Chapter 9. Pathways That Harvest Chemical Energy (HOMEWORK & QUIZ)

Which reaction is not an oxidation-reduction reaction? (A) NADH + ½ O2 + H+ → NAD+ + H2O (B) FAD + H2O → FADH2 + ½ O2 (C) NADH + acetaldehyde → NAD+ + ethanol (D) AH2 + B → A + BH2 (E) R — CH = CH — CH3 + H2O → RCH2 — CH (OH) — CH3

(E) R — CH = CH — CH3 + H2O → RCH2 — CH (OH) — CH3

ATP synthase is the protein complex that A) transfers electrons to oxygen in the final step of the respiratory chain. B) transfers electrons from the inner mitochondrial space to the mitochondrial matrix. C) creates a proton-motive force when glucose is oxidized. D) rotates when ATP is hydrolyzed in the mitochondrial matrix. E) captures the potential energy of the proton gradient in the intermembrane space as the chemical energy in phosphate bonds of ATP.

E) captures the potential energy of the proton gradient in the intermembrane space as the chemical energy in phosphate bonds of ATP.

Fermentation A) completely oxidizes glucose to CO2 and H2O. B) is endergonic. C) does not involve substrate-level ADP synthesis. D) occurs under aerobic conditions in yeasts. E) results in the formation of either lactic acid or ethanol.

E) results in the formation of either lactic acid or ethanol.

What is an example of anabolic interconversion?

Gluconeogenesis

Which group represents the net outputs of glycolysis?

Pyruvate, 2 NADH, 2 ATP

Cyanide inhibits the enzyme in the mitochondrial electron transport chain that reduces O2 to water. Suppose you added cyanide to a suspension of muscle cells from a rat. Which statement is accurate with respect to the effects of cyanide on glucose catabolism?

The citric acid cycle would be inhibited, but glycolysis would not and so lactic acid would accumulate.

Energy production occurs in different locations in prokaryotic and eukaryotic cells. Which statement is true for prokaryotes?

The respiratory chain enzymes are found on the cell membrane.

If an experiment based on the ones using thylakoids from chloroplasts were carried out, which thylakoids would produce the most ATP?

Thylakoids preincubated in a pH 4 solution and then moved to a pH 7.5 solution containing ADP and Pi

Organisms regulate certain metabolic enzymes in cells in order to maintain

a balance between catabolism and anabolism.

Which statement regarding glycolysis is true? (A)Glucose is not catabolized. (B)Oxygen is not required. (C)Pyruvate is not formed. (D)ATP is not formed. (E)NADH is not formed.

(B)Oxygen is not required.

A student wants to develop a demonstration to explain the energy changes taking place as electrons are transferred along the respiratory chain. Which everyday objects could he use to accomplish his goal?

A ball rolling down a staircase

The carbon-containing molecule that enters glycolysis differs from the one that enters the citric acid cycle. How do the numbers of carbon atoms per molecule compare in these two cases?

A six carbon molecule enters glycolysis, while a two carbon molecule enters the citric acid cycle.

Products from the citric acid cycle include A) FADH2. B) GDP. C) NAD+. D) ATP. E) acetyl CoA.

A) FADH2.

If the regeneration of NAD+ were inhibited during lactic acid fermentation, which of the following would likely occur? A) The rate of glucose converted to pyruvate would increase. B) The rate of lactic acid production would decrease. C) The concentration of ATP would increase. D) The rate of pyruvate production would remain the same. E) The concentration of NAD+ would increase.

B) The rate of lactic acid production would decrease.

A recently identified organism produces methane (CH4) when provided with glucose in the absence of oxygen. This means the organism is A) capable of aerobic catabolism and uses carbon dioxide in place of oxygen as its terminal electron acceptor. B) capable of anaerobic catabolism and uses carbon dioxide in place of oxygen as its terminal electron acceptor. C) capable of aerobic catabolism and uses acetate in place of oxygen as its terminal electron acceptor. D) capable of anaerobic catabolism and uses acetate in place of oxygen as its terminal electron acceptor. E) capable of aerobic catabolism and uses sulfate in place of oxygen as its terminal electron acceptor.

