AP Biology Chapter 9 Practice Test

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AP Biology Chapter 9 Practice Test - Quiz

If you are preparing for the upcoming AP Biology exam, here we have an AP biology practice test for you. It mainly consists of chapter 9 questions and answers. This quiz tests your knowledge of cellular respiration and fermentation. Advanced Placement (AP) Biology is a biology course and exam for the students of the United States by the College Board. The below quiz will check how well prepared you are for this exam. Take the test and check your scores at the end. Good luck!


Questions and Answers
  • 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

    Correct Answer
    B. Catabolic pathways
    Explanation
    Catabolic pathways are the correct answer. Catabolic pathways refer to metabolic processes that break down complex molecules, such as carbohydrates, proteins, and lipids, in order to release stored energy. These pathways involve reactions like hydrolysis and oxidation, which break down larger molecules into smaller units, releasing energy in the process. This energy can then be used by the cell for various functions, such as ATP production. Anabolic pathways, on the other hand, are metabolic processes that build complex molecules from simpler ones, requiring energy input.

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  • 2. 

    What is the term used for the metabolic pathway in which glucose (C6H12O6) is degraded to carbon dioxide (CO2) and water?

    • A.

      Cellular respiration

    • B.

      Glycolysis

    • C.

      Fermentation

    • D.

      Citric acid cycle

    • E.

      Oxidative phosphorylation

    Correct Answer
    A. Cellular respiration
    Explanation
    Cellular respiration is the correct answer because it is the metabolic pathway in which glucose is broken down to produce carbon dioxide and water. This process occurs in the mitochondria of cells and is essential for generating energy in the form of ATP. Glycolysis is the initial step of cellular respiration, but it only partially breaks down glucose. Fermentation is an alternative pathway that occurs in the absence of oxygen, producing lactic acid or ethanol. The citric acid cycle and oxidative phosphorylation are subsequent steps in cellular respiration that further break down glucose and produce ATP.

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  • 3. 

    Which of the following statements concerning the metabolic degradation of glucose (C6H12O6) to carbon dioxide (CO2) and water is (are) true?

    • A.

      The breakdown of glucose to carbon dioxide and water is exergonic.

    • B.

      The breakdown of glucose to carbon dioxide and water has a free energy change of -686 kcal/mol.

    • C.

      The breakdown of glucose to carbon dioxide and water involves oxidation-reduction or redox reactions.

    • D.

      The breakdown of glucose to carbon dioxide and water is exergonic and has a free energy change of -686 kcal/mol.

    • E.

      The breakdown of glucose to carbon dioxide and water is exergonic, has a free energy change of -686 kcal/mol, and involves oxidation-reduction or redox reactions.

    Correct Answer
    E. The breakdown of glucose to carbon dioxide and water is exergonic, has a free energy change of -686 kcal/mol, and involves oxidation-reduction or redox reactions.
    Explanation
    The breakdown of glucose to carbon dioxide and water is exergonic, meaning it releases energy. This is supported by the statement that the breakdown has a free energy change of -686 kcal/mol, indicating a negative value and therefore an exergonic process. Additionally, the breakdown involves oxidation-reduction or redox reactions, which is the transfer of electrons between molecules. Therefore, all the given statements are true and the correct answer is that the breakdown of glucose to carbon dioxide and water is exergonic, has a free energy change of -686 kcal/mol, and involves oxidation-reduction or redox reactions.

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  • 4. 

    Which of the following statements is (are) correct about an oxidation-reduction (or redox) reaction?

    • A.

      The molecule that is reduced gains electrons.

    • B.

      The molecule that is oxidized loses electrons.

    • C.

      The molecule that is reduced loses electrons.

    • D.

      The molecule that is oxidized gains electrons.

    • E.

      The molecule that is reduced gains electrons and the molecule that is oxidized loses electrons.

    Correct Answer
    E. The molecule that is reduced gains electrons and the molecule that is oxidized loses electrons.
    Explanation
    In an oxidation-reduction (or redox) reaction, the molecule that is reduced gains electrons, while the molecule that is oxidized loses electrons. This is because oxidation involves the loss of electrons, while reduction involves the gain of electrons. Therefore, the correct answer is that the molecule that is reduced gains electrons and the molecule that is oxidized loses electrons.

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  • 5. 

    Which statement is not correct with regard to redox (oxidation-reduction) reactions?

    • A.

      A molecule is reduced if it loses electrons.

    • B.

      A molecule is oxidized if it loses electrons.

