Selective permeability Knowledge-Based Download PDF

Questions

1. 1.

   Which of the following best describes the primary biological function of selective permeability in the plasma membrane?

   • A) It ensures that all extracellular solutes enter the cytoplasm at identical diffusion rates.
   • B) It completely prevents the bidirectional movement of polar solvent molecules such as water.
   • C) It enables the cell to maintain an internal chemical environment that is distinct from its external surroundings.
   • D) It allows large macromolecules such as proteins and nucleic acids to diffuse freely across the bilayer.
2. 2.

   Which of the following best explains why large, uncharged polar molecules such as glucose cannot readily diffuse across an intact phospholipid bilayer without transport proteins?

   • A) They are electrostatically repelled by the negatively charged phosphate heads on the bilayer surface.
   • B) They form stable covalent linkages with the glycerol backbone of phospholipids upon contact.
   • C) They behave as nonpolar solutes in water, causing them to aggregate away from the membrane interface.
   • D) Their large size and extensive hydration shells make entering the hydrophobic hydrocarbon core thermodynamically unfavorable.
3. 3.

   How do transport proteins contribute to the selective permeability of the plasma membrane?

   • A) They break down the hydrophobic fatty acid tails to allow external molecules to enter indiscriminately.
   • B) They create large non-specific pores that permit any polar or nonpolar solute to diffuse freely across the bilayer.
   • C) They synthesize new phospholipids within the membrane to seal physical gaps that cause solute leakage.
   • D) They provide specialized pathways that allow specific hydrophilic molecules and ions to cross the hydrophobic core.
4. 4.

   Which characteristic of the plasma membrane's phospholipid bilayer primarily prevents the free diffusion of small charged ions, such as $\text{Na}^+$ and $\text{Cl}^-$, into or out of the cell?

   • A) The dense network of peripheral proteins lining the cytosolic face
   • B) The hydrophobic interior composed of fatty acid hydrocarbon tails
   • C) The hydrophilic outer layer formed by negatively charged phosphate heads
   • D) The carbohydrate chains of glycoproteins projecting into the extracellular space
5. 5.

   The selective permeability of the plasma membrane allows only certain substances to pass directly through the phospholipid bilayer. Which of the following substances can cross the hydrophobic interior of the membrane via simple diffusion without the aid of transport proteins?

   • A) Sodium ions ($\text{Na}^+$)
   • B) Glucose
   • C) Oxygen gas ($\text{O}_2$)
   • D) Sucrose