Campbell’s Biology, 9e (Reece et al.)
Chapter 8 An Introduction to Metabolism
This chapter lays the foundations for the chapters on respiration and photosynthesis. Key concepts are as
follows: The laws of thermodynamics govern energy transformations by living organisms, metabolic
reactions couple energy-harvesting reactions to reactions that accomplish cellular work, and enzymes
increase the rates of reaction. Understanding the properties of enzymes, how they work, and how their
activities are regulated is necessary to achieve an understanding of metabolic pathways.
Multiple-Choice Questions
1) Which term most precisely describes the cellular process of breaking down large molecules into
smaller ones?
A) catalysis
B) metabolism
C) anabolism
D) dehydration
E) catabolism
2) Which of the following is (are) true for anabolic pathways?
A) They do not depend on enzymes.
B) They are usually highly spontaneous chemical reactions.
C) They consume energy to build up polymers from monomers.
D) They release energy as they degrade polymers to monomers.
E) They consume energy to decrease the entropy of the organism and its environment.
3) Which of the following is a statement of the first law of thermodynamics?
A) Energy cannot be created or destroyed.
B) The entropy of the universe is decreasing.
C) The entropy of the universe is constant.
D) Kinetic energy is stored energy that results from the specific arrangement of matter.
E) Energy cannot be transferred or transformed.
4) For living organisms, which of the following is an important consequence of the first law of
thermodynamics?
A) The energy content of an organism is constant.
B) The organism ultimately must obtain all of the necessary energy for life from its environment.
C) The entropy of an organism decreases with time as the organism grows in complexity.
D) Organisms grow by converting energy into organic matter.
E) Life does not obey the first law of thermodynamics.
5) 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?
A) Living organisms do not obey the second law of thermodynamics, which states that entropy must
increase with time.
B) Life obeys the second law of thermodynamics because the decrease in entropy as the organism grows
is exactly balanced by an increase in the entropy of the universe.
C) Living organisms do not follow the laws of thermodynamics.
D) As a consequence of growing, organisms cause a greater increase in entropy in their environment
than the decrease in entropy associated with their growth.
E) Living organisms are able to transform energy into entropy.
6) Whenever energy is transformed, there is always an increase in the
A) free energy of the system.
B) free energy of the universe.
C) entropy of the system.
D) entropy of the universe.
E) enthalpy of the universe.
7) Which of the following statements is a logical consequence of the second law of thermodynamics?
A) If the entropy of a system increases, there must be a corresponding decrease in the entropy of the
universe.
B) If there is an increase in the energy of a system, there must be a corresponding decrease in the energy
of the rest of the universe.
C) Every energy transfer requires activation energy from the environment.
D) Every chemical reaction must increase the total entropy of the universe.
E) Energy can be transferred or transformed, but it cannot be created or destroyed.
8) Which of the following statements is representative of the second law of thermodynamics?
A) Conversion of energy from one form to another is always accompanied by some gain of free energy.
B) Heat represents a form of energy that can be used by most organisms to do work.
C) Without an input of energy, organisms would tend toward decreasing entropy.
D) Cells require a constant input of energy to maintain their high level of organization.
E) Every energy transformation by a cell decreases the entropy of the universe.
9) Which of the following types of reactions would decrease the entropy within a cell?
A) anabolic reactions
B) hydrolysis
C) respiration
D) digestion
E) catabolic reactions
10) Biological evolution of life on Earth, from simple prokaryote-like cells to large, multicellar
eukaryotic organisms,
A) has occurred in accordance with the laws of thermodynamics.
B) has caused an increase in the entropy of the planet.
C) has been made possible by expending Earth’s energy resources.
D) has occurred in accordance with the laws of thermodynamics, by expending Earth’s energy resources
and causing an increase in the entropy of the planet.
E) violates the laws of thermodynamics because Earth is a closed system.
11) Which of the following is an example of potential rather than kinetic energy?
