Transport mechanisms across the cell membrane are fundamental for drug absorption, distribution, and cellular homeostasis. This topic covers passive diffusion, facilitated diffusion, carrier-mediated transport, primary and secondary active transport, ion channels, uniport/symport/antiport systems, ATP-driven pumps (e.g., Na+/K+-ATPase), and vesicular processes like endocytosis and exocytosis. B.Pharm students must understand concentration and electrochemical gradients, membrane permeability, transport kinetics (Tm, Michaelis–Menten), and pharmacological inhibitors to predict drug movement and design therapeutics. Understanding transporter specificity, competitive inhibition, and electrogenic effects is crucial for interpreting drug interactions and optimizing dosage regimens and formulation strategies. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What best describes passive diffusion across the cell membrane?
- Movement of small nonpolar molecules down their concentration gradient through the lipid bilayer
- Transport of ions via ATP-dependent pumps
- Vesicular uptake of macromolecules
- Carrier-mediated transport that requires ATP
Correct Answer: Movement of small nonpolar molecules down their concentration gradient through the lipid bilayer
Q2. Which statement correctly characterizes facilitated diffusion?
- Requires ATP hydrolysis and moves solutes against the gradient
- Is carrier- or channel-mediated movement down an electrochemical gradient without ATP
- Involves vesicle fusion with the plasma membrane to release contents
- Is exclusively for gaseous molecules such as O2 and CO2
Correct Answer: Is carrier- or channel-mediated movement down an electrochemical gradient without ATP
Q3. Which feature distinguishes primary active transport from secondary active transport?
- Primary active transport uses ATP directly; secondary uses ion gradients established by primary pumps
- Primary uses carriers only; secondary uses channels only
- Primary is energy-independent; secondary requires ATP directly
- Primary occurs only in prokaryotes; secondary only in eukaryotes
Correct Answer: Primary active transport uses ATP directly; secondary uses ion gradients established by primary pumps
Q4. What is the stoichiometry of the Na+/K+-ATPase per ATP hydrolyzed?
- 3 Na+ out, 2 K+ in
- 2 Na+ out, 3 K+ in
- 1 Na+ out, 1 K+ in
- 3 Na+ in, 2 K+ out
Correct Answer: 3 Na+ out, 2 K+ in
Q5. The Na+/glucose cotransporter (SGLT) is an example of which transport type?
- Symport secondary active transport
- Antiport primary active transport
- Facilitated diffusion uniport
- Vesicular transport (endocytosis)
Correct Answer: Symport secondary active transport
Q6. Which term defines a transporter that moves a single solute down its gradient?
- Uniporter
- Symporter
- Antiporter
- Pump
Correct Answer: Uniporter
Q7. How do ion channels differ from carrier proteins in transport kinetics?
- Channels allow high throughput and are not saturable; carriers are saturable and show Michaelis–Menten kinetics
- Channels require ATP; carriers never require ATP
- Channels transport only neutral molecules; carriers only ions
- Channels are slower than carriers and always electrogenic
Correct Answer: Channels allow high throughput and are not saturable; carriers are saturable and show Michaelis–Menten kinetics
Q8. What does the transport maximum (Tm) represent for carrier-mediated transport?
- The maximal transport rate when all carriers are saturated
- The minimal energy required for transport to begin
- The membrane potential at which transport reverses
- The diffusion coefficient for a solute across lipids
Correct Answer: The maximal transport rate when all carriers are saturated
Q9. Which pump directly maintains low intracellular Ca2+ by ATP hydrolysis?
- Ca2+-ATPase (SERCA/PMCA)
- Na+/K+-ATPase
- H+/K+-ATPase
- ABC transporter
Correct Answer: Ca2+-ATPase (SERCA/PMCA)
Q10. Which process describes receptor-mediated endocytosis?
- Selective uptake of ligands bound to specific cell-surface receptors into clathrin-coated vesicles
- Nonselective ingestion of large particles like bacteria
- Release of neurotransmitters by vesicle fusion
- Passive diffusion of lipophilic drugs
Correct Answer: Selective uptake of ligands bound to specific cell-surface receptors into clathrin-coated vesicles
Q11. Which of the following is an example of an electrogenic pump contributing to membrane potential?
- Na+/K+-ATPase creating net outward positive charge
- GLUT transporter equilibrating glucose
- Aquaporin facilitating water movement
- Pinocytosis increasing intracellular fluid volume
Correct Answer: Na+/K+-ATPase creating net outward positive charge
Q12. Which property most increases passive permeability of a drug across the lipid bilayer?
- High lipid solubility and small molecular size
- High polarity and large molecular size
- Strong ionic charge at physiological pH
- Protein binding in the extracellular fluid
Correct Answer: High lipid solubility and small molecular size
Q13. Which gastric membrane pump is targeted by proton pump inhibitors (e.g., omeprazole)?
- H+/K+-ATPase (gastric proton pump)
- Na+/K+-ATPase in parietal cells
- V-ATPase in lysosomes
- Ca2+-ATPase on the sarcoplasmic reticulum
Correct Answer: H+/K+-ATPase (gastric proton pump)
Q14. Which endocytic pathway primarily mediates fluid-phase uptake?
- Pinocytosis
- Phagocytosis
- Receptor-mediated endocytosis
- Autophagy
Correct Answer: Pinocytosis
Q15. LDL uptake into hepatocytes primarily occurs by which mechanism?