B) capable of anaerobic catabolism and uses carbon dioxide in place of oxygen as its terminal electron acceptor.

Oxidative phosphorylation has two major components: _______ and _______.

electron transport; chemiosmosis

The synthesis of ATP from ADP and Pi is an _______ reaction. In mitochondria, ATP synthesis is driven by the flow of _______ down a concentration gradient established by _______.

endergonic; protons; electron transport

NADH

is a key electron carrier in redox rections

Metabolic pathways are

large sets of interconnected chemical transformational steps, each with a specific enzyme.

The difference between oxidation and reduction is that

oxidation reduces the number of electrons, while reduction increases the number of electrons.

The end products of glycolysis are

pyruvate, ATP, and NADH.

Choose the phrase that does not correctly complete this sentence: Oxidative phosphorylation is a process

that requires a membrane that is permeable to protons.

Which component of the respiratory chain is a peripheral protein?

Cytochrome c

What is the cellular location of glycolysis in eukaryotes?

Cytosol

Which describes how the components of the respiratory chain are ordered? A) From low to high free energy relative to oxygen B) From low to high ability to pass electrons to oxygen C) From high to low ability to pump protons across the inner membrane D) From high to low reduction potential relative to oxygen E) From large to small mass

D) From high to low reduction potential relative to oxygen

How many enzymatic steps are involved in glycolysis in animals? A) One B) Three C) Five D) Eight E) Ten

E) 10

Some poisons are compounds that interfere with metabolic pathways. Which poison would interfere with the citric acid cycle but not affect glycolysis? A) A compound that accelerates ATP hydrolysis B) A compound that accelerates pyruvate oxidation C) A compound that inhibits regeneration of NAD+ from NADH D) A compound that accelerates coenzyme A synthesis E) A compound that inhibits pyruvate dehydrogenase

E) A compound that inhibits pyruvate dehydrogenase

A microbiologist is characterizing a newly discovered microorganism that requires an anaerobic environment to live and uses either lactic acid or alcoholic fermentation in its energy metabolism. Which would be a way to determine the type of fermentation the microorganism uses?

Analyze whether two molecules of carbon dioxide are released for every one molecule of glucose fermented.

What is the net free energy captured by 32 moles of ATP? A) 7.3 kcal B) 52.4 kcal C) 234 kcal D) 686 kcal E) 730 kcal

C) 234 kcal

Which reaction is not an example of an oxidation-reduction reaction? A) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O B) CH4 + ½ O2 → CH3OH + H+ C) ADP + Pi → ATP + H2O D) NADH + H+ + ½ O2 → NAD+ + H2O E) C2H5OH + NAD+ → C2H4O + NADH + H+

C) ADP + Pi → ATP + H2O

Proteins are built from carbons that can come directly from A) electron transport. B) the citric acid cycle. C) acetyl CoA. D) pyruvate oxidation. E) pyruvate.

B) the citric acid cycle.

Which compounds link glycolysis and the citric acid cycle to the electron transport chain?

FADH2 and NADH

Which sequence represents a possible path of a carbon atom as it moves through a catabolic series of reactions in a cell?

Fatty acid → acetyl CoA → carbon dioxide

In eukaryotes, the proton-motive force allows protons to move passively through ATP synthase in which direction?

From the mitochondrial inner membrane space to the mitochondrial matrix

A student made this table as a study guide for learning the various catabolic pathways that cells use for harvesting energy from glucose. Which statement best evaluates the accuracy of the student's efforts?

In eukaryotes, pyruvate oxidation is carried out in the mitochondrial matrix, not in the cytosol.

Which statement about the citric acid cycle is false?

It releases less energy than glycolysis.

