Biology · Cell: The Unit of Life · NEET
The fluid mosaic model was proposed by Singer and Nicolson in 1972. NCERT calls it an 'improved model' of the membrane and it is now widely accepted. NEET often confuses students by putting Singer and Nicolson as an option for cell theory. Remember: cell theory = Schleiden and Schwann; fluid mosaic model = Singer and Nicolson.
'Fluid' comes from the quasi-fluid nature of the lipids. Because the lipids are semi-fluid (not solid), the proteins can move sideways within the bilayer. 'Mosaic' means a picture made of many small scattered tiles. The proteins are scattered across the lipid sea like tiles, so the membrane looks like a mosaic. Both words together = a moving lipid sea with scattered proteins.
Quasi-fluid means 'almost fluid' or semi-liquid. The lipid molecules in the bilayer are not fixed like a solid; they can move a little. NCERT states clearly: 'the quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer.' This is the exact reason the membrane is fluid, so this line is very important for NEET.
Lateral movement means the proteins can slide sideways (left-right) within the bilayer, but they normally do not flip from one layer to the other. The ability of the membrane components to move within the membrane is measured as its fluidity. High fluidity = components move easily.
Membrane proteins are classified by how easily they can be extracted. Peripheral proteins lie on the surface of the membrane (easy to remove). Integral proteins are partially or totally buried inside the membrane (hard to remove). NEET loves this exact wording, so memorise: peripheral = surface, integral = buried.
Fluidity lets the membrane do many jobs. NCERT lists these functions: cell growth, formation of intercellular junctions, secretion, endocytosis, and cell division. If the membrane were solid, the cell could not divide, fold, or take in material. So fluidity is needed for the cell to work and grow.
Select the correct statements regarding cell membrane in eukaryotic cell. A. Membrane of human RBCs has approximately 52% protein. B. Major phospholipids are arranged in a bilayer. C. Extensions of the plasma membrane into the cell form mesosomes. D. Tails towards the inner part of lipids are hydrophobic and thus protected from aqueous medium. E. Glycocalyx is present on the outer surface of the plasma membrane.
Match List-I with List-II: List I: A. Centromere B. Cilium C. Cristae D. Cell membrane List II: I. Mitochondrion II. Cell division III. Cell movement IV. Phospholipid Bilayer
Cell theory was formulated by ______________.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. NCERT calls it an improved and widely accepted model of the cell membrane. It is the model you must know for NEET.
No. In the fluid mosaic model, proteins mainly move sideways (lateral movement) within the bilayer. Flipping between layers is not the fluidity NCERT describes.
Lipids (mainly phospholipids arranged in a bilayer, plus cholesterol) and proteins (integral and peripheral). Carbohydrates are also present on the outer surface as sugar chains.
About 52 per cent protein and 40 per cent lipids. This exact number is a common NEET fact, so memorise 52% protein for the erythrocyte membrane.
Earlier models showed a fixed, static arrangement. The fluid mosaic model added that the lipids are quasi-fluid and proteins can move laterally, making the membrane dynamic, not rigid.
