Cellular Energetics Practice Quiz 1

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

Cellular respiration

Glycolysis

Fermentation

Citric acid cycle

Oxidative phosphorylation

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 essential for the production of ATP, the main energy currency of the cell. Glycolysis, fermentation, citric acid cycle, and oxidative phosphorylation are all steps or components of cellular respiration, but cellular respiration encompasses the entire process of glucose degradation to CO2 and water.

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 essential for the production of ATP, the main energy currency of the cell. Glycolysis, fermentation, citric acid cycle, and oxidative phosphorylation are all steps or components of cellular respiration, but cellular respiration encompasses the entire process of glucose degradation to CO2 and water.

2. Organisms that can exist with light as an energy source and an inorganic form of carbon and other raw materials

Are called photoautotrophs.

Do not exist in nature.

Are called heterotrophs.

Are best classified as decomposers.

Both C and D

Organisms that can exist with light as an energy source and an inorganic form of carbon and other raw materials are called photoautotrophs. This means that these organisms are capable of using sunlight to produce their own food through photosynthesis, using inorganic sources of carbon such as carbon dioxide. They do not rely on consuming other organisms for energy, distinguishing them from heterotrophs. Additionally, they are not classified as decomposers, as decomposers break down organic matter. Therefore, the correct answer is that they are called photoautotrophs.

Explanation

Organisms that can exist with light as an energy source and an inorganic form of carbon and other raw materials are called photoautotrophs. This means that these organisms are capable of using sunlight to produce their own food through photosynthesis, using inorganic sources of carbon such as carbon dioxide. They do not rely on consuming other organisms for energy, distinguishing them from heterotrophs. Additionally, they are not classified as decomposers, as decomposers break down organic matter. Therefore, the correct answer is that they are called photoautotrophs.

3. When hydrogen ions are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, the result is the

Formation of ATP.

Reduction of NAD+.

Restoration of the Na+/K+ balance across the membrane.

Creation of a proton gradient.

Lowering of pH in the mitochondrial matrix.

When hydrogen ions (protons) are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, it creates a concentration gradient or a proton gradient. This gradient represents a difference in the concentration of protons on either side of the membrane. This proton gradient is a form of potential energy that can be used by the ATP synthase enzyme to produce ATP through a process called oxidative phosphorylation. Therefore, the correct answer is the creation of a proton gradient.

Explanation

When hydrogen ions (protons) are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, it creates a concentration gradient or a proton gradient. This gradient represents a difference in the concentration of protons on either side of the membrane. This proton gradient is a form of potential energy that can be used by the ATP synthase enzyme to produce ATP through a process called oxidative phosphorylation. Therefore, the correct answer is the creation of a proton gradient.

4. Which of the following is true of enzymes?

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.

All of the above are true of enzymes.

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.

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.

5. You have a friend who lost 7 kg (about 15 pounds) of fat on a "low carb" diet. How did the fat leave her body?

It was released as CO2 and H2O.

Chemical energy was converted to heat and then released.

It was converted to ATP, which weighs much less than fat.

It was broken down to amino acids and eliminated from the body.

It was converted to urine and eliminated from the body.

When the body breaks down fat molecules for energy, the carbon atoms in the fat combine with oxygen to form carbon dioxide (CO2) and the hydrogen atoms combine with oxygen to form water (H2O). These waste products are then eliminated from the body through exhalation (CO2) and urine (H2O). Therefore, the fat leaves the body as CO2 and H2O.

Explanation

When the body breaks down fat molecules for energy, the carbon atoms in the fat combine with oxygen to form carbon dioxide (CO2) and the hydrogen atoms combine with oxygen to form water (H2O). These waste products are then eliminated from the body through exhalation (CO2) and urine (H2O). Therefore, the fat leaves the body as CO2 and H2O.

6. A plant has a unique photosynthetic pigment. The leaves of this plant appear to be reddish yellow. What wavelengths of visible light are not being absorbed by this pigment?

Red and yellow

Blue and violet

Green and yellow

Blue, green, and red

Green, blue, and violet

The plant's unique photosynthetic pigment appears reddish yellow, indicating that it absorbs blue and green wavelengths of visible light. Since the pigment is not absorbing red and yellow wavelengths, these colors are reflected or transmitted, making the leaves appear reddish yellow.

Explanation

The plant's unique photosynthetic pigment appears reddish yellow, indicating that it absorbs blue and green wavelengths of visible light. Since the pigment is not absorbing red and yellow wavelengths, these colors are reflected or transmitted, making the leaves appear reddish yellow.

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

They do not depend on enzymes.

They consume energy to build up polymers from monomers.

They release energy as they degrade polymers to monomers.

They lead to the synthesis of catabolic compounds.

Both A and B

Catabolic pathways are metabolic processes that involve the breakdown of complex molecules into simpler ones. These pathways rely on enzymes to catalyze the chemical reactions involved in the breakdown process. They release energy as they degrade polymers to monomers, which can be used by the cell for various purposes. Therefore, the correct answer is "They release energy as they degrade polymers to monomers."

Explanation

Catabolic pathways are metabolic processes that involve the breakdown of complex molecules into simpler ones. These pathways rely on enzymes to catalyze the chemical reactions involved in the breakdown process. They release energy as they degrade polymers to monomers, which can be used by the cell for various purposes. Therefore, the correct answer is "They release energy as they degrade polymers to monomers."

8. What is the term for metabolic pathways that release stored energy by breaking down complex molecules?

Anabolic pathways

Catabolic pathways

Fermentation pathways

Thermodynamic pathways

Bioenergetic pathways

Catabolic pathways are the correct answer because they refer to metabolic processes that break down complex molecules to release stored energy. These pathways involve the breakdown of larger molecules into smaller ones, such as the breakdown of carbohydrates, lipids, and proteins through processes like glycolysis, beta oxidation, and protein degradation. This release of energy is essential for various cellular activities and is a fundamental aspect of metabolism. Anabolic pathways, on the other hand, are metabolic processes that build complex molecules from simpler ones, requiring energy input.

