Cellular Energetics Practice Quiz

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Cellular Energetics Practice Quiz - Quiz

Quiz over AP Biology Unit 3: Cellular Energetics (Cell Respiration and Photosynthesis)


Questions and Answers
  • 1. 

    Which of the following describe(s) some aspect of metabolism?

    • A.

      Synthesis of macromoleculessynthesis of macromolecules

    • B.

      Breakdown of macromolecules

    • C.

      Control of enzyme activity

    • D.

      A and B only

    • E.

      A, B, and C

    Correct Answer
    E. A, B, and C
    Explanation
    The correct answer is A, B, and C. This is because metabolism involves the synthesis of macromolecules, the breakdown of macromolecules, and the control of enzyme activity. These processes are essential for the functioning and regulation of cells and organisms.

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  • 2. 

    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

    Correct Answer
    E. Catabolism
    Explanation
    Catabolism is the correct answer because it refers to the cellular process of breaking down large molecules into smaller ones. This process involves the release of energy and the breakdown of complex molecules such as proteins, carbohydrates, and fats into simpler molecules that can be used for energy production or other cellular functions.

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  • 3. 

    Which of the following statements correctly describe(s) catabolic pathways?

    • A.

      They do not depend on enzymes.

    • B.

      They consume energy to build up polymers from monomers.

    • C.

      They release energy as they degrade polymers to monomers.

    • D.

      They lead to the synthesis of catabolic compounds.

    • E.

      Both A and B

    Correct Answer
    C. They release energy as they degrade polymers to monomers.
    Explanation
    Catabolic pathways involve the breakdown of larger molecules into smaller ones, such as polymers being broken down into monomers. This process releases energy, which is a characteristic feature of catabolic pathways. The statement that they do not depend on enzymes is incorrect, as enzymes are essential for catalyzing the reactions involved in catabolism. The statement that they consume energy to build up polymers from monomers is also incorrect, as this is a characteristic of anabolic pathways, which are the opposite of catabolic pathways. Therefore, the correct statement is that catabolic pathways release energy as they degrade polymers to monomers.

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  • 4. 

    Which of the following is (are) true for anabolic pathways?

    • A.

      They do not depend on enzymes.

    • B.

      They are highly regulated sequences of chemical reactions.

    • C.

      They consume energy to build up polymers from monomers.

    • D.

      They release energy as they degrade polymers to monomers.

    • E.

      Both B and C

    Correct Answer
    E. Both B and C
    Explanation
    Anabolic pathways are highly regulated sequences of chemical reactions that consume energy to build up polymers from monomers. This means that both statement B and statement C are true for anabolic pathways. Statement A is false because anabolic pathways do depend on enzymes to catalyze the chemical reactions involved.

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  • 5. 

    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. These pathways involve the breakdown of complex molecules to release stored energy. They are responsible for breaking down molecules such as carbohydrates, fats, and proteins into smaller units, releasing energy in the process. Catabolic pathways play a crucial role in cellular respiration and provide the energy needed for various cellular activities.

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  • 6. 

    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 refers to the metabolic pathway in which glucose is broken down into carbon dioxide and water. This process occurs in the mitochondria of cells and is important for the production of ATP, the energy currency of the cell. Glycolysis, fermentation, citric acid cycle, and oxidative phosphorylation are all components or stages of cellular respiration.

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  • 7. 

      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.

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

    • D.

      Only A and B are correct.

    • E.

      A, B, and C are correct.

    Correct Answer
    E. A, B, and C are correct.
  • 8. 

    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.

      Both A and B are correct.

    Correct Answer
    E. Both A and B are correct.
    Explanation
    In an oxidation-reduction (redox) reaction, one molecule is oxidized and another is reduced. The molecule that is reduced gains electrons, which causes a decrease in its oxidation state. On the other hand, the molecule that is oxidized loses electrons, resulting in an increase in its oxidation state. Therefore, both statements A and B are correct.

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  • 9. 