A) the muscle contractions of a person mowing grass
B) water rushing over Niagara Falls
C) light flashes emitted by a firefly
D) a molecule of glucose
E) the flight of an insect foraging for food
12) Which of the following is the smallest closed system?
A) a cell
B) an organism
C) an ecosystem
D) Earth
E) the universe
13) Which of the following is true of metabolism in its entirety in all organisms?
A) Metabolism depends on a constant supply of energy from food.
B) Metabolism depends on an organism’s adequate hydration.
C) Metabolism uses all of an organism’s resources.
D) Metabolism consists of all the energy transformation reactions in an organism.
E) Metabolism manages the increase of entropy in an organism.
14) The mathematical expression for the change in free energy of a system is ΔG =ΔH – TΔS. Which of
the following is (are) correct?
A) ΔS is the change in enthalpy, a measure of randomness.
B) ΔH is the change in entropy, the energy available to do work.
C) ΔG is the change in free energy.
D) T is the temperature in degrees Celsius.
15) A system at chemical equilibrium
A) consumes energy at a steady rate.
B) releases energy at a steady rate.
C) consumes or releases energy, depending on whether it is exergonic or endergonic.
D) has zero kinetic energy.
E) can do no work.
16) Which of the following is true for all exergonic reactions?
A) The products have more total energy than the reactants.
B) The reaction proceeds with a net release of free energy.
C) The reaction goes only in a forward direction: all reactants will be converted to products, but no
products will be converted to reactants.
D) A net input of energy from the surroundings is required for the reactions to proceed.
E) The reactions are rapid.
17) Chemical equilibrium is relatively rare in living cells. Which of the following could be an example
of a reaction at chemical equilibrium in a cell?
A) a reaction in which the free energy at equilibrium is higher than the energy content at any point away
from equilibrium
B) a chemical reaction in which the entropy change in the reaction is just balanced by an opposite
entropy change in the cell’s surroundings
C) an endergonic reaction in an active metabolic pathway where the energy for that reaction is supplied
only by heat from the environment
D) a chemical reaction in which both the reactants and products are not being produced or used in any
active metabolic pathway
E) no possibility of having chemical equilibrium in any living cell
18) Which of the following shows the correct changes in thermodynamic properties for a chemical
reaction in which amino acids are linked to form a protein?
A) +ΔH, +ΔS, +ΔG
B) +ΔH, –ΔS, –ΔG
C) +ΔH, –ΔS, +ΔG
D) –ΔH, –ΔS, +ΔG
E) –ΔH, +ΔS, +ΔG
19) When glucose monomers are joined together by glycosidic linkages to form a cellulose polymer, the
changes in free energy, total energy, and entropy are as follows:
A) +ΔG, +ΔH, +ΔS.
B) +ΔG, +ΔH, –ΔS.
C) +ΔG, –ΔH, –ΔS.
D) –ΔG, +ΔH, +ΔS.
E) –ΔG, –ΔH, –ΔS.
20) A chemical reaction that has a positive ΔG is correctly described as
A) endergonic.
B) endothermic.
C) enthalpic.
D) spontaneous.
E) exothermic.
21) Which of the following best describes enthalpy (H)?
A) the total kinetic energy of a system
B) the heat content of a chemical system
C) the system’s entropy
D) the cell’s energy equilibrium
E) the condition of a cell that is not able to react
22) For the hydrolysis of ATP to ADP + i, the free energy change is -7.3 kcal/mol under standard
conditions (1 M concentration of both reactants and products). In the cellular environment, however, the
free energy change is about -13 kcal/mol. What can we conclude about the free energy change for the
formation of ATP from ADP and i under cellular conditions?
A) It is +7.3 kcal/mol.
B) It is less than +7.3 kcal/mol.
C) It is about +13 kcal/mol.
D) It is greater than +13 kcal/mol.
E) The information given is insufficient to deduce the free energy change.
