Content Curator
Plasma Membrane is a thin delicate sheet which protects the cell from its surroundings. It acts as a barrier between the internal aqueous section and external aqueous section of the cell. In this article, we will discuss more about the plasma membrane, its structure, functions and components.
Plasma Membrane
Plasma Membrane or cell membrane, is a kind of thin sheet which is present in all cells. It plays a crucial role in separating the internal part of the cell from the exterior. It comprises a lipid layer known as semipermeable membrane. It helps in regulating the flow of materials and allows the substance to move in and out of the cell.
Functions of Plasma Membrane
Plasma Membrane comprises a bilayer which is implanted with proteins and it helps in forming a barrier between two aqueous sections that are outside and inside of a cell membrane. The embedded proteins in plasma membranes help in performing various functions. The following are the main functions performed by the plasma membrane:-
- Recognition of cells and assists in transportation of molecules.
- Helps in protecting the cell by maintaining a proper environment within the cell.
- Allows the movement of white and red blood cells.
- Helps the cytoskeleton of a cell to provide a proper shape and structure to the cell.
- Maintaining the potential limit of a cell and is also responsible for interacting with other cells.
- Monitoring and providing a proper chemical climate to the cell.
Components of Plasma Membrane
Plasma Membrane comprises of following components :-
- Cholesterol :- It is folded between the hydrophobic tails of phospholipid membrane.
- Phospholipids :- It helps in forming the ultimate fabric of the membrane and is one of the most important components of a plasma or a cell membrane.
- Peripheral proteins :- They are present either on the internal or external surface of the phospholipid bilayer.
- Carbohydrates:- It is attached either to the lipids or to the protein on the extracellular part of the plasma membrane. It leads to the formation of glycolipids and glycoproteins.
- Integral Proteins :- They are located in the phospholipid bilayer.
Structure of Plasma Membrane
Plasma Membrane is a type of fluid substance which is made up of carbohydrates, proteins and lipids. The transmembrane proteins play a major role in regulating the concentration of ions and providing the necessary nutrients to the cell.
Plasma Membrane comprises a phospholipid bilayer. Phospholipid is a type of lipid substance and it is associated with a phosphate group. A phospholipid mainly consists of a single head and two tails. The head part of the phospholipid is hydrophilic in nature while the tail is hydrophobic in nature.
Water loving substances are known as polar substances whereas water fearing substances are known as non polar substances. So, the head is a polar substance and the tail is a nonpolar substance.
Things to Remember Based on Plasma Membrane
- Plasma Membrane or cell membrane, is a thin sheet which is present in all cells.
- It separates the internal part of the cell from the exterior.
- It regulates the flow of materials and allows the substance to move in and out of the cell.
- It monitors and provides a proper chemical climate to the cell.
- It maintains the potential limit of a cell.
- Plasma membrane is responsible for the interaction between the cells.
Important Questions Based on Plasma Membrane
Ques: What is endoplasmic reticulum? (1 Mark)
Ans: Endoplasmic reticulum connects the nuclear membrane with the plasma membrane. It is the system of a complex folded network of membranous tubes and allows the movement of substances within the cell.
Ques: What are the main functions of the cell wall? (2 Marks)
Ans: The main functions of the cell wall are:
- It gives a definite shape to the cell.
- It protects the internal organelles.
- It prevents the cell from desiccation.
- It provides support to the plasma membrane.
- It helps in the transportation of materials and metabolites in and out of the cell.
Ques: What are the main functional regions of a cell? Explain. (3 Marks)
Ans: Main functional regions of a cell are Plasma membrane, Cytoplasm and Nucleus.
- Plasma membrane: Plasma membrane makes the outer boundary of the cells. The membrane is very thin, delicate and permeable.
- Cytoplasm: Cytoplasm is a transparent jelly-like substance of the cell. It is viscous in nature and contains cell organelles.
- Nucleus: Nucleus is responsible for the overall working of the cell. It is dense and oval in structure and lies in the protoplasm of the cell.
Ques: Define plasma membrane and state its functions. (3 Marks)
Ans: Plasma membrane or cell membrane is a thin membrane which surrounds the cytoplasm. Some of the important functions of cell membrane are:
- It provides a definite shape to the cell.
- Helps in protecting the cell by maintaining a proper environment within the cell.
- It allows the movement of substances from both inside and outside the cells.
- It helps in regulating the movement of materials through the cells.
Ques: What is the role of the plasma membrane in the compartmentalization of the cell? (3 Marks)
Ans: Every cell is covered from all sides by a membrane called the plasma membrane. The major roles of plasma membrane in compartmentalization of the cell are:
- It prevents the cell from mixing the cell contents with extracellular materials and maintains the individuality of the cell.
- The cell membrane regulates the exchange of materials in a cell.
- In animals, the cell membrane helps the cells to defend themselves against microbes.
- The cell membrane also exchanges messages between the cells.
- In aquatic animals, the cell membrane selectively allows the passage of certain molecules and ions from the seawater.
Ques: Describe the fluid mosaic model of the plasma membrane. (5 Marks)
Ans: Garth L. Nicolson and S.J.singer proposed the model in 1972 which shows the structure of plasma membranes and the model is named Fluid Mosaic model. This model is considered as the best model to provide the functions and structure of the plasma membrane.
Thickness of the membrane is about 5-10nm.The proportion of plasma membrane varies from cell to cell. The inner membrane of the mitochondria consists of 76% protein and the rest 24% is lipids whereas in myelin, the percentage for lipids present is 76% and proteins are just 18%.
The major fabric of the membrane consists of amphiphilic phospholipid molecules. The hydraulic part of these remains in contact with the fluid inside and outside of the cell. A single phosphorylated molecule comprises a 3 carbon glycerol backbone and 2 fatty acid molecules associated with 1 st and 2nd carbon and another phosphate is connected to the 3rd carbon.
This provides a specified region,known as head of the molecule and we have seen that head is a polar character and it interacts with non polar tails .
Comments