    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 addition of electrons to a molecule, which leads to a decrease in its oxidation state. On the other hand, oxidation occurs when a molecule loses electrons, resulting in an increase in its oxidation state. Therefore, the statement "A molecule is reduced if it loses electrons" is not correct in the context of redox reactions.

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  • 10. 

    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 reducing agent is the molecule that donates electrons. When a molecule donates electrons, it loses them, resulting in a loss of energy. Therefore, the correct answer is "loses electrons and loses energy."

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  • 11. 

    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 movement of electrons from atoms with a lower affinity for electrons to atoms with a higher affinity for electrons releases energy. This is because the transfer of electrons allows the atoms to achieve a more stable and energetically favorable state. In the case of the oxidation of organic compounds, the carbon atoms, which have a lower affinity for electrons, transfer their electrons to oxygen atoms, which have a higher affinity for electrons. This transfer of electrons releases energy, making the oxidation process exergonic.

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  • 12. 

    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.

    Correct Answer
    A. C6H12O6 is oxidized and O2 is reduced.
    Explanation
    In this reaction, glucose (C6H12O6) is oxidized, meaning it loses electrons, while oxygen (O2) is reduced, meaning it gains electrons. This is evident from the fact that glucose is converted into carbon dioxide (CO2) and water (H2O), and oxygen is converted into water. The production of energy also indicates that a redox reaction is occurring, as the transfer of electrons releases energy. Therefore, the correct answer is that C6H12O6 is oxidized and O2 is reduced.

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  • 13. 

    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 the loss of electrons or an increase in the oxidation state of an atom or molecule. In this case, the glucose molecule loses a hydrogen atom, which means it has lost an electron. Therefore, the correct answer is oxidized.

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  • 14. 

    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 the oxidized form of NADH, meaning it has less chemical energy. During glycolysis and the citric acid cycle, NAD+ is reduced to NADH by accepting electrons. NAD+ is reduced by dehydrogenases, and it can transfer the electrons it receives to the electron transport chain for oxidative phosphorylation. In the absence of NAD+, glycolysis cannot proceed, as NAD+ is required as an electron acceptor. Therefore, the statement "NAD+ has more chemical energy than NADH" is false.

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  • 15. 

    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.

      A and B are both correct.

    • E.

      A, B, and C are all correct.

    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 this process must be greater than the energy required to transfer the electrons to NAD+. This ensures that the reaction is thermodynamically favorable and can proceed spontaneously. A negative charge on the organic molecule or glucose is not necessary for this process, and the presence of oxygen is not directly related to the removal of electrons from the organic molecules. Therefore, options A and B are incorrect, and the correct answer is C.

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  • 16. 

    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 a metabolic pathway that occurs in the cytosol of cells. It is the first step in cellular respiration and involves the breakdown of glucose into pyruvate. The cytosol is the fluid portion of the cytoplasm, where many cellular processes take place. Therefore, glycolysis occurs in the cytosol.

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  • 17. 

    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. However, most of the energy from glucose is retained in the pyruvate molecules. This is because glycolysis is an anaerobic process, meaning it does not require oxygen. As a result, the pyruvate molecules produced during glycolysis still contain a significant amount of energy that can be further utilized in other metabolic pathways, such as the citric acid cycle and oxidative phosphorylation, to produce more ATP.

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  • 18. 

    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.

      . A and B only

    • E.

      A, B and C

    Correct Answer
    B. It provides energy coupling between exergonic and endergonic reactions.
    Explanation
    ATP is an important molecule in metabolism because it provides energy coupling between exergonic and endergonic reactions. This means that ATP can transfer energy from exergonic reactions (reactions that release energy) to endergonic reactions (reactions that require energy). By transferring a phosphate group to another molecule, ATP can provide the necessary energy for the endergonic reaction to occur. This process allows cells to efficiently use and transfer energy, making ATP a crucial molecule in metabolic processes.

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  • 19. 

    The hydrolysis of ATP to ADP and inorganic phosphate (ATP + H2O --> ADP + Pi )

    • A.

      Has a G of about -7 kcal/mol under standard conditions.