Explanation

Catabolic pathways are the correct answer because they refer to metabolic processes that break down complex molecules to release stored energy. These pathways involve the breakdown of larger molecules into smaller ones, such as the breakdown of carbohydrates, lipids, and proteins through processes like glycolysis, beta oxidation, and protein degradation. This release of energy is essential for various cellular activities and is a fundamental aspect of metabolism. Anabolic pathways, on the other hand, are metabolic processes that build complex molecules from simpler ones, requiring energy input.

9. All of the events listed below occur in the light reactions of photosynthesis except

Oxygen is produced.

NADP+ is reduced to NADPH.

Carbon dioxide is incorporated into PGA.

ADP is phosphorylated to yield ATP.

Light is absorbed and funneled to reaction-center chlorophyll a.

In the light reactions of photosynthesis, oxygen is produced as a byproduct of splitting water molecules. NADP+ is reduced to NADPH, which acts as an electron carrier. ADP is phosphorylated to yield ATP, which is the energy currency of the cell. Light is absorbed and funneled to reaction-center chlorophyll a, which is essential for the initiation of photosynthesis. However, carbon dioxide is not incorporated into PGA (phosphoglycerate), a molecule formed during the Calvin cycle, which is a part of the dark reactions of photosynthesis. Therefore, the correct answer is "carbon dioxide is incorporated into PGA."

Explanation

In the light reactions of photosynthesis, oxygen is produced as a byproduct of splitting water molecules. NADP+ is reduced to NADPH, which acts as an electron carrier. ADP is phosphorylated to yield ATP, which is the energy currency of the cell. Light is absorbed and funneled to reaction-center chlorophyll a, which is essential for the initiation of photosynthesis. However, carbon dioxide is not incorporated into PGA (phosphoglycerate), a molecule formed during the Calvin cycle, which is a part of the dark reactions of photosynthesis. Therefore, the correct answer is "carbon dioxide is incorporated into PGA."

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

Transferred to ADP, forming ATP.

Transferred directly to ATP.

Retained in the pyruvate.

Stored in the NADH produced.

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

During glycolysis, glucose is catabolized to pyruvate. The process involves the breakdown of glucose molecules into two molecules of pyruvate. Most of the energy from glucose is captured and retained in the pyruvate molecules. This energy is stored in the form of high-energy electrons and hydrogen atoms, which are transferred to NAD+ to produce NADH. The NADH molecules carry this energy to the electron transport chain, where it is ultimately used to generate ATP through oxidative phosphorylation. Therefore, the correct answer is retained in the pyruvate.

Explanation

During glycolysis, glucose is catabolized to pyruvate. The process involves the breakdown of glucose molecules into two molecules of pyruvate. Most of the energy from glucose is captured and retained in the pyruvate molecules. This energy is stored in the form of high-energy electrons and hydrogen atoms, which are transferred to NAD+ to produce NADH. The NADH molecules carry this energy to the electron transport chain, where it is ultimately used to generate ATP through oxidative phosphorylation. Therefore, the correct answer is retained in the pyruvate.

11. ATP generally energizes a cellular process by

Releasing heat upon hydrolysis.

Acting as a catalyst.

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

Breaking a high-energy bond.

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

ATP is known as the energy currency of the cell because it provides the necessary energy for cellular processes. It achieves this by coupling the free energy released during its hydrolysis (breakdown) to other reactions that require energy. This means that when ATP is hydrolyzed, it releases energy that can be used to drive other reactions in the cell. Therefore, the correct answer is that ATP couples the free energy released by its hydrolysis to the free energy needed by other reactions.

Explanation

ATP is known as the energy currency of the cell because it provides the necessary energy for cellular processes. It achieves this by coupling the free energy released during its hydrolysis (breakdown) to other reactions that require energy. This means that when ATP is hydrolyzed, it releases energy that can be used to drive other reactions in the cell. Therefore, the correct answer is that ATP couples the free energy released by its hydrolysis to the free energy needed by other reactions.

12. How can one increase the rate of a chemical reaction?

Increase the activation energy needed.

Cool the reactants.

Decrease the concentration of the reactants.

Add a catalyst.

Increase the entropy of the reactants.

Adding a catalyst to a chemical reaction can increase the rate of the reaction. A catalyst is a substance that speeds up the reaction by providing an alternative pathway with lower activation energy. It does not get consumed in the reaction and can be used repeatedly. By lowering the activation energy, a catalyst allows more reactant molecules to have sufficient energy to overcome the energy barrier and react. This results in an increased rate of reaction without being consumed in the process.

Explanation

Adding a catalyst to a chemical reaction can increase the rate of the reaction. A catalyst is a substance that speeds up the reaction by providing an alternative pathway with lower activation energy. It does not get consumed in the reaction and can be used repeatedly. By lowering the activation energy, a catalyst allows more reactant molecules to have sufficient energy to overcome the energy barrier and react. This results in an increased rate of reaction without being consumed in the process.

13. How many carbon atoms are fed into the citric acid cycle as a result of the oxidation of one molecule of pyruvate?

2

4

6

8

10

In the citric acid cycle, one molecule of pyruvate is oxidized to produce one molecule of acetyl-CoA. Acetyl-CoA has two carbon atoms. Therefore, as a result of the oxidation of one molecule of pyruvate, two carbon atoms are fed into the citric acid cycle.

Explanation

In the citric acid cycle, one molecule of pyruvate is oxidized to produce one molecule of acetyl-CoA. Acetyl-CoA has two carbon atoms. Therefore, as a result of the oxidation of one molecule of pyruvate, two carbon atoms are fed into the citric acid cycle.

14. Which of the following statements describes the results of this reaction?

C₆H₁₂O₆ + 6 O₂ --> 6 CO₂ + 6 H₂O + Energy

C6H12O6 is oxidized and O2 is reduced.

O2 is oxidized and H2O is reduced.

CO2 is reduced and O2 is oxidized.

C6H12O6 is reduced and CO2 is oxidized.