What is the cellular location of the citric acid cycle?

Mitochondrial matrix

If 0.5 mole of glucose is oxidized by lactic acid fermentation, the amount of ATP generated in the cytosol will be

1.0 mole.

What amount of free energy is released by the oxidation of 2 moles of NADH?

104.8 kcal

According to the chemiosmotic mechanism, what is the direct source of the energy used to synthesize ATP from ADP in chloroplasts and in mitochondria? A) Proton gradient B) Glucose C) Electrons D) Water

A) Proton gradient

Which product of glycolysis is transported across the mitochondrial membrane, where it is converted to the molecule that enters the citric acid cycle? A) Pyruvate B) Glucose C) NADH + H+ D) Acetyl CoA E) ATP synthase

A) Pyruvate

When purified cytochrome oxidase is exposed to cyanide, the cyanide binds reversibly and with high affinity to the enzyme's active site. What will be the likely outcome if mitochondria are exposed to high levels of cyanide? A) The cyanide will inhibit transfer of electrons from NADH to initiate electron transport. B) The cyanide will prevent oxygen from reaching the mitochondrial matrix. C) The cyanide will prevent movement of electrons along the electron transport chain. D) The cyanide will block movement of protons across the inner mitochondrial membrane.

A) The cyanide will inhibit transfer of electrons from NADH to initiate electron transport.

Which statement regarding glycolysis is true? A) Two ATP molecules are required in the first three steps per glucose molecule. B) ATP is not formed. C) NADH is not formed. D) Two molecules of glucose are catabolized to form two molecules of pyruvate. E) The first two steps are endergonic.

A) Two ATP molecules are required in the first three steps per glucose molecule.

Suppose you are constructing a diagram to show the results of experiments with vesicles made to contain both bacteriorhodopsin and ATP synthase. The diagram would show light stimulating A) bacteriorhodopsin to pump hydrogen ions into the vesicle, which then move back outside the vesicle through ATP synthase, causing it to catalyze ATP formation. B) ATP synthase to pump hydrogen ions out of the vesicle, which then cause the formation of ATP as they move back into the vesicle interior through bacteriorhodopsin. C) bacteriorhodopsin to pump hydrogen ions out of the vesicle, which then move back into the vesicle interior through ATP synthase, causing it to catalyze ATP formation. D) ATP synthase to catalyze formation of ATP, which then drives the pumping of hydrogen ions into the vesicle interior by bacteriorhodopsin.

A) bacteriorhodopsin to pump hydrogen ions into the vesicle, which then move back outside the vesicle through ATP synthase, causing it to catalyze ATP formation.

Metabolic pathways can be controlled through the availability of enzymes and modulation of their catalytic activities. Enzyme availability can be regulated via _______, while enzyme activity is commonly regulated via _______. A) gene expression; allosteric activation and inhibition B) covalent modification; proteolytic breakdown C) proteolytic breakdown; gene expression D) gene expression; covalent modification E) allosteric activation and inhibition; covalent modification

A) gene expression; allosteric activation and inhibition

The reduction of pyruvate to lactic acid during fermentation allows glycolysis to continue in the absence of O2 because this reaction A) is coupled to the oxidation of NADH to NAD+. B) produces H2O. C) is coupled to the formation of ATP. D) is a kinase reaction. E) is coupled to the reduction of NAD+ to NADH.

A) is coupled to the oxidation of NADH to NAD+.

In eukaryotes, the organelle containing the enzyme(s) necessary for oxidation of glucose beyond glycolysis is the A) mitochondrion. B)nucleus. C) peroxisome. D) Golgi apparatus. E) lysosome.

A) mitochondrion.

The electron transport chain A) oxidizes the intermediate electron carriers NADH and FADH2. B) oxidizes water to ½ O2 and 2 H+. C) is the site of most reactions of the citric acid cycle. D) pumps protons into the mitochondrial matrix during electron transport. E) synthesizes ATP.