    • B.

      Involves hydrolysis of a terminal phosphate bond of ATP.

    • C.

      Can occur spontaneously under appropriate conditions.

    • D.

      Only A and B are correct.

    • E.

      A, B, and C are correct.

    Correct Answer
    E. A, B, and C are correct.
    Explanation
    The hydrolysis of ATP to ADP and inorganic phosphate (ATP + H2O --> ADP + Pi) has a G of about -7 kcal/mol under standard conditions. This indicates that the reaction is exergonic, meaning it releases energy. The reaction involves the hydrolysis of a terminal phosphate bond of ATP, which is the high-energy bond that stores energy. Lastly, the hydrolysis of ATP can occur spontaneously under appropriate conditions, meaning it can happen without the input of additional energy. Therefore, all three statements A, B, and C are correct.

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  • 20. 

    When 10,000 molecules of ATP are hydrolyzed to ADP and Pi in a test tube, about twice as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation?

    • A.

      Cells are open systems, but a test tube is a closed system.

    • B.

      Cells are less efficient at heat production than nonliving systems.

    • C.

      The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test tube.

    • D.

      The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes.

    • E.

      Cells convert some of the energy of ATP hydrolysis into other forms of energy besides heat.

    Correct Answer
    E. Cells convert some of the energy of ATP hydrolysis into other forms of energy besides heat.
    Explanation
    When ATP is hydrolyzed to ADP and Pi in a cell, some of the energy released is used for cellular processes other than heat production. This is because cells are highly organized and have specific mechanisms to utilize the energy from ATP hydrolysis for various functions such as muscle contraction, active transport, and synthesis of macromolecules. In contrast, in a test tube, where there is no cellular machinery, all the energy released from ATP hydrolysis is converted into heat. Therefore, the observation that cells release less heat than a test tube when hydrolyzing the same amount of ATP suggests that cells convert some of the energy into other forms of energy besides heat.

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  • 21. 

    ATP generally energizes a cellular process by

    • A.

      Releasing heat upon hydrolysis.

    • B.

      Acting as a catalyst.

    • C.

      Coupling free energy released by ATP hydrolysis to free energy needed by other reactions.

    • D.

      Breaking a high-energy bond.

    • E.

      Binding directly to the substrate(s) of the enzyme.

    Correct Answer
    C. Coupling free energy released by ATP hydrolysis to free energy needed by other reactions.
    Explanation
    ATP is a molecule that stores and transfers energy within cells. It does so by undergoing hydrolysis, where a phosphate group is cleaved from ATP, releasing energy. This energy is then used to power other cellular reactions that require energy. Therefore, the correct answer states that ATP couples the free energy released during its hydrolysis to the free energy needed by other reactions, effectively transferring and providing energy for cellular processes.

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  • 22. 

    What term is used to describe the transfer of free energy from catabolic pathways to anabolic pathways?

    • A.

      Feedback regulationfeedback regulation

    • B.

      Bioenergetics

    • C.

      Energy coupling

    • D.

      Entropy

    • E.

      Cooperativity

    Correct Answer
    C. Energy coupling
    Explanation
    Energy coupling is the term used to describe the transfer of free energy from catabolic pathways (which break down molecules to release energy) to anabolic pathways (which build molecules using energy). This process allows the energy released from catabolism to be used for the synthesis of complex molecules in anabolic reactions. Energy coupling is essential for maintaining the energy balance in cells and ensuring that the energy released from one reaction is efficiently utilized in another reaction.

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  • 23. 

    Which of the following statements is true concerning catabolic pathways?

    • A.

      They combine molecules into more energy-rich molecules.

    • B.

      They are usually coupled with anabolic pathways to which they supply energy in the form of ATP.

    • 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.

    Correct Answer
    B. They are usually coupled with anabolic pathways to which they supply energy in the form of ATP.
    Explanation
    Catabolic pathways involve the breakdown of complex molecules into simpler ones, releasing energy in the process. This energy is often used to fuel anabolic pathways, which build complex molecules from simpler ones. Therefore, catabolic pathways are usually coupled with anabolic pathways, supplying energy in the form of ATP.