O2 is reduced and CO2 is oxidized.

In this reaction, glucose (C6H12O6) is being oxidized, meaning it is losing electrons and becoming more positively charged. Oxygen (O2) is being reduced, meaning it is gaining electrons and becoming more negatively charged. Therefore, the correct answer is that C6H12O6 is oxidized and O2 is reduced.

Explanation

In this reaction, glucose (C6H12O6) is being oxidized, meaning it is losing electrons and becoming more positively charged. Oxygen (O2) is being reduced, meaning it is gaining electrons and becoming more negatively charged. Therefore, the correct answer is that C6H12O6 is oxidized and O2 is reduced.

15.

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?

Most of the free energy available from the oxidation of glucose is used in the production of ATP in glycolysis.

Glycolysis is a very inefficient reaction, with much of the energy of glucose released as heat.

Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.

There is no CO2 or water produced as products of glycolysis.

Glycolysis consists of many enzymatic reactions, each of which extracts some energy from the glucose molecule.

During glycolysis, glucose is oxidized to pyruvate. However, only a small amount of the free energy available from the oxidation of glucose is captured in the form of ATP and NADH. Most of the free energy is actually stored in the pyruvate molecules that are produced. This is why only two molecules of NADH are formed during glycolysis, despite the potential for more. The majority of the free energy is still present in the pyruvate, which can then be further metabolized in other pathways to extract more energy.

Explanation

During glycolysis, glucose is oxidized to pyruvate. However, only a small amount of the free energy available from the oxidation of glucose is captured in the form of ATP and NADH. Most of the free energy is actually stored in the pyruvate molecules that are produced. This is why only two molecules of NADH are formed during glycolysis, despite the potential for more. The majority of the free energy is still present in the pyruvate, which can then be further metabolized in other pathways to extract more energy.

16. During aerobic cellular respiration, a proton gradient in mitochondria is generated by ____ and used primarily for ____.

The electron transport chain; ATP synthesis

The electron transport chain; substrate-level phosphorylation

Glycolysis; production of H2O

Fermentation; NAD+ reduction

Diffusion of protons; ATP synthesis

During aerobic cellular respiration, the electron transport chain plays a crucial role in generating a proton gradient in the mitochondria. This occurs as electrons are transferred through a series of protein complexes in the inner mitochondrial membrane, pumping protons from the matrix into the intermembrane space. This creates a concentration gradient of protons, with a higher concentration in the intermembrane space. The protons then flow back into the matrix through ATP synthase, an enzyme that utilizes the energy from this proton gradient to produce ATP through a process called chemiosmosis. Therefore, the correct answer is "the electron transport chain; ATP synthesis."

Explanation

During aerobic cellular respiration, the electron transport chain plays a crucial role in generating a proton gradient in the mitochondria. This occurs as electrons are transferred through a series of protein complexes in the inner mitochondrial membrane, pumping protons from the matrix into the intermembrane space. This creates a concentration gradient of protons, with a higher concentration in the intermembrane space. The protons then flow back into the matrix through ATP synthase, an enzyme that utilizes the energy from this proton gradient to produce ATP through a process called chemiosmosis. Therefore, the correct answer is "the electron transport chain; ATP synthesis."

17. Each time a molecule of glucose (C₆H₁₂O₆) is completely oxidized via aerobic respiration, how many oxygen molecules (O₂). are required?

1

2

6

12

38

During aerobic respiration, glucose is completely oxidized to produce carbon dioxide and water. The balanced equation for this process is C6H12O6 + 6O2 → 6CO2 + 6H2O. From the equation, we can see that for each molecule of glucose, 6 molecules of oxygen are required. Therefore, the correct answer is 6.

Explanation

During aerobic respiration, glucose is completely oxidized to produce carbon dioxide and water. The balanced equation for this process is C6H12O6 + 6O2 → 6CO2 + 6H2O. From the equation, we can see that for each molecule of glucose, 6 molecules of oxygen are required. Therefore, the correct answer is 6.

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

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+.

A and B are both correct.

A, B, and C are all correct.

For NAD+ to remove electrons from glucose or other organic molecules, the free energy released during this process must be greater than the energy needed to transfer the electrons to NAD+. This is because the transfer of electrons requires energy input, and if the energy released is not greater than the energy required, the reaction will not proceed. Therefore, option C is correct. The other options are incorrect because they do not address the energy requirement for electron transfer.

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 needed to transfer the electrons to NAD+. This is because the transfer of electrons requires energy input, and if the energy released is not greater than the energy required, the reaction will not proceed. Therefore, option C is correct. The other options are incorrect because they do not address the energy requirement for electron transfer.

19. Which of the following normally occurs whether or not oxygen (O₂) is present?

Glycolysis

Fermentation

Oxidation of pyruvate to acetyl CoA

Citric acid cycle

Oxidative phosphorylation (chemiosmosis)

Glycolysis is the process of breaking down glucose into pyruvate, which occurs in the cytoplasm of cells. It is an anaerobic process, meaning it does not require oxygen, and is the first step in both aerobic and anaerobic respiration. Therefore, glycolysis normally occurs whether or not oxygen is present.

Explanation

Glycolysis is the process of breaking down glucose into pyruvate, which occurs in the cytoplasm of cells. It is an anaerobic process, meaning it does not require oxygen, and is the first step in both aerobic and anaerobic respiration. Therefore, glycolysis normally occurs whether or not oxygen is present.

20. Where does the Calvin cycle take place?

Stroma of the chloroplast

Thylakoid membrane

Cytoplasm surrounding the chloroplast

Chlorophyll molecule

Outer membrane of the chloroplast

The Calvin cycle takes place in the stroma of the chloroplast. The stroma is the fluid-filled space inside the chloroplast where various metabolic reactions occur. The Calvin cycle is a series of biochemical reactions that take place in the stroma and are responsible for converting carbon dioxide into glucose during photosynthesis. The thylakoid membrane is where the light-dependent reactions occur, while the cytoplasm surrounding the chloroplast and the outer membrane of the chloroplast are not directly involved in the Calvin cycle. The chlorophyll molecule is responsible for capturing light energy, but it is not the site of the Calvin cycle.