A) oxidizes the intermediate electron carriers NADH and FADH2.

Anaerobic conditions" means that there is an absence of A) oxygen. B) lactate. C) glucose. D) pyruvate. E) carbon dioxide.

A) oxygen.

ATP molecules are important in metabolism because ATP can A) release chemical energy, which drives endergonic reactions. B) release chemical energy, which drives exergonic reactions. C) substitute for glucose as an energy source for cells. D) absorb chemical energy from another reaction as it is hydrolyzed. E) store chemical energy for long periods of time in the body.

A) release chemical energy, which drives endergonic reactions.

In the complete oxidation of glucose, six CO2 molecules are formed per glucose molecule. The number of CO2 molecules released by glycolysis is _______, by pyruvate oxidation is _______, and by the citric acid cycle is _______. A) zero; zero; six B) zero; two; four C) one; one; four D) one; two; three E) two; two; two

B ) zero; two; four

The compound 2,4-dinitrophenol (DNP) is a lipid soluble compound that has been used as a weight loss agent. It functions this way by causing the inner mitochondrial membrane to become leaky with respect to protons. Which result might be expected if cells treated with DNP were examined in detail? A) The rate of oxygen consumption would be slower in these cells than in untreated cells. B) ATP production would be slower in these cells than in untreated cells. C) The ratio of ATP produced to glucose oxidized would be greater in these cells than in untreated cells. D) Electron transport in these cells would be completely blocked. E) The pH difference across the mitochondrial inner membrane would be greater in these cells than in untreated cells.

B) ATP production would be slower in these cells than in untreated cells.

Which list places the molecules, from left to right, from most oxidized to least oxidized? A) CH2O > CO2 > CH3OH > CH4 B) CO2 > CHOOH > CH3OH > CH4 C) HCOOH > CH4 > CH3OH > CO2 D) CH4 > CH3OH > CHOOH > CO2 E) CO2 > CH2O > HCOOH > CH4

B) CO2 > CHOOH > CH3OH > CH4

Studies on human aging have shown that the levels of coenzyme Q10 (ubiquinone), measured in tissues such as heart muscle, are significantly lower in individuals over 70 years old than in younger individuals. This lower level is associated with significantly reduced contractile force of their heart muscle. Which is the most likely explanation for the reduced heart muscle function in these older individuals? A) Coenzyme Q10 is a lipid found in brown fat; brown fat is a major source of energy for all tissues in the body. B) Coenzyme Q10 is an electron carrier in the electron transport chain in mitochondria; lower levels of it will result in less ATP being made by mitochondria during cellular respiration. C) Coenzyme Q10 is used in cleaving a 6-carbon sugar into two 3-carbon sugars during glycolysis; lower levels of it will result in lower amounts of ATP being produced. D) Coenzyme Q10 is used to convert pyruvate to acetyl CoA; lower levels of it will result in a less efficient citric acid cycle, which will slow down the production of ATP. E) Coenzyme Q10 is an uncoupling protein found in mitochondria; lower levels of it will result in less efficient mitochondria.

B) Coenzyme Q10 is an electron carrier in the electron transport chain in mitochondria; lower levels of it will result in less ATP being made by mitochondria during cellular respiration.

Which statement could be used as part of a description of how carbohydrate, lipid, and protein are linked through catabolic and anabolic pathways? A) Glycolysis and fermentation only partially oxidize glucose, while the citric acid cycle and oxidative phosphorylation allow for full oxidation of glucose and transfer of its free energy to ATP. B) Glycolysis and the citric acid cycle occupy a central position in cell metabolism, connecting to lipid, protein, and carbohydrate breakdown and synthesis through small molecule intermediates. C) Metabolic pathways are compartmentalized in the cell, which allows physical boundaries to organize the large numbers of metabolic interconversions taking place at any one time in a cell. D) Metabolic pathways for lipids, proteins, and carbohydrates all share the same characteristic, in that they represent a series of separate chemical reactions that together accomplish a complex chemical transformation. E) Metabolism is a cyclical process of energy conversion in which chemical energy is harvested from nutrients in catabolic reactions and used to synthesize new molecules in anabolic reactions.

