This Document Contains Chapters 6 to 7 Chapter 6: An Introduction to Metabolism 6.1 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 Answer: E 2) Which of the following is 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. Answer: C 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. Answer: A 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. Answer: B 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. Answer: D 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. Answer: D 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. Answer: D 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. Answer: D 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 Answer: A 10) Biological evolution of life on Earth, from simple prokaryote-like cells to large, multicellular 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. Answer: A 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 Answer: D 12) 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. Answer: D 13) The mathematical expression for the change in free energy of a system is ΔG = ΔH - TΔS. Which of the following is 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. Answer: C 14) 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. Answer: E 15) 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. Answer: B 16) A chemical reaction that has a positive ΔG is best described as A) endergonic. B) entropic C) enthalpic. D) spontaneous. E) exergonic. Answer: A 17) 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 Answer: B 18) 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. Answer: C 19) 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. Answer: B 20) When 10,000 molecules of ATP are hydrolyzed to ADP and ℗i in a test tube, about half 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 an isolated 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. Answer: E 21) 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 Answer: C 22) 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. Answer: B 23) 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. Answer: D 24) When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell? A) It is secreted as waste. B) It is used only to regenerate more ATP. C) It is added to water and excreted as a liquid. D) It may be used to form a phosphorylated intermediate. E) It enters the nucleus and affects gene expression. Answer: D 25) 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. Answer: C 26) 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. Answer: E 27) 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. Answer: A 28) 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. Answer: B 29) 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 easily be surmounted at room temperature. D) starch cannot be hydrolyzed in the presence of so much water. E) starch hydrolysis is nonspontaneous. Answer: C 30) 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. Answer: B 31) 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 Answer: B 32) 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. Answer: B 33) 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. Answer: D 34) Mutations that result in single amino acid substitutions in an enzyme A) cannot affect the activity or properties of the enzyme. B) will almost always destroy the activity of the enzyme. C) will often change the substrate specificity of the enzyme. D) may change the enzyme’s optimal temperature or optimal pH. E) may, in rare cases, cause the enzyme to run reactions in reverse. Answer: D 35) Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? A) denaturation of the enzyme B) allosteric inhibition C) competitive inhibition D) saturation of the enzyme activity E) insufficient cofactors Answer: C 36) 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. Answer: D 37) 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. Answer: D 38) 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. Answer: B 39) 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) anywhere, with equal probability Answer: A 40) Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue on the target protein. Many are located on the plasma membrane as integral membrane proteins or peripheral membrane proteins. What purpose may be served by their plasma membrane localization? A) ATP is more abundant near the plasma membrane. B) They can more readily encounter and phosphorylate other membrane proteins. C) Membrane localization lowers the activation energy of the phosphorylation reaction. D) They flip back and forth across the membrane to access target proteins on either side. E) They require phospholipids as a cofactor. Answer: B 41) When you have a severe fever, what grave consequence may occur if the fever is not controlled? A) destruction of your enzymes' primary structure B) removal of amine groups from your proteins C) change in the tertiary structure of your enzymes D) removal of the amino acids in the active sites of your enzymes E) binding of your enzymes to inappropriate substrates Answer: C 42) How does a noncompetitive inhibitor decrease the rate of an enzyme reaction? A) by binding at the active site of the enzyme B) by changing the shape of the enzyme's active site C) by changing the free-energy change of the reaction D) by acting as a coenzyme for the reaction E) by decreasing the activation energy of the reaction Answer: B 43) In experimental tests of enzyme evolution, where a gene encoding an enzyme is subjected to multiple cycles of random mutagenesis and selection for altered substrate