MCAT Biological and Biochemical Foundations of Living Systems Quiz: 1d Bioenergetics Thermodynamics

What this quiz covers

This quiz focuses on 1d Bioenergetics Thermodynamics, giving you a quick way to practice the rules, question types, and explanations that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Nonspontaneity implies the reaction has a high activation energy, not an unfavorable $\Delta G$
2. $\Delta S$ must be positive because exothermic reactions always increase disorder
3. $\Delta G$ and $\Delta H$ must always have the same sign, so the observation is impossible
4. $\Delta S$ must be sufficiently negative so that $-T\Delta S$ outweighs the negative $\Delta H$ (correct answer)

Question 2

1. Removing product affects rate but cannot affect $\Delta G$ because free energy depends only on temperature
2. Removing product increases $Q$, making $RT\ln Q$ more positive and driving $\Delta G$ downward
3. Removing product changes \Delta G^\circ' by altering the enzyme's active site
4. Removing product decreases $Q$, making $RT\ln Q$ more negative and driving $\Delta G$ downward (correct answer)

Question 3

1. Catalyst 1 must make $\Delta G^\circ$ more negative, increasing the driving force
2. Catalyst 1 must increase $K_{eq}$, shifting equilibrium more toward products
3. Catalyst 1 likely lowers activation energy more, increasing rate without changing $\Delta G^\circ$ or $K_{eq}$ (correct answer)
4. Catalyst 1 increases entropy of the system, which is why equilibrium is reached sooner

Question 4

1. ATP synthesis increases because the proton gradient provides free energy to drive an otherwise unfavorable phosphorylation (correct answer)
2. ATP synthesis decreases because gradients always oppose chemical work
3. ATP synthesis is unchanged because ATP synthase only lowers activation energy
4. ATP synthesis occurs only if $\Delta H$ for ADP+$P_i$ is negative

Question 5

1. Forward reaction is spontaneous only if temperature decreases, since $RT\ln Q$ becomes positive
2. Forward reaction cannot be spontaneous because \Delta G^\circ' is positive
3. Forward reaction is spontaneous only if an enzyme is added to change \Delta G^\circ'
4. Forward reaction can be spontaneous despite positive \Delta G^\circ' because $\ln Q$ is negative (correct answer)

Question 6

1. Coupling changes each reaction's $K_{eq}$ so that both become strongly product-favored
2. The coupled process must be nonspontaneous because one step has positive $\Delta G^\circ$
3. The coupled process has $\Delta H^\circ=0$, so it is at equilibrium
4. The coupled process has $\Delta G^\circ=0$ and can be driven forward by maintaining nonstandard concentrations (correct answer)

Question 7

1. ATP synthesis increases because removing the gradient lowers the activation energy for ATP synthase
2. Electron transport slows because it requires ATP hydrolysis to proceed
3. Energy from electron transport is released as heat rather than conserved in the proton-motive force (correct answer)
4. The uncoupler makes $\Delta G$ for ATP formation negative by increasing $K_{eq}$ for ADP phosphorylation

Question 8

1. The report is inconsistent; enzymes do not change state functions like $\Delta G$ between fixed initial and final states (correct answer)
2. The report is consistent because enzymes convert heat into work, decreasing entropy
3. The report is consistent only if the enzyme binds product more tightly than substrate
4. The report is consistent because enzymes increase $K_{eq}$ by stabilizing the transition state

Question 9

1. Increase $K_d$ to 100 nM
2. Decrease $K_d$ to 1 nM (correct answer)
3. Increase $\Delta H$ to a more positive value
4. Increase temperature so that $RT\ln K_d$ becomes more negative for the same $K_d$

Question 10

1. The reaction is less favorable than standard because $Q<1$ increases $\Delta G$
2. The reaction is more favorable than standard because $Q<1$ makes $RT\ln Q$ negative (correct answer)
3. The reaction is at equilibrium because \Delta G^\circ' is negative
4. Spontaneity cannot be assessed without knowing $\Delta H$

