Human Physiology
HUMAN PHYSIOLOGY EXAM READY - VERIFIED QUESTIONS AND
EXPLAINED VERIFIED ANSWERS - LATEST VERSION
1. What is the primary function of the phospholipid bilayer in the plasma
membrane?
ANSWER : It forms a selectively permeable barrier that separates the intracellular
from the extracellular environment.
Explanation: The hydrophobic fatty acid tails face inward and the hydrophilic
phosphate heads face outward, blocking free passage of ions and polar molecules while
allowing lipid-soluble substances to diffuse through.
2. Define simple diffusion and give an example of a substance that moves this way.
ANSWER : Simple diffusion is the passive movement of a substance from an area of
high concentration to low concentration across a membrane without a carrier protein;
oxygen and carbon dioxide diffuse this way.
Explanation: Because O2 and CO2 are small nonpolar gases, they pass directly through
the lipid bilayer down their concentration gradients without needing a transport
protein.
3. What distinguishes facilitated diffusion from simple diffusion?
ANSWER : Facilitated diffusion requires a carrier or channel protein to move a
substance down its concentration gradient, whereas simple diffusion does not.
Explanation: Polar or charged molecules such as glucose cannot cross the lipid bilayer
directly, so they rely on specific transport proteins (e.g., GLUT transporters) even though
no ATP is used.
4. Explain primary active transport using the Na+/K+ ATPase as an example.
ANSWER : Primary active transport uses ATP hydrolysis directly to move ions
against their concentration gradient; the Na+/K+ pump moves 3 Na+ out and 2 K+
into the cell per ATP consumed.
Explanation: This pump maintains the steep Na+ and K+ gradients across the
membrane that are essential for resting membrane potential and secondary active
transport.
5. How does secondary active transport differ from primary active transport?
ANSWER : Secondary active transport uses the energy stored in an ion gradient
(created by primary active transport) to move another substance against its gradient,
rather than using ATP directly.
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, Human Physiology
Explanation: For example, the Na+/glucose symporter uses the inward Na+ gradient
established by the Na+/K+ ATPase to co-transport glucose into the cell against its
concentration gradient.
6. What is osmosis and what determines its direction?
ANSWER : Osmosis is the diffusion of water across a selectively permeable
membrane, moving toward the compartment with higher solute concentration (lower
water concentration).
Explanation: Water moves to equalize osmotic pressure between compartments; the
direction is dictated by the relative concentration of non-permeating solutes on each side
of the membrane.
7. Define tonicity and explain what happens to a red blood cell placed in a
hypotonic solution.
ANSWER : Tonicity describes a solution's effect on cell volume; in a hypotonic
solution the cell swells and may lyse because water moves into the cell.
Explanation: A hypotonic solution has a lower effective solute concentration than the
cytoplasm, so water enters the cell by osmosis to equalize concentrations, increasing cell
volume.
8. What is the resting membrane potential of a typical neuron and why is it
negative?
ANSWER : The resting membrane potential is approximately -70 mV, negative
because the cell membrane is more permeable to K+ than Na+, allowing K+ to diffuse
outward and leave the inside relatively negative.
Explanation: The Goldman equation shows that the membrane potential reflects a
weighted average of the equilibrium potentials of permeant ions, and since resting
permeability favors K+, the potential lies close to the K+ equilibrium potential (~-90 mV).
9. Explain the role of the Na+/K+ ATPase in establishing ionic gradients.
ANSWER : It actively pumps Na+ out of and K+ into the cell against their
concentration gradients, maintaining high extracellular Na+ and high intracellular K+.
Explanation: These gradients are essential for generating the resting membrane
potential and for driving secondary active transport and action potential repolarization.
10. What is the equilibrium potential for an ion and how is it calculated?
ANSWER : The equilibrium potential is the membrane voltage at which the electrical
and chemical driving forces for that ion are equal and opposite, calculated using the
Nernst equation.
Explanation: The Nernst equation, E = (61/z) log([ion]out/[ion]in) at body
temperature, predicts the membrane potential at which net flux of that specific ion is
zero.
11. Describe receptor-mediated endocytosis.
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, Human Physiology
ANSWER : It is a process in which specific ligands bind receptors on the cell surface,
triggering the membrane to invaginate and form a vesicle that internalizes the ligand-
receptor complex.
Explanation: This mechanism allows selective, efficient uptake of substances such as
LDL cholesterol, unlike bulk-phase pinocytosis which is nonspecific.