Explanation

The Calvin cycle takes place in the stroma of the chloroplast. The stroma is the fluid-filled space inside the chloroplast where various metabolic reactions occur. The Calvin cycle is a series of biochemical reactions that take place in the stroma and are responsible for converting carbon dioxide into glucose during photosynthesis. The thylakoid membrane is where the light-dependent reactions occur, while the cytoplasm surrounding the chloroplast and the outer membrane of the chloroplast are not directly involved in the Calvin cycle. The chlorophyll molecule is responsible for capturing light energy, but it is not the site of the Calvin cycle.

21. Why is ATP an important molecule in metabolism?

Its hydrolysis provides an input of free energy for exergonic reactions.

It provides energy coupling between exergonic and endergonic reactions.

Its terminal phosphate group contains a strong covalent bond that when hydrolyzed releases free energy.

. A and B only

A, B and C

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 energy transfer allows cells to efficiently use and transfer energy, making ATP crucial for various metabolic processes.

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 energy transfer allows cells to efficiently use and transfer energy, making ATP crucial for various metabolic processes.

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

ATP serves as a main energy shuttle inside cells.

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

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

A and B only

A, B, and C

ATP serves as a main energy shuttle inside cells, as it carries energy between different cellular processes. ATP drives endergonic reactions in the cell by transferring its phosphate group to specific reactants through enzymatic reactions. Additionally, the regeneration of ATP from ADP and phosphate is an endergonic reaction, meaning it requires energy input. Therefore, statements A, B, and C are all correct.

Explanation

ATP serves as a main energy shuttle inside cells, as it carries energy between different cellular processes. ATP drives endergonic reactions in the cell by transferring its phosphate group to specific reactants through enzymatic reactions. Additionally, the regeneration of ATP from ADP and phosphate is an endergonic reaction, meaning it requires energy input. Therefore, statements A, B, and C are all correct.

23. Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's

Entropy.

Activation energy.

Endothermic level.

Heat content.

Free-energy content.

In a chemical reaction, reactants need to overcome a thermodynamic barrier called activation energy in order to form products. Activation energy is the minimum amount of energy required for a reaction to occur, and it determines the rate at which the reaction proceeds. It is necessary to provide enough energy to break the existing bonds in the reactants and initiate the formation of new bonds in the products. Once the activation energy is surpassed, the reaction can proceed spontaneously. Therefore, activation energy is the correct answer in this case.

Explanation

In a chemical reaction, reactants need to overcome a thermodynamic barrier called activation energy in order to form products. Activation energy is the minimum amount of energy required for a reaction to occur, and it determines the rate at which the reaction proceeds. It is necessary to provide enough energy to break the existing bonds in the reactants and initiate the formation of new bonds in the products. Once the activation energy is surpassed, the reaction can proceed spontaneously. Therefore, activation energy is the correct answer in this case.

24. An enzyme catalyzes a reaction by

Supplying the energy to speed up a reaction.

Lowering the energy of activation of a reaction.

Lowering the G of a reaction.

Changing the equilibrium of a spontaneous reaction.

Increasing the amount of free energy of a reaction.

Enzymes are biological catalysts that speed up chemical reactions by lowering the energy of activation, which is the energy required to start a reaction. By lowering this energy barrier, enzymes allow reactions to occur more easily and at a faster rate. This is achieved by providing an alternative reaction pathway with a lower activation energy, making it easier for reactant molecules to reach the necessary energy threshold for the reaction to proceed. Therefore, the correct answer is "lowering the energy of activation of a reaction."

Explanation

Enzymes are biological catalysts that speed up chemical reactions by lowering the energy of activation, which is the energy required to start a reaction. By lowering this energy barrier, enzymes allow reactions to occur more easily and at a faster rate. This is achieved by providing an alternative reaction pathway with a lower activation energy, making it easier for reactant molecules to reach the necessary energy threshold for the reaction to proceed. Therefore, the correct answer is "lowering the energy of activation of a reaction."

25. 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?

-40 kcal/mol

-20 kcal/mol

0 kcal/mol

+20 kcal/mol

+40 kcal/mol

When the amount of enzyme in a reaction is doubled, it does not affect the value of G, which represents the change in Gibbs free energy. The value of G remains the same at -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 Gibbs free energy. The value of G remains the same at -20 kcal/mol.

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

Metabolic inhibition.metabolic inhibition.

Feedback inhibition.

Allosteric inhibition.

Noncooperative inhibition.

Reversible inhibition.

Feedback inhibition is the mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway. This allows the cell to regulate the production of certain molecules by slowing down or stopping the pathway when enough of the end product has been produced. This helps maintain homeostasis and prevent the accumulation of excess molecules. Feedback inhibition is a common regulatory mechanism in many metabolic pathways and is essential for proper cellular function.

Explanation

Feedback inhibition is the mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway. This allows the cell to regulate the production of certain molecules by slowing down or stopping the pathway when enough of the end product has been produced. This helps maintain homeostasis and prevent the accumulation of excess molecules. Feedback inhibition is a common regulatory mechanism in many metabolic pathways and is essential for proper cellular function.

27. The primary function of the mitochondrion is the production of ATP. To carry out this function, the mitochondrion must have all of the following except

The membrane-bound electron transport chain carrier molecules.

Proton pumps embedded in the inner mitochondrial membrane.

Enzymes for glycolysis.

Enzymes for the citric acid cycle.

Mitochondrial ATP synthase.

The mitochondrion is responsible for producing ATP through a process called cellular respiration. This process involves multiple steps, including the electron transport chain and ATP synthase, which are mentioned as necessary components in the answer choices. Glycolysis, on the other hand, occurs in the cytoplasm of the cell and does not require the presence of mitochondria. Therefore, enzymes for glycolysis are not necessary for the primary function of the mitochondrion, which is the production of ATP.

