Selective permeability Knowledge-Based Practice

Questions

1. 1.

   Artificial phospholipid vesicles lacking membrane proteins are placed in an aqueous solution containing equal concentrations of ethanol and sucrose. Which of the following describes the movement of these two solutes based on the selective permeability of the lipid bilayer?

   • A) Sucrose diffuses rapidly across the bilayer, whereas ethanol remains strictly excluded.
   • B) Both ethanol and sucrose cross the lipid bilayer at identical rates via simple diffusion.
   • C) Ethanol readily crosses the bilayer by simple diffusion, whereas sucrose is effectively prevented from crossing.
   • D) Neither ethanol nor sucrose can cross the lipid bilayer due to their polar hydroxyl groups.
2. 2.

   Which component of the plasma membrane is primarily responsible for granting passage to specific polar molecules and charged ions that are otherwise prevented from crossing the hydrophobic core?

   • A) Cholesterol molecules embedded within the hydrophobic core
   • B) Integral transport proteins embedded within the lipid bilayer
   • C) Peripheral proteins located on the cytoplasmic face of the membrane
   • D) Carbohydrate chains of glycolipids facing the extracellular fluid
3. 3.

   Which of the following would be the most immediate consequence for a living cell if its plasma membrane completely lost its selective permeability?

   • A) The cell would synthesize additional transport proteins to restore nutrient uptake.
   • B) Water molecules would no longer be able to pass through the lipid bilayer.
   • C) Concentration gradients of ions and small solutes across the membrane would dissipate.
   • D) Metabolic enzymes would begin diffusing freely out of the cell while maintaining cellular respiration.
4. 4.

   Which of the following substances can cross an intact phospholipid bilayer directly by simple diffusion without the assistance of transport proteins?

   • A) Glucose
   • B) Sodium ions
   • C) Oxygen gas
   • D) Adenosine triphosphate
5. 5.

   Which of the following statements correctly explains why the plasma membrane exhibits selective permeability?

   • A) The hydrophilic outer surfaces attract and transport all charged ions equally across the membrane.
   • B) The hydrophobic interior formed by fatty acid tails restricts polar and charged solutes while allowing small nonpolar molecules to diffuse freely.
   • C) Peripheral proteins form permanent open pores that allow all water-soluble nutrients to enter simultaneously.
   • D) Surface carbohydrate chains actively pump macromolecules directly through the phospholipid bilayer.

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