B) Glycolysis and the citric acid cycle occupy a central position in cell metabolism, connecting to lipid, protein, and carbohydrate breakdown and synthesis through small molecule intermediates.

A recently identified organism produces methane when provided with glucose in the absence of oxygen. This means the organism is A) capable of aerobic catabolism and uses carbon dioxide in place of oxygen as its terminal electron acceptor. B) capable of anaerobic catabolism and uses carbon dioxide in place of oxygen as its terminal electron acceptor. C) capable of aerobic catabolism and uses acetate in place of oxygen as its terminal electron acceptor. D) capable of anaerobic catabolism and uses acetate in place of oxygen as its terminal electron acceptor. E) capable of aerobic catabolism and uses sulfate in place of oxygen as its terminal electron acceptor.

B) capable of anaerobic catabolism and uses carbon dioxide in place of oxygen as its terminal electron acceptor.

Cellular respiration refers to the metabolic process that A) produces 30 ATP. B) involves the oxidation of pyruvate to carbon dioxide. C) starts with sucrose. D) involves the oxidation of glucose to pyruvate. E) releases less usable energy for a cell than fermentation.

B) involves the oxidation of pyruvate to carbon dioxide.

Which is a viable path that a carbon atom could take as it moves through metabolic pathways in a cell? A) Amino acid → acetyl CoA → purine → pyrimidine → glycerol → fatty acid → lactic acid → glucose B) Pyrimidine → fatty acid → purine → amino acid → acetyl CoA → glucose → pyruvate → lactic acid C) Amino acid → purine → DNA → purine → amino acid → acetyl CoA → fatty acid → triglyceride D) Fatty acid → amino acid → pyrimidine → purine → glucose → glycerol → acetyl CoA → amino acid E) Glucose → glycerol → triglyceride → fatty acid → purine → DNA → pyrimidine → amino acid

C) Amino acid → purine → DNA → purine → amino acid → acetyl CoA → fatty acid → triglyceride

How are steps 1-3 of glycolysis different from steps 6-10? A) Steps 1-3 occur in the cytoplasm, while steps 6-10 occur in the mitochondrial matrix. B) Steps 1-3 catalyze changes in a six-carbon molecule, while steps 6-10 catalyze changes in a four-carbon molecule. C) Steps 1-3 catalyze reactions that require ATP, while steps 6-10 catalyze changes that produce NADH and ATP. D) Steps 1-3 catalyze reactions that require ATP, while steps 6-10 catalyze changes that require NADH. E) Steps 1-3 catalyze reactions that require ATP, while steps 6-10 catalyze changes that produce NADH and GTP.

C) Steps 1-3 catalyze reactions that require ATP, while steps 6-10 catalyze changes that produce NADH and ATP.

Which is required for wine production? A) Purified chloroplasts only B) An aerobic environment C) Yeast and a source of glucose D) Plant cells devoid of sugar E) Lactic acid fermentation from glucose

C) Yeast and a source of glucose

Catabolic interconversion is a metabolic pathway in which A) many small molecules are combined into larger molecules and a pathway that requires energy. B) large molecules are built up into even larger molecules and a pathway that requires energy. C) a large molecule is broken down into its constituent molecules and releases energy. D) small molecules are broken down into CO2 and water molecules and release energy. E) a citric acid intermediate is a starting point.

C) a large molecule is broken down into its constituent molecules and releases energy.