specificity, the resulting enzyme had multiple amino acid changes associated with altered substrate specificity. Where in the enzyme were these amino acid changes located? A) only in the active site B) only in the active site or near the active site C) in or near the active site and at surface sites away from the active site D) only at surface sites away from the active site E) only in the hydrophobic interior of the folded protein Answer: C 44) How might an amino acid change at a site distant from the active site of the enzyme alter the enzyme's substrate specificity? A) by changing the enzyme's stability B) by changing the enzyme's location in the cell C) by changing the shape of the protein D) by changing the enzyme's pH optimum E) an amino acid change away from the active site cannot alter the enzyme's substrate specificity Answer: C 45) The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as A) metabolic inhibition. B) feedback inhibition. C) allosteric inhibition. D) noncooperative inhibition. E) reversible inhibition. Answer: B 46) Which of the following statements describes enzyme cooperativity? A) A multienzyme complex contains all the enzymes of a metabolic pathway. B) A product of a pathway serves as a competitive inhibitor of an early enzyme in the pathway. C) A substrate molecule bound to an active site of one subunit promotes substrate binding to the active site of other subunits. D) Several substrate molecules can be catalyzed by the same enzyme. E) A substrate binds to an active site and inhibits cooperation between enzymes in a pathway. Answer: C 47) Allosteric enzyme regulation is usually associated with A) lack of cooperativity. B) feedback inhibition. C) activating activity. D) an enzyme with more than one subunit. E) the need for cofactors. Answer: D 48) Which of the following is an example of cooperativity? A) the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway B) one enzyme in a metabolic pathway passing its product to act as a substrate for the next enzyme in the pathway C) a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three D) the effect of increasing temperature on the rate of an enzymatic reaction E) binding of an ATP molecule along with one of the substrate molecules in an active site Answer: C 49) Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity? A) cessation of cellular protein synthesis B) localization of enzymes into specific organelles or membranes C) exporting enzymes out of the cell D) connecting enzymes into large aggregates E) hydrophobic interactions Answer: B 6.2 Art Questions Figure 6.1 1) Which of the following is the most correct interpretation of Figure 6.1? A) Inorganic phosphate is created from organic phosphate. B) Energy from catabolism can be used directly for performing cellular work. C) ADP + ℗i are a set of molecules that store energy for catabolism. D) ATP is a molecule that acts as an intermediary to store energy for cellular work. E) ℗i acts as a shuttle molecule to move energy from ATP to ADP. Answer: D 2) How do cells use the ATP cycle shown in Figure 6.1? A) Cells use the cycle to recycle ADP and phosphate. B) Cells use the cycle to recycle energy released by ATP hydrolysis. C) Cells use the cycle to recycle ADP, phosphate, and the energy released by ATP hydrolysis. D) Cells use the cycle to generate or consume water molecules as needed. E) Cells use the cycle primarily to generate heat. Answer: A Figure 6.2 Rate of an enzyme-catalyzed reaction as a function of varying reactant concentration, with the concentration of enzyme constant. 3) For the enzyme-catalyzed reaction shown in Figure 6.2, which of these treatments will cause the greatest increase in the rate of the reaction, if the initial reactant concentration is 1.0 micromolar? A) doubling the activation energy needed B) cooling the reaction by 10°C C) doubling the concentration of the reactants to 2.0 micromolar D) doubling the enzyme concentration E) increasing the concentration of reactants to 10.0 micromolar, while reducing the concentration of enzyme by 1/2 Answer: D 4) In Figure 6.2, why does the reaction rate plateau at higher reactant concentrations? A) Feedback inhibition by product occurs at high reactant concentrations. B) Most enzyme molecules are occupied by substrate at high reactant concentrations. C) The reaction nears equilibrium at high reactant concentrations. D) The activation energy for the reaction increases with reactant concentration. E) The rate of the reverse reaction increases with reactant concentration. Answer: B Figure 6.3 Activity of various enzymes at various temperatures (a) and at various pH (b). 5) Which curve(s) on the graphs may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot springs at temperatures of 70°C or higher? A) curves 1 and 5 B) curves 2 and 4 C) curves 2 and 5 D) curves 3 and 4 E) curves 3 and 5 Answer: E 6) Which temperature and pH profile curves on the graphs were most likely generated from analysis of an enzyme from a human stomach, where conditions are strongly acid? A) curves 1 and 4 B) curves 1 and 5 C) curves 2 and 4 D) curves 2 and 5 E) curves 3 and 4 Answer: A The following questions are based on the reaction A + B ↔ C + D shown in Figure 6.4. Figure 6.4 7) Which of the following terms best describes the forward reaction in Figure 6.4? A) endergonic, ∆G > 0 B) exergonic, ∆G < 0 C) endergonic, ∆G 0 E) chemical equilibrium, ∆G = 0 Answer: B 8) Which of the following represents the ΔG of the reaction in Figure 6.4? A) a B) b C) c D) d E) e Answer: D 9) Which of the following in Figure 