12. What is the difference between exocytosis and endocytosis?
ANSWER : Exocytosis is the release of intracellular vesicle contents to the outside of
the cell, while endocytosis is the internalization of extracellular material by membrane
invagination.
Explanation: Exocytosis is used for secretion (e.g., neurotransmitter release), whereas
endocytosis is used for uptake (e.g., nutrient absorption or antigen presentation).
13. What role does the mitochondrion play in cellular physiology?
ANSWER : It generates ATP through oxidative phosphorylation, the primary energy
source for cellular processes.
Explanation: The electron transport chain located in the inner mitochondrial
membrane uses oxygen as the final electron acceptor to drive ATP synthase, producing
most of the cell's usable energy.
14. What is the function of the sodium-potassium pump in maintaining cell volume?
ANSWER : It prevents osmotic swelling by continuously pumping Na+ out of the cell,
offsetting the tendency of intracellular proteins to draw water inward.
Explanation: Without this pump, the negatively charged intracellular proteins (the
Gibbs-Donnan effect) would cause continuous water influx and cell lysis.
15. Explain the concept of the Gibbs-Donnan equilibrium in cell physiology.
ANSWER : It describes how the presence of non-diffusible, negatively charged
intracellular proteins alters the passive distribution of permeant ions across the
membrane, favoring higher total intracellular osmotic particles.
Explanation: Because proteins cannot cross the membrane, cations are drawn in and
anions are pushed out to maintain electroneutrality, which would cause cell swelling if
not counteracted by active Na+/K+ pumping.
16. What triggers the depolarization phase of an action potential?
ANSWER : A stimulus that depolarizes the membrane to threshold opens voltage-
gated Na+ channels, allowing rapid Na+ influx.
Explanation: Once threshold (~-55 mV) is reached, the resulting Na+ influx is
regenerative, driving the membrane potential rapidly toward the Na+ equilibrium
potential (~+60 mV).
17. What causes the repolarization phase of an action potential?
ANSWER : Inactivation of voltage-gated Na+ channels combined with delayed
opening of voltage-gated K+ channels allows K+ efflux, returning the membrane
potential toward resting levels.
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, Human Physiology
Explanation: Na+ channels close automatically (inactivation gate) shortly after
opening, while K+ channels open more slowly, so outward K+ current dominates and
repolarizes the membrane.
18. Define the absolute refractory period.
ANSWER : It is the period during and immediately after an action potential when a
second action potential cannot be triggered regardless of stimulus strength.
Explanation: This occurs because voltage-gated Na+ channels are inactivated and
cannot reopen until the membrane repolarizes, ensuring unidirectional propagation of
the impulse.
19. How does myelination increase conduction velocity?
ANSWER : Myelin insulates the axon and forces action potentials to jump between
nodes of Ranvier (saltatory conduction), greatly increasing conduction speed.
Explanation: Because ion channels are concentrated at the nodes, the depolarizing
current passively spreads to the next node with minimal loss, allowing much faster
propagation than continuous conduction in unmyelinated axons.
20. What is the role of voltage-gated calcium channels at the presynaptic terminal?
ANSWER : Their opening in response to depolarization allows Ca2+ influx, which
triggers fusion of synaptic vesicles with the presynaptic membrane and
neurotransmitter release.
Explanation: Ca2+ binds synaptotagmin on vesicle membranes, initiating SNARE-
complex-mediated exocytosis of neurotransmitter into the synaptic cleft.
21. Differentiate between an excitatory postsynaptic potential (EPSP) and an
inhibitory postsynaptic potential (IPSP).
ANSWER : An EPSP is a depolarization that brings the postsynaptic membrane closer
to threshold, while an IPSP is a hyperpolarization (or stabilization) that moves it
further from threshold.
Explanation: EPSPs typically result from Na+ influx through ligand-gated channels,
while IPSPs typically result from Cl- influx or K+ efflux, making the neuron less likely to
fire.
22. What is temporal summation?
ANSWER : It is the additive effect of successive postsynaptic potentials arriving in
rapid succession from a single presynaptic neuron, which can bring the membrane to
threshold.
Explanation: Because postsynaptic potentials decay gradually, closely spaced impulses
can summate before the first one dissipates, increasing the likelihood of reaching
threshold.
23. What is spatial summation?
ANSWER : It is the combined effect of postsynaptic potentials from multiple different
presynaptic neurons arriving simultaneously at the postsynaptic cell.
