Plasma Membrane – Class 11 | Chapter – 10 | Biology Short Notes Series PDF

Plasma Membrane: The plasma membrane, also called the cell membrane, is the membrane found in all cells that separates the interior of the cell from the outside environment. In bacterial and plant cells, a cell wall is attached to the plasma membrane on its outside surface. It consists of a lipid bilayer that is semipermeable. It regulates the transport of materials entering and exiting the cell.


plasma membrane

 The Plasma Membrane’s primary roles are as follows:

  • Keeping the inside cell’s integrity intact.
  • Providing support and keeping the cell’s form.
  • Helps to regulate cell development by balancing endocytosis and exocytosis.
  • It is also involved in cell signaling and communication.
  • It functions as a selectively permeable membrane, admitting only certain chemicals enter the cell.

Plasma Membrane Composition

Proteins and lipids are major components of the Plasma Membrane. Different processes are responsible for incorporating and removing materials into  and out of the membrane. The fusing of the cell membrane with intracellular vesicles leads to the expulsion of the contents of the vesicles.

Cell Membrane

Phospholipids: Phospholipids are an important component of cell membranes. Phospholipids naturally arrange their hydrophilic (attracted to water) head portions to face the aqueous cytosol and extracellular fluid, while their hydrophobic (repelled by water) tail areas face away from the cytosol and extracellular fluid. The lipid bilayer is semi-permeable, enabling only specific molecules to pass through.

Carbohydrates: Carbohydrates, or sugars, are occasionally discovered coupled to proteins or lipids on the exterior of a cell membrane. They can only be found on the extracellular side of a cell membrane. These sugars combine to produce the glycocalyx.

Glycolipids: Glycolipids are carbohydrate sugar chains that are linked to cell membrane surfaces. They assist the cell in recognizing other cells in the body.

Cholesterol: Another lipid component of animal cell membranes is cholesterol. Cholesterol molecules are spread preferentially between membrane phospholipids. Preventing phospholipids from being too densely packed together, helps to protect cell membranes from becoming rigid. Cholesterol is not present in plant cell membranes.

Functions of Plasma Membrane

A cell membrane shields the cell’s structures. Cell membranes are semipermeable, which means that only specific items may flow through them. Cell membranes also form and sustain the cell’s structure.

  • To keep the cell’s physical integrity that is, to physically surround the contents of the cell and to govern the passage of particles, such as ions or molecules, into and out of the cell.
  • The cell membrane protects the cell’s physical integrity. In the case of animal cells (which lack cell walls), the cell membrane binds the cell together by encapsulating the cytoplasm and organelles inside it.
  • The cell membrane physically divides internal components (eukaryotic cells’ organelles) from the external environment. The cell membrane shields the cell from some of the hazardous substances found in its surroundings.
  • It also prevents the loss of valuable biological macromolecules retained within the cell by the plasma membrane.
  • A cell membrane is composed of proteins and lipids. A cell membrane contains three types of proteins: structural proteins, transport proteins, and glycoproteins. These maintain cell structure and form, transport substances across the membrane, and send messages between cells.
  • Cell membranes frequently include receptor sites for certain biochemicals such as hormones, neurotransmitters, and immunological proteins. This allows the cell to perceive and interpret signals from the extracellular environment.
  • Cell membranes are selectively permeable and enclose cells (within the cell wall in the case of plant cells and prokaryotic cells). That is, the structure of these membranes allows certain particles, such as molecules, but not others, to flow through the membrane and therefore into or out of the cell.
  • The process by which cells ingest molecules by engulfing them is known as endocytosis. The plasma membrane forms a tiny inward distortion termed an invagination, which captures the material to be delivered. Endocytosis is the process by which solid particles (“cell eating” or phagocytosis), tiny molecules and ions (“cell drinking” or pinocytosis), and macromolecules are internalized. Endocytosis is a type of active transport since it requires energy.

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By Team Learning Mantras