6.4 would be the same in either an enzyme-catalyzed or a noncatalyzed reaction? A) a B) b C) c D) d E) e Answer: D 10) Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in Figure 6.4? A) a B) b C) c D) d E) e Answer: A 11) Which of the following represents the difference between the free-energy content of the reactants and the free-energy content of the products in Figure 6.4? A) a B) b C) c D) d E) e Answer: D 12) Which of the following represents the activation energy required for the enzyme-catalyzed reaction in Figure 6.4? A) a B) b C) c D) d E) e Answer: B 13) Which of the following represents the activation energy required for a noncatalyzed reaction in Figure 6.4? A) a B) b C) c D) d E) e Answer: C 14) Which of the following represents the activation energy needed for the noncatalyzed reverse reaction, C + D → A + B, in Figure 6.4? A) a B) b C) c D) d E) e Answer: E 6.3 Scenario Questions 1) 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 at that time in the cell E) no possibility of having chemical equilibrium in any living cell Answer: D Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. 2) Based on this information, which of the following is correct? A) Succinate dehydrogenase is the enzyme, and fumarate is the substrate. B) Succinate dehydrogenase is the enzyme, and malonic acid is the substrate. C) Succinate is the substrate, and fumarate is the product. D) Fumarate is the product, and malonic acid is a noncompetitive inhibitor. E) Malonic acid is the product, and fumarate is a competitive inhibitor. Answer: C 3) What is malonic acid's role with respect to succinate dehydrogenase? A) It is a competitive inhibitor. B) It blocks the binding of fumarate. C) It is a noncompetitive inhibitor. D) It is able to bind to succinate. E) It is an allosteric regulator. Answer: A A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. 4) What is substance X? A) a coenzyme B) an allosteric inhibitor C) a substrate D) an intermediate E) the product Answer: C 5) With respect to the enzyme that converts X to Y, substance A functions as A) a coenzyme. B) an allosteric inhibitor. C) the substrate. D) an intermediate. E) a competitive inhibitor. Answer: B 6.4 End-of-Chapter Questions 1) Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ________ is to ________. A) exergonic; spontaneous B) exergonic; endergonic C) free energy; entropy D) work; energy E) entropy; heat Answer: B 2) Most cells cannot harness heat to perform work because A) heat does not involve a transfer of energy. B) cells do not have much heat; they are relatively cool. C) temperature is usually uniform throughout a cell. D) heat can never be used to do work. E) heat must remain constant during work. Answer: C 3) Which of the following metabolic processes can occur without a net influx of energy from some other process? A) ADP + ℗i → ATP + H2O B) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O C) 6 CO2 + 6 H2O → C6H12O6 + 6 O2 D) amino acids → protein E) glucose + fructose → sucrose Answer: B 4) If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to A) add more of the enzyme. B) heat the solution to 90°C. C) add more substrate. D) add an allosteric inhibitor. E) add a noncompetitive inhibitor. Answer: A 5) Some bacteria are metabolically active in hot springs because A) they are able to maintain a lower internal temperature. B) high temperatures make catalysis unnecessary. C) their enzymes have high optimal temperatures. D) their enzymes are completely insensitive to temperature. E) they use molecules other than proteins or RNAs as their main catalysts. Answer: C 6) If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur? A) Additional product will be formed. B) Additional substrate will be formed. C) The reaction will change from endergonic to exergonic. D) The free energy of the system will change. E) Nothing; the reaction will stay at equilibrium Answer: E Chapter 7: Cellular Respiration and Fermentation 7.1 Multiple-Choice Questions 1) What is the term for metabolic pathways that release stored energy by breaking down complex molecules? A) anabolic pathways B) catabolic pathways C) fermentation pathways D) thermodynamic pathways E) bioenergetic pathways Answer: B 2) The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction A) gains electrons and gains potential energy. B) loses electrons and loses potential energy. C) gains electrons and loses potential energy. D) loses electrons and gains potential energy. E) neither gains nor loses electrons, but gains or loses potential energy. Answer: B 3) When electrons move closer to a more electronegative atom, what happens? A) The more electronegative atom is reduced, and energy is released. B) The more electronegative atom is reduced, and energy is consumed. C) The more electronegative atom is oxidized, and energy is consumed. D) The more electronegative atom is oxidized, and energy is released. E) The more electronegative atom is reduced, and entropy decreases. Answer: A 4) Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy? A) The covalent bonds in organic molecules and molecular oxygen have more kinetic energy than the covalent bonds in water and carbon dioxide. B) Electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O). C) The oxidation of organic compounds can be used to make ATP. D) The electrons have a higher potential energy when associated with water and CO2 than they do in organic compounds. E) The covalent bond in O2 is unstable and easily broken by electrons from organic molecules. Answer: B 5) Which of the following statements describes the results of this reaction? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy A) C6H12O6 is oxidized and O2 is reduced. B) O2 is oxidized and H2O is reduced. C) CO2 is reduced and O2 is oxidized. D) C6H12O6 is reduced and CO2 is oxidized. E) O2 is reduced and CO2 is oxidized. Answer: A 6) When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the molecule becomes A) hydrolyzed. B) hydrogenated. C) oxidized. D) reduced. E) an oxidizing agent. Answer: C 7) When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the molecule becomes A) dehydrogenated. B) oxidized. C) reduced. D) redoxed. E) hydrolyzed. Answer: C 8) Which of the following statements describes NAD+? A) NAD+ is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle. B) NAD+ has more chemical energy than NADH. C) NAD+ is oxidized by the action of hydrogenases. D) NAD+ can donate electrons for use in oxidative phosphorylation. E) In the absence of NAD+, glycolysis can still function. Answer: A 9) Where does glycolysis take place in eukaryotic cells? A) mitochondrial matrix B) mitochondrial outer membrane C) mitochondrial inner membrane D) mitochondrial intermembrane space E) cytosol Answer: E 10) The ATP made during glycolysis is generated by A) substrate-level phosphorylation. B) electron transport. C) photophosphorylation. D) chemiosmosis. E) oxidation of NADH to NAD+. Answer: A 11) The oxygen consumed during cellular respiration is involved directly in which process or event? A) glycolysis B) accepting electrons at the end of the electron transport chain C) the citric acid cycle D) the oxidation of pyruvate to acetyl CoA E) the phosphorylation of ADP to form ATP Answer: B 12) An electron loses potential energy when it A) shifts to a less electronegative atom. B) shifts to a more electronegative atom. C) increases its kinetic energy. D) increases its activity as an oxidizing agent. E) moves further away from the nucleus of the atom. Answer: B 13) Why are carbohydrates and fats considered high-energy foods? A) They have a lot of oxygen atoms. B) They have no nitrogen in their makeup. C) They can have very long carbon skeletons. D) They have a lot of electrons associated with hydrogen. E) They are easily reduced. Answer: D 14) During aerobic respiration, electrons travel downhill in which sequence? A) food → citric acid cycle → ATP → NAD+ B) food → NADH → electron transport chain → oxygen C) glucose → pyruvate → ATP → oxygen D) glucose → ATP → electron transport chain → NADH E) food → glycolysis → citric acid cycle → NADH → ATP Answer: B 15) How many oxygen molecules (O2) are required each time a molecule of glucose (C6H12O6) is completely oxidized to carbon dioxide and water via aerobic respiration? A) 1 B) 3 C) 6 D) 12 E) 30 Answer: C 16) In prokaryotes, the respiratory electron transport chain is located A) in the mitochondrial inner membrane. B) in the mitochondrial outer membrane. C) in the plasma membrane. D) in the cytoplasm. E) in the bacterial outer membrane. Answer: C 17) Even though plants carry on photosynthesis, plant cells still use their mitochondria for oxidation of pyruvate. When and where will this occur? A) in photosynthetic cells in the light, while photosynthesis occurs concurrently B) in non-photosynthesizing cells only C) in cells that are storing glucose only D) in all cells all the time E) in photosynthesizing cells in the light and in other tissues in the dark Answer: D 18) Which process in eukaryotic cells will proceed normally whether oxygen (O2) is present or absent? A) electron transport B) glycolysis C) the citric acid cycle D) oxidative phosphorylation E) chemiosmosis Answer: B 19) Substrate-level phosphorylation accounts for approximately what percentage of the ATP formed by the reactions of glycolysis? A) 0% B) 2% C) 10% D) 38% E) 100% Answer: E 20) During glycolysis, when each molecule of glucose is catabolized to two molecules of pyruvate, most of the potential energy contained in glucose is A) transferred to ADP, forming ATP. B) transferred directly to ATP. C) retained in the two pyruvates. D) stored in the NADH produced. E) used to phosphorylate fructose to form fructose 6-phosphate. Answer: C 21) In addition to ATP, what are the end products of glycolysis? A) CO2 and H2O B) CO2 and pyruvate C) NADH and pyruvate D) CO2 and NADH E) H2O, FADH2, and citrate Answer: C 22) The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol and the free energy for the reduction of NAD+ to NADH is +53 kcal/mol. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed? A) Most of the free energy available from the oxidation of glucose is used in the production of ATP in glycolysis. B) Glycolysis is a very inefficient reaction, with much of the energy of glucose released as heat. C) Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis. D) There is no CO2 or water produced as products of glycolysis. E) Glycolysis consists of many enzymatic reactions, each of which extracts some energy from the glucose molecule. Answer: C 23) Starting with one molecule of glucose, the energy-containing products of glycolysis are A) 2 NAD+, 2 pyruvate, and 2 ATP. B) 2 NADH, 2 pyruvate, and 2 ATP. C) 2 FADH2, 2 pyruvate, and 4 ATP. D) 6 CO2, 2 pyruvate, and 2 ATP. E) 6 CO2, 2 pyruvate, and 30 ATP. Answer: B 24) In glycolysis, for each molecule of glucose oxidized to pyruvate A) two molecules of ATP are used and two molecules of ATP are produced. B) two molecules of ATP are used and four molecules of ATP are produced. C) four molecules of ATP are used and two molecules of ATP are produced. D) two molecules