BIO 336 Exam 1 Human Physiology
Questions with Answers| San Diego State University| Pass
Guaranteed
1. Which structural feature of the phospholipid bilayer allows it to
spontaneously form a closed membrane in an aqueous environment?
A. Hydrophilic phosphate heads face outward toward water while hydrophobic
fatty acid tails face inward, away from water
B. Hydrophobic tails face outward toward water
C. Phospholipids are entirely hydrophobic and repel all water
D. Phospholipids form a single layer, not a bilayer, in water
Answer: A
Rationale: Phospholipids are amphipathic: the phosphate-containing head is
polar/hydrophilic and the fatty acid tails are nonpolar/hydrophobic. In water,
thermodynamics favors heads facing the aqueous cytosol and extracellular fluid
while tails cluster together away from water, spontaneously forming a stable
bilayer — the basis of all cellular membranes.
2. Which factor increases membrane fluidity at a given temperature?
A. Increased proportion of saturated fatty acid tails
B. Increased proportion of unsaturated fatty acid tails, whose kinks prevent
tight packing
C. Decreased cholesterol content at all temperatures
D. Longer fatty acid chain length uniformly increases fluidity
Answer: B
Rationale: Unsaturated fatty acids contain double bonds that introduce kinks into
the tail, preventing tight, orderly packing of phospholipids and thus increasing
fluidity. Saturated tails pack tightly and decrease fluidity. Cholesterol has a dual,
temperature-dependent effect (stabilizing fluidity by preventing both excessive
rigidity and excessive fluidity), rather than uniformly decreasing it.
3. According to the fluid mosaic model, membrane proteins are best described
as:
A. Fixed in a rigid, immobile lattice within the bilayer
, B. Embedded within or attached to a fluid lipid bilayer, able to move laterally
within the plane of the membrane
C. Located exclusively outside the lipid bilayer
D. Composed entirely of phospholipid, not protein
Answer: B
Rationale: The fluid mosaic model describes the membrane as a two-dimensional
fluid in which lipids and proteins can diffuse laterally within the plane of the
bilayer, giving the membrane both structural integrity and dynamic flexibility,
allowing proteins to cluster, move, and be inserted or removed as needed.
4. Simple diffusion of a small nonpolar molecule (e.g., O2) across the membrane
occurs via which mechanism?
A. Movement directly through the lipid bilayer down its concentration gradient,
without a carrier protein or energy expenditure
B. Facilitated transport through a specific protein channel requiring ATP
C. Active transport against its concentration gradient
D. Vesicular transport via endocytosis
Answer: A
Rationale: Small, nonpolar (lipophilic) molecules like O2 and CO2 can dissolve
directly into and diffuse across the hydrophobic lipid bilayer, moving passively
down their concentration gradient with no need for a membrane protein or energy
input — a hallmark of simple diffusion.
5. Glucose transport into most cells via GLUT transporters is an example of
which transport mechanism?
A. Simple diffusion through the lipid bilayer
B. Facilitated diffusion: a carrier protein allows glucose to move down its
concentration gradient without direct ATP use
C. Primary active transport requiring direct ATP hydrolysis
D. Secondary active transport coupled to a sodium gradient
Answer: B
Rationale: Glucose is polar and too large to cross the lipid bilayer directly, so it
requires GLUT carrier proteins. Because glucose moves down its concentration
gradient (from higher to lower concentration) without direct ATP hydrolysis by the
,transporter itself, this is classified as facilitated diffusion, distinct from the
Na+/glucose symporter (SGLT), which is secondary active transport.
6. The Na+/K+ ATPase pump is best classified as which type of transport, and
what does it accomplish per cycle?
A. Passive transport; moves 3 Na+ in and 2 K+ out
B. Primary active transport; uses ATP hydrolysis to pump 3 Na+ out of the cell
and 2 K+ into the cell against their concentration gradients
C. Facilitated diffusion; moves ions down their gradients only
D. Secondary active transport coupled to glucose movement
Answer: B
Rationale: The Na+/K+ ATPase directly hydrolyzes ATP to phosphorylate itself,
driving a conformational change that extrudes 3 Na+ ions out of the cell and
imports 2 K+ ions in, both against their respective electrochemical gradients. This
primary active transport pump establishes the concentration gradients essential
for resting membrane potential and secondary active transport.
7. Which statement correctly describes secondary active transport, using the
Na+/glucose symporter (SGLT) as an example?
