LIFESCI 7A MIDTERM 1 REVIEW ANSWER
KEY | QUESTIONS AND ANSWERS |
2026/27 UDATED COMPLETE - UCLA.
68 Questions with Answers and Detailed Rationales
100 PERCENT GUARANTEED PASS
INSTANT DOWNLOAD ANSWERS INCLUDED
IMPORTANCE OF THIS DOCUMENT
This comprehensive examination preparation guide has been meticulously developed to help you succeed in the
LIFESCI 7A MIDTERM 1 REVIEW ANSWER KEY | QUESTIONS AND ANSWERS | 2026/27 UDATED
COMPLETE - UCLA.. It contains 68 carefully selected questions that reflect the most current exam content and
testing strategies. Each question is accompanied by a correct answer and a detailed rationale that explains the
underlying pathophysiology, pharmacology, or clinical reasoning.
Self-Assessment – Test your knowledge and Exam Preparation – Familiarize yourself with the
identify areas requiring further question format and content
study areas
Concept Reinforcement – Deepen your Confidence Building – Develop test-taking
understanding through strategies and reduce
evidence-based exam anxiety
rationales
Time Management – Practice answering
questions under simulated
exam conditions
Review Summary 68 Questions
Foundations - Application - Lifesci 7a 1 Review KEY AND 2026/27 Udated Complete - UCLA Lifesci 7a 1
Review KEY AND 2026/27 Udated Complete - UCLA University
All answers with rationales
,Table of Contents
Content Area Questions Key Topics
Chemistry OF LIFE Water PH 1-12 Potential, Membrane, Likely, Initial, Current
AND Biological Molecules
Macromolecules Structure 13-24 Replication, Eukaryotic, Round, Mutation, Likely
AND Function OF Proteins
Nucleic Acids Carbohydrates
AND Lipids
CELL Structure AND 25-36 Mutation, Likely, Transcription, Factor, Concentration
Function Prokaryotic VS
Eukaryotic Cells Organelles
Membrane Structure AND 37-48 Potential, Membrane, Replication, Concentration, Glucose
Transport Passive AND
Active Transport Osmosis
Enzymes AND Metabolism 49-60 Population, Mutation, Current, Assuming, Studying
Kinetics Inhibition AND
Regulation
Cellular Respiration 61-68 Administered, Distribution, First, Elimination, Plasma
Glycolysis Citric ACID Cycle
Oxidative Phosphorylation
TOTAL 68 All questions include answers and detailed rationales
,Section A - Chemistry OF LIFE Water PH AND Biological
Molecules
Q1.
In a voltage-clamp experiment on a squid giant axon, the membrane potential is stepped
from -70 mV to +20 mV for 5 ms. Which ion movement dominates the initial transient
inward current and the subsequent steady-state outward current?
A. Na+ influx; K+ efflux B. Na+ efflux; K+ influx
C. Ca2+ influx; Cl- efflux D. K+ efflux; Na+ influx
Correct: A - Na+ influx; K+ efflux
Rationale:Depolarization to +20 mV opens voltage-gated Na+ channels, causing a transient
Na+ influx (inward current) that inactivates. Then voltage-gated K+ channels open, producing
a sustained K+ efflux (outward current) that repolarizes the membrane.
Why the other answers are wrong:
B. Na+ moves down its electrochemical gradient into the cell (influx), not out, and K+ moves
out, not in.
C. Ca2+ currents are minor in squid axon; Cl- does not produce the delayed outward current.
D. The initial current is carried by Na+ influx, not K+ efflux.
Reference: Kandel, E.R. et al. (2021). Principles of Neural Science, 6th ed., Ch. 11
Q2.
A drug that blocks the sodium-potassium ATPase pump is applied to a neuron. Which
immediate effect on the resting membrane potential is most likely, and why?
A. Depolarization due to loss of the B. Hyperpolarization due to increased
electrogenic contribution and ion gradient intracellular Na+
rundown
C. No change because the pump is D. Depolarization due to increased K+
electrically neutral conductance
Correct: A - Depolarization due to loss of the electrogenic contribution and ion gradient
rundown
Rationale:The Na+/K+ ATPase exports 3 Na+ and imports 2 K+ per ATP, contributing a net
outward current (electrogenic). Blocking it eliminates this hyperpolarizing contribution and
gradually dissipates ion gradients, causing depolarization. The effect is slow because the
pump's immediate electrogenic contribution is small relative to leak conductances.
Why the other answers are wrong:
B. Blocking the pump does not directly hyperpolarize; increased intracellular Na+ would reduce
Page 3
, Section A - Chemistry OF LIFE Water PH AND Biological Molecules
the gradient and depolarize.