of ATP are used and six molecules of ATP are produced. E) six molecules of ATP are used and six molecules of ATP are produced. Answer: B 25) A molecule that is phosphorylated A) has been reduced as a result of a redox reaction involving the loss of an inorganic phosphate. B) has a decreased chemical reactivity; it is less likely to provide energy for cellular work. C) has been oxidized as a result of a redox reaction involving the gain of an inorganic phosphate. D) has an increased chemical potential energy; it is primed to do cellular work. E) has less energy than before its phosphorylation and therefore less energy for cellular work. Answer: D 26) Which kind of metabolic poison would most directly interfere with glycolysis? A) an agent that reacts with oxygen and depletes its concentration in the cell B) an agent that binds to pyruvate and inactivates it C) an agent that closely mimics the structure of glucose but is not metabolized D) an agent that reacts with NADH and oxidizes it to NAD+ E) an agent that blocks the passage of electrons along the electron transport chain Answer: C 27) Why is glycolysis described as having an investment phase and a payoff phase? A) It both splits molecules and assembles molecules. B) It attaches and detaches phosphate groups. C) It uses glucose and generates pyruvate. D) It shifts molecules from cytosol to mitochondrion. E) It uses stored ATP and then forms a net increase in ATP. Answer: E 28) How many carbon atoms are fed into the citric acid cycle as a result of the oxidation of one molecule of pyruvate? A) 2 B) 4 C) 6 D) 8 E) 10 Answer: A 29) Carbon dioxide (CO2) is released during which of the following stages of cellular respiration? A) glycolysis and the oxidation of pyruvate to acetyl CoA B) oxidation of pyruvate to acetyl CoA and the citric acid cycle C) the citric acid cycle and oxidative phosphorylation D) oxidative phosphorylation and fermentation E) fermentation and glycolysis Answer: B 30) A young dog has never had much energy. He is brought to a veterinarian for help and she decides to conduct several diagnostic tests. She discovers that the dog's mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of the dog’s condition? A) His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane. B) His cells cannot move NADH from glycolysis into the mitochondria. C) His cells contain something that inhibits oxygen use in his mitochondria. D) His cells lack the enzyme in glycolysis that forms pyruvate. E) His cells have a defective electron transport chain, so glucose goes to lactate instead of to acetyl CoA. Answer: A 31) What fraction of the carbon dioxide exhaled by animals is generated by the reactions of the citric acid cycle, if glucose is the sole energy source? A) 1/6 B) 1/3 C) 1/2 D) 2/3 E) all of it Answer: D 32) Where are the proteins of the electron transport chain located? A) cytosol B) mitochondrial outer membrane C) mitochondrial inner membrane D) mitochondrial intermembrane space E) mitochondrial matrix Answer: C 33) In cellular respiration, the energy for most ATP synthesis is supplied by A) high-energy phosphate bonds in organic molecules. B) a proton gradient across a membrane. C) converting oxygen to ATP. D) transferring electrons from organic molecules to pyruvate. E) generating carbon dioxide and oxygen in the electron transport chain. Answer: B 34) During aerobic respiration, which of the following directly donates electrons to the electron transport chain at the lowest energy level? A) NAD+ B) NADH C) ATP D) ADP + ℗i E) FADH2 Answer: E 35) The primary role of oxygen in cellular respiration is to A) yield energy in the form of ATP as it is passed down the respiratory chain. B) act as an acceptor for electrons and hydrogen, forming water. C) combine with carbon, forming CO2. D) combine with lactate, forming pyruvate. E) catalyze the reactions of glycolysis. Answer: B 36) Inside an active mitochondrion, most electrons follow which pathway? A) glycolysis → NADH → oxidative phosphorylation → ATP → oxygen B) citric acid cycle → FADH2 → electron transport chain → ATP C) electron transport chain → citric acid cycle → ATP → oxygen D) pyruvate → citric acid cycle → ATP → NADH → oxygen E) citric acid cycle → NADH → electron transport chain → oxygen Answer: E 37) During aerobic respiration, H2O is formed. Where does the oxygen atom for the formation of the water come from? A) carbon dioxide (CO2) B) glucose (C6H12O6) C) molecular oxygen (O2) D) pyruvate (C3H3O3-) E) lactate (C3H5O3-) Answer: C 38) In chemiosmosis, what is the most direct source of energy that is used to convert ADP + ℗i to ATP? A) energy released as electrons flow through the electron transport system B) energy released from substrate-level phosphorylation C) energy released from dehydration synthesis reactions D) energy released from movement of protons through ATP synthase, down their electrochemical gradient E) No external source of energy is required because the reaction is exergonic. Answer: D 39) Energy released by the electron transport chain is used to pump H+ into which location in eukaryotic cells? A) cytosol B) mitochondrial outer membrane C) mitochondrial inner membrane D) mitochondrial intermembrane space E) mitochondrial matrix Answer: D 40) The direct energy source that drives ATP synthesis during respiratory oxidative phosphorylation in eukaryotic cells is A) oxidation of glucose to CO2 and water. B) the thermodynamically favorable flow of electrons from NADH to the mitochondrial electron transport carriers. C) the final transfer of electrons to