Facilitated diffusion Knowledge-Based Download PDF

Questions

1. 1.

   Under which condition will the net transport of an uncharged polar solute across a plasma membrane via facilitated diffusion cease?

   • A) When the concentration of the solute becomes equal on both sides of the membrane
   • B) When intracellular supplies of ATP are completely exhausted
   • C) When the electrical potential across the membrane reaches zero
   • D) When the extracellular sodium ion gradient is eliminated
2. 2.

   Why does glucose require facilitated diffusion rather than simple diffusion to cross the plasma membrane down its concentration gradient?

   • A) It is a large, polar molecule that cannot readily penetrate the hydrophobic hydrocarbon interior of the lipid bilayer.
   • B) It must be actively transported against its thermodynamic equilibrium using metabolic energy.
   • C) It is a nonpolar hydrocarbon that binds irreversibly to the hydrophilic phosphate head groups.
   • D) It lacks kinetic energy and requires membrane proteins to generate heat for membrane translocation.
3. 3.

   During facilitated diffusion, how do carrier proteins differ functionally from channel proteins when transporting solute molecules across the plasma membrane?

   • A) Carrier proteins hydrolyze ATP to drive solute transport against an electrochemical gradient, whereas channel proteins require no energy input.
   • B) Carrier proteins form fixed, open pores for nonpolar macromolecules, whereas channel proteins cycle through mechanical conformations to move polar solutes.
   • C) Carrier proteins bind specific solutes and undergo alternating conformational changes, whereas channel proteins provide continuous hydrophilic pores through the membrane.
   • D) Carrier proteins engulf extracellular solutes through vesicle formation, whereas channel proteins directly dissolve solutes into the hydrophobic lipid core.
4. 4.

   Why does the rate of facilitated diffusion reach a maximum plateau at high extracellular solute concentrations, whereas the rate of simple diffusion continues to increase linearly?

   • A) The concentration gradient across the membrane is completely abolished.
   • B) Cellular ATP reserves become depleted, preventing the proteins from functioning.
   • C) All available membrane transport proteins become saturated with solute molecules.
   • D) The hydrophobic core of the phospholipid bilayer undergoes a phase transition and loses fluidity.
5. 5.

   Which of the following statements correctly describes a defining characteristic of facilitated diffusion across a biological membrane?

   • A) It moves substances against their concentration gradient using metabolic energy derived from ATP hydrolysis.
   • B) It allows nonpolar molecules to dissolve directly through the hydrophobic phospholipid bilayer without protein involvement.
   • C) It relies on vesicles fusing with the plasma membrane to release large macromolecules into the extracellular space.
   • D) It moves specific polar or charged solutes down their concentration gradient with the assistance of membrane transport proteins without requiring ATP.