Explanation

The mitochondrion is responsible for producing ATP through a process called cellular respiration. This process involves multiple steps, including the electron transport chain and ATP synthase, which are mentioned as necessary components in the answer choices. Glycolysis, on the other hand, occurs in the cytoplasm of the cell and does not require the presence of mitochondria. Therefore, enzymes for glycolysis are not necessary for the primary function of the mitochondrion, which is the production of ATP.

28. Which of the following occurs in the cytosol of the cell?

Glycolysis and fermentation

Fermentation and chemiosmosis

Oxidation of pyruvate to acetyl CoA

Citric acid cycle

Oxidative phosphorylation

Glycolysis and fermentation occur in the cytosol of the cell. Glycolysis is the first step in cellular respiration, where glucose is converted into pyruvate. This process takes place in the cytosol. Fermentation, on the other hand, occurs when there is no oxygen present and pyruvate is converted into either lactate or ethanol, also happening in the cytosol. The other options listed, such as chemiosmosis, oxidation of pyruvate to acetyl CoA, citric acid cycle, and oxidative phosphorylation, all occur in different parts of the cell, such as the mitochondria.

Explanation

Glycolysis and fermentation occur in the cytosol of the cell. Glycolysis is the first step in cellular respiration, where glucose is converted into pyruvate. This process takes place in the cytosol. Fermentation, on the other hand, occurs when there is no oxygen present and pyruvate is converted into either lactate or ethanol, also happening in the cytosol. The other options listed, such as chemiosmosis, oxidation of pyruvate to acetyl CoA, citric acid cycle, and oxidative phosphorylation, all occur in different parts of the cell, such as the mitochondria.

29. Some photosynthetic organisms contain chloroplasts that lack photosystem II, yet are able to survive. The best way to detect the lack of photosystem II in these organisms would be

To determine if they have thylakoids in the chloroplasts.

To test for liberation of O2 in the light.

To test for CO2 fixation in the dark.

To do experiments to generate an action spectrum.

To test for production of either sucrose or starch.

The best way to detect the lack of photosystem II in these organisms would be to test for liberation of O2 in the light. Photosystem II is responsible for the initial step of photosynthesis, which is the splitting of water molecules and release of oxygen. If an organism lacks photosystem II, it would not be able to produce oxygen during photosynthesis. Therefore, testing for liberation of O2 in the light would indicate whether photosystem II is present or not.

Explanation

The best way to detect the lack of photosystem II in these organisms would be to test for liberation of O2 in the light. Photosystem II is responsible for the initial step of photosynthesis, which is the splitting of water molecules and release of oxygen. If an organism lacks photosystem II, it would not be able to produce oxygen during photosynthesis. Therefore, testing for liberation of O2 in the light would indicate whether photosystem II is present or not.

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

The molecule that is reduced gains electrons.

The molecule that is oxidized loses electrons.

The molecule that is reduced loses electrons.

The molecule that is oxidized gains electrons.

Both A and B are correct.

In an oxidation-reduction (or redox) reaction, the molecule that is reduced gains electrons, which means it is being reduced. On the other hand, the molecule that is oxidized loses electrons, which means it is being oxidized. Therefore, both statements A and B are correct.

Explanation

In an oxidation-reduction (or redox) reaction, the molecule that is reduced gains electrons, which means it is being reduced. On the other hand, the molecule that is oxidized loses electrons, which means it is being oxidized. Therefore, both statements A and B are correct.

31. A molecule that is phosphorylated

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

Has a decreased chemical reactivity; it is less likely to provide energy for cellular work.

Has been oxidized as a result of a redox reaction involving the gain of an inorganic phosphate.

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

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

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, releasing energy that can be used for cellular work. Therefore, a phosphorylated molecule is primed and ready to participate in various cellular processes and provide energy for 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, releasing energy that can be used for cellular work. Therefore, a phosphorylated molecule is primed and ready to participate in various cellular processes and provide energy for cellular work.

32. What is the primary function of the light reactions of photosynthesis?

To produce energy-rich glucose from carbon dioxide and water

To produce ATP and NADPH

To produce NADPH used in respiration

To convert light energy to the chemical energy of PGAL

To use ATP to make glucose

The primary function of the light reactions of photosynthesis is to produce ATP and NADPH. These two molecules are essential for the second stage of photosynthesis, known as the Calvin cycle, where they provide the energy and reducing power needed to convert carbon dioxide into glucose. ATP is the main energy currency of cells, while NADPH is a coenzyme that carries high-energy electrons used in the synthesis of glucose. Therefore, the production of ATP and NADPH through the light reactions is crucial for the overall process of photosynthesis.

Explanation

The primary function of the light reactions of photosynthesis is to produce ATP and NADPH. These two molecules are essential for the second stage of photosynthesis, known as the Calvin cycle, where they provide the energy and reducing power needed to convert carbon dioxide into glucose. ATP is the main energy currency of cells, while NADPH is a coenzyme that carries high-energy electrons used in the synthesis of glucose. Therefore, the production of ATP and NADPH through the light reactions is crucial for the overall process of photosynthesis.

33. Where is the electron transport chain found in plant cells?

Thylakoid membranes of chloroplasts

Stroma of chloroplasts

Inner membrane of mitochondria

Matrix of mitochondria

Cytoplasm

The electron transport chain is found in the thylakoid membranes of chloroplasts. This is where the process of photosynthesis takes place in plant cells. The thylakoid membranes contain the pigments and protein complexes necessary for capturing light energy and converting it into chemical energy in the form of ATP and NADPH. The electron transport chain is a series of protein complexes embedded in the thylakoid membranes that transfer electrons and generate a proton gradient, which is used to produce ATP through chemiosmosis.

Explanation

The electron transport chain is found in the thylakoid membranes of chloroplasts. This is where the process of photosynthesis takes place in plant cells. The thylakoid membranes contain the pigments and protein complexes necessary for capturing light energy and converting it into chemical energy in the form of ATP and NADPH. The electron transport chain is a series of protein complexes embedded in the thylakoid membranes that transfer electrons and generate a proton gradient, which is used to produce ATP through chemiosmosis.