oxygen. D) the proton-motive force across the inner mitochondrial membrane. E) the thermodynamically favorable transfer of phosphate from glycolysis and the citric acid cycle intermediate molecules of ADP. Answer: D 41) When hydrogen ions are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, the result is A) the formation of ATP. B) the reduction of NAD+. C) the restoration of the Na+/K+ balance across the membrane. D) the creation of a proton-motive force. E) the lowering of pH in the mitochondrial matrix. Answer: D 42) Where is ATP synthase located in the mitochondrion? A) cytosol B) electron transport chain C) outer membrane D) inner membrane E) mitochondrial matrix Answer: D 43) Which of the following produces the most ATP when glucose (C6H12O6) is completely oxidized to carbon dioxide (CO2) and water? A) glycolysis B) fermentation C) oxidation of pyruvate to acetyl CoA D) citric acid cycle E) oxidative phosphorylation (chemiosmosis) Answer: E 44) Approximately how many molecules of ATP are produced from the complete oxidation of two molecules of glucose (C6H12O6) in aerobic cellular respiration? A) 2 B) 4 C) 15 D) 30-32 E) 60-64 Answer: E 45) The synthesis of ATP by oxidative phosphorylation, using the energy released by movement of protons across the membrane down their electrochemical gradient, is an example of A) active transport. B) an endergonic reaction coupled to an exergonic reaction. C) a reaction with a positive ΔG . D) osmosis. E) allosteric regulation. Answer: B 46) If a cell is able to synthesize 30 ATP molecules for each molecule of glucose completely oxidized to carbon dioxide and water, approximately how many ATP molecules can the cell synthesize for each molecule of pyruvate oxidized to carbon dioxide and water? A) 0 B) 1 C) 12 D) 14 E) 26 Answer: D 47) What is proton-motive force? A) the force required to remove an electron from hydrogen B) the force provided by a transmembrane hydrogen ion gradient C) the force that moves hydrogen into the intermembrane space D) the force that moves hydrogen into the mitochondrion E) the force that moves hydrogen to NAD+ Answer: B 48) In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve? A) It allows for an increased rate of glycolysis. B) It allows for an increased rate of the citric acid cycle. C) It increases the surface for oxidative phosphorylation. D) It increases the surface for substrate-level phosphorylation. E) It allows the liver cell to have fewer mitochondria. Answer: C 49) Brown fat cells produce a protein called thermogenin in their mitochondrial inner membrane. Thermogenin is a channel for facilitated transport of protons across the membrane. What will occur in the brown fat cells when they produce thermogenin? A) ATP synthesis and heat generation will both increase. B) ATP synthesis will increase, and heat generation will decrease. C) ATP synthesis will decrease, and heat generation will increase. D) ATP synthesis and heat generation will both decrease. E) ATP synthesis and heat generation will stay the same. Answer: C 50) In a mitochondrion, if the matrix ATP concentration is high, and the intermembrane space proton concentration is too low to generate sufficient proton-motive force, then A) ATP synthase will increase the rate of ATP synthesis. B) ATP synthase will stop working. C) ATP synthase will hydrolyze ATP and pump protons into the intermembrane space. D) ATP synthase will hydrolyze ATP and pump protons into the matrix. Answer: C 51) Chemiosmotic ATP synthesis (oxidative phosphorylation) occurs in A) all cells, but only in the presence of oxygen. B) only eukaryotic cells, in the presence of oxygen. C) only in mitochondria, using either oxygen or other electron acceptors. D) all respiring cells, both prokaryotic and eukaryotic, using either oxygen or other electron acceptors. E) all cells, in the absence of respiration. Answer: D 52) In vertebrate animals, brown fat tissue's color is due to abundant blood vessels and capillaries. White fat tissue, on the other hand, is specialized for fat storage and contains relatively few blood vessels or capillaries. Brown fat cells have a specialized protein that dissipates the proton-motive force across the mitochondrial membranes. Which of the following might be the function of the brown fat tissue? A) to increase the rate of oxidative phosphorylation from its few mitochondria B) to allow the animals to regulate their metabolic rate when it is especially hot C) to increase the production of ATP D) to allow other membranes of the cell to perform mitochondrial functions E) to regulate temperature by converting most of the energy from NADH oxidation to heat Answer: E 53) What carbon sources can yeast cells metabolize to make ATP from ADP under anaerobic conditions? A) glucose B) ethanol C) pyruvate D) lactic acid E) either ethanol or lactic acid Answer: A 54) Yeast cells that have defective mitochondria incapable of respiration will be able to grow by catabolizing which of the following carbon sources for energy? A) glucose B) proteins C) fatty acids D) glucose, proteins, and fatty acids E) Such yeast cells will not be capable of catabolizing any food molecules, and will therefore die. Answer: A 55) Which catabolic processes may have been used by cells on ancient Earth before free oxygen became available? A) glycolysis and fermentation only B) glycolysis and the citric acid cycle only C) glycolysis, pyruvate oxidation, and the citric acid cycle D) oxidative phosphorylation only E) glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation, using an electron