Page 4 of 36
HUMAN PHYSIOLOGY EXAM READY - VERIFIED QUESTIONS AND
EXPLAINED VERIFIED ANSWERS - LATEST VERSION
1. What is the primary function of the phospholipid bilayer in the plasma
membrane?
ANSWER : It forms a selectively permeable barrier that separates the intracellular
from the extracellular environment.
Explanation: The hydrophobic fatty acid tails face inward and the hydrophilic
phosphate heads face outward, blocking free passage of ions and polar molecules while
allowing lipid-soluble substances to diffuse through.
2. Define simple diffusion and give an example of a substance that moves this way.
ANSWER : Simple diffusion is the passive movement of a substance from an area of
high concentration to low concentration across a membrane without a carrier protein;
oxygen and carbon dioxide diffuse this way.
Explanation: Because O2 and CO2 are small nonpolar gases, they pass directly through
the lipid bilayer down their concentration gradients without needing a transport
protein.
3. What distinguishes facilitated diffusion from simple diffusion?
ANSWER : Facilitated diffusion requires a carrier or channel protein to move a
substance down its concentration gradient, whereas simple diffusion does not.
Explanation: Polar or charged molecules such as glucose cannot cross the lipid bilayer
directly, so they rely on specific transport proteins (e.g., GLUT transporters) even though
no ATP is used.
4. Explain primary active transport using the Na+/K+ ATPase as an example.
ANSWER : Primary active transport uses ATP hydrolysis directly to move ions
against their concentration gradient; the Na+/K+ pump moves 3 Na+ out and 2 K+
into the cell per ATP consumed.
Explanation: This pump maintains the steep Na+ and K+ gradients across the
membrane that are essential for resting membrane potential and secondary active
transport.
5. How does secondary active transport differ from primary active transport?
ANSWER : Secondary active transport uses the energy stored in an ion gradient
(created by primary active transport) to move another substance against its gradient,
rather than using ATP directly.
Page 1 of 36
, Human Physiology
Explanation: For example, the Na+/glucose symporter uses the inward Na+ gradient
established by the Na+/K+ ATPase to co-transport glucose into the cell against its
concentration gradient.
6. What is osmosis and what determines its direction?
ANSWER : Osmosis is the diffusion of water across a selectively permeable
membrane, moving toward the compartment with higher solute concentration (lower
water concentration).
Explanation: Water moves to equalize osmotic pressure between compartments; the
direction is dictated by the relative concentration of non-permeating solutes on each side
of the membrane.
7. Define tonicity and explain what happens to a red blood cell placed in a
hypotonic solution.
ANSWER : Tonicity describes a solution's effect on cell volume; in a hypotonic
solution the cell swells and may lyse because water moves into the cell.
Explanation: A hypotonic solution has a lower effective solute concentration than the
cytoplasm, so water enters the cell by osmosis to equalize concentrations, increasing cell
volume.
8. What is the resting membrane potential of a typical neuron and why is it
negative?
ANSWER : The resting membrane potential is approximately -70 mV, negative
because the cell membrane is more permeable to K+ than Na+, allowing K+ to diffuse
outward and leave the inside relatively negative.
Explanation: The Goldman equation shows that the membrane potential reflects a
weighted average of the equilibrium potentials of permeant ions, and since resting
permeability favors K+, the potential lies close to the K+ equilibrium potential (~-90 mV).
9. Explain the role of the Na+/K+ ATPase in establishing ionic gradients.
ANSWER : It actively pumps Na+ out of and K+ into the cell against their
concentration gradients, maintaining high extracellular Na+ and high intracellular K+.
Explanation: These gradients are essential for generating the resting membrane
potential and for driving secondary active transport and action potential repolarization.
10. What is the equilibrium potential for an ion and how is it calculated?
ANSWER : The equilibrium potential is the membrane voltage at which the electrical
and chemical driving forces for that ion are equal and opposite, calculated using the
Nernst equation.
Explanation: The Nernst equation, E = (61/z) log([ion]out/[ion]in) at body
temperature, predicts the membrane potential at which net flux of that specific ion is
zero.
11. Describe receptor-mediated endocytosis.
Page 2 of 36
, Human Physiology
ANSWER : It is a process in which specific ligands bind receptors on the cell surface,
triggering the membrane to invaginate and form a vesicle that internalizes the ligand-
receptor complex.
Explanation: This mechanism allows selective, efficient uptake of substances such as
LDL cholesterol, unlike bulk-phase pinocytosis which is nonspecific.
