Question 1

Which statement best describes the First Law of Thermodynamics as it applies to biological systems?

Accepted Answer

Energy cannot be created or destroyed, but can be transformed from one form to another.

Question 2

A chemical reaction has a $$\Delta G of$$ $$-20 kJ/$$mol. Which of the following is true about this reaction?

Accepted Answer

It is exergonic and will occur spontaneously.

Question 3

Which of the following best explains why energy conversions in cells are never 100% efficient?

Accepted Answer

Some energy is always converted to heat, increasing entropy.

Question 4

Consider the reaction: $$\mathrm{CH_3COOCH_3} + \mathrm{H_2O} \rightarrow \mathrm{CH_3COOH} + \mathrm{CH_3OH}. $$What type of reaction is this and why?

Accepted Answer

Exergonic, because it breaks chemical bonds and releases energy.

Question 5

Which equation correctly represents the change in free energy for a chemical reaction?

Accepted Answer

$$\Delta G = G_{products} - G_{reactants}$$

Question 6

Which of the following statements about enzymes is correct?

Accepted Answer

Enzymes lower the activation energy ($$E_A) of a $$reaction.

Question 7

A reaction has a high activation energy ($$E_A) $$and a negative $$\Delta G. $$What is the most likely effect of adding an enzyme to this reaction?

Accepted Answer

The activation energy will decrease, increasing the reaction rate.

Question 8

Which of the following best describes the Second Law of Thermodynamics?

Accepted Answer

Entropy, or disorder, tends to increase in a closed system.

Question 9

Which of the following reactions is most likely to be endergonic?

Accepted Answer

Formation of a peptide bond between two amino acids

Question 10

If a cell couples an exergonic reaction ($$\Delta G = -30 kJ/$$mol) with an endergonic reaction ($$\Delta G = +20 kJ/$$mol), what is the net $$\Delta G$$ for the coupled process?

Accepted Answer

$$\Delta G = -10 kJ/$$mol

Question 11

Which molecule is the primary energy currency of the cell, and what feature makes it suitable for this role?

Accepted Answer

ATP, because it contains high-energy phosphate bonds.

Question 12

Which of the following best describes the role of high-energy electrons in cellular metabolism?

Accepted Answer

They transfer energy between exergonic and endergonic reactions.

Question 13

In a redox reaction, which molecule is the oxidizing agent?

Accepted Answer

The molecule that gains electrons.

Question 14

Which of the following scenarios best illustrates the concept of entropy?

Accepted Answer

A solid crystal dissolving into a solution, increasing randomness.

Question 15

Which statement about spontaneous reactions is correct?

Accepted Answer

Spontaneous reactions have a negative $$\Delta G.$$

Question 16

Which of the following is true about the activation energy ($$E_A) of a $$reaction?

Accepted Answer

It is the minimum energy required to start a chemical reaction.

Question 17

During cellular metabolism, how is energy from exergonic reactions typically used?

Accepted Answer

It is captured by endergonic reactions to do cellular work.

Question 18

Which process is an example of a coupled reaction in cells?

Accepted Answer

ATP hydrolysis driving the synthesis of a peptide bond.

Question 19

Which of the following is NOT a function of enzymes in biological reactions?

Accepted Answer

Changing the sign or value of $$\Delta G$$ for a reaction.

Question 20

A cell needs to synthesize a complex molecule from simple precursors. Which type of reaction is this, and what must the cell do to make it occur?

Accepted Answer

Endergonic; the cell must supply energy, often from ATP hydrolysis.

Energy, Thermodynamics, and Chemical Reactions in Biology

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