23) Why is ATP an important molecule in metabolism?
A) Its hydrolysis provides an input of free energy for exergonic reactions.
B) It provides energy coupling between exergonic and endergonic reactions.
C) Its terminal phosphate group contains a strong covalent bond that, when hydrolyzed, releases free
energy.
D) Its terminal phosphate bond has higher energy than the other two.
E) It is one of the four building blocks for DNA synthesis.
24) When 10,000 molecules of ATP are hydrolyzed to ADP and i in a test tube, about twice as much
heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best
explanation for this observation?
A) Cells are open systems, but a test tube is a closed system.
B) Cells are less efficient at heat production than nonliving systems.
C) The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test
tube.
D) The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need
enzymes.
E) Reactant and product concentrations in the test tube are different from those in the cell.
25) Which of the following is most similar in structure to ATP?
A) a pentose sugar
B) a DNA nucleotide
C) an RNA nucleotide
D) an amino acid with three phosphate groups attached
E) a phospholipid
26) Which of the following statements is true concerning catabolic pathways?
A) They combine molecules into more energy-rich molecules.
B) They supply energy, primarily in the form of ATP, for the cell’s work.
C) They are endergonic.
D) They are spontaneous and do not need enzyme catalysis.
E) They build up complex molecules such as protein from simpler compounds.
27) When chemical, transport, or mechanical work is done by an organism, what happens to the heat
generated?
A) It is used to power yet more cellular work.
B) It is used to store energy as more ATP.
C) It is used to generate ADP from nucleotide precursors.
D) It is lost to the environment.
E) It is transported to specific organs such as the brain.
28) When ATP releases some energy, it also releases inorganic phosphate. What purpose does this serve
(if any) in the cell?
A) The phosphate is released as an excretory waste.
B) The phosphate can only be used to regenerate more ATP.
C) The phosphate can be added to water and excreted as a liquid.
D) The phosphate may be incorporated into any molecule that contains phosphate.
E) It enters the nucleus to affect gene expression.
29) A number of systems for pumping ions across membranes are powered by ATP. Such ATP-powered
pumps are often called ATPases although they don’t often hydrolyze ATP unless they are
simultaneously transporting ions. Because small increases in calcium ions in the cytosol can trigger a
number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low
under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport
calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a
resting muscle cell’s cytosol has a free calcium ion concentration of 10-7 while the concentration in the
SR is 10-2, then how is the ATPase acting?
A) ATPase activity must be powering an inflow of calcium from the outside of the cell into the SR.
B) ATPase activity must be transferring i to the SR to enable this to occur.
C) ATPase activity must be pumping calcium from the cytosol to the SR against the concentration
gradient.
D) ATPase activity must be opening a channel for the calcium ions to diffuse back into the SR along the
concentration gradient.
E) ATPase activity must be routing calcium ions from the SR to the cytosol, and then to the cell’s
environment.
30) What is the difference (if any) between the structure of ATP and the structure of the precursor of the
A nucleotide in RNA?
A) The sugar molecule is different.
B) The nitrogen-containing base is different.
C) The number of phosphates is three instead of one.
D) The number of phosphates is three instead of two.
E) There is no difference.
31) Which of the following statements is true about enzyme-catalyzed reactions?
A) The reaction is faster than the same reaction in the absence of the enzyme.
B) The free energy change of the reaction is opposite from the reaction that occurs in the absence of the
enzyme.
C) The reaction always goes in the direction toward chemical equilibrium.
D) Enzyme-catalyzed reactions require energy to activate the enzyme.
E) Enzyme-catalyzed reactions release more free energy than noncatalyzed reactions.
32) Reactants capable of interacting to form products in a chemical reaction must first overcome a
thermodynamic barrier known as the reaction’s
A) entropy.
B) activation energy.
C) endothermic level.
D) equilibrium point.
E) free-energy content.
