Plasma membrane function | Plasma definition

1. Plasma definition

2. Plasma membrane function

3. Structure of Plasma Membrane


Plasma definition

The cell membrane is a selective semi-permeable living membrane that surrounds the protoplasm of each living cell. The base of the cell membrane is made up of three layers, out of which the outer and inner layers are the protein membrane and the middle layer is the phospholipid layer. 

The cell membrane maintains the shape of the cell and protects the cytoplasm. Along with controlling the action of intracellular diffusion and osmosis, it also helps in the formation of various structures. 

Plasma membrane function

The cell membrane surrounds the cytoplasm of living cells, physically separated from the extracellular components. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix and holding other cells together to form tissues. 

Fungi, bacteria, most archaea and plants have a cell wall, which provides mechanical support to the cell and prevents the passage of large molecules. 

The cell membrane is selectively permeable and is able to regulate entry and exit of the cell, thus facilitating the transport of materials necessary for survival. 

The movement of substances across the membrane can be either “passive”, which occurs without the input of cellular energy, or “active”, requiring the cell to expend energy in transport. The membrane also maintains the cell potential. The cell membrane thus acts as a selective filter that allows only certain things to enter or exit the cell. 

Structure of Plasma Membrane 

Plasma membrane function | Plasma definition

Although this model has undergone many changes over time, the fluid mosaic model is the model most often used to describe the structure of the plasma membrane. 

According to this model, the plasma membrane is composed of freely moving (in a fluid-like manner) components (phospholipids, proteins, and cholesterol). Its consistency has been likened to that of salad oil at body temperature. 

Here, then, the plasma membrane depicted in books may be thought of as a snapshot of a structure that is always in motion. 

Due to the fluid nature of the plasma membrane, it would continue to flow around an object (e.g. very fine needle) if the object was inserted into a cell. 

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