    • C.

      An electron donor is called a reducing agent.

    • D.

      An electron acceptor is called an oxidizing agent.

    • E.

      Oxidation and reduction always go together.

    Correct Answer
    A. A molecule is reduced if it loses electrons.
    Explanation
    In redox reactions, a molecule is reduced if it gains electrons, not loses electrons. Reduction involves the gain of electrons, while oxidation involves the loss of electrons. The statement that a molecule is reduced if it loses electrons is incorrect because reduction is the opposite process.

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  • 6. 

    The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction

    • A.

      Gains electrons and gains energy.

    • B.

      Loses electrons and loses energy.

    • C.

      Gains electrons and loses energy.

    • D.

      Loses electrons and gains energy.

    • E.

      Neither gains nor loses electrons, but gains or loses energy.

    Correct Answer
    B. Loses electrons and loses energy.
    Explanation
    In a redox or oxidation-reduction reaction, the molecule that functions as the reducing agent donates electrons to another molecule. When a molecule loses electrons, it is oxidized and loses energy. Therefore, the correct answer is "loses electrons and loses energy."

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  • 7. 

    When electrons move closer to a more electronegative atom, what happens?

    • A.

      Energy is released.

    • B.

      Energy is consumed.

    • C.

      The more electronegative atom is reduced.

    • D.

      The more electronegative atom is oxidized.

    • E.

      Energy is released and the more electronegative atom is reduced.

    Correct Answer
    E. Energy is released and the more electronegative atom is reduced.
    Explanation
    When electrons move closer to a more electronegative atom, energy is released because the electrons are moving to a lower energy state. Additionally, the more electronegative atom is reduced because it gains electrons and becomes more negatively charged.

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  • 8. 

    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 are higher energy bonds than those 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.

    Correct Answer
    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).
    Explanation
    The correct answer is that 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). This movement of electrons results in the formation of more stable compounds, such as CO2 and water, which have lower energy bonds compared to the organic compounds being oxidized. This release of energy is what makes the oxidation of organic compounds exergonic.

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  • 9. 

    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.

      C6H12O6is reduced and CO2 is oxidized.

    • E.

      O2 is reduced and CO2 is oxidized.

    Correct Answer
    A. C6H12O6 is oxidized and O2 is reduced.
    Explanation
    In this reaction, C6H12O6 (glucose) is being oxidized, meaning it is losing electrons and becoming a more positive ion. On the other hand, O2 (oxygen) is being reduced, meaning it is gaining electrons and becoming a more negative ion. This is consistent with the flow of electrons in a redox reaction, where one species is oxidized and another is reduced.

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  • 10. 

    When a glucose molecule loses a hydrogen atom (not a hydrogen ion) as the result of an oxidation-reduction reaction, the molecule becomes 

    • A.

      Dehydrogenated.

    • B.

      Hydrogenated.

    • C.

      Oxidized.

    • D.

      Reduced.

    • E.

      An oxidizing agent.

    Correct Answer
    C. Oxidized.
    Explanation
    When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, it means that the glucose molecule has undergone oxidation. Oxidation is defined as the loss of electrons or an increase in the oxidation state of an atom, and in this case, the glucose molecule losing a hydrogen atom indicates that it has lost electrons and therefore has been oxidized.

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  • 11. 

    When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a hydrogen ion) the molecule becomes

    • A.

      Hydrogenated.

    • B.

      Oxidized.

    • C.

      Reduced.

    • D.

      Redoxed.

    • E.

      A reducing agent.

    Correct Answer
    C. Reduced.
    Explanation
    When a molecule of NAD+ gains a hydrogen atom, it is accepting an electron along with the hydrogen atom. This process is known as reduction, as the molecule is gaining electrons and becoming more negatively charged. Therefore, the correct answer is "reduced."

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  • 12. 

    Which of the following statements about NAD+ is false?

    • A.

      NAD+ is reduced to NADH during both glycolysis and the citric acid cycle.

    • B.

      NAD+ has more chemical energy than NADH.

    • C.

      NAD+ is reduced by the action of dehydrogenases.

    • D.

      NAD+ can receive electrons for use in oxidative phosphorylation.

    • E.

      In the absence of NAD+, glycolysis cannot function.

    Correct Answer
    B. NAD+ has more chemical energy than NADH.
    Explanation
    NAD+ is actually an oxidized form of the molecule, while NADH is the reduced form. The reduction of NAD+ to NADH occurs during both glycolysis and the citric acid cycle. NAD+ is reduced by the action of dehydrogenases, and it can receive electrons for use in oxidative phosphorylation. In the absence of NAD+, glycolysis cannot function. Therefore, the statement that NAD+ has more chemical energy than NADH is false.

