Fluid Mosaic Model of Cell Membrane — NEET Biology
📚 Practice ConceptAn improved model of the structure of cell membrane was proposed by Singer and Nicolson (1972) widely accepted as fluid mosaic model. According to this, the quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer. This ability is more important for the functions of the membrane.
Which of the following statements regarding the plasma membrane and its transport mechanisms is NOT correct? S1: The fluid mosaic model describes the plasma membrane as a rigid, static structure with embedded proteins. S2: The plasma membrane is selectively permeable, regulating the passage of molecules across it. S3: Simple diffusion involves the movement of neutral solutes across the membrane along the concentration gradient, without energy expenditure. S4: Polar molecules require carrier proteins to facilitate their transport across the nonpolar lipid bilayer. S5: Active transport moves molecules from a region of higher concentration to lower concentration, utilizing ATP.
View solution & NCERT explanation
Correct answer: B — S1 and S5
NCERT core concept: The structure, fluidity, selective permeability, and transport mechanisms of the plasma membrane. S1: Incorrect. The fluid mosaic model (Singer and Nicolson, 1972) describes the plasma membrane as having a quasi-fluid nature, enabling lateral movement of proteins within the lipid bilayer, which implies it is not rigid or static (NCERT page 94). S2: Correct. One of the most important functions of the plasma membrane is the transport of molecules across it, and it is selectively permeable to some molecules (NCERT page 94). S3: Correct. Neutral solutes may move across the membrane by simple diffusion along the concentration gradient (from higher to lower concentration) without any requirement of energy (NCERT page 94). S4: Correct. Polar molecules cannot pass through the nonpolar lipid bilayer and therefore require a carrier protein of the membrane to facilitate their transport (NCERT page 94). S5: Incorrect. Active transport is the movement of ions or molecules across the membrane against their concentration gradient (from lower to higher concentration), which is an energy-dependent process utilizing ATP (NCERT page 94). The statement incorrectly describes movement along the concentration gradient. Therefore, statements S1 and S5 are NOT correct. Recap: The plasma membrane is a dynamic, selectively permeable barrier that regulates substance passage through various transport mechanisms, including passive and active processes.
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