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  • 24. 

    Which of the following statements regarding ATP is (are) correct?

    • A.

      ATP serves as a main energy shuttle inside cells.

    • B.

      ATP drives endergonic reactions in the cell by the enzymatic transfer of the phosphate group to specific reactants.

    • C.

      The regeneration of ATP from ADP and phosphate is an endergonic reaction.

    • D.

      A and B only

    • E.

      A, B, and C

    Correct Answer
    E. A, B, and C
    Explanation
    ATP serves as a main energy shuttle inside cells, meaning it transfers energy within the cell to where it is needed. It also drives endergonic reactions in the cell by transferring a phosphate group to specific reactants, providing the necessary energy for these reactions to occur. Additionally, the regeneration of ATP from ADP and phosphate is an endergonic reaction, meaning it requires energy input. Therefore, all statements A, B, and C are correct.

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  • 25. 

    Which of the following statements is (are) 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 the same as the reaction in the absence of the enzyme.

    • C.

      The reaction always goes in the direction toward chemical equilibrium.

    • D.

      A and B only

    • E.

      A, B, and C

    Correct Answer
    A. The reaction is faster than the same reaction in the absence of the enzyme.
    Explanation
    Enzymes are biological catalysts that increase the rate of a reaction by lowering the activation energy required for the reaction to occur. This means that the reaction can proceed at a faster rate in the presence of an enzyme compared to the same reaction in the absence of the enzyme. The statement "The reaction is faster than the same reaction in the absence of the enzyme" accurately describes this characteristic of enzyme-catalyzed reactions. However, the other statements are not true. The free energy change of the reaction can be affected by the enzyme, and the reaction does not always go towards chemical equilibrium.

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  • 26. 

    How can one increase the rate of a chemical reaction?

    • A.

      Increase the activation energy needed.

    • B.

      Cool the reactants.

    • C.

      Decrease the concentration of the reactants.

    • D.

      Add a catalyst.

    • E.

      Increase the entropy of the reactants.

    Correct Answer
    D. Add a catalyst.
    Explanation
    Adding a catalyst can increase the rate of a chemical reaction by providing an alternative pathway with a lower activation energy. A catalyst is a substance that increases the rate of a reaction without being consumed in the process. It works by providing an alternative reaction pathway that has a lower activation energy, allowing more reactant molecules to have sufficient energy to undergo the reaction. This lowers the energy barrier for the reaction, enabling it to proceed at a faster rate. Therefore, adding a catalyst can effectively increase the rate of a chemical reaction.

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  • 27. 

    Sucrose is a disaccharide, composed of the monosaccharides glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase results in

    • A.

      Bringing glucose and fructose together to form sucrose.

    • B.

      The release of water from sucrose as the bond between glucose and fructose is broken.

    • C.

      Breaking the bond between glucose and fructose and forming new bonds from the atoms of water.

    • D.

      Production of water from the sugar as bonds are broken between the glucose monomers.

    • E.

      Utilization of water as a covalent bond is formed between glucose and fructose to form sucrase.

    Correct Answer
    C. Breaking the bond between glucose and fructose and forming new bonds from the atoms of water.
    Explanation
    The correct answer is breaking the bond between glucose and fructose and forming new bonds from the atoms of water. When sucrose is hydrolyzed by the enzyme sucrase, the bond between glucose and fructose is broken, and new bonds are formed using the atoms of water. This results in the separation of glucose and fructose molecules from sucrose.

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  • 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.

      Heat content.

    • E.

      Free-energy content.

    Correct Answer
    B. Activation energy.
    Explanation
    In a chemical reaction, reactants need to overcome a thermodynamic barrier called activation energy in order to form products. Activation energy refers to the minimum amount of energy required for a reaction to occur. It acts as a barrier that reactant molecules must surpass in order to reach the transition state and proceed with the reaction. Once the activation energy is surpassed, the reaction can proceed spontaneously and products can be formed. Therefore, activation energy is the correct answer in this case.

