The Function of Cell Membrane : Key Points

Cell Membrane is an important part of the cell. It helps in various activities done by the cell. The function of cell membrane are  given below –

1. Regulation of Shape

• In animal cells it is the outer membrane of the cell. It controls the cell shape.

2. In Security

• It protects the protoplasm from external injuries and also has the ability to heal the injury or wound.

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3. As a Barrier

• It separates the intracellular fluid or cytoplasm from extracellular fluid, which is a very important work.

4. In the Transport of Substances 

Various types of substances enters & excreted from the cell when needed. The transport of substances are done by following process –

                           i.          Passive Transport Or Osmosis

• Energy is not involved in this process.
• It follows the simple law of diffusion. In which the molecules flows from high concentration to low concentration through the plasma membrane. There are channels or tubules present in the cell membrane for the transport.
• This is a physical process.
• This is non - selective and two - directional process.
• This is not helpful to maintain the osmotic pressure of the cell.
• This is not affected by the temperature, availability of oxygen and presence of toxic excretory materials.

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Active & Passive Transport

                          ii.          Active Transport

• This process involves energy.
• In this the molecules transport from low concentration to high concentration, which is against the law of osmosis.
• This a bio - chemical process.
• This is a selective and one - directional process.
• This is done by the carriers molecules.
• The aim of active transport is to maintain the osmotic pressure of extra cellular fluid & cell.
• This is affected by the temperature, availability of oxygen and presence of toxic excretory materials.

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                         iii.          Pinocytosis

• Ingestion of liquid substances through cell membrane of the cell is known as Pinocytosis.
• Proteins with high molecular weight enter the cell through this process as they are unable to enter in the cell through cell membrane.
• In this firstly the molecules are absorbed at the surface of cell membrane, after that infolding of cell membrane occurs , which is called pinocytic vesicle or pinosome.

Pinocytosis

• After this the pinosome released in the cytoplasm and floats freely.
• These pinosomes are taken by the Lysosomes and digested.
• After digestion it is released in the cytoplasm.

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                           iv.          Phagocytosis

• Ingestion of solid substances through cell membrane is known as phagocytosis.
• This is found in protozoa and metazoan creatures.
• During this process pseudopodia are surrounds the large particle and ingest it directly in the cytoplasm.
• The ingested particle is called as phagosomes.
• Phagosomes are taken by the Lysosomes and digested.

Phagocytosis

5. Regulation on the Passage of Materials 

The cell membrane is selectively permeable. Thus only essential substances can enter into the cell. The harmful and excretory substances remain outside of the cell. Thus cell membrane controls the transport of substances.

6. In Locomotion 

• In a few unicellular organisms like Amoeba , it forms pseudopodia, which helps it to move the organism.

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7. Excretion  

• By the diffusion process, Nitrogenous substances are excreted from the cell.

8. Contact With Neighbouring Cells 

• The joints presents on the cell membrane, helps to communicate with neighbouring cells .

9. Cytoplasmic Continuity   

• Cell membrane helps in the formation of Plasmodesmata. And plasmodesmata helps to maintain cytoplasmic continuity of the adjacent cells.

Function of Protein Molecules Present on Plasma Membrane

     The molecules of protein present on both sides of the lipids helps in various activities such as carrier, receptor also acts as a enzyme molecules. The function of protein molecules present on plasma membrane is categories as follows –

1.        In the form of carrier molecules
2.        In the form of receptor molecules
3.        In the form of enzyme molecules

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     1. In the Form of Carrier Molecules

•        The proteins present on cell membrane are normally permease.
•        The protein molecules works as a carrier protein.
•        Carrier protein allows only some selected substance to enter & exit from cell membrane.
•        Firstly these carrier proteins combine with the specific molecules which are being transported,   after that the combines molecules are allows to enter or exit from cell.

     2. In the Form of Receptor Molecules

•        Oligosaccharides called as glycoprotein, found on the surface of the plasma membrane, act as receptors.
•        Their main function is to recognize and bind the specific molecules present near the cell.
•        Hormones, various chemical substances and other cell membrane are the specific molecules.
•        These protein molecules recognizes the epinephrine & insulin like hormones and binds them   with the receptor of the cell membrane.

     3. In the Form of Enzyme Molecules

•       Enzymes are present on every cell membrane for work done by cell membrane.
•       For example – accessory enzymes are present in the inner membrane of mitochondria to help in the electron transport system ( ETS ) of respiration.

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