Question 1

Which of the following best describes the main thermodynamic reason why cells must constantly expend energy to maintain concentration gradients across membranes?

Accepted Answer

Because gradients correspond to states with decreased entropy, which are less probable and require energy to maintain.

Question 2

A reaction has $$\Delta H  0. $$According to the equation $$\Delta G = \Delta H - T\Delta S$$, what can you conclude about the spontaneity of this reaction at any temperature?

Accepted Answer

The reaction is always spontaneous.

Question 3

Which type of biological work is illustrated by the active transport of protons (H+) out of the mitochondrial matrix, creating a membrane potential?

Accepted Answer

Electrical work

Question 4

In the context of the first law of thermodynamics, which of the following statements is correct?

Accepted Answer

The total energy of the universe remains constant during any physical or chemical change.

Question 5

Which equation correctly relates the standard free energy change ($$\Delta G^\circ') to $$the equilibrium constant ($$K'_{eq}) $$for a reaction?

Accepted Answer

$$\Delta G^\circ' = -RT \ln K'_{eq}$$

Question 6

A cell maintains a much higher concentration of glucose-6-phosphate than fructose-6-phosphate, even though the standard free energy change ($$\Delta G^\circ') $$for their interconversion is positive. What does this indicate about the actual free energy change ($$\Delta G') in $$the cell?

Accepted Answer

$$\Delta G' is $$negative, so the reaction is spontaneous in the cell.

Question 7

Which of the following best describes an open system in biological terms?

Accepted Answer

A system that exchanges both energy and matter with its surroundings.

Question 8

Which of the following is an example of mechanical work in cells?

Accepted Answer

The contraction of muscle fibers during weight lifting.

Question 9

If a reaction has $$\Delta G \u003e 0$$, which of the following statements is true?

Accepted Answer

The reaction is endergonic and will not proceed spontaneously.

Question 10

Which of the following best explains why the maintenance of body temperature in endotherms (such as humans) is a major use of energy?

Accepted Answer

Because regulated heat production is necessary to maintain a constant internal environment.

Question 11

Which of the following equations allows you to calculate the free energy change ($$\Delta G) $$for a reaction under non-standard conditions?

Accepted Answer

$$\Delta G = \Delta G^\circ' + RT \ln \frac{[B]_{pr}}{[A]_{pr}}$$

Question 12

Which of the following statements about the relationship between thermodynamics and kinetics is correct?

Accepted Answer

Thermodynamics determines if a reaction can occur, while kinetics determines how fast it will proceed.

Question 13

A cell couples an endergonic reaction ($$\Delta G = +3$$ kcal/mol) with an exergonic reaction ($$\Delta G = -5$$ kcal/mol). What is the overall $$\Delta G$$ for the coupled process, and will it be spontaneous?

Accepted Answer

$$\Delta G = -2$$ kcal/mol; spontaneous

Question 14

Which of the following best describes the meaning of 'spontaneous' in thermodynamics?

Accepted Answer

A reaction that can occur under the given conditions.

Question 15

Which of the following is true for a reaction at equilibrium?

Accepted Answer

The forward and reverse reactions occur at the same rate.

Question 16

Which of the following is an example of synthetic work in cells?

Accepted Answer

The process of photosynthesis in plants.

Question 17

If the molar ratio $$\frac{[B]}{[A]}$$ for a reaction $$A \rightleftharpoons B is $$less than $$K_{eq}$$, in which direction will the reaction proceed to reach equilibrium?

Accepted Answer

To the right, generating more product.

Question 18

Which of the following best explains why bioluminescence is considered a form of biological work?

Accepted Answer

Because it involves the conversion of chemical energy (often from ATP) into light.

Bioenergetics: The Flow of Energy in the Cell

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