Question 11

1. $\Delta G^\circ$ is negative because $K_{eq}$ is less than 1
2. $\Delta G^\circ$ is positive because $\ln(10^{-2})$ is negative (correct answer)
3. $\Delta G^\circ$ equals zero because $K_{eq}$ is dimensionless
4. $\Delta G^\circ$ cannot be determined without $\Delta H^\circ$

Question 12

1. E makes $\Delta G^\circ$ more negative by stabilizing P, increasing $K_{eq}$ above 10
2. E decreases the activation energy but does not change $\Delta G^\circ$ or $K_{eq}$ (correct answer)
3. E increases the activation energy to slow the reverse reaction, shifting equilibrium toward P
4. E changes $\Delta G^\circ$ by increasing the entropy term, making the reaction spontaneous only with enzyme present

Question 13

1. $K_{eq}>1$, so B predominates at equilibrium
2. $K_{eq}=1$ because the sign of $\Delta G^\circ$ does not affect equilibrium
3. $K_{eq}<1$, so A predominates at equilibrium (correct answer)
4. The reaction is spontaneous in the forward direction at any concentrations because $\Delta G^\circ$ is defined at equilibrium

Question 14

1. Binding is spontaneous only if $\Delta H$ is negative, regardless of $\Delta S$
2. Binding is nonspontaneous because any positive $\Delta H$ makes $\Delta G$ positive
3. Binding is spontaneous because the positive entropy term can outweigh the positive enthalpy (correct answer)
4. Binding is at equilibrium because $\Delta S$ is positive

Question 15

1. Hydrolyze 1 ATP to pump 4 mol ions
2. Hydrolyze 1 ATP to pump 3 mol ions (correct answer)
3. Hydrolyze 1 ATP to pump 2 mol ions
4. Hydrolyze 1 ATP to pump 5 mol ions

Question 16

1. Net $\Delta G$ is $-34\ \text{kJ/mol}$, so phosphorylation can proceed when coupled to ATP hydrolysis (correct answer)
2. Net $\Delta G$ is $+46\ \text{kJ/mol}$ because the magnitudes add regardless of sign
3. Net $\Delta G$ is $+6\ \text{kJ/mol}$ because enzymes cannot change free energy
4. Net $\Delta G$ must be zero because coupling implies equilibrium

Question 17

1. $\Delta G$ becomes more negative (more favorable) because products are higher
2. $\Delta G$ becomes less negative (less favorable) because $RT\ln Q$ increases (correct answer)
3. $\Delta G$ is unchanged because \Delta G^\circ' is constant for ATP
4. $\Delta G$ becomes zero because ATP hydrolysis is always at equilibrium in cells

Question 18

1. Net transport is thermodynamically unfavorable because $+20\ \text{kJ/mol}$ indicates nonspontaneity
2. Net coupled process is favorable with $\Delta G_{net}=-30\ \text{kJ/mol}$ (correct answer)
3. Net coupled process is at equilibrium because the enzyme cancels free-energy changes
4. Net coupled process becomes favorable only if $\Delta H$ is negative, regardless of $\Delta G$

Question 19

1. Correct; $\Delta G<0$ implies products predominate at equilibrium
2. Incorrect; $\Delta G<0$ depends on $Q$ as well as $K_{eq}$, so $K_{eq}$ could be <1 (correct answer)
3. Correct only if an enzyme is present to lower $\Delta G^\circ$
4. Incorrect; $K_{eq}$ is determined by activation energy, not free energy

Question 20

1. The reaction becomes nonspontaneous at high [S] because $v_0$ approaches a maximum
2. The enzyme approaches saturation, so increasing [S] no longer substantially increases the fraction of ES complexes (correct answer)
3. At high [S], $\Delta G^\circ$ becomes less negative, limiting the rate
4. The plateau indicates equilibrium has been reached, so $K_{eq}$ must be 1