C. The pump is electrogenic (3:2 stoichiometry), so it is not electrically neutral.
D. The pump does not directly alter K+ conductance; depolarization results from loss of pump current and gradient rundown.
Reference: Purves, D. et al. (2018). Neuroscience, 6th ed., Ch. 3
Q3.
A researcher measures the reversal potential of an EPSP before and after reducing
extracellular Na+ concentration from 145 mM to 72.5 mM. Assuming the synapse is purely
glutamatergic AMPA, what change in reversal potential is expected at 20°C?
A. Shift by about -18 mV (more negative) B. Shift by about +18 mV (more positive)
C. No shift because AMPA receptors are D. Shift by about -9 mV (more negative)
also permeable to K+
Correct: A - Shift by about -18 mV (more negative)
Rationale:AMPA receptors are primarily permeable to Na+ and K+. The reversal potential is
determined mainly by the Na+ gradient. Halving extracellular Na+ changes the Nernst
potential for Na+ by (RT/F) ln(2) 58 mV * ln(2) at 20°C? Actually, using 58 mV per decade at
20°C, a 2-fold change gives 58*log10(2) 17.5 mV. Since E_Na becomes more negative, the
reversal potential shifts negatively by ~18 mV.
Why the other answers are wrong:
B. Reducing extracellular Na+ makes the Na+ equilibrium potential more negative, not more
positive.
C. AMPA receptors are permeable to both Na+ and K+, but Na+ gradient dominates; the shift is
still significant.
D. The shift is approximately -18 mV, not -9 mV, for a 2-fold change.
Reference: Kandel, E.R. et al. (2021). Principles of Neural Science, 6th ed., Ch. 7
Q4.
During the action potential upstroke, which condition best explains why the membrane
potential does not simply stop at the Na+ equilibrium potential?
A. Inactivation of Na+ channels and B. The Na+ equilibrium potential is not the
activation of K+ channels only ion gradient
C. The membrane capacitance slows the D. Na+ channels are only partially selective
voltage change
Correct: A - Inactivation of Na+ channels and activation of K+ channels
Rationale:The upstroke is driven by Na+ influx, but as the membrane depolarizes, Na+
channels inactivate and voltage-gated K+ channels activate, increasing K+ efflux. These
opposing currents prevent the membrane from reaching E_Na and instead drive
repolarization toward E_K.
Page 4
KEY | QUESTIONS AND ANSWERS |
2026/27 UDATED COMPLETE - UCLA.
68 Questions with Answers and Detailed Rationales
100 PERCENT GUARANTEED PASS
INSTANT DOWNLOAD ANSWERS INCLUDED
IMPORTANCE OF THIS DOCUMENT
This comprehensive examination preparation guide has been meticulously developed to help you succeed in the
LIFESCI 7A MIDTERM 1 REVIEW ANSWER KEY | QUESTIONS AND ANSWERS | 2026/27 UDATED
COMPLETE - UCLA.. It contains 68 carefully selected questions that reflect the most current exam content and
testing strategies. Each question is accompanied by a correct answer and a detailed rationale that explains the
underlying pathophysiology, pharmacology, or clinical reasoning.
Self-Assessment – Test your knowledge and Exam Preparation – Familiarize yourself with the
identify areas requiring further question format and content
study areas
Concept Reinforcement – Deepen your Confidence Building – Develop test-taking
understanding through strategies and reduce
evidence-based exam anxiety
rationales
Time Management – Practice answering
questions under simulated
exam conditions
Review Summary 68 Questions
Foundations - Application - Lifesci 7a 1 Review KEY AND 2026/27 Udated Complete - UCLA Lifesci 7a 1
Review KEY AND 2026/27 Udated Complete - UCLA University
All answers with rationales
,Table of Contents
Content Area Questions Key Topics
Chemistry OF LIFE Water PH 1-12 Potential, Membrane, Likely, Initial, Current
AND Biological Molecules
Macromolecules Structure 13-24 Replication, Eukaryotic, Round, Mutation, Likely
AND Function OF Proteins
Nucleic Acids Carbohydrates
AND Lipids
CELL Structure AND 25-36 Mutation, Likely, Transcription, Factor, Concentration
Function Prokaryotic VS
Eukaryotic Cells Organelles
Membrane Structure AND 37-48 Potential, Membrane, Replication, Concentration, Glucose
Transport Passive AND
Active Transport Osmosis
Enzymes AND Metabolism 49-60 Population, Mutation, Current, Assuming, Studying
Kinetics Inhibition AND
Regulation
Cellular Respiration 61-68 Administered, Distribution, First, Elimination, Plasma
Glycolysis Citric ACID Cycle
Oxidative Phosphorylation
TOTAL 68 All questions include answers and detailed rationales
,Section A - Chemistry OF LIFE Water PH AND Biological
Molecules
Q1.
