PCB3023C Cell Biology - Exam 2 Comprehensive Practice 2026 |FGCU
1. Which component of the plasma membrane is primarily responsible for
forming the permeability barrier to water-soluble molecules?
A. Peripheral proteins
B. Phospholipid bilayer
C. Cholesterol
D. Glycoproteins
Answer: B
Rationale: The hydrophobic tails of the phospholipid bilayer prevent the free passage of
water-soluble (hydrophilic) substances.
2. How does cholesterol affect membrane fluidity at high temperatures?
A. It increases fluidity by disrupting tail packing
B. It decreases fluidity by restraining phospholipid movement
C. It has no effect on fluidity
D. It causes the membrane to dissolve
Answer: B
Rationale: Cholesterol acts as a fluidity buffer; at high temperatures, it stiffens the
membrane, while at low temperatures, it prevents freezing.
,3. Which of the following is an example of an amphipathic molecule found in
the cell membrane?
A. Glucose
B. Triacylglycerol
C. Phosphatidylcholine
D. Sodium ions
Answer: C
Rationale: Amphipathic molecules, like phosphatidylcholine, contain both a hydrophilic
head and a hydrophobic tail.
4. What is the primary function of flippases in the cell?
A. To transfer specific phospholipids from the extracellular leaflet to the cytosolic leaflet in the plasma
membrane
B. To synthesize new lipids from fatty acids
C. To move phospholipids from the cytosolic to the non-cytosolic leaflet of the ER membrane
D. To degrade damaged membrane proteins
Answer: A
Rationale: Flippases use ATP to maintain the asymmetric distribution of phospholipids in
the plasma membrane by flipping them to the cytosolic side.
5. Which type of membrane protein is attached to the membrane only by non-
covalent interactions with other membrane proteins?
A. Transmembrane protein
B. Monolayer-associated protein
C. Peripheral membrane protein
D. Lipid-linked protein
Answer: C
Rationale: Peripheral proteins do not enter the hydrophobic core and are usually bound to
integral proteins via weak interactions.
, 6. The cell cortex in animal cells is primarily made of which protein?
A. Actin
B. Tubulin
C. Spectrin
D. Keratin
Answer: C
Rationale: In red blood cells specifically, spectrin forms the meshwork of the cell cortex,
providing mechanical support.
7. Which of these molecules would diffuse most slowly (or not at all) across a
lipid bilayer without the help of a transport protein?
A. CO2
B. Ethanol
C. Ca2+
D. H2O
Answer: C
Rationale: Ions like Ca2+ are highly charged and cannot pass through the hydrophobic
interior of the lipid bilayer without assistance.
8. What is the typical concentration gradient for Sodium (Na+) in a resting
animal cell?
A. Higher outside the cell than inside
B. Equal inside and outside
C. Higher inside the cell than outside
D. Sodium is not found in animal cells
Answer: A
Rationale: Animal cells maintain a high concentration of Na+ outside the cell and a high
concentration of K+ inside.
1. Which component of the plasma membrane is primarily responsible for
forming the permeability barrier to water-soluble molecules?
A. Peripheral proteins
B. Phospholipid bilayer
C. Cholesterol
D. Glycoproteins
Answer: B
Rationale: The hydrophobic tails of the phospholipid bilayer prevent the free passage of
water-soluble (hydrophilic) substances.
2. How does cholesterol affect membrane fluidity at high temperatures?
A. It increases fluidity by disrupting tail packing
B. It decreases fluidity by restraining phospholipid movement
C. It has no effect on fluidity
D. It causes the membrane to dissolve
Answer: B
Rationale: Cholesterol acts as a fluidity buffer; at high temperatures, it stiffens the
membrane, while at low temperatures, it prevents freezing.
,3. Which of the following is an example of an amphipathic molecule found in
the cell membrane?
A. Glucose
B. Triacylglycerol
C. Phosphatidylcholine
D. Sodium ions
Answer: C
Rationale: Amphipathic molecules, like phosphatidylcholine, contain both a hydrophilic
head and a hydrophobic tail.
4. What is the primary function of flippases in the cell?
A. To transfer specific phospholipids from the extracellular leaflet to the cytosolic leaflet in the plasma
membrane
B. To synthesize new lipids from fatty acids
C. To move phospholipids from the cytosolic to the non-cytosolic leaflet of the ER membrane
D. To degrade damaged membrane proteins
Answer: A
Rationale: Flippases use ATP to maintain the asymmetric distribution of phospholipids in
the plasma membrane by flipping them to the cytosolic side.
5. Which type of membrane protein is attached to the membrane only by non-
covalent interactions with other membrane proteins?
A. Transmembrane protein
B. Monolayer-associated protein
C. Peripheral membrane protein
D. Lipid-linked protein
Answer: C
Rationale: Peripheral proteins do not enter the hydrophobic core and are usually bound to
integral proteins via weak interactions.
, 6. The cell cortex in animal cells is primarily made of which protein?
A. Actin
B. Tubulin
C. Spectrin
D. Keratin
Answer: C
Rationale: In red blood cells specifically, spectrin forms the meshwork of the cell cortex,
providing mechanical support.
7. Which of these molecules would diffuse most slowly (or not at all) across a
lipid bilayer without the help of a transport protein?
A. CO2
B. Ethanol
C. Ca2+
D. H2O
Answer: C
Rationale: Ions like Ca2+ are highly charged and cannot pass through the hydrophobic
interior of the lipid bilayer without assistance.
8. What is the typical concentration gradient for Sodium (Na+) in a resting
animal cell?
A. Higher outside the cell than inside
B. Equal inside and outside
C. Higher inside the cell than outside
D. Sodium is not found in animal cells
Answer: A
Rationale: Animal cells maintain a high concentration of Na+ outside the cell and a high
concentration of K+ inside.