34. Which metabolic pathway is common to both cellular respiration and fermentation?

The oxidation of pyruvate to acetyl CoA

The citric acid cycle

Oxidative phosphorylation

Glycolysis

Chemiosmosis

Glycolysis is the correct answer because it is a metabolic pathway that occurs in both cellular respiration and fermentation. It is the initial step in both processes, where glucose is broken down into pyruvate. In cellular respiration, pyruvate is further oxidized to produce energy through the citric acid cycle and oxidative phosphorylation. In fermentation, pyruvate is converted into other compounds like lactic acid or ethanol, without the involvement of oxygen. Therefore, glycolysis is the common pathway that occurs in both cellular respiration and fermentation.

Explanation

Glycolysis is the correct answer because it is a metabolic pathway that occurs in both cellular respiration and fermentation. It is the initial step in both processes, where glucose is broken down into pyruvate. In cellular respiration, pyruvate is further oxidized to produce energy through the citric acid cycle and oxidative phosphorylation. In fermentation, pyruvate is converted into other compounds like lactic acid or ethanol, without the involvement of oxygen. Therefore, glycolysis is the common pathway that occurs in both cellular respiration and fermentation.

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

Dehydrogenated.

Hydrogenated.

Oxidized.

Reduced.

An oxidizing agent.

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 process of losing electrons or gaining oxygen atoms, and in this case, the glucose molecule has lost a hydrogen atom, which is equivalent to losing an electron. Therefore, the correct answer is 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 process of losing electrons or gaining oxygen atoms, and in this case, the glucose molecule has lost a hydrogen atom, which is equivalent to losing an electron. Therefore, the correct answer is oxidized.

36. The hydrolysis of ATP to ADP and inorganic phosphate (ATP + H₂O --> ADP + P_i )

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

Involves hydrolysis of a terminal phosphate bond of ATP.

Can occur spontaneously under appropriate conditions.

Only A and B are correct.

A, B, and C are correct.

The hydrolysis of ATP to ADP and inorganic phosphate has a negative Gibbs free energy (G) value of about -7 kcal/mol under standard conditions, indicating that it is an energetically favorable reaction. This reaction involves the hydrolysis of a terminal phosphate bond of ATP, which releases energy. Additionally, the hydrolysis of ATP can occur spontaneously under appropriate conditions, further supporting the statement that A, B, and C are all correct.

Explanation

The hydrolysis of ATP to ADP and inorganic phosphate has a negative Gibbs free energy (G) value of about -7 kcal/mol under standard conditions, indicating that it is an energetically favorable reaction. This reaction involves the hydrolysis of a terminal phosphate bond of ATP, which releases energy. Additionally, the hydrolysis of ATP can occur spontaneously under appropriate conditions, further supporting the statement that A, B, and C are all correct.

37. Which of the following statements is true concerning catabolic pathways?

They combine molecules into more energy-rich molecules.

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

They are endergonic.

They are spontaneous and do not need enzyme catalysis.

They build up complex molecules such as protein from simpler compounds.

Catabolic pathways involve the breakdown of larger molecules into smaller ones, releasing energy in the process. This energy is then used to power anabolic pathways, which build up complex molecules from simpler compounds. Therefore, catabolic pathways are usually coupled with anabolic pathways to supply them with energy in the form of ATP.

Explanation

Catabolic pathways involve the breakdown of larger molecules into smaller ones, releasing energy in the process. This energy is then used to power anabolic pathways, which build up complex molecules from simpler compounds. Therefore, catabolic pathways are usually coupled with anabolic pathways to supply them with energy in the form of ATP.

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

1 FADH2 and 4 NADH

2 FADH2 and 8 NADH

4 FADH2 and 12 NADH

1 FAD and 4 NAD+

4 FAD+ and 12 NAD+

In the citric acid cycle, each turn produces 1 FADH2 and 3 NADH. Since there are four turns of the cycle, the total number of reduced dinucleotides produced would be 4 FADH2 and 12 NADH.

Explanation

In the citric acid cycle, each turn produces 1 FADH2 and 3 NADH. Since there are four turns of the cycle, the total number of reduced dinucleotides produced would be 4 FADH2 and 12 NADH.

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

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

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

3 ATP, 3 CO2, 3 NADH, and 3 FADH2

3 ATP, 6 CO2, 9 NADH, and 3 FADH2

38 ATP, 6 CO2, 3 NADH, and 12 FADH2

In each turn of the citric acid cycle, one ATP is produced through substrate-level phosphorylation. Two CO2 molecules are released as byproducts. Three NADH molecules are produced through redox reactions, and one FADH2 molecule is also produced. Since the question asks for the products after three turns of the cycle, we multiply each of the quantities by three. Therefore, the correct answer is 3 ATP, 6 CO2, 9 NADH, and 3 FADH2.

Explanation

In each turn of the citric acid cycle, one ATP is produced through substrate-level phosphorylation. Two CO2 molecules are released as byproducts. Three NADH molecules are produced through redox reactions, and one FADH2 molecule is also produced. Since the question asks for the products after three turns of the cycle, we multiply each of the quantities by three. Therefore, the correct answer is 3 ATP, 6 CO2, 9 NADH, and 3 FADH2.

40. Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle?

Pyruvate

Malate or fumarate

Acetyl CoA

Alpha-ketoglutarate

Succinyl CoA

The catabolic products of fatty acid breakdown enter into the citric acid cycle through acetyl CoA. Acetyl CoA is derived from the breakdown of fatty acids and serves as the entry point for fatty acid metabolism in the citric acid cycle. It combines with oxaloacetate to form citrate, initiating the cycle and allowing for the production of energy through the oxidation of acetyl CoA.

