Class 11 Biology Cell : The Unit of Life Cell membrane

Cell membrane

  • The cell membrane is composed of lipids that are arranged in a bilayer.
  • The lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner part, which ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment.
  • The lipid component of the membrane mainly consists of phosphoglycerides.
  • Cell membranes also possess protein and carbohydrate.
  • Membrane proteins can be classified as integral
  • Peripheral proteins lie on the surface of membrane while the integral proteins are partially or totally buried in the membrane.
  • Fluid mosaic model of cell membrane was proposed by Singer and Nicolson.
  • According to Fluid mosaic model, the quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer, and the ability to move within the membrane is measured as its fluidity.
  • The membrane is selectively permeable and the most important functions of the plasma membrane is the transport of the molecules across it.
  • Movement of water by diffusion from higher to lower concentration is called
  • The energy dependent process, in which ATP is utilised and a few ions or molecules are transported across the membrane against their concentration gradient is called active transport. Example- Na+/K+ Pump.


Fig. Fluid mosaic model

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