Facilitated diffusion Knowledge-Based Practice

Questions

1. 1.

   Which of the following provides the direct driving force for the net movement of an uncharged solute across the plasma membrane during facilitated diffusion?

   • A) The hydrolysis of adenosine triphosphate (ATP) by the transport protein
   • B) The electrochemical proton gradient maintained by metabolic ion pumps
   • C) The concentration gradient of the solute across the membrane
   • D) The covalent phosphorylation of cytoplasmic regulatory domains
2. 2.

   In carrier-mediated facilitated diffusion, what mechanism enables the transport of a polar molecule across the hydrophobic core of the plasma membrane?

   • A) A reversible conformational change in the carrier protein that shifts the solute-binding site from one side of the membrane to the other
   • B) Direct enzymatic hydrolysis of adenosine triphosphate that forces the solute against its electrochemical gradient
   • C) Formation of an endocytic transport vesicle that pinches off the plasma membrane to engulf the solute
   • D) Transient enzymatic breakdown of membrane phospholipids that allows the solute to diffuse through the lipid core
3. 3.

   When the extracellular concentration of a specific solute is progressively increased, its rate of entry into the cell initially rises but eventually plateaus at a maximal transport rate ($V_{max}$). Which property of facilitated diffusion accounts for this plateau?

   • A) The gradual depletion of cellular ATP stores required to power transport proteins
   • B) The complete structural breakdown of the phospholipid bilayer at elevated solute concentrations
   • C) The rapid reversal of the solute concentration gradient across the membrane
   • D) The finite number and binding saturation of membrane transport proteins
4. 4.

   Which of the following characteristics distinguishes facilitated diffusion from simple diffusion across a plasma membrane?

   • A) Reaching a maximum rate of transport due to the saturation of membrane proteins
   • B) Requiring metabolic energy in the form of ATP to drive solute movement
   • C) Transporting solutes exclusively against their electrochemical gradient
   • D) Allowing molecules to dissolve directly through the hydrophobic core of the bilayer
5. 5.

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

   • A) It moves specific polar or charged solutes down their concentration gradient through transport proteins without cellular energy expenditure.
   • B) It directly hydrolyzes adenosine triphosphate (ATP) to pump small hydrophobic molecules against their concentration gradient.
   • C) It enables nonpolar gases to pass directly through the phospholipid bilayer without the assistance of membrane proteins.
   • D) It uses vesicle formation and cytoskeletal rearrangement to bring large macromolecules into the cytoplasm.

Answers and step-by-step solutions appear after you finish the test.