A. It directly hydrolyzes ATP to move both Na+ and glucose
B. It uses the energy stored in the Na+ electrochemical gradient (established
by the Na+/K+ ATPase) to move glucose against its concentration gradient,
without directly consuming ATP itself
C. It transports only ions, never organic molecules
D. It moves Na+ down its gradient and glucose down its gradient
simultaneously, requiring no energy input at all
Answer: B
Rationale: Secondary active transport does not directly hydrolyze ATP; instead it
harnesses the potential energy stored in an ion gradient (here, the inward Na+
gradient created by the ATP-dependent Na+/K+ pump) to move a second solute
(glucose) against its own concentration gradient, coupling the two movements
through a shared carrier protein (symporter).
8. A red blood cell placed in a hypotonic solution swells and may lyse. What is
the underlying mechanism?
, A. Water moves by osmosis from the area of lower solute concentration
(outside) to higher solute concentration (inside the cell), causing the cell to
gain volume
B. Solutes move into the cell against their gradient, drawing no water
C. The cell actively pumps water out, but is overwhelmed
D. The hypotonic solution has higher osmolarity than the cytoplasm
Answer: A
Rationale: A hypotonic solution has a lower solute concentration (and thus higher
water concentration) than the cell's cytoplasm. Water moves passively by osmosis
down its own concentration gradient, from the hypotonic extracellular fluid into
the relatively hypertonic cytoplasm, causing the cell to swell and potentially lyse if
the membrane cannot withstand the pressure.
9. Which type of membrane protein specifically forms a water-filled pore that
allows rapid, passive movement of specific ions down their electrochemical
gradient?
A. Peripheral membrane protein
B. Ion channel (gated or non-gated)
C. Cytoskeletal anchor protein
D. Glycolipid receptor
Answer: B
Rationale: Ion channels are integral membrane proteins that form aqueous pores
through the bilayer, allowing rapid, passive (no ATP required) flow of specific ions
down their electrochemical gradient when the channel is open. This distinguishes
them from carrier proteins (like GLUT or SGLT), which bind and conformationally
shuttle their substrate rather than forming a continuous open pore.
10. Ligand-gated ion channels, such as the nicotinic acetylcholine receptor, open
in response to which stimulus?
A. A change in membrane voltage alone
B. Binding of a specific chemical messenger (ligand) to the channel/receptor
protein, causing a conformational change that opens the pore
C. Mechanical deformation of the membrane only
D. A rise in intracellular ATP concentration exclusively
Answer: B
Questions with Answers| San Diego State University| Pass
Guaranteed
1. Which structural feature of the phospholipid bilayer allows it to
spontaneously form a closed membrane in an aqueous environment?
A. Hydrophilic phosphate heads face outward toward water while hydrophobic
fatty acid tails face inward, away from water
B. Hydrophobic tails face outward toward water
C. Phospholipids are entirely hydrophobic and repel all water
D. Phospholipids form a single layer, not a bilayer, in water
Answer: A
Rationale: Phospholipids are amphipathic: the phosphate-containing head is
polar/hydrophilic and the fatty acid tails are nonpolar/hydrophobic. In water,
thermodynamics favors heads facing the aqueous cytosol and extracellular fluid
while tails cluster together away from water, spontaneously forming a stable
bilayer — the basis of all cellular membranes.
2. Which factor increases membrane fluidity at a given temperature?
A. Increased proportion of saturated fatty acid tails
B. Increased proportion of unsaturated fatty acid tails, whose kinks prevent
tight packing
C. Decreased cholesterol content at all temperatures
D. Longer fatty acid chain length uniformly increases fluidity
Answer: B
Rationale: Unsaturated fatty acids contain double bonds that introduce kinks into
the tail, preventing tight, orderly packing of phospholipids and thus increasing
fluidity. Saturated tails pack tightly and decrease fluidity. Cholesterol has a dual,
temperature-dependent effect (stabilizing fluidity by preventing both excessive
rigidity and excessive fluidity), rather than uniformly decreasing it.
3. According to the fluid mosaic model, membrane proteins are best described
as:
A. Fixed in a rigid, immobile lattice within the bilayer
, B. Embedded within or attached to a fluid lipid bilayer, able to move laterally
within the plane of the membrane
C. Located exclusively outside the lipid bilayer
D. Composed entirely of phospholipid, not protein
Answer: B
Rationale: The fluid mosaic model describes the membrane as a two-dimensional
fluid in which lipids and proteins can diffuse laterally within the plane of the
bilayer, giving the membrane both structural integrity and dynamic flexibility,
allowing proteins to cluster, move, and be inserted or removed as needed.
4. Simple diffusion of a small nonpolar molecule (e.g., O2) across the membrane
occurs via which mechanism?