acceptor other than oxygen Answer: E 56) Which of the following normally occurs regardless of whether or not oxygen (O2) is present? A) glycolysis B) fermentation C) oxidation of pyruvate to acetyl CoA D) citric acid cycle E) oxidative phosphorylation (chemiosmosis) Answer: A 57) Which of the following occur(s) in the cytosol of a eukaryotic cell? A) glycolysis and fermentation B) fermentation and chemiosmosis C) oxidation of pyruvate to acetyl CoA D) citric acid cycle E) oxidative phosphorylation Answer: A 58) Which metabolic pathway is common to both cellular respiration and fermentation? A) the oxidation of pyruvate to acetyl CoA B) the citric acid cycle C) oxidative phosphorylation D) glycolysis E) chemiosmosis Answer: D 59) The ATP made during fermentation is generated by which of the following? A) the electron transport chain B) substrate-level phosphorylation C) chemiosmosis D) oxidative phosphorylation E) aerobic respiration Answer: B 60) In the absence of oxygen, yeast cells can obtain energy by fermentation, resulting in the production of A) ATP, CO2, and ethanol (ethyl alcohol). B) ATP, CO2, and lactate. C) ATP, NADH, and pyruvate. D) ATP, pyruvate, and oxygen. E) ATP, pyruvate, and acetyl CoA. Answer: A 61) In alcohol fermentation, NAD+ is regenerated from NADH by A) reduction of acetaldehyde to ethanol (ethyl alcohol). B) oxidation of pyruvate to acetyl CoA. C) reduction of pyruvate to form lactate. D) oxidation of ethanol to acetyl CoA. E) reduction of ethanol to pyruvate. Answer: A 62) One function of both alcohol fermentation and lactic acid fermentation is to A) reduce NAD+ to NADH. B) reduce FAD+ to FADH2. C) oxidize NADH to NAD+. D) reduce FADH2 to FAD+. E) do none of the above. Answer: C 63) An organism is discovered that thrives both in the presence and absence of oxygen in the air. Curiously, the consumption of sugar increases as oxygen is removed from the organism's environment, even though the organism does not gain much weight. This organism A) must use a molecule other than oxygen to accept electrons from the electron transport chain. B) is a normal eukaryotic organism. C) is photosynthetic. D) is an anaerobic organism. E) is a facultative anaerobe. Answer: E 64) Which statement best supports the hypothesis that glycolysis is an ancient metabolic pathway that originated before the last universal common ancestor of life on Earth? A) Glycolysis is widespread and is found in the domains Bacteria, Archaea, and Eukarya. B) Glycolysis neither uses nor needs O2. C) Glycolysis is found in all eukaryotic cells. D) The enzymes of glycolysis are found in the cytosol rather than in a membrane-enclosed organelle. E) Ancient prokaryotic cells, the most primitive of cells, made extensive use of glycolysis long before oxygen was present in Earth's atmosphere. Answer: A 65) Why is glycolysis considered to be one of the first metabolic pathways to have evolved? A) It produces much less ATP than does oxidative phosphorylation. B) It does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms. C) It is found in prokaryotic cells but not in eukaryotic cells. D) It relies on chemiosmosis, which is a metabolic mechanism present only in the first cells' prokaryotic cells. E) It requires the presence of membrane-enclosed cell organelles found only in eukaryotic cells. Answer: B 66) When an individual is exercising heavily and when the muscle becomes oxygen-deprived, muscle cells convert pyruvate to lactate. What happens to the lactate in skeletal muscle cells? A) It is converted to NAD+. B) It produces CO2 and water. C) It is taken to the liver and converted back to pyruvate. D) It reduces FADH2 to FAD+. E) It is converted to alcohol. Answer: C 67) A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells? A) The mutant yeast will be unable to grow anaerobically. B) The mutant yeast will grow anaerobically only when given glucose. C) The mutant yeast will be unable to metabolize glucose. D) The mutant yeast will die because they cannot regenerate NAD+ from NAD. E) The mutant yeast will metabolize only fatty acids. Answer: A 68) You have a friend who lost 7 kg (about 15 pounds) of fat on a regimen of strict diet and exercise. How did the fat leave her body? A) It was released as CO2 and H2O. B) It was converted to heat and then released. C) It was converted to ATP, which weighs much less than fat. D) It was broken down to amino acids and eliminated from the body. E) It was converted to urine and eliminated from the body. Answer: A 69) What is the purpose of beta oxidation in respiration? A) oxidation of glucose B) oxidation of pyruvate C) feedback regulation D) control of ATP accumulation E) breakdown of fatty acids Answer: E 70) Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle? A) pyruvate B) malate or fumarate C) acetyl CoA D) α-ketoglutarate E) succinyl CoA Answer: C 71) During intense exercise, as skeletal muscle cells switch to fermentation, the human body will increase its catabolism of A) fats only. B) carbohydrates only. C) proteins only. D) fats, carbohydrates, and proteins. E) fats and proteins only. Answer: B 7.2 Art Questions Figure 7.1 The citric acid cycle. 