BIO201L Straightline
Diffusion & Osmosis
Pre Lab Questions
(With Solutions)
2025
1
,1. In a diffusion cell experiment, a student holds membrane thickness
and diffusion coefficient constant but doubles the concentration
difference across the membrane. According to Fick’s first law, the
solute flux will:
A. Remain unchanged
B. Increase two-fold
C. Increase four-fold
D. Decrease by half
ANS: B
Rationale: Fick’s first law (J = –D·ΔC/Δx) predicts flux (J) is directly
proportional to the concentration difference (ΔC); doubling ΔC
doubles J.
2. A synthetic lipid bilayer has a measured partition coefficient (Kp)
for a drug. If Kp increases, the transmembrane diffusion rate of that
drug will:
A. Increase, because more drug dissolves in the membrane
B. Decrease, because the membrane becomes more rigid
C. Remain unchanged, as Kp does not appear in Fick’s law
D. Become unpredictable
ANS: A
Rationale: Higher partitioning into the lipid phase raises the effective
concentration inside the membrane, enhancing net flux.
3. When measuring glucose uptake via GLUT1 in erythrocytes, a
student observes a hyperbolic velocity–concentration curve. This
indicates:
A. Simple diffusion
B. Facilitated diffusion exhibiting Michaelis–Menten kinetics
C. Active transport requiring ATP
2
, D. Osmotic swelling
ANS: B
Rationale: Saturable carrier-mediated transport displays Michaelis–
Menten kinetics, yielding a hyperbolic uptake plot.
4. A red blood cell is placed in a solution of 600 mM urea (a permeant
solute). After equilibration, cell volume will:
A. Increase, causing lysis
B. Decrease, causing crenation
C. Remain unchanged
D. Oscillate due to urea cycling
ANS: C
Rationale: Urea freely equilibrates across the membrane; net
osmosis is driven only by non-penetrating solutes, so solution is
effectively isotonic.
5. A researcher uses the van’t Hoff equation (π = iCRT) to calculate
osmotic pressure. If solute concentration doubles and van ’t Hoff
factor (i) remains constant, π will:
A. Halve
B. Remain the same
C. Double
D. Increase four-fold
ANS: C
Rationale: π is directly proportional to solute concentration (C);
doubling C doubles π.
6. In a large-scale ultrafiltration device, which modification will most
effectively increase water flux across the semipermeable barrier?
A. Increasing membrane thickness
B. Lowering hydrostatic pressure difference
C. Raising temperature
3
Diffusion & Osmosis
Pre Lab Questions
(With Solutions)
2025
1
,1. In a diffusion cell experiment, a student holds membrane thickness
and diffusion coefficient constant but doubles the concentration
difference across the membrane. According to Fick’s first law, the
solute flux will:
A. Remain unchanged
B. Increase two-fold
C. Increase four-fold
D. Decrease by half
ANS: B
Rationale: Fick’s first law (J = –D·ΔC/Δx) predicts flux (J) is directly
proportional to the concentration difference (ΔC); doubling ΔC
doubles J.
2. A synthetic lipid bilayer has a measured partition coefficient (Kp)
for a drug. If Kp increases, the transmembrane diffusion rate of that
drug will:
A. Increase, because more drug dissolves in the membrane
B. Decrease, because the membrane becomes more rigid
C. Remain unchanged, as Kp does not appear in Fick’s law
D. Become unpredictable
ANS: A
Rationale: Higher partitioning into the lipid phase raises the effective
concentration inside the membrane, enhancing net flux.
3. When measuring glucose uptake via GLUT1 in erythrocytes, a
student observes a hyperbolic velocity–concentration curve. This
indicates:
A. Simple diffusion
B. Facilitated diffusion exhibiting Michaelis–Menten kinetics
C. Active transport requiring ATP
2
, D. Osmotic swelling
ANS: B
Rationale: Saturable carrier-mediated transport displays Michaelis–
Menten kinetics, yielding a hyperbolic uptake plot.
4. A red blood cell is placed in a solution of 600 mM urea (a permeant
solute). After equilibration, cell volume will:
A. Increase, causing lysis
B. Decrease, causing crenation
C. Remain unchanged
D. Oscillate due to urea cycling
ANS: C
Rationale: Urea freely equilibrates across the membrane; net
osmosis is driven only by non-penetrating solutes, so solution is
effectively isotonic.
5. A researcher uses the van’t Hoff equation (π = iCRT) to calculate
osmotic pressure. If solute concentration doubles and van ’t Hoff
factor (i) remains constant, π will:
A. Halve
B. Remain the same
C. Double
D. Increase four-fold
ANS: C
Rationale: π is directly proportional to solute concentration (C);
doubling C doubles π.
6. In a large-scale ultrafiltration device, which modification will most
effectively increase water flux across the semipermeable barrier?
A. Increasing membrane thickness
B. Lowering hydrostatic pressure difference
C. Raising temperature
3