When NADH is the electron donor to the respiratory chain, 2.5 ATP are formed, but when FADH2 is the electron donor, only 1.5 ATP are formed. This difference occurs because A) complex I accepts electrons from both NADH and FADH2 but donates the electrons to different sites on the complex, which produces a larger proton gradient for NADH. B) NADH interacts with ATP synthase more efficiently than FADH2, resulting in more ATP production. C) complex I accepts electrons from NADH but not FADH2, resulting in an extra step that allows a larger proton gradient to form. D) complex II accepts electrons from both NADH and FADH2 but donates the electrons to different sites on the complex, which produces a larger proton gradient for NADH. E) energy, in the form of heat, is lost when FADH2, but not NADH, is the electron donor, resulting in lower energy yield.

C) complex I accepts electrons from NADH but not FADH2, resulting in an extra step that allows a larger proton gradient to form.

Like glycolysis, fermentation occurs in the.. A) mitochondria. B) chloroplasts. C) cytoplasm. D) inner mitochondrial space. E) mitochondrial matrix.

C) cytoplasm.

Reagents, such as dinitrophenol, increase the permeability of the mitochondrial inner membrane to protons. The addition of dinitrophenol to a suspension of animal cells should A) stimulate ATP synthesis by mitochondria. B) increase lactic acid production. C) inhibit mitochondrial ATP synthesis. D) decrease the rate of oxidation of NADH. E) decrease the rate of pyruvate oxidation.

C) inhibit mitochondrial ATP synthesis.

The ________ of the mitochondrion contains the proteins making up the ________ that carry out electron transport. A) outer mitochondrial membrane; respiratory chain B) mitochondrial intermembrane space; proton gradient C) inner mitochondrial membrane; respiratory chain D) inner mitochondrial membrane; proton gradient

C) inner mitochondrial membrane; respiratory chain

Malate dehydrogenase is responsible for catalyzing which reaction? A) Reduction of malate to oxaloacetate B) Substrate phosphorylation of ADP to ATP C) Oxidation of malate to oxaloacetate D) Oxidation of NADH to NAD+ E) Decarboxylation of a five-carbon molecule to a four-carbon molecule

C) oxidation of malate to oxaloacetate.

The conversion of malate to oxaloacetate in the citric acid cycle takes place with the conversion of NAD+ to NADH. In this reaction, NAD+ is a(n) A) feedback inhibitor. B) allosteric inhibitor. C) oxidizing agent. D) allosteric activator. E) reducing agent.

C) oxidizing agent

The cell harvests a very large amount of free energy from glucose in the form of ATP. Which statement can be used as part of an explanation about how the cell accomplishes this harvesting process with high efficiency (i.e., with very little loss in energy as heat)? A) The net energy change for the transfer of electrons from NADH to oxygen is very large. B) Electron flow through the respiratory chain results in the active transport of protons across the inner mitochondrial membrane, creating a proton concentration gradient. C) Electron transport uses a series of several proteins, each of which functions to capture a portion of the total energy of the electrons entering the chain. D) NADH and FADH2 enter the electron transport chain at different points. E) Pyruvate oxidation and the citric acid cycle cannot operate unless oxygen is available to function as the final acceptor of electrons.

C) transport uses a series of several proteins, each of which functions to capture a portion of the total energy of the electrons entering the chain.

How many reaction steps are involved in the citric acid cycle? A) One B) Three C) Five D) Eight E) Ten

D) 8

A suspension of yeast supplied with glucose as its source of energy was transferred from an aerobic environment to an anaerobic one. Which result would you predict for the rate of glucose utilization and the rate of ethanol production after the transfer? Assume that the yeast must expend the same amount of energy to survive in both environments. A) Glucose usage would not change, and ethanol production would increase. B) Glucose usage would increase, and ethanol production would decrease. C) Glucose usage would decrease, and ethanol production would increase. D) Both glucose usage and ethanol production would increase. E) Neither glucose usage nor ethanol production would change..

D) Both glucose usage and ethanol production would increase.

Under anaerobic conditions, pyruvate A) is broken down on the cell membrane. B) enters the citric acid cycle. C) is reduced to lactate. D) is fermented to lactate or alcohol. E) is converted to lactate or tricarboxylic acids.