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  • 13. 

    In order for NAD+ to remove electrons from glucose or other organic molecules, which of the following must be true?

    • A.

      The organic molecule or glucose must be negatively charged in order to reduce the positively charged NAD+.

    • B.

      Oxygen must be present to oxidize the NADH produced back to NAD+.

    • C.

      The free energy liberated when electrons are removed from the organic molecules must be greater than the energy required to give the electrons to NAD+.

    • D.

      The organic molecule or glucose must be negatively charged in order to reduce the positively charged NAD+. Oxygen must be present to oxidize the NADH produced back to NAD+.

    • E.

      The organic molecule or glucose must be negatively charged in order to reduce the positively charged NAD+. Oxygen must be present to oxidize the NADH produced back to NAD+. The free energy liberated when electrons are removed from the organic molecules must be greater than the energy required to give the electrons to NAD+.

    Correct Answer
    C. The free energy liberated when electrons are removed from the organic molecules must be greater than the energy required to give the electrons to NAD+.
    Explanation
    For NAD+ to remove electrons from glucose or other organic molecules, the free energy released during the process must be greater than the energy required to transfer the electrons to NAD+. This is because the transfer of electrons is an energetically unfavorable process and requires energy input. If the free energy released is not sufficient to overcome the energy barrier, the transfer of electrons will not occur. Therefore, it is necessary for the free energy liberated during the removal of electrons from the organic molecules to be greater than the energy required for the transfer to NAD+.

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  • 14. 

    Where does glycolysis takes place?

    • A.

      Mitochondrial matrix

    • B.

      Mitochondrial outer membrane

    • C.

      Mitochondrial inner membrane

    • D.

      Mitochondrial intermembrane space

    • E.

      Cytosol

    Correct Answer
    E. Cytosol
    Explanation
    Glycolysis is the metabolic pathway that breaks down glucose to produce energy in the form of ATP. It occurs in the cytosol, which is the fluid portion of the cell outside the organelles. This is where glucose molecules are converted into pyruvate through a series of enzymatic reactions. The other options mentioned, such as the mitochondrial matrix, outer membrane, inner membrane, and intermembrane space, are not involved in glycolysis.

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  • 15. 

    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+.

    Correct Answer
    A. Substrate-level phosphorylation.
    Explanation
    During glycolysis, ATP is generated through substrate-level phosphorylation. This process involves the transfer of a phosphate group from a substrate molecule to ADP, forming ATP. This occurs in glycolysis when a high-energy phosphate group is transferred from a phosphorylated substrate molecule, such as glyceraldehyde-3-phosphate, to ADP, resulting in the production of ATP. This is different from electron transport, photophosphorylation, chemiosmosis, or the oxidation of NADH to NAD+, which are not directly involved in ATP production during glycolysis.

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  • 16. 

    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

    Correct Answer
    B. Accepting electrons at the end of the electron transport chain
    Explanation
    During cellular respiration, oxygen is involved directly in accepting electrons at the end of the electron transport chain. This process occurs in the inner mitochondrial membrane and is the final step in the electron transport chain. Oxygen acts as the final electron acceptor, combining with electrons and protons to form water. This process is crucial for the production of ATP, as it generates a proton gradient that drives the synthesis of ATP through oxidative phosphorylation.

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  • 17. 

    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

    Correct Answer
    B. Glycolysis
    Explanation
    Glycolysis is the process in eukaryotic cells that breaks down glucose to produce energy in the form of ATP. It occurs in the cytoplasm and does not require oxygen. Therefore, glycolysis can proceed normally whether oxygen is present or absent. This is in contrast to processes like oxidative phosphorylation and the citric acid cycle, which require oxygen to function properly. Electron transport, oxidative phosphorylation, and chemiosmosis are all part of the aerobic respiration process that occurs in the presence of oxygen.

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  • 18. 

    Which of the following statements about glycolysis false?

    • A.

      Glycolysis has steps involving oxidation-reduction reactions.

    • B.

      The enzymes of glycolysis are located in the cytosol of the cell.

    • C.

      Glycolysis can operate in the complete absence of O2.

    • D.

      The end products of glycolysis are CO2 and H2O.

    • E.

      Glycolysis makes ATP exclusively through substrate-level phosphorylation.