33) A solution of starch at room temperature does not readily decompose to form a solution of simple
sugars because
A) the starch solution has less free energy than the sugar solution.
B) the hydrolysis of starch to sugar is endergonic.
C) the activation energy barrier for this reaction cannot be surmounted.
D) starch cannot be hydrolyzed in the presence of so much water.
E) starch hydrolysis is nonspontaneous.
34) Which of the following statements regarding enzymes is true?
A) Enzymes increase the rate of a reaction by making the reaction more exergonic.
B) Enzymes increase the rate of a reaction by lowering the activation energy barrier.
C) Enzymes increase the rate of a reaction by reducing the rate of reverse reactions.
D) Enzymes change the equilibrium point of the reactions they catalyze.
E) Enzymes make the rate of a reaction independent of substrate concentrations.
35) During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20
kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?
A) -40 kcal/mol
B) -20 kcal/mol
C) 0 kcal/mol
D) +20 kcal/mol
E) +40 kcal/mol
36) The active site of an enzyme is the region that
A) binds allosteric regulators of the enzyme.
B) is involved in the catalytic reaction of the enzyme.
C) binds noncompetitive inhibitors of the enzyme.
D) is inhibited by the presence of a coenzyme or a cofactor.
37) According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?
A) The binding of the substrate depends on the shape of the active site.
B) Some enzymes change their structure when activators bind to the enzyme.
C) A competitive inhibitor can outcompete the substrate for the active site.
D) The binding of the substrate changes the shape of the enzyme’s active site.
E) The active site creates a microenvironment ideal for the reaction.
38) Mutations that result in single amino acid substitutions in an enzyme
A) can have no effect on the activity or properties of the enzyme.
B) will almost always destroy the activity of the enzyme.
C) will often cause a change in the substrate specificity of the enzyme.
D) may affect the physicochemical properties of the enzyme such as its optimal temperature and pH.
E) may, in rare cases, cause the enzyme to run reactions in reverse.
39) Increasing the substrate concentration in an enzymatic reaction could overcome which of the
following?
A) denaturization of the enzyme
B) allosteric inhibition
C) competitive inhibition
D) saturation of the enzyme activity
E) insufficient cofactors
40) Which of the following is true of enzymes?
A) Nonprotein cofactors alter the substrate specificity of enzymes.
B) Enzyme function is increased if the 3-D structure or conformation of an enzyme is altered.
C) Enzyme function is independent of physical and chemical environmental factors such as pH and
temperature.
D) Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
E) Enzymes increase the rate of chemical reaction by providing activation energy to the substrate.
41) Zinc, an essential trace element for most organisms, is present in the active site of the enzyme
carboxypeptidase. The zinc most likely functions as a(n)
A) competitive inhibitor of the enzyme.
B) noncompetitive inhibitor of the enzyme.
C) allosteric activator of the enzyme.
D) cofactor necessary for enzyme activity.
E) coenzyme derived from a vitamin.
42) In order to attach a particular amino acid to the tRNA molecule that will transport it, an enzyme, an
aminoacyl-tRNA synthetase, is required, along with ATP. Initially, the enzyme has an active site for
ATP and another for the amino acid, but it is not able to attach the tRNA. What must occur in order for
the final attachment to occur?
A) The ATP must first have to attach to the tRNA.
B) The binding of the first two molecules must cause a 3-D change that opens another active site on the
enzyme.
C) The ATP must be hydrolyzed to allow the amino acid to bind to the synthetase.
D) The tRNA molecule must have to alter its shape in order to be able to fit into the active site with the
other two molecules.
E) The 3′ end of the tRNA must have to be cleaved before it can have an attached amino acid.
43) Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse
transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires
mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in
the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant
viruses?
A) in or near the active site
B) at an allosteric site
C) at a cofactor binding site
D) in regions of the protein that determine packaging into the virus capsid
E) such mutations could occur anywhere with equal probability