12. What is the difference between exocytosis and endocytosis?
ANSWER : Exocytosis is the release of intracellular vesicle contents to the outside of
the cell, while endocytosis is the internalization of extracellular material by membrane
invagination.
Explanation: Exocytosis is used for secretion (e.g., neurotransmitter release), whereas
endocytosis is used for uptake (e.g., nutrient absorption or antigen presentation).
13. What role does the mitochondrion play in cellular physiology?
ANSWER : It generates ATP through oxidative phosphorylation, the primary energy
source for cellular processes.
Explanation: The electron transport chain located in the inner mitochondrial
membrane uses oxygen as the final electron acceptor to drive ATP synthase, producing
most of the cell's usable energy.
14. What is the function of the sodium-potassium pump in maintaining cell volume?
ANSWER : It prevents osmotic swelling by continuously pumping Na+ out of the cell,
offsetting the tendency of intracellular proteins to draw water inward.
Explanation: Without this pump, the negatively charged intracellular proteins (the
Gibbs-Donnan effect) would cause continuous water influx and cell lysis.
15. Explain the concept of the Gibbs-Donnan equilibrium in cell physiology.
ANSWER : It describes how the presence of non-diffusible, negatively charged
intracellular proteins alters the passive distribution of permeant ions across the
membrane, favoring higher total intracellular osmotic particles.
Explanation: Because proteins cannot cross the membrane, cations are drawn in and
anions are pushed out to maintain electroneutrality, which would cause cell swelling if
not counteracted by active Na+/K+ pumping.
16. What triggers the depolarization phase of an action potential?
ANSWER : A stimulus that depolarizes the membrane to threshold opens voltage-
gated Na+ channels, allowing rapid Na+ influx.
Explanation: Once threshold (~-55 mV) is reached, the resulting Na+ influx is
regenerative, driving the membrane potential rapidly toward the Na+ equilibrium
potential (~+60 mV).
17. What causes the repolarization phase of an action potential?
ANSWER : Inactivation of voltage-gated Na+ channels combined with delayed
opening of voltage-gated K+ channels allows K+ efflux, returning the membrane
potential toward resting levels.
Page 3 of 36
, Human Physiology
Explanation: Na+ channels close automatically (inactivation gate) shortly after
opening, while K+ channels open more slowly, so outward K+ current dominates and
repolarizes the membrane.
18. Define the absolute refractory period.
ANSWER : It is the period during and immediately after an action potential when a
second action potential cannot be triggered regardless of stimulus strength.
Explanation: This occurs because voltage-gated Na+ channels are inactivated and
cannot reopen until the membrane repolarizes, ensuring unidirectional propagation of
the impulse.
19. How does myelination increase conduction velocity?
ANSWER : Myelin insulates the axon and forces action potentials to jump between
nodes of Ranvier (saltatory conduction), greatly increasing conduction speed.
Explanation: Because ion channels are concentrated at the nodes, the depolarizing
current passively spreads to the next node with minimal loss, allowing much faster
propagation than continuous conduction in unmyelinated axons.
20. What is the role of voltage-gated calcium channels at the presynaptic terminal?
ANSWER : Their opening in response to depolarization allows Ca2+ influx, which
triggers fusion of synaptic vesicles with the presynaptic membrane and
neurotransmitter release.
Explanation: Ca2+ binds synaptotagmin on vesicle membranes, initiating SNARE-
complex-mediated exocytosis of neurotransmitter into the synaptic cleft.
21. Differentiate between an excitatory postsynaptic potential (EPSP) and an
inhibitory postsynaptic potential (IPSP).
ANSWER : An EPSP is a depolarization that brings the postsynaptic membrane closer
to threshold, while an IPSP is a hyperpolarization (or stabilization) that moves it
further from threshold.
Explanation: EPSPs typically result from Na+ influx through ligand-gated channels,
while IPSPs typically result from Cl- influx or K+ efflux, making the neuron less likely to
fire.
22. What is temporal summation?
ANSWER : It is the additive effect of successive postsynaptic potentials arriving in
rapid succession from a single presynaptic neuron, which can bring the membrane to
threshold.
Explanation: Because postsynaptic potentials decay gradually, closely spaced impulses
can summate before the first one dissipates, increasing the likelihood of reaching
threshold.
23. What is spatial summation?
ANSWER : It is the combined effect of postsynaptic potentials from multiple different
presynaptic neurons arriving simultaneously at the postsynaptic cell.
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