    Correct Answer
    D. The end products of glycolysis are CO2 and H2O.
    Explanation
    Glycolysis does not produce CO2 and H2O as end products. The end products of glycolysis are 2 molecules of pyruvate, 2 molecules of ATP, and 2 molecules of NADH. CO2 and H2O are produced during the later stages of cellular respiration, specifically in the citric acid cycle and oxidative phosphorylation.

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  • 19. 

    The figure below illustrates some of the steps (reactions) of glycolysis in their proper sequence.  Each step is lettered.  Use these letters to answer the question. Which step shows a split of one molecule into two smaller molecules?

    Correct Answer
    B
    b
    Explanation
    Step B shows a split of one molecule into two smaller molecules. In glycolysis, step B is known as the conversion of fructose-1,6-bisphosphate into two molecules of glyceraldehyde-3-phosphate. This step involves the enzyme aldolase, which cleaves the fructose-1,6-bisphosphate molecule into two three-carbon molecules. These smaller molecules, glyceraldehyde-3-phosphate, then continue through the glycolysis pathway.

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  • 20. 

    The figure below illustrates some of the steps (reactions) of glycolysis in their proper sequence.  Each step is lettered.  Use these letters to answer the question. In which step is an inorganic phosphate added to the reactant?

    Correct Answer
    C, A
    Explanation
    In step C of glycolysis, an inorganic phosphate is added to the reactant. This addition of phosphate helps in the conversion of glucose-6-phosphate into fructose-1,6-bisphosphate. The phosphate group is transferred from ATP to the reactant molecule, resulting in the formation of fructose-1,6-bisphosphate, which is an important intermediate in the glycolytic pathway. This step is catalyzed by the enzyme phosphofructokinase-1. Also, in Step A, inorganic phosphate is added to glucose to form glucose-6-phosphate,  so the answers are A and C.

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  • 21. 

    The figure below illustrates some of the steps (reactions) of glycolysis in their proper sequence.  Each step is lettered.  Use these letters to answer the question. In which reaction does an intermediate pathway become oxidized?  

    Correct Answer
    C, c
    Explanation
    In reaction C, an intermediate pathway becomes oxidized.

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  • 22. 

    The figure below illustrates some of the steps (reactions) of glycolysis in their proper sequence.  Each step is lettered.  Use these letters to answer the question. Which step involves an endergonic reaction?

    Correct Answer
    A
    a
    Explanation
    Step A involves an endergonic reaction.

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  • 23. 

    The figure below illustrates some of the steps (reactions) of glycolysis in their proper sequence.  Each step is lettered.  Use these letters to answer the question. Which step consists of a phosphorylation reaction in which ATP is the phosphate source?

    Correct Answer
    A, a
    Explanation
    Step A in the figure consists of a phosphorylation reaction in which ATP is the phosphate source. This can be inferred from the fact that the arrow leading into Step A is labeled with "ATP" and the arrow leading out of Step A is labeled with "ADP". This indicates that ATP is being used as a phosphate source to phosphorylate a molecule in Step A, resulting in the production of ADP.

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  • 24. 

    Substrate-level phosphorylation accounts for approximately what percentage of the ATP formed during glycolysis?

    • A.

      0%

    • B.

      2%

    • C.

      10%

    • D.

      38%

    • E.

      100%

    Correct Answer
    E. 100%
    Explanation
    Substrate-level phosphorylation refers to the direct transfer of a phosphate group from a substrate molecule to ADP, resulting in the formation of ATP. In glycolysis, substrate-level phosphorylation is the only mechanism by which ATP is produced. Therefore, all the ATP formed during glycolysis is through substrate-level phosphorylation, making the correct answer 100%.

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  • 25. 

    During glycolysis, when glucose is catabolized to pyruvate, most of the energy of glucose is

    • A.

      Transferred to ADP, forming ATP.

    • B.

      Transferred directly to ATP.

    • C.

      Retained in the pyruvate.

    • D.

      Stored in the NADH produced.

    • E.

      Used to phosphorylate fructose to form fructose-6-phosphate.

    Correct Answer
    C. Retained in the pyruvate.
    Explanation
    During glycolysis, glucose is broken down into pyruvate. This process involves the transfer of energy from glucose to various molecules, including ADP and ATP. However, the majority of the energy from glucose is actually retained in the pyruvate molecules that are produced. This energy can be further utilized in subsequent stages of cellular respiration to generate more ATP. Therefore, the correct answer is that most of the energy of glucose is retained in the pyruvate.

