Question 1

Which of the following statements is an important consequence of the first law of thermodynamics for a living organism?

Accepted Answer

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed. Living organisms must obtain energy from their environment to sustain life processes.

Question 2

Which of the following statements describes the first law of thermodynamics?

Accepted Answer

The first law of thermodynamics is also known as the law of conservation of energy, which states that energy cannot be created or destroyed but can only be transferred or transformed from one form to another.

Question 3

Which of the following is an example of potential rather than kinetic energy?

Accepted Answer

A molecule of glucose has potential energy stored in its chemical bonds, whereas the other options involve objects and actions with kinetic energy (moving water, flashing light, crawling beetle).

Question 4

Why do hydrolysis reactions occur more readily in solution than dehydration reactions?

Accepted Answer

Hydrolysis reactions involve breaking down complex molecules by adding a water molecule. This process releases energy and increases entropy, which favors the reaction proceeding in solution. Dehydration reactions, on the other hand, involve removing a water molecule to form a covalent bond between two molecules. This process requires energy and decreases entropy, making it less favorable in solution. Therefore, hydrolysis reactions occur more readily in solution than dehydration reactions.

Question 5

Which of the following terms most precisely describes the cellular process of breaking down large molecules into smaller ones?

Accepted Answer

Catabolism is the specific process where complex molecules are broken down into simple ones, typically releasing energy in the process. Metabolism and anabolism are broader terms that encompass all of the chemical reactions in a cell, including both building and breaking down molecules. Dehydration is a process where water is removed from a molecule, but it does not necessarily involve breaking down larger molecules into smaller ones.

Question 6

Which of the following statements about the evolution of life on Earth, from simple prokaryote-like cells to multicellular eukaryotic organisms, is true?

Accepted Answer

The answer of Which of the following statements about the...

Question 7

The mathematical expression for the change in free energy of a system is ΔG = ΔH - TΔS. Which of the following statements is correct?

Accepted Answer

ΔG is the change in free energy, which is the energy that can be used to do work under constant temperature and pressure. ΔH is the change in enthalpy, which is an indication of the total heat content of the system, while ΔS is the change in entropy, which is a measure of the degree of randomness or disorder in the system. T represents the temperature in Kelvin.

Question 8

Which of the following statements is a logical consequence of the second law of thermodynamics?

Accepted Answer

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. Therefore, each chemical reaction in an organism, which is part of the universe, must increase the total entropy of the universe.

Question 9

A chemical reaction that has a positive ΔG is best described as ________.

Accepted Answer

A positive ΔG indicates that the reaction requires energy input to occur, making it endergonic.

Question 10

Which of the following types of reactions would decrease the entropy within a cell?

Accepted Answer

Anabolic reactions involve the synthesis of large molecules from smaller subunits. This process typically requires energy input and results in a decrease in entropy within a cell.

Question 11

Which of the following statements about anabolic pathways is true?

Accepted Answer

Anabolic pathways involve building up polymers from monomers, which requires an input of energy. This is the opposite of catabolic pathways, which break down polymers into monomers and release energy. Therefore, statement B is correct. Statement A is incorrect because anabolic reactions usually require an input of energy, and therefore are not spontaneous. Statement C is incorrect because it describes a catabolic pathway. Statement D is incorrect because the decrease in entropy that occurs during anabolic pathways is compensated for by an increase in entropy elsewhere in the system, so the overall entropy of the organism and its environment is not necessarily decreased.

Question 12

Chemical equilibrium is relatively rare in living cells because metabolic pathways are interconnected. Which of the following statements describes an example of a reaction that may be at chemical equilibrium in a cell?

Accepted Answer

In a cell, metabolic pathways are interconnected, meaning that reactants are continuously being produced and consumed, and products are being further processed or used in other reactions. This state of constant flux makes it unlikely that a reaction will reach a true state of equilibrium. However, there may be instances where a particular reaction is not actively part of any metabolic pathway at a specific time in the cell, and therefore may reach equilibrium. In such a scenario, neither the reactants nor the products are being produced or consumed, and the reaction may come to equilibrium.

Question 13

Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics?

Accepted Answer

The second law of thermodynamics states that the entropy of an isolated system will always increase over time. However, living organisms are not isolated systems and can decrease their own entropy by increasing in complexity through growth. This decrease in entropy is offset by an increase in entropy in their environment as they consume energy and produce waste.

Question 14

The relationship between catabolism and anabolism is most similar to the relationship between which of the following pairs of terms?

Accepted Answer

Catabolism is the breakdown of complex molecules into simpler ones, releasing energy, which is exergonic. Anabolism is the synthesis of complex molecules from simpler ones, requiring energy, which is endergonic. Therefore, the relationship between catabolism and anabolism is similar to the relationship between exergonic and endergonic reactions.

Question 15

Which of the following statements is true of metabolism in its entirety in all organisms?

Accepted Answer

Metabolism consists of all the energy transformation reactions in an organism, which includes both anabolism (building up molecules) and catabolism (breaking down molecules). While energy from food is a common source of energy for metabolism, not all organisms depend on this source (e.g. photosynthetic organisms can derive energy from sunlight). Metabolism does not necessarily use all of an organism's resources and while it helps manage entropy, it does not prevent the overall increase of entropy in the universe.

Question 16

Which of the following statements is true for a system at chemical equilibrium?

Accepted Answer

At chemical equilibrium, the forward and backward reactions are occurring at the same rate, meaning there is no net change in the concentrations of reactants and products. This also means that there is no net production or consumption of energy or work, making option D the correct statement.

Question 17

Which of the following statements is consistent with the second law of thermodynamics?

Accepted Answer

The second law of thermodynamics states that in any energy transfer or transformation, the total entropy of a closed system always increases over time. This means that to maintain a high level of organization in a system - such as a cell or organism - a constant input of energy is required, otherwise the system will become disordered and entropy will increase. A, C, and D are all inconsistent with the second law.

Question 18

A decrease in entropy is associated with which type of reaction?

Accepted Answer

Dehydration reactions involve the removal of water molecules, resulting in a decrease in entropy.

Question 19

Which of the following statements is true for all exergonic reactions?

Accepted Answer

Exergonic reactions release free energy, meaning that the products have less total energy than the reactants. Thus, choice A is incorrect. Exergonic reactions go in the forward direction and may reach equilibrium, but the reverse reaction is possible under different conditions, so choice C is incorrect. Finally, choice D is incorrect because exergonic reactions release energy, so they do not require an input of energy from the surroundings. Therefore, the only correct option is B, which states that exergonic reactions proceed with a net release of free energy.

Question 20

Most cells cannot harness heat to perform work because ________.

Accepted Answer

Temperature is usually uniform throughout a cell, which means there is no temperature difference to drive heat flow and perform work. Heat is a form of energy, and it can be used to do work, but there must be a temperature gradient for it to be harnessed. The statement that heat must remain constant during work is incorrect.

Quiz 8: An Introduction to Metabolism