Explanation

The catabolic products of fatty acid breakdown enter into the citric acid cycle through acetyl CoA. Acetyl CoA is derived from the breakdown of fatty acids and serves as the entry point for fatty acid metabolism in the citric acid cycle. It combines with oxaloacetate to form citrate, initiating the cycle and allowing for the production of energy through the oxidation of acetyl CoA.

41. What are the products of the light reactions that are subsequently used by the Calvin cycle?

Oxygen and carbon dioxide

Carbon dioxide and RuBP

Water and carbon

Electrons and photons

ATP and NADPH

The products of the light reactions, ATP and NADPH, are subsequently used by the Calvin cycle. ATP is a molecule that provides energy for cellular processes, including the synthesis of glucose during the Calvin cycle. NADPH is a molecule that carries high-energy electrons and hydrogen ions, which are also used in the Calvin cycle to convert carbon dioxide into glucose. Therefore, ATP and NADPH are essential for the Calvin cycle to occur and for the production of glucose.

Explanation

The products of the light reactions, ATP and NADPH, are subsequently used by the Calvin cycle. ATP is a molecule that provides energy for cellular processes, including the synthesis of glucose during the Calvin cycle. NADPH is a molecule that carries high-energy electrons and hydrogen ions, which are also used in the Calvin cycle to convert carbon dioxide into glucose. Therefore, ATP and NADPH are essential for the Calvin cycle to occur and for the production of glucose.

42. In mitochondria, chemiosmosis translocates protons from the matrix into the intermembrane space, whereas in chloroplasts, chemiosmosis translocates protons from

The stroma to the photosystem II.

The matrix to the stroma.

The stroma to the thylakoid space.

The intermembrane space to the matrix.

ATP synthase to NADP+ reductase.

In chloroplasts, chemiosmosis is responsible for the translocation of protons from the stroma to the thylakoid space. This process occurs during photosynthesis and is essential for the generation of ATP. The movement of protons creates an electrochemical gradient, which drives the synthesis of ATP by ATP synthase. This gradient is established by the transfer of electrons through the electron transport chain in the thylakoid membrane. Therefore, the correct answer is "the stroma to the thylakoid space."

Explanation

In chloroplasts, chemiosmosis is responsible for the translocation of protons from the stroma to the thylakoid space. This process occurs during photosynthesis and is essential for the generation of ATP. The movement of protons creates an electrochemical gradient, which drives the synthesis of ATP by ATP synthase. This gradient is established by the transfer of electrons through the electron transport chain in the thylakoid membrane. Therefore, the correct answer is "the stroma to the thylakoid space."

43. According to the induced fit hypothesis of enzyme catalysis, which of the following is CORRECT?

The binding of the substrate depends on the shape of the active site.

Some enzymes change their structure when activators bind to the enzyme.

A competitive inhibitor can outcompete the substrate for the active site.

The binding of the substrate changes the shape of the enzyme's active site.

The active site creates a microenvironment ideal for the reaction.

The induced fit hypothesis of enzyme catalysis suggests 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, enhancing the catalytic activity. This explanation aligns with the given correct answer that states "The binding of the substrate changes the shape of the enzyme's active site."

Explanation

The induced fit hypothesis of enzyme catalysis suggests 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, enhancing the catalytic activity. This explanation aligns with the given correct answer that states "The binding of the substrate changes the shape of the enzyme's active site."

44. During oxidative phosphorylation, H₂O is formed. Where does the oxygen for the synthesis of the water come from?

Carbon dioxide (CO2)

Glucose (C6H12O6)

Molecular oxygen (O2)

Pyruvate (C3H3O3–)

Lactate (C3H5O3–-)

During oxidative phosphorylation, H2O is formed through the process of electron transport chain. The electrons that are transferred through the electron transport chain ultimately combine with molecular oxygen (O2) to form water (H2O). This occurs in the final step of the electron transport chain, where oxygen acts as the final electron acceptor and is reduced to form water. Therefore, the oxygen for the synthesis of water during oxidative phosphorylation comes from molecular oxygen (O2).

Explanation

During oxidative phosphorylation, H2O is formed through the process of electron transport chain. The electrons that are transferred through the electron transport chain ultimately combine with molecular oxygen (O2) to form water (H2O). This occurs in the final step of the electron transport chain, where oxygen acts as the final electron acceptor and is reduced to form water. Therefore, the oxygen for the synthesis of water during oxidative phosphorylation comes from molecular oxygen (O2).

45. Which of the following produces the most ATP when glucose (C₆H₁₂O₆) is completely oxidized to carbon dioxide (CO₂) and water?

Glycolysis

Fermentation

Oxidation of pyruvate to acetyl CoA

Citric acid cycle

Oxidative phosphorylation (chemiosmosis)

Oxidative phosphorylation (chemiosmosis) produces the most ATP when glucose is completely oxidized to carbon dioxide and water. This process occurs in the mitochondria and involves the electron transport chain and ATP synthase. During oxidative phosphorylation, electrons from NADH and FADH2 are transferred along the electron transport chain, creating a proton gradient across the inner mitochondrial membrane. This gradient drives the synthesis of ATP by ATP synthase. Overall, oxidative phosphorylation produces a total of 36-38 ATP molecules per glucose molecule, making it the most efficient process for ATP production.

Explanation

Oxidative phosphorylation (chemiosmosis) produces the most ATP when glucose is completely oxidized to carbon dioxide and water. This process occurs in the mitochondria and involves the electron transport chain and ATP synthase. During oxidative phosphorylation, electrons from NADH and FADH2 are transferred along the electron transport chain, creating a proton gradient across the inner mitochondrial membrane. This gradient drives the synthesis of ATP by ATP synthase. Overall, oxidative phosphorylation produces a total of 36-38 ATP molecules per glucose molecule, making it the most efficient process for ATP production.

46. Where does glycolysis takes place?

Mitochondrial matrix

Mitochondrial outer membrane

Mitochondrial inner membrane

Mitochondrial intermembrane space

Cytosol

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. This process does not require oxygen and is common to both aerobic and anaerobic organisms. The cytosol, which is the liquid component of the cytoplasm, provides the necessary environment and enzymes for glycolysis to take place. Therefore, the correct answer is 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. This process does not require oxygen and is common to both aerobic and anaerobic organisms. The cytosol, which is the liquid component of the cytoplasm, provides the necessary environment and enzymes for glycolysis to take place. Therefore, the correct answer is cytosol.

