Plasma Membrane

Table of Contents

The outer covering, which covers the surface of a cell is termed the membrane.

What is Plasma Membrane?

An outermost envelope-like membrane or a structure, which surrounds the cell and its organelles is called the plasma membrane. It is a double membraned cell organelle, which is also called the phospholipid bilayer and is present both in prokaryotic and eukaryotic cells.

In all living cells, the plasma membrane functions as the boundary and is selectively permeable, by allowing the entry and exit of certain selective substances. Along with these, the plasma membrane also acts as a connecting system by providing a connection between the cell and its environment.

Explore more: Cell organelles

Structure of Plasma Membrane

A plasma membrane is mainly composed of carbohydrates, phospholipids, proteins, and conjugated molecules, and it is about 5 to 8 nm in thickness.

The plasma membrane is a flexible, lipid bilayer that surrounds and contains the cytoplasm of the cell. Based on their arrangement of molecules and the presence of certain specialized components, it is also described as the fluid mosaic model.

The fluid mosaic model was first proposed in the year 1972 by American biologists Garth L. Nicolson and Seymour Jonathan Singer. The fluid mosaic model describes in detail, the plasma membrane structure in the eukaryotic cells, and how well it is arranged along with their components – phospholipids, proteins, carbohydrates and cholesterol. These components give a fluid appearance to the plasma membrane.

Plasma Membrane Structure
Explore more: The fluid mosaic model

Functions of Plasma Membrane

  • The plasma membrane functions as a physical barrier between the external environment and the inner cell organelles.
  • The plasma membrane is a selectively permeable membrane, which permits the movement of only certain molecules both in and out of the cell.
  • The plasma membranes play an important role in both the endocytosis and exocytosis processes.
  • The plasma membrane also functions by facilitating communication and signalling between the cells.
  • The plasma membrane plays a vital role in anchoring the cytoskeleton to provide shape to the cell and also maintain the cell potential.

Facts about Plasma Membrane

Both cell membrane and plasma membrane are often confused because of the similarity in words. But these two are the protective organelles of the cell and are very much different in their structure, composition and functions. The cell membrane is a type of plasma membrane and is not always the outermost layer of the cell.

For more information refer: Difference Between Cell Membrane and Plasma Membrane

This article concludes the introduction to plasma membranes, their facts and their importance. To know more about plasma membranes, their structure, functions, other related topics and important questions, keep visiting our website at BYJU’S Biology.

Frequently Asked Questions

Q1

Define plasma membrane.

Plasma membrane is defined as the boundary between the cell and its environment.
Q2

Is the plasma membrane permeable?

The plasma membrane is selectively permeable. It allows hydrophobic molecules and small polar molecules to diffuse through the lipid layer but does not allow ions and large polar molecules to diffuse through the membrane.
Q3

Who discovered plasma membrane?

In the late 1600’s Robert Hooke’s discovery of cells led to the proposal of the cell theory. Later in 1839, Schwann studied the different types of animal cells and reported that they have a thin outer layer which is now known as the plasma membrane. In 1855, Cramer and Nageli named them as cell membranes.
Q4

What is plasmalemma?

Plasmalemma is a thin layer that encloses a cell’s cytoplasm. It is the less common term for the cell membrane or plasma membrane. The term plasmalemma was given by J. Q. Plowe in 1931.
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