1) Starting with one molecule of isocitrate and ending with fumarate, how many ATP molecules can be made through substrate-level phosphorylation (see Figure 7.1)? A) 1 B) 2 C) 11 D) 12 E) 24 Answer: A 2) Carbon skeletons for amino acid biosynthesis are supplied by intermediates of the citric acid cycle. Which intermediate would supply the carbon skeleton for synthesis of a five-carbon amino acid (see Figure 7.1)? A) succinate B) malate C) citrate D) α-ketoglutarate E) isocitrate Answer: D 3) For each mole of glucose (C6H12O6) oxidized by cellular respiration, how many moles of CO2 are released in the citric acid cycle (see Figure 7.1)? A) 2 B) 4 C) 6 D) 12 E) 3 Answer: B 4) If pyruvate oxidation is blocked, what will happen to the levels of oxaloacetate and citric acid in the citric acid cycle shown in Figure 7.1? A) There will be no change in the levels of oxaloacetate and citric acid. B) Oxaloacetate will decrease and citric acid will accumulate. C) Oxaloacetate will accumulate and citric acid will decrease. D) Both oxaloacetate and citric acid will decrease. E) Both oxaloacetate and citric acid will accumulate. Answer: C 5) Starting with citrate, which of the following combinations of products would result from three acetyl CoA molecules entering the citric acid cycle (see Figure 7.1)? A) 1 ATP, 2 CO2, 3 NADH, and 1 FADH2 B) 2 ATP, 2 CO2, 3 NADH, and 3 FADH2 C) 3 ATP, 3 CO2, 3 NADH, and 3 FADH2 D) 3 ATP, 6 CO2, 9 NADH, and 3 FADH2 E) 38 ATP, 6 CO2, 3 NADH, and 12 FADH2 Answer: D 6) For each molecule of glucose that is metabolized by glycolysis and the citric acid cycle (see Figure 7.1), what is the total number of NADH + FADH2 molecules produced? A) 4 B) 5 C) 6 D) 10 E) 12 Answer: E Figure 7.2 7) Figure 7.2 shows the electron transport chain. Which of the following is the combination of substances that is initially added to the chain? A) oxygen, carbon dioxide, and water B) NAD+, FAD, and electrons C) NADH, FADH2, and protons D) NADH, FADH2, and O2 E) oxygen and protons Answer: D 8) Which of the following most accurately describes what is happening along the electron transport chain in Figure 7.2? A) Chemiosmosis is coupled with electron transfer. B) Each electron carrier alternates between being reduced and being oxidized. C) ATP is generated at each step. D) Energy of the electrons increases at each step. E) Molecules in the chain give up some of their potential energy. Answer: B 9) Which of the protein complexes labeled with Roman numerals in Figure 7.2 will transfer electrons to O2? A) complex I B) complex II C) complex III D) complex IV E) All of the complexes can transfer electrons to O2. Answer: D 10) What happens at the end of the chain in Figure 7.2? A) Two electrons combine with a proton and a molecule of NAD+. B) Two electrons combine with a molecule of oxygen and two hydrogen atoms. C) Four electrons combine with a molecule of oxygen and 4 protons. D) Four electrons combine with four hydrogen and two oxygen atoms. E) One electron combines with a molecule of oxygen and a hydrogen atom. Answer: C 7.3 Scenario Questions In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A. 1) These three steps result in the formation of A) acetyl CoA, O2, and ATP. B) acetyl CoA, FADH2, and CO2. C) acetyl CoA, FAD, H2, and CO2. D) acetyl CoA, NADH, H+, and CO2. E) acetyl CoA, NAD+, ATP, and CO2. Answer: D 2) How does the addition of coenzyme A, a sulfur-containing molecule derived from a B vitamin, function in the subsequent reaction? A) It provides the sulfur needed for the molecule to enter the mitochondrion. B) It utilizes this portion of a B vitamin, which would otherwise be a waste product from another pathway. C) It provides a relatively unstable molecule whose acetyl portion can be readily transferred to a compound in the citric acid cycle. D) It drives the reaction that regenerates NAD+. E) It removes one molecule of CO2. Answer: C 3) Which one of the following is formed by the removal of a carbon (as CO2) from a molecule of pyruvate? A) lactate B) glyceraldehyde-3-phosphate C) oxaloacetate D) acetyl CoA E) citrate Answer: D 7.4 End-of-Chapter Questions 1) The immediate energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylation is the A) oxidation of glucose and other organic compounds. B) flow of electrons down the electron transport chain. C) affinity of oxygen for electrons. D) H+ movement down its concentration gradient. E) transfer of phosphate to ADP. Answer: D 2) Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule? A) the citric acid cycle B) the electron transport chain C) glycolysis D) synthesis of acetyl CoA from pyruvate E) reduction of pyruvate to lactate Answer: C 3) In mitochondria, exergonic redox reactions A) are the source of energy driving prokaryotic ATP synthesis. B) are directly coupled to substrate-level phosphorylation. C) provide the energy that establishes the proton gradient. D) reduce carbon atoms to carbon dioxide. E) use ATP to pump H+ out of the mitochondrion. Answer: C 4) The final electron acceptor of the electron transport chain that functions in aerobic oxidative phosphorylation is A) oxygen. B) water. C) NAD+. D) pyruvate. E) ADP. Answer: A 5) What is the oxidizing agent in the following reaction? Pyruvate + NADH + H+ → Lactate + NAD+ A) oxygen B) NADH C) NAD+ D) lactate E) pyruvate Answer: E 6) When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs? A) The pH of the matrix increases. B) ATP synthase pumps protons by active transport. C) The electrons gain free energy. D) The cytochromes phosphorylate ADP to form ATP. E) NAD+ is oxidized. Answer: A 7) Most CO2 from catabolism is released during A) glycolysis. B) the citric acid cycle. C) lactate fermentation. D) electron transport. E) oxidative phosphorylation. Answer: B Test Bank for Campbell Biology in Focus Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson, Jane B. Reece 9780321813664, 9780321962751, 9780134710679
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