- Receptor-mediated endocytosis via LDL receptors
- Passive diffusion through lipid bilayer
- Na+-dependent symport
- Transcytosis through tight junctions
Correct Answer: Receptor-mediated endocytosis via LDL receptors
Q16. Which statement about CFTR (cystic fibrosis transmembrane conductance regulator) is correct?
- CFTR is an ATP-gated chloride channel belonging to the ABC transporter family
- CFTR is a Na+/glucose symporter that uses secondary active transport
- CFTR is a voltage-gated potassium channel exclusive to neurons
- CFTR is a proton pump in parietal cells
Correct Answer: CFTR is an ATP-gated chloride channel belonging to the ABC transporter family
Q17. Which toxin or drug is a classical inhibitor of Na+/K+-ATPase?
- Ouabain (cardiac glycoside)
- Verapamil (calcium channel blocker)
- Amiloride (ENaC blocker)
- Rifampicin (RNA polymerase inhibitor)
Correct Answer: Ouabain (cardiac glycoside)
Q18. Secondary active transport uses which form of energy?
- Energy stored in ion gradients established by primary active transport
- Direct ATP hydrolysis by the transporter itself
- Light energy absorbed by membrane pigments
- Heat generated by cellular metabolism only
Correct Answer: Energy stored in ion gradients established by primary active transport
Q19. Which experimental technique measures single ion-channel currents and gating properties?
- Patch-clamp electrophysiology
- Western blotting
- ELISA
- Mass spectrometry
Correct Answer: Patch-clamp electrophysiology
Q20. GLUT family transporters exemplify which transport mechanism for glucose?
- Facilitated diffusion via uniporter proteins
- ATP-driven active transport pumping glucose into cells
- Na+-coupled secondary active transport of glucose into cells
- Endocytic uptake of glucose-containing vesicles
Correct Answer: Facilitated diffusion via uniporter proteins
Q21. The Na+/Ca2+ exchanger typically operates as which type of transporter?
- Antiporter (secondary active transport) moving Na+ and Ca2+ in opposite directions
- Uniporter for Ca2+ into the cell driven by diffusion
- ATPase that hydrolyzes ATP to extrude Ca2+
- Facilitated diffusion channel that transports both ions simultaneously without coupling
Correct Answer: Antiporter (secondary active transport) moving Na+ and Ca2+ in opposite directions
Q22. Phagocytosis is best described as:
- Engulfment of large particles or microbes by specialized cells forming phagosomes
- Nonselective uptake of extracellular fluid by all cell types
- Secretion of vesicular contents to the extracellular space
- Passive movement of proteins across membranes
Correct Answer: Engulfment of large particles or microbes by specialized cells forming phagosomes
Q23. Which change will increase the rate of carrier-mediated transport of a solute across a membrane?
- Upregulation (increase) of transporter number in the membrane
- Decrease in the concentration gradient for the solute
- Mutation that reduces transporter affinity for the substrate
- Complete lipidation of the transporter enhancing membrane rigidity
Correct Answer: Upregulation (increase) of transporter number in the membrane
Q24. Osmosis is defined as:
- Net movement of water across a semipermeable membrane from low solute to high solute concentration
- Diffusion of solutes down their concentration gradient through channels
- Active pumping of water molecules using ATP
- Vesicular transport of water-rich endosomes
Correct Answer: Net movement of water across a semipermeable membrane from low solute to high solute concentration
Q25. Which statement about facilitated diffusion is FALSE?
- It requires ATP hydrolysis to move substrates across the membrane
- It is carrier- or channel-mediated
- It moves solutes down their electrochemical gradients
- Transport can be saturated at high substrate concentrations for carrier proteins
Correct Answer: It requires ATP hydrolysis to move substrates across the membrane
Q26. Which molecule readily diffuses through the lipid bilayer without specific transporters?
- Oxygen (O2)
- Glucose
- Na+
- ATP
Correct Answer: Oxygen (O2)
Q27. Transporters that follow Michaelis–Menten kinetics exhibit which behavior as substrate concentration increases?
- Rate approaches a maximum (Vmax/Tm) as carriers become saturated
- Rate increases linearly without limit
- Rate decreases due to channel closure at high substrate
- Rate becomes independent of transporter number
Correct Answer: Rate approaches a maximum (Vmax/Tm) as carriers become saturated
Q28. Which transport mechanism is most important for maintaining very low cytosolic Ca2+ levels?
- Plasma membrane Ca2+-ATPase and SERCA pumps extruding/sequestering Ca2+
- Na+/K+-ATPase directly pumping Ca2+ out of the cell
- Facilitated diffusion of Ca2+ through aquaporins
- Passive leakage through tight junctions
Correct Answer: Plasma membrane Ca2+-ATPase and SERCA pumps extruding/sequestering Ca2+
Q29. Which property of a drug will decrease its passive transcellular absorption across intestinal epithelium?
- High polarity and ionization at physiological pH
- High lipophilicity and small size
- Neutral nonpolar structure
- Low molecular weight and lack of charge
Correct Answer: High polarity and ionization at physiological pH
Q30. How does membrane potential influence ion movement across the membrane?
- It contributes to the electrochemical gradient and can drive or oppose ion flux independent of concentration gradient
- It only affects neutral solutes and not charged ions
- It is irrelevant when ATP-driven pumps are active
- It always favors cation efflux and anion influx regardless of gradients
Correct Answer: It contributes to the electrochemical gradient and can drive or oppose ion flux independent of concentration gradient
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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