A. Movement directly through the lipid bilayer down its concentration gradient,
without a carrier protein or energy expenditure
B. Facilitated transport through a specific protein channel requiring ATP
C. Active transport against its concentration gradient
D. Vesicular transport via endocytosis
Answer: A
Rationale: Small, nonpolar (lipophilic) molecules like O2 and CO2 can dissolve
directly into and diffuse across the hydrophobic lipid bilayer, moving passively
down their concentration gradient with no need for a membrane protein or energy
input — a hallmark of simple diffusion.
5. Glucose transport into most cells via GLUT transporters is an example of
which transport mechanism?
A. Simple diffusion through the lipid bilayer
B. Facilitated diffusion: a carrier protein allows glucose to move down its
concentration gradient without direct ATP use
C. Primary active transport requiring direct ATP hydrolysis
D. Secondary active transport coupled to a sodium gradient
Answer: B
Rationale: Glucose is polar and too large to cross the lipid bilayer directly, so it
requires GLUT carrier proteins. Because glucose moves down its concentration
gradient (from higher to lower concentration) without direct ATP hydrolysis by the
,transporter itself, this is classified as facilitated diffusion, distinct from the
Na+/glucose symporter (SGLT), which is secondary active transport.
6. The Na+/K+ ATPase pump is best classified as which type of transport, and
what does it accomplish per cycle?
A. Passive transport; moves 3 Na+ in and 2 K+ out
B. Primary active transport; uses ATP hydrolysis to pump 3 Na+ out of the cell
and 2 K+ into the cell against their concentration gradients
C. Facilitated diffusion; moves ions down their gradients only
D. Secondary active transport coupled to glucose movement
Answer: B
Rationale: The Na+/K+ ATPase directly hydrolyzes ATP to phosphorylate itself,
driving a conformational change that extrudes 3 Na+ ions out of the cell and
imports 2 K+ ions in, both against their respective electrochemical gradients. This
primary active transport pump establishes the concentration gradients essential
for resting membrane potential and secondary active transport.
7. Which statement correctly describes secondary active transport, using the
Na+/glucose symporter (SGLT) as an example?
A. It directly hydrolyzes ATP to move both Na+ and glucose
B. It uses the energy stored in the Na+ electrochemical gradient (established
by the Na+/K+ ATPase) to move glucose against its concentration gradient,
without directly consuming ATP itself
C. It transports only ions, never organic molecules
D. It moves Na+ down its gradient and glucose down its gradient
simultaneously, requiring no energy input at all
Answer: B
Rationale: Secondary active transport does not directly hydrolyze ATP; instead it
harnesses the potential energy stored in an ion gradient (here, the inward Na+
gradient created by the ATP-dependent Na+/K+ pump) to move a second solute
(glucose) against its own concentration gradient, coupling the two movements
through a shared carrier protein (symporter).
8. A red blood cell placed in a hypotonic solution swells and may lyse. What is
the underlying mechanism?
, A. Water moves by osmosis from the area of lower solute concentration
(outside) to higher solute concentration (inside the cell), causing the cell to
gain volume
B. Solutes move into the cell against their gradient, drawing no water
C. The cell actively pumps water out, but is overwhelmed
D. The hypotonic solution has higher osmolarity than the cytoplasm
Answer: A
Rationale: A hypotonic solution has a lower solute concentration (and thus higher
water concentration) than the cell's cytoplasm. Water moves passively by osmosis
down its own concentration gradient, from the hypotonic extracellular fluid into
the relatively hypertonic cytoplasm, causing the cell to swell and potentially lyse if
the membrane cannot withstand the pressure.
9. Which type of membrane protein specifically forms a water-filled pore that
allows rapid, passive movement of specific ions down their electrochemical
gradient?
A. Peripheral membrane protein
B. Ion channel (gated or non-gated)
C. Cytoskeletal anchor protein
D. Glycolipid receptor
Answer: B
Rationale: Ion channels are integral membrane proteins that form aqueous pores
through the bilayer, allowing rapid, passive (no ATP required) flow of specific ions
down their electrochemical gradient when the channel is open. This distinguishes
them from carrier proteins (like GLUT or SGLT), which bind and conformationally
shuttle their substrate rather than forming a continuous open pore.
10. Ligand-gated ion channels, such as the nicotinic acetylcholine receptor, open
in response to which stimulus?
A. A change in membrane voltage alone
B. Binding of a specific chemical messenger (ligand) to the channel/receptor
protein, causing a conformational change that opens the pore
C. Mechanical deformation of the membrane only
D. A rise in intracellular ATP concentration exclusively
Answer: B
