BIOL 355 Foundations in Molecular Cell Biology | Exams 1–3 |
2026/2027 Complete Practice Questions, Correct Answers &
Detailed Rationales | University of Washington
EXAM 1 — CELL BIOLOGY FOUNDATIONS, EXPERIMENTAL METHODS &
MEMBRANES
Questions 1–85
1. Which feature best distinguishes eukaryotic cells from prokaryotic
cells?
A. Presence of DNA
B. Presence of ribosomes
C. Presence of membrane-bound organelles
D. Presence of a plasma membrane
Correct Answer: C. Presence of membrane-bound organelles
Rationale: Eukaryotic cells contain membrane-bound organelles such as
nuclei, mitochondria, and endoplasmic reticulum.
2. Which cellular structure is primarily responsible for maintaining
selective permeability?
A. Nucleolus
B. Plasma membrane
C. Cytoskeleton
D. Ribosome
Correct Answer: B. Plasma membrane
Rationale: The plasma membrane regulates movement of substances
into and out of the cell.
,3. The fluid mosaic model describes the plasma membrane as:
A. A rigid lipid shell
B. A carbohydrate layer surrounding proteins
C. A dynamic lipid bilayer containing proteins
D. A protein bilayer containing DNA
Correct Answer: C. A dynamic lipid bilayer containing proteins
Rationale: Lipids form the bilayer while proteins move within or
associate with it.
4. Which membrane component contributes most directly to
membrane fluidity?
A. Phospholipids
B. DNA
C. Glycogen
D. RNA
Correct Answer: A. Phospholipids
Rationale: Phospholipid composition, fatty-acid saturation, and
cholesterol influence membrane fluidity.
5. Increasing the proportion of unsaturated fatty acids generally
makes a membrane:
A. More fluid
B. Less fluid
C. Impermeable
D. Completely rigid
,Correct Answer: A. More fluid
Rationale: Double bonds introduce bends that prevent phospholipid
tails from packing tightly.
6. What is the major role of cholesterol in animal cell membranes?
A. It eliminates membrane movement
B. It helps regulate membrane fluidity
C. It transports DNA
D. It synthesizes proteins
Correct Answer: B. It helps regulate membrane fluidity
Rationale: Cholesterol buffers membrane fluidity and influences
permeability.
7. Which molecule crosses a lipid bilayer most readily by simple
diffusion?
A. Na⁺
B. Glucose
C. O₂
D. ATP
Correct Answer: C. O₂
Rationale: Small nonpolar molecules diffuse readily through the
hydrophobic membrane interior.
8. Facilitated diffusion requires:
A. ATP hydrolysis
B. A membrane protein
C. DNA replication
D. Vesicle formation
, Correct Answer: B. A membrane protein
Rationale: Channels or carriers facilitate movement down an
electrochemical gradient without direct ATP consumption.
9. Active transport differs from simple diffusion because active
transport:
A. Always moves molecules down their gradient
B. Requires no membrane proteins
C. Can move substances against their gradient
D. Occurs only in dead cells
Correct Answer: C. Can move substances against their gradient
Rationale: Active transport uses energy to move substances against
concentration or electrochemical gradients.
10. Osmosis refers specifically to movement of:
A. Proteins
B. Water
C. ATP
D. DNA
Correct Answer: B. Water
Rationale: Osmosis is the net movement of water across a selectively
permeable membrane.
11. A cell placed in a strongly hypertonic solution will generally:
A. Gain water
B. Lose water
C. Stop all metabolism immediately
D. Replicate DNA
2026/2027 Complete Practice Questions, Correct Answers &
Detailed Rationales | University of Washington
EXAM 1 — CELL BIOLOGY FOUNDATIONS, EXPERIMENTAL METHODS &
MEMBRANES
Questions 1–85
1. Which feature best distinguishes eukaryotic cells from prokaryotic
cells?
A. Presence of DNA
B. Presence of ribosomes
C. Presence of membrane-bound organelles
D. Presence of a plasma membrane
Correct Answer: C. Presence of membrane-bound organelles
Rationale: Eukaryotic cells contain membrane-bound organelles such as
nuclei, mitochondria, and endoplasmic reticulum.
2. Which cellular structure is primarily responsible for maintaining
selective permeability?
A. Nucleolus
B. Plasma membrane
C. Cytoskeleton
D. Ribosome
Correct Answer: B. Plasma membrane
Rationale: The plasma membrane regulates movement of substances
into and out of the cell.
,3. The fluid mosaic model describes the plasma membrane as:
A. A rigid lipid shell
B. A carbohydrate layer surrounding proteins
C. A dynamic lipid bilayer containing proteins
D. A protein bilayer containing DNA
Correct Answer: C. A dynamic lipid bilayer containing proteins
Rationale: Lipids form the bilayer while proteins move within or
associate with it.
4. Which membrane component contributes most directly to
membrane fluidity?
A. Phospholipids
B. DNA
C. Glycogen
D. RNA
Correct Answer: A. Phospholipids
Rationale: Phospholipid composition, fatty-acid saturation, and
cholesterol influence membrane fluidity.
5. Increasing the proportion of unsaturated fatty acids generally
makes a membrane:
A. More fluid
B. Less fluid
C. Impermeable
D. Completely rigid
,Correct Answer: A. More fluid
Rationale: Double bonds introduce bends that prevent phospholipid
tails from packing tightly.
6. What is the major role of cholesterol in animal cell membranes?
A. It eliminates membrane movement
B. It helps regulate membrane fluidity
C. It transports DNA
D. It synthesizes proteins
Correct Answer: B. It helps regulate membrane fluidity
Rationale: Cholesterol buffers membrane fluidity and influences
permeability.
7. Which molecule crosses a lipid bilayer most readily by simple
diffusion?
A. Na⁺
B. Glucose
C. O₂
D. ATP
Correct Answer: C. O₂
Rationale: Small nonpolar molecules diffuse readily through the
hydrophobic membrane interior.
8. Facilitated diffusion requires:
A. ATP hydrolysis
B. A membrane protein
C. DNA replication
D. Vesicle formation
, Correct Answer: B. A membrane protein
Rationale: Channels or carriers facilitate movement down an
electrochemical gradient without direct ATP consumption.
9. Active transport differs from simple diffusion because active
transport:
A. Always moves molecules down their gradient
B. Requires no membrane proteins
C. Can move substances against their gradient
D. Occurs only in dead cells
Correct Answer: C. Can move substances against their gradient
Rationale: Active transport uses energy to move substances against
concentration or electrochemical gradients.
10. Osmosis refers specifically to movement of:
A. Proteins
B. Water
C. ATP
D. DNA
Correct Answer: B. Water
Rationale: Osmosis is the net movement of water across a selectively
permeable membrane.
11. A cell placed in a strongly hypertonic solution will generally:
A. Gain water
B. Lose water
C. Stop all metabolism immediately
D. Replicate DNA