D) Is fermented to lactate or alcohol

Which statement best describes how key molecules are regenerated to allow continued metabolism in a cell? A) FADH2 can donate its electrons to the electron transport chain and be regenerated to allow glycolysis to continue. B) ATP can donate its electrons to the electron transport chain and be regenerated to allow the citric acid cycle to continue. C) GTP, NADH, and FADH2 can donate their electrons to the electron transport chain and be regenerated to allow the citric acid cycle to continue. D) NADH and FADH2 can donate their electrons to the electron transport chain and be regenerated to allow the citric acid cycle to continue. E) GTP can donate its electrons to the electron transport chain and be regenerated to allow pyruvate oxidation to continue.

D) NADH and FADH2 can donate their electrons to the electron transport chain and be regenerated to allow the citric acid cycle to continue.

Which statement about metabolic pathways is correct? A) In eukaryotes, all metabolic reactions occur in the cytoplasm. B) Inhibitors that target some key enzymes in a pathway increase the rate of reaction. C) Activators that target some key enzymes in a pathway have no effect on the rate of reaction. D) One enzyme usually catalyzes all of the transformational steps. E) Chemical transformations occur in a series of separate chemical reactions.

E) Chemical transformations occur in a series of separate chemical reactions.

If a cell is fed a large supply of fatty acids, which outcome can be expected? A) Glycolysis and pyruvate oxidation will be stimulated, causing citrate to build up and activate fatty acid synthase. B) Glycolysis will be stimulated and pyruvate oxidation will be inhibited as acetyl CoA builds up to high levels in the cell. C) Oxidation of fatty acids to form acetyl CoA will be stimulated, which will stimulate gluconeogenesis to form glucose that the cell can store as an energy resource. D) Oxidation of fatty acids through the citric acid cycle will be stimulated until ATP builds up and inhibits citrate synthase, diverting fatty acids into storage molecules such as triglycerides. E) The excess fatty acids will deplete the oxygen supply, causing everything except glycolysis to shut down and activating the lactic acid fermentation pathway.

D) Oxidation of fatty acids through the citric acid cycle will be stimulated until ATP builds up and inhibits citrate synthase, diverting fatty acids into storage molecules such as triglycerides.

Why is oxygen important in the electron transport pathway and ATP synthesis? A) Oxygen combines with hydrogen to produce water, a molecule that is essential for life. B) Oxygen donates electrons to the electron transport chain, initiating the electron transport process. C) Oxygen is needed to drive the formation of ATP by ATP synthase. D) Oxygen accepts electrons at the end of the electron transport chain to free the pathway for a new set of electrons.

D) Oxygen accepts electrons at the end of the electron transport chain to free the pathway for a new set of electrons.

Energy production occurs in different locations in prokaryotic and eukaryotic cells. Which statement is true for eukaryotes? A) The conversion of pyruvate to lactate occurs in the mitochondria. B) The conversion of glucose to pyruvate occurs in the mitochondria. C) The citric acid cycle enzymes are found in the cytoplasm. D) The conversion of pyruvate to CO2 and H2O occurs in the mitochondria. E) The respiratory chain enzymes are found at the plasma membrane.

D) The conversion of pyruvate to CO2 and H2O occurs in the mitochondria.

The types of chemical reactions involved in the aerobic breakdown of glucose by a cell include A) reductions. B) oxidations. C) reductions and phosphorylations. D) oxidation-reduction reactions and phosphorylations. E) oxidations and phosphorylations.

D) oxidation-reduction reactions and phosphorylations.

Which statement about the citric acid cycle is true? A) It releases less energy than glycolysis. B) It takes place in the cytoplasm of eukaryotic cells. C) It requires NADH and GTP. D) It operates under anaerobic conditions. E) CO2 is released during operation of the cycle.

E) CO2 is released during operation of the cycle.