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  • 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 be surmounted.

    • D.

      Starch cannot be hydrolyzed in the presence of so much water.

    • E.

      Starch hydrolysis is nonspontaneous.

    Correct Answer
    C. The activation energy barrier for this reaction cannot be surmounted.
    Explanation
    The correct answer is "the activation energy barrier for this reaction cannot be surmounted." This means that the energy required to break the bonds in starch and convert it into simple sugars is too high to occur at room temperature. Therefore, the starch solution does not readily decompose into a solution of simple sugars.

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  • 30. 

    An enzyme catalyzes a reaction by

    • A.

      Supplying the energy to speed up a reaction.

    • B.

      Lowering the energy of activation of a reaction.

    • C.

      Lowering the G of a reaction.

    • D.

      Changing the equilibrium of a spontaneous reaction.

    • E.

      Increasing the amount of free energy of a reaction.

    Correct Answer
    B. Lowering the energy of activation of a reaction.
    Explanation
    Enzymes are biological catalysts that speed up chemical reactions in cells. They achieve this by lowering the energy of activation, which is the energy required to start a reaction. By lowering this energy barrier, enzymes enable the reactant molecules to reach the transition state more easily, increasing the reaction rate. Enzymes do not supply energy to the reaction or change the equilibrium or amount of free energy of a reaction. Therefore, the correct answer is "lowering the energy of activation of a reaction."

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  • 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

    Correct Answer
    B. -20 kcal/mol
    Explanation
    When the amount of enzyme in a reaction is doubled, it does not affect the value of G, which represents the change in free energy. Therefore, the G for the new reaction will still be -20 kcal/mol.

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  • 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 the products of the catalytic reaction.

    • D.

      Is inhibited by the presence of a coenzyme or a cofactor.

    • E.

      Both A and B

    Correct Answer
    B. Is involved in the catalytic reaction of the enzyme.
    Explanation
    The active site of an enzyme is the region that is involved in the catalytic reaction of the enzyme. This means that it is the specific area where the enzyme binds to its substrate and facilitates the chemical reaction. The active site provides a suitable environment for the reaction to occur, including the necessary amino acid residues and functional groups that participate in the catalysis. The binding of the substrate to the active site allows for the formation of enzyme-substrate complexes and the subsequent conversion of the substrate into product. Therefore, the active site plays a crucial role in the catalytic function of the enzyme.

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  • 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.

    Correct Answer
    D. The binding of the substrate changes the shape of the enzyme's active site.
    Explanation
    The induced fit hypothesis of enzyme catalysis states that the binding of the substrate causes a conformational change in the enzyme's active site. This change in shape allows for a better fit between the enzyme and the substrate, leading to an increase in catalytic activity. This explanation aligns with the answer choice "The binding of the substrate changes the shape of the enzyme's active site."

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  • 34. 

    Many different things can alter enzyme activity. Which of the following underlie all types of enzyme regulation?

    • A.

      Changes in the activation energy of the reaction

    • B.

      Changes in the active site of the enzyme

    • C.

      Changes in the free energy of the reaction

    • D.

      A and B only

    • E.

      A, B, and C

    Correct Answer
    D. A and B only
    Explanation
    Enzyme activity can be altered by changes in the activation energy of the reaction and changes in the active site of the enzyme. Activation energy is the energy required to initiate a chemical reaction, and any changes in this energy can affect the rate at which the reaction occurs. Similarly, changes in the active site of the enzyme, which is the region where the substrate binds and the reaction takes place, can also impact enzyme activity. Therefore, both A and B are factors that underlie all types of enzyme regulation.

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  • 35. 

    As temperature decreases, the rate of an enzyme-catalyzed reaction also decreases. Which of the following explain(s) why this occurs?

    • A.

      Fewer substrates have sufficient energy to get over the activation energy barrier.

    • B.

      Motion in the active site of the enzyme is slowed, thus slowing the catalysis of the enzyme.

