-membrane cell organelle, also known as the phospholipid bilayer, is found in both prokaryotic and eukaryotic cells.

The plasma membrane plays a pivotal role in endocytosis and exocytosis processes. It protects the cell from the external environment, governs interactions with surroundings, and supports essential cellular functions.

Structure of the Plasma Membrane

The plasma membrane consists of a lipid bilayer, with two layers of lipids forming its foundation. Embedded within this lipid matrix are various proteins that contribute to its functionality. Among these proteins, receptor proteins enable cell communication, while adhesion proteins promote cellular cohesion. Serving as a protective barrier, the membrane regulates the passage of particles, displaying selective permeability that allows small particles to diffuse freely, and larger ones require specific transport channels.

In 1972 fluid mosaic model was given by S.J. Singer and G.L. Nicolson. It described the complex structure of the plasma membrane with proteins embedded in a fluid lipid bilayer.

Diagram of Plasma Membrane

The labeled diagram of plans membrane is shown below:

Cell Membrane

Functions of Plasma Membrane

The plasma membrane acts as a physical barrier between the cytoplasm and extracellular space and allows biochemical reactions necessary for life to occur. The functions of plasma membrane are as follows:

  • Barrier: Separates cell contents from the external environment.
  • Selective Permeability: Regulates the entry and exit of substances.
  • Cell Communication: Contains receptor proteins for signal detection.
  • Cell Cohesion: Adhesion proteins help cells stick together.
  • Endocytosis & Exocytosis: Facilitates material transport in and out of the cell.
  • Homeostasis: Maintains internal balance by controlling molecule movement.
  • Environment Interaction: Governs interactions with surrounding cells and molecules.
  • Recognition: Displays unique patterns for cell identification.
  • Flexibility: Allows cells to change shape and respond to the environment.
  • Supports Essential Functions: Essential for cell survival, growth, and reproduction

FAQs on Plasma Membrane

1. What is a plasma membrane?

Answer:

The plasma membrane is a cell’s outermost envelops or structure, that encircles both the cell and its organelles. This double-membrane cell organelle, also known as the phospholipid bilayer, is found in both prokaryotic and eukaryotic cells.

2. What are the main functions of the plasma membrane?

Answer:

The main function of the cell membrane is to protect the cell from its surroundings, regulation of solute exchange through it, and isolate cytoplasm from its surroundings.

3: What is the structure of plasma membrane?

Answer: 

The lipid bilayer forms the plasma membrane, interspersed with proteins. On the membrane’s surface, there are receptor and adhesion proteins. Receptors aid cell signaling, while adhesion proteins promote cell cohesion.

4. Is the cell membrane the same as the plasma membrane?

Answer:

Yes, the cell membrane, also referred to as the plasma membrane, is present in all cells, act as a boundary between the cell’s interior and the external surroundings. It Comprises of a lipid bilayer, and exhibits semi – permeability.

5. Why plasma membrane is called so?

Answer:

Cell is made up of protoplasm(or simply plasma) which is semi-fluid matter. The fluid is contained inside a membrane called the plasma membrane. 


Last Updated : 05 Sep, 2023
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