In a voltage-clamp experiment on a squid giant axon, the membrane potential is stepped
from -70 mV to +20 mV for 5 ms. Which ion movement dominates the initial transient
inward current and the subsequent steady-state outward current?
A. Na+ influx; K+ efflux B. Na+ efflux; K+ influx
C. Ca2+ influx; Cl- efflux D. K+ efflux; Na+ influx
Correct: A - Na+ influx; K+ efflux
Rationale:Depolarization to +20 mV opens voltage-gated Na+ channels, causing a transient
Na+ influx (inward current) that inactivates. Then voltage-gated K+ channels open, producing
a sustained K+ efflux (outward current) that repolarizes the membrane.
Why the other answers are wrong:
B. Na+ moves down its electrochemical gradient into the cell (influx), not out, and K+ moves
out, not in.
C. Ca2+ currents are minor in squid axon; Cl- does not produce the delayed outward current.
D. The initial current is carried by Na+ influx, not K+ efflux.
Reference: Kandel, E.R. et al. (2021). Principles of Neural Science, 6th ed., Ch. 11
Q2.
A drug that blocks the sodium-potassium ATPase pump is applied to a neuron. Which
immediate effect on the resting membrane potential is most likely, and why?
A. Depolarization due to loss of the B. Hyperpolarization due to increased
electrogenic contribution and ion gradient intracellular Na+
rundown
C. No change because the pump is D. Depolarization due to increased K+
electrically neutral conductance
Correct: A - Depolarization due to loss of the electrogenic contribution and ion gradient
rundown
Rationale:The Na+/K+ ATPase exports 3 Na+ and imports 2 K+ per ATP, contributing a net
outward current (electrogenic). Blocking it eliminates this hyperpolarizing contribution and
gradually dissipates ion gradients, causing depolarization. The effect is slow because the
pump's immediate electrogenic contribution is small relative to leak conductances.
Why the other answers are wrong:
B. Blocking the pump does not directly hyperpolarize; increased intracellular Na+ would reduce
Page 3
, Section A - Chemistry OF LIFE Water PH AND Biological Molecules
the gradient and depolarize.
C. The pump is electrogenic (3:2 stoichiometry), so it is not electrically neutral.
D. The pump does not directly alter K+ conductance; depolarization results from loss of pump current and gradient rundown.
Reference: Purves, D. et al. (2018). Neuroscience, 6th ed., Ch. 3
Q3.
A researcher measures the reversal potential of an EPSP before and after reducing
extracellular Na+ concentration from 145 mM to 72.5 mM. Assuming the synapse is purely
glutamatergic AMPA, what change in reversal potential is expected at 20°C?
A. Shift by about -18 mV (more negative) B. Shift by about +18 mV (more positive)
C. No shift because AMPA receptors are D. Shift by about -9 mV (more negative)
also permeable to K+
Correct: A - Shift by about -18 mV (more negative)
Rationale:AMPA receptors are primarily permeable to Na+ and K+. The reversal potential is
determined mainly by the Na+ gradient. Halving extracellular Na+ changes the Nernst
potential for Na+ by (RT/F) ln(2) 58 mV * ln(2) at 20°C? Actually, using 58 mV per decade at
20°C, a 2-fold change gives 58*log10(2) 17.5 mV. Since E_Na becomes more negative, the
reversal potential shifts negatively by ~18 mV.
Why the other answers are wrong:
B. Reducing extracellular Na+ makes the Na+ equilibrium potential more negative, not more
positive.
C. AMPA receptors are permeable to both Na+ and K+, but Na+ gradient dominates; the shift is
still significant.
D. The shift is approximately -18 mV, not -9 mV, for a 2-fold change.
Reference: Kandel, E.R. et al. (2021). Principles of Neural Science, 6th ed., Ch. 7
Q4.
During the action potential upstroke, which condition best explains why the membrane
potential does not simply stop at the Na+ equilibrium potential?
A. Inactivation of Na+ channels and B. The Na+ equilibrium potential is not the
activation of K+ channels only ion gradient
C. The membrane capacitance slows the D. Na+ channels are only partially selective
voltage change
Correct: A - Inactivation of Na+ channels and activation of K+ channels
Rationale:The upstroke is driven by Na+ influx, but as the membrane depolarizes, Na+
channels inactivate and voltage-gated K+ channels activate, increasing K+ efflux. These
opposing currents prevent the membrane from reaching E_Na and instead drive
repolarization toward E_K.
Page 4