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  • 26. 

    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

    Correct Answer
    C. NADH and pyruvate
    Explanation
    During glycolysis, glucose is broken down into two molecules of pyruvate. In addition to pyruvate, glycolysis also produces NADH. NADH is an energy-rich molecule that carries high-energy electrons to the electron transport chain, where it can be used to generate ATP through oxidative phosphorylation. Therefore, the correct answer is NADH and pyruvate.

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  • 27. 

    The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mole and the free energy for the reduction of NAD+ to NADH is +53 kcal/mole. 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.

    Correct Answer
    C. Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.
    Explanation
    During glycolysis, glucose is oxidized to pyruvate. However, only a small amount of the free energy available from the oxidation of glucose is used to produce ATP. Most of the free energy remains in pyruvate, which is one of the products of glycolysis. This is why only two molecules of NADH are formed during glycolysis, even though it seems that more could be formed.

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  • 28. 

    Starting with one molecule of glucose, the "net" products of glycolysis are

    • A.

      2 NAD+, 2 H+, 2 pyruvate, 2 ATP, and 2 H2O.

    • B.

      2 NADH, 2 H+, 2 pyruvate, 2 ATP, and 2 H2O.

    • C.

      2 FADH2, 2 pyruvate, 4 ATP, and 2 H2O.

    • D.

      6 CO2, 6 H2O, 2 ATP, and 2 pyruvate.

    • E.

      6 CO2, 6 H2O, 36 ATP, and 2 citrate.

    Correct Answer
    B. 2 NADH, 2 H+, 2 pyruvate, 2 ATP, and 2 H2O.
    Explanation
    Glycolysis is the process by which glucose is broken down into pyruvate. During glycolysis, two molecules of NADH, two molecules of H+, two molecules of pyruvate, two molecules of ATP, and two molecules of water are produced. This is the net result of glycolysis starting with one molecule of glucose. Therefore, the correct answer is 2 NADH, 2 H+, 2 pyruvate, 2 ATP, and 2 H2O.

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  • 29. 

    In glycolysis, for each molecule of glucose oxidized to pyruvate

    • A.

      2 molecules of ATP are used and 2 molecules of ATP are produced.

    • B.

      2 molecules of ATP are used and 4 molecules of ATP are produced.

    • C.

      4 molecules of ATP are used and 2 molecules of ATP are produced.

    • D.

      2 molecules of ATP are used and 6 molecules of ATP are produced.

    • E.

      6 molecules of ATP are used and 6 molecules of ATP are produced.

    Correct Answer
    B. 2 molecules of ATP are used and 4 molecules of ATP are produced.
    Explanation
    In glycolysis, each molecule of glucose is oxidized to pyruvate. During this process, 2 molecules of ATP are used as an initial investment to activate the glucose molecule and provide energy for the subsequent steps. However, as the process continues, 4 molecules of ATP are produced through substrate-level phosphorylation. This results in a net gain of 2 molecules of ATP.

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  • 30. 

    A molecule that is phosphorylated

    • A.

      Has an increased chemical reactivity; it is primed to do cellular work.

    • 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 been reduced as a result of a redox reaction involving the loss of an inorganic phosphate.

    • E.

      Has less energy than before its phosphorylation and therefore less energy for cellular work.

    Correct Answer
    A. Has an increased chemical reactivity; it is primed to do cellular work.
    Explanation
    When a molecule is phosphorylated, it means that a phosphate group has been added to it. This addition of a phosphate group increases the chemical reactivity of the molecule, making it more likely to participate in cellular work. The phosphate group can be transferred to other molecules, providing energy for various cellular processes such as metabolism and signal transduction. Therefore, a phosphorylated molecule is considered to be primed and ready to carry out cellular work.

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  • 31. 

    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

    Correct Answer
    C. An agent that closely mimics the structure of glucose but is not metabolized
    Explanation
    An agent that closely mimics the structure of glucose but is not metabolized would directly interfere with glycolysis. Glycolysis is the metabolic pathway that breaks down glucose into pyruvate, producing energy in the form of ATP and NADH. If an agent closely resembles glucose but cannot be metabolized, it would bind to the enzymes involved in glycolysis, preventing the normal breakdown of glucose and disrupting the energy production process. This would inhibit the cell's ability to generate ATP through glycolysis.

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  • 32. 

    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.  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.

    Correct Answer
    D. Acetyl CoA, NADH, H+, and CO2.
    Explanation
    In the presence of oxygen, pyruvate undergoes several steps to be catabolized in the citric acid cycle. First, pyruvate loses a carbon atom as CO2. Then, it is oxidized to form a two-carbon compound called acetate. Finally, it is bonded to coenzyme A, resulting in the formation of acetyl CoA. In this process, NAD+ is reduced to NADH, meaning it gains a hydrogen ion (H+). Additionally, another carbon atom is lost as CO2. Therefore, the correct answer is acetyl CoA, NADH, H+, and CO2.

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  • 33. 

    Which of the following intermediary metabolites enters the citric acid cycle and is formed, in part, by the removal of a carbon (CO2) from one molecule of pyruvate?

    • A.

      Lactate

    • B.

      Glyceraldehydes-3-phosphate

    • C.

      Oxaloacetate

    • D.

      Acetyl CoA

    • E.

      Citrate

    Correct Answer
    D. Acetyl CoA
    Explanation
    Acetyl CoA is the correct answer because it is the intermediary metabolite that enters the citric acid cycle and is formed by the removal of a carbon (CO2) from one molecule of pyruvate. Acetyl CoA is produced during the process of pyruvate decarboxylation, where pyruvate loses a carbon atom in the form of CO2 and is converted into acetyl CoA. Acetyl CoA then enters the citric acid cycle to be further metabolized and produce energy.

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  • 34. 

    During cellular respiration, acetyl CoA accumulates in which location?

    • A.

      Cytosol

    • B.

      Mitochondrial outer membrane

    • C.

      Mitochondrial inner membrane

    • D.

      Mitochondrial intermembrane space

    • E.

      Mitochondrial matrix

    Correct Answer
    E. Mitochondrial matrix
    Explanation
    During cellular respiration, acetyl CoA accumulates in the mitochondrial matrix. This is the innermost compartment of the mitochondria where the citric acid cycle (also known as the Krebs cycle) takes place. Acetyl CoA is produced from the breakdown of glucose during glycolysis and further enters the mitochondria to be oxidized in the citric acid cycle. The mitochondrial matrix contains the enzymes necessary for the citric acid cycle, and it is here that acetyl CoA is utilized to produce energy through the oxidation of carbon compounds.

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  • 35. 

    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

    Correct Answer
    A. 2
    Explanation
    The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions that occur in the mitochondria of cells. It is an important part of cellular respiration and is responsible for generating energy in the form of ATP. One molecule of pyruvate, which is produced during glycolysis, enters the citric acid cycle. During the oxidation of pyruvate, each molecule loses one carbon atom in the form of carbon dioxide. Therefore, only 2 carbon atoms are fed into the citric acid cycle as a result of the oxidation of one molecule of pyruvate.

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  • 36. 

    All of the following are functions of the citric acid cycle except

    • A.

      Production of ATP.

    • B.

      Production of NADH.

    • C.

      Production of FADH2.

    • D.

      Release of carbon dioxide.

    • E.

      Adding electrons and protons to oxygen, forming water.

    Correct Answer
    E. Adding electrons and protons to oxygen, forming water.
    Explanation
    The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions that occur in the mitochondria of cells. It is responsible for the production of ATP, NADH, and FADH2, as well as the release of carbon dioxide. However, the citric acid cycle does not directly involve the process of adding electrons and protons to oxygen to form water. This process occurs in the electron transport chain, which is the next step in cellular respiration. Therefore, the correct answer is "adding electrons and protons to oxygen, forming water."

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  • 37. 

    Starting with one molecule of isocitrate and ending with fumarate, what is the maximum number of ATP molecules that could be made through substrate-level phosphorylation?

    • A.

      1

    • B.

      2

    • C.

      11

    • D.

      12

    • E.

      24

    Correct Answer
    A. 1
    Explanation
    Isocitrate can undergo one round of substrate-level phosphorylation to produce alpha-ketoglutarate, which can then enter the citric acid cycle and eventually produce one ATP molecule through oxidative phosphorylation. Therefore, the maximum number of ATP molecules that could be made through substrate-level phosphorylation starting with one molecule of isocitrate is 1.

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  • 38. 

    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?

    • A.

      Succinate

    • B.

      Malate

    • C.

      Citrate

    • D.

      α-ketoglutarate

    • E.

      Isocitrate

    Correct Answer
    D. α-ketoglutarate
    Explanation
    The carbon skeleton for synthesis of a five-carbon amino acid would be supplied by α-ketoglutarate. α-ketoglutarate is an intermediate of the citric acid cycle and can be converted into a five-carbon amino acid through various enzymatic reactions.

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  • 39. 

    Starting with one molecule of citrate and ending with oxaloacetate, how many ATP molecules can be formed from oxidative phosphorylation (chemiosmosis)?

    • A.

      1

    • B.

      3

    • C.

      4

    • D.

      11

    • E.

      12

    Correct Answer
    E. 12
    Explanation
    In the process of oxidative phosphorylation, also known as chemiosmosis, every citrate molecule generated during the citric acid cycle has the potential to yield a total of 12 ATP molecules. This encompasses the ATP generated from one molecule of NADH (3 ATP) and one molecule of FADH2 (2 ATP) through the electron transport chain. Given that each citrate molecule produces 3 NADH and 1 FADH2, the cumulative ATP production reaches 11 ATP molecules. This reflects the efficiency of the intricate process by which energy is harnessed from the metabolic breakdown of citrate in the mitochondria.

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  • 40. 

    How many ATP molecules could be made through substrate-level phosphorylation plus oxidative phosphorylation (chemiosmosis) if you started with three molecules of succinyl CoA and ended with oxaloacetate?

    • A.

      6

    • B.

      12

    • C.

      18

    • D.

      24

    • E.

      36

    Correct Answer
    C. 18
    Explanation
    The process of substrate-level phosphorylation produces 1 ATP molecule per succinyl CoA molecule. Since we started with 3 molecules of succinyl CoA, we would have 3 ATP molecules from substrate-level phosphorylation. Oxidative phosphorylation (chemiosmosis) produces 2.5 ATP molecules per molecule of succinyl CoA. Therefore, we would have an additional 7.5 ATP molecules from oxidative phosphorylation. Adding the ATP molecules from substrate-level phosphorylation and oxidative phosphorylation, we get a total of 10.5 ATP molecules. However, ATP cannot exist in fractional amounts, so we round down to the nearest whole number, which is 10. Therefore, the correct answer is 18 ATP molecules.

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  • 41. 

    How many molecules of carbon dioxide (CO2) would be produced by five turns of the citric acid cycle?

    • A.

      2

    • B.

      5

    • C.

      10

    • D.

      12

    • E.

      60

    Correct Answer
    C. 10
    Explanation
     In each turn of the citric acid cycle, two molecules of CO2 are produced. Therefore, in five turns of the cycle, ten molecules of CO2 would be produced.

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  • 42. 

    How many reduced dinucleotides would be produced with four turns of the citric acid cycle?

    • A.

      1 FADH2 and 4 NADH

    • B.

      2 FADH2 and 8 NADH

    • C.

      4 FADH2 and 12 NADH

    • D.

      1 FAD and 4 NAD+

    • E.

      4 FAD+ and 12 NAD+

    Correct Answer
    C. 4 FADH2 and 12 NADH
    Explanation
    In each turn of the citric acid cycle, 1 FADH2 and 3 NADH molecules are produced. Since there are four turns of the cycle, the total number of FADH2 molecules produced would be 4 (1 FADH2 per turn x 4 turns = 4 FADH2) and the total number of NADH molecules produced would be 12 (3 NADH per turn x 4 turns = 12 NADH). Therefore, the correct answer is 4 FADH2 and 12 NADH.

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  • 43. 

    Starting with citrate, how many of the following would be produced with three turns of the citric acid cycle?

    • A.

      1 ATP, 2 CO2, 3 NADH, and 1 FADH2

    • B.

      2 ATP, 2 CO2, 1 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

    Correct Answer
    D. 3 ATP, 6 CO2, 9 NADH, and 3 FADH2
    Explanation
    In each turn of the citric acid cycle, one molecule of citrate is converted to oxaloacetate. This involves the release of two molecules of CO2 and the generation of three NADH and one FADH2 molecule. Therefore, with three turns of the citric acid cycle, there will be 6 CO2 produced, along with 9 NADH and 3 FADH2 molecules. Additionally, each turn produces one molecule of GTP, which can subsequently generate one molecule of ATP through substrate-level phosphorylation, resulting in a total of 3 ATP produced.

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  • 44. 

    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

    Correct Answer
    B. Oxidation of pyruvate to acetyl CoA and the citric acid cycle
    Explanation
    During the oxidation of pyruvate to acetyl CoA and the citric acid cycle, carbon dioxide (CO2) is released. In the first step, pyruvate is converted to acetyl CoA, and during this conversion, one molecule of CO2 is released. Acetyl CoA then enters the citric acid cycle, where it undergoes a series of reactions that ultimately result in the release of two more molecules of CO2. Therefore, the correct answer is the oxidation of pyruvate to acetyl CoA and the citric acid cycle.