    • C.

      The motion of the substrate molecules decreases, allowing them to bind more easily to the active site.

    • D.

      A and B only

    • E.

      A, B, and C

    Correct Answer
    D. A and B only
    Explanation
    The correct answer is A and B only because both options explain why the rate of an enzyme-catalyzed reaction decreases as temperature decreases. Option A states that fewer substrates have sufficient energy to overcome the activation energy barrier, which is a key factor in the rate of a reaction. Option B states that the motion in the active site of the enzyme is slowed, which affects the catalysis of the enzyme. Option C, on the other hand, suggests that the motion of the substrate molecules decreases, allowing them to bind more easily to the active site, but this does not directly explain why the rate of the reaction decreases with decreasing temperature.

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  • 36. 

    What is a nonprotein "helper" of an enzyme molecule called?

    • A.

      Accessory enzyme

    • B.

      Allosteric group

    • C.

      Coenzyme

    • D.

      Functional group

    • E.

      Enzyme activator

    Correct Answer
    C. Coenzyme
    Explanation
    A nonprotein "helper" of an enzyme molecule is called a coenzyme. Coenzymes are small organic molecules that aid in the catalytic function of enzymes. They bind to the enzyme and assist in the transfer of chemical groups or electrons during the enzymatic reaction. Coenzymes are often derived from vitamins and are essential for the proper functioning of many enzymes in the body.

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  • 37. 

    Which of the following is true of enzymes?

    • A.

      Enzymes may require a nonprotein cofactor or ion for catalysis to take place.

    • B.

      Enzyme function is reduced if the three-dimensional structure or conformation of an enzyme is altered.

    • C.

      Enzyme function is influenced by physical and chemical environmental factors such as pH and temperature.

    • D.

      Enzymes increase the rate of chemical reaction by lowering activation energy barriers.

    • E.

      All of the above are true of enzymes.

    Correct Answer
    E. All of the above are true of enzymes.
    Explanation
    Enzymes may require a nonprotein cofactor or ion for catalysis to take place. Enzyme function is reduced if the three-dimensional structure or conformation of an enzyme is altered. Enzyme function is influenced by physical and chemical environmental factors such as pH and temperature. Enzymes increase the rate of chemical reaction by lowering activation energy barriers. Therefore, all of the above statements are true of enzymes.

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  • 38. 

    The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is known as

    • A.

      Metabolic inhibition.metabolic inhibition.

    • B.

      Feedback inhibition.

    • C.

      Allosteric inhibition.

    • D.

      Noncooperative inhibition.

    • E.

      Reversible inhibition.

    Correct Answer
    B. Feedback inhibition.
    Explanation
    Feedback inhibition is the mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway. This process helps regulate the production of the end product, preventing an excessive accumulation. When the concentration of the end product reaches a certain level, it binds to an enzyme involved in an earlier step, causing a conformational change that inhibits the enzyme's activity. This negative feedback loop helps maintain homeostasis and balance in metabolic pathways.

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  • 39. 

    Which of the following statements is true regarding enzyme cooperativity?

    • A.

      A multi-enzyme 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 affects the active site of several 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.

    Correct Answer
    C. A substrate molecule bound to an active site affects the active site of several subunits.
    Explanation
    When a substrate molecule binds to an active site of an enzyme, it can induce a conformational change that affects the active sites of several subunits within the enzyme complex. This phenomenon is known as enzyme cooperativity. It allows for allosteric regulation of enzyme activity, where the binding of a substrate to one subunit can enhance or inhibit the activity of other subunits within the complex. This mechanism allows for efficient control and coordination of metabolic pathways.

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  • 40. 

    How does a non-competitive inhibitor decrease the rate of an enzyme reaction?

    • A.

      By binding at the active site of the enzyme

    • B.