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

Feedback regulationfeedback regulation

Bioenergetics

Energy coupling

Entropy

Cooperativity

Energy coupling is the term used to describe the transfer of free energy from catabolic pathways to anabolic pathways. This process involves the use of energy released from the breakdown of molecules in catabolic pathways to drive the synthesis of molecules in anabolic pathways. Energy coupling is essential for the overall functioning and maintenance of cells, as it allows for the conversion and utilization of energy in different forms to support various cellular processes.

Explanation

Energy coupling is the term used to describe the transfer of free energy from catabolic pathways to anabolic pathways. This process involves the use of energy released from the breakdown of molecules in catabolic pathways to drive the synthesis of molecules in anabolic pathways. Energy coupling is essential for the overall functioning and maintenance of cells, as it allows for the conversion and utilization of energy in different forms to support various cellular processes.

48. The active site of an enzyme is the region that

Binds allosteric regulators of the enzyme.

Is involved in the catalytic reaction of the enzyme.

Binds the products of the catalytic reaction.

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

Both A and B

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 location where the substrate binds and the chemical reaction takes place. The active site typically has a specific shape and chemical properties that allow it to interact with the substrate and facilitate the conversion of the substrate into product. The binding of allosteric regulators, products of the catalytic reaction, and the inhibition by coenzymes or cofactors may occur at other regions of the enzyme, but they are not directly related to the catalytic reaction itself.

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 location where the substrate binds and the chemical reaction takes place. The active site typically has a specific shape and chemical properties that allow it to interact with the substrate and facilitate the conversion of the substrate into product. The binding of allosteric regulators, products of the catalytic reaction, and the inhibition by coenzymes or cofactors may occur at other regions of the enzyme, but they are not directly related to the catalytic reaction itself.

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

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

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

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

A and B only

A, B, and C

As temperature decreases, the kinetic energy of the molecules decreases, resulting in fewer substrates having sufficient energy to overcome the activation energy barrier. This is explained by option A. Additionally, the motion in the active site of the enzyme is slowed down at lower temperatures, which affects the catalysis of the enzyme. This is explained by option B. Therefore, the correct answer is A and B only.

Explanation

As temperature decreases, the kinetic energy of the molecules decreases, resulting in fewer substrates having sufficient energy to overcome the activation energy barrier. This is explained by option A. Additionally, the motion in the active site of the enzyme is slowed down at lower temperatures, which affects the catalysis of the enzyme. This is explained by option B. Therefore, the correct answer is A and B only.

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

Accessory enzyme

Allosteric group

Coenzyme

Functional group

Enzyme activator

A nonprotein "helper" of an enzyme molecule is called a coenzyme. Coenzymes are small organic molecules that bind to the enzyme and assist in the catalytic process. They are essential for the proper functioning of many enzymes as they provide necessary chemical groups or transfer chemical groups between enzymes. Coenzymes often act as carriers of specific atoms or functional groups during enzymatic reactions. They can be derived from vitamins or synthesized within the body.

Explanation

A nonprotein "helper" of an enzyme molecule is called a coenzyme. Coenzymes are small organic molecules that bind to the enzyme and assist in the catalytic process. They are essential for the proper functioning of many enzymes as they provide necessary chemical groups or transfer chemical groups between enzymes. Coenzymes often act as carriers of specific atoms or functional groups during enzymatic reactions. They can be derived from vitamins or synthesized within the body.

51. Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?

Catalysis

Metabolism

Anabolism

Dehydration

Catabolism

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 into simpler ones. It is the opposite of anabolism, which is the process of building up complex molecules from simpler ones. Catalysis refers to the process of speeding up a chemical reaction, while dehydration is the process of removing water molecules. Therefore, catabolism is the most precise term to describe the given cellular process.

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 into simpler ones. It is the opposite of anabolism, which is the process of building up complex molecules from simpler ones. Catalysis refers to the process of speeding up a chemical reaction, while dehydration is the process of removing water molecules. Therefore, catabolism is the most precise term to describe the given cellular process.

52.

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

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

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

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

Only A and B are correct.

A, B, and C are correct.

The breakdown of glucose to carbon dioxide and water is exergonic, meaning it releases energy. This process has a free energy change of -686 kcal/mol, indicating that it is energetically favorable. Additionally, the breakdown of glucose to carbon dioxide and water involves oxidation-reduction or redox reactions, where glucose is oxidized and carbon dioxide is reduced. Therefore, all statements A, B, and C are correct.

Explanation

The breakdown of glucose to carbon dioxide and water is exergonic, meaning it releases energy. This process has a free energy change of -686 kcal/mol, indicating that it is energetically favorable. Additionally, the breakdown of glucose to carbon dioxide and water involves oxidation-reduction or redox reactions, where glucose is oxidized and carbon dioxide is reduced. Therefore, all statements A, B, and C are correct.

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

Gains electrons and gains energy.

Loses electrons and loses energy.

Gains electrons and loses energy.

Loses electrons and gains energy.

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

In a redox or oxidation-reduction reaction, the reducing agent is the molecule that 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."

Explanation

In a redox or oxidation-reduction reaction, the reducing agent is the molecule that 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."

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

Synthesis of macromoleculessynthesis of macromolecules

Breakdown of macromolecules

Control of enzyme activity

A and B only

A, B, and C

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 biological systems.

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 biological systems.

55. Which metabolic process is most closely associated with intracellular membranes?

Substrate-level phosphorylation

Oxidative phosphorylation

Glycolysis

The citric acid cycle

Alcohol fermentation

Oxidative phosphorylation is the correct answer because it is the metabolic process that occurs in the mitochondria and is closely associated with intracellular membranes. This process involves the transfer of electrons through a series of protein