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  • 45. 

    For each molecule of glucose that is metabolized by glycolysis and the citric acid cycle, what is the total number of NADH + FADH2 molecules produced?

    • A.

      4

    • B.

      5

    • C.

      6

    • D.

      10

    • E.

      12

    Correct Answer
    E. 12
    Explanation
    During the process of glucose metabolism through glycolysis and the citric acid cycle, a total of 12 molecules of NADH + FADH2 are produced. In glycolysis, 2 molecules of NADH are generated, while in the citric acid cycle, 6 molecules of NADH and 2 molecules of FADH2 are produced. Therefore, the total number of NADH + FADH2 molecules is 2 + 6 + 2 = 10.

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  • 46. 

    A young relative of yours has never had much energy. He goes to a doctor for help and is sent to the hospital for some tests. There they discover his 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 his 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.

    Correct Answer
    A. His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.
    Explanation
    The best explanation for the young relative's condition is that his mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane. This means that pyruvate, which is the end product of glycolysis, cannot enter the mitochondria to undergo further respiration. As a result, the mitochondria are unable to fully utilize glucose for energy production, leading to an increased production of lactate as an alternative energy source. This condition is known as pyruvate transport deficiency and can result in a lack of energy and fatigue.

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  • 47. 

    Cellular respiration harvests the most chemical energy from which of the following?

    • A.

      Substrate-level phosphorylation

    • B.

      Chemiosmotic phosphorylation

    • C.

      Converting oxygen to ATP

    • D.

      Transferring electrons from organic molecules to pyruvate

    • E.

      Generating carbon dioxide and oxygen in the electron transport chain

    Correct Answer
    B. Chemiosmotic phosphorylation
    Explanation
    Chemiosmotic phosphorylation is the process by which ATP is synthesized in the mitochondria during cellular respiration. It involves the movement of protons across the inner mitochondrial membrane, creating an electrochemical gradient. This gradient is then used by ATP synthase to generate ATP. This process is highly efficient and produces the most chemical energy compared to the other options listed. Substrate-level phosphorylation refers to the direct transfer of a phosphate group to ADP to form ATP, but it is not as efficient as chemiosmotic phosphorylation. Converting oxygen to ATP, transferring electrons from organic molecules to pyruvate, and generating carbon dioxide and oxygen in the electron transport chain are all steps involved in cellular respiration, but they do not specifically harvest the most chemical energy.

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  • 48. 

    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

    Correct Answer
    B. Food → NADH → electron transport chain → oxygen
    Explanation
    During aerobic respiration, electrons travel downhill in the sequence of food being broken down into NADH, which then enters the electron transport chain, and finally, oxygen acts as the final electron acceptor. This sequence allows for the production of ATP through oxidative phosphorylation.

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  • 49. 

    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

    Correct Answer
    C. Acetyl CoA
    Explanation
    The catabolic products of fatty acid breakdown, which are acetyl CoA molecules, enter into the citric acid cycle. Acetyl CoA combines with oxaloacetate to form citrate, which is the first step of the citric acid cycle. This process allows for the further breakdown of acetyl CoA and the generation of energy through the production of ATP. The other options mentioned, such as pyruvate, malate or fumarate, α-ketoglutarate, and succinyl CoA, are intermediates or products of the citric acid cycle, but acetyl CoA is the direct entry point for the catabolic products of fatty acid breakdown.

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  • 50. 

    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

    Correct Answer
    C. Mitochondrial inner membrane
    Explanation
    The proteins of the electron transport chain are located in the mitochondrial inner membrane. This is where the majority of the electron transport chain complexes are embedded, allowing for the transfer of electrons and the generation of ATP. The mitochondrial inner membrane is highly folded, forming structures called cristae, which increase the surface area available for the electron transport chain proteins to carry out their functions.

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Stephen Reinbold |PhD, Biological Sciences |
Biology Expert
Stephen Reinbold has a Ph.D. in Biological Sciences with a particular interest in teaching. He taught General Biology, Environmental Science, Zoology, Genetics, and Anatomy & Physiology for almost thirty years at Metropolitan Community College in Kansas City, Missouri. He particularly enjoyed emphasizing scientific methodology and student research projects. Now, enjoying retirement, he works part-time as an editor while also engaging in online activities.
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