      By changing the structure of the enzyme

    • 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

    Correct Answer
    B. By changing the structure of the enzyme
    Explanation
    A non-competitive inhibitor decreases the rate of an enzyme reaction by changing the structure of the enzyme. This means that the inhibitor binds to a site on the enzyme that is not the active site, causing a change in the enzyme's shape. This change in structure prevents the enzyme from properly binding to the substrate and carrying out the reaction efficiently, ultimately slowing down the rate of the reaction.

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  • 41. 

    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. This process also produces NADH, which is an energy carrier molecule. Therefore, the end products of glycolysis are NADH and pyruvate.

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  • 42. 

      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 partially oxidized to form two molecules of pyruvate. This oxidation releases a small amount of free energy, which is used to produce ATP. However, the majority of the free energy available from the oxidation of glucose remains in pyruvate. This is why only two molecules of NADH are formed during glycolysis, even though it seems like more could be formed. The remaining free energy in pyruvate can be further extracted through other metabolic pathways, such as the citric acid cycle, to produce additional NADH and ATP.

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  • 43. 

    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. The phosphate group contains high-energy bonds that can be easily broken, providing energy for cellular work. Therefore, a phosphorylated molecule is primed and ready to participate in cellular processes and perform work. This explains why a phosphorylated molecule has an increased chemical reactivity and is ready to do cellular work.

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  • 44. 

    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 is produced in the cytosol through the breakdown of glucose in the process of glycolysis. Acetyl CoA then enters the mitochondria and undergoes further oxidation in the Krebs cycle. The Krebs cycle takes place in the mitochondrial matrix, where acetyl CoA is completely broken down to produce energy in the form of ATP. Therefore, the correct location where acetyl CoA accumulates during cellular respiration is the mitochondrial matrix.

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  • 45. 

    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
    During the citric acid cycle, one molecule of pyruvate is oxidized to produce one molecule of acetyl-CoA. Acetyl-CoA enters the citric acid cycle by combining with a four-carbon molecule, oxaloacetate, to form a six-carbon molecule, citrate. As the cycle progresses, citrate is gradually oxidized and decarboxylated, resulting in the release of two carbon dioxide molecules. Therefore, the oxidation of one molecule of pyruvate leads to the entry of two carbon atoms into the citric acid cycle.

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  • 46. 

    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
    The conversion of isocitrate to fumarate involves several steps in the citric acid cycle. However, substrate-level phosphorylation, which directly produces ATP, only occurs during the conversion of succinyl-CoA to succinate. This step produces 1 ATP molecule. Therefore, the maximum number of ATP molecules that could be made through substrate-level phosphorylation in this pathway is 1.

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  • 47. 

    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.

      Alpha-ketoglutarate

    • E.

      Isocitrate

    Correct Answer
    D. Alpha-ketoglutarate
    Explanation
    Alpha-ketoglutarate is an intermediate of the citric acid cycle and can supply the carbon skeleton for the synthesis of a five-carbon amino acid. It is converted into glutamate, which can then be used to synthesize various amino acids, including those with five carbon atoms. Therefore, alpha-ketoglutarate is the correct answer as it provides the necessary carbon skeleton for the synthesis of a five-carbon amino acid.

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  • 48. 

    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
    D. 11
    Explanation
    In oxidative phosphorylation (chemiosmosis), ATP is produced through the electron transport chain. Each NADH molecule can produce 3 ATP molecules, while each FADH2 molecule can produce 2 ATP molecules. One molecule of citrate can generate 3 NADH and 1 FADH2 through the citric acid cycle. Therefore, the total ATP molecules that can be formed from oxidative phosphorylation is 3 x 3 + 1 x 2 = 11.

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  • 49. 

    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
    The citric acid cycle produces 2 molecules of carbon dioxide (CO2) per turn. Since there are 5 turns of the cycle, the total number of CO2 molecules produced would be 2 x 5 = 10.

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  • 50. 

    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
    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, which produces energy in the form of ATP. Each turn of the citric acid cycle produces 1 ATP, 2 CO2, 3 NADH, and 1 FADH2. Therefore, with three turns of the cycle, the correct answer is 3 ATP, 6 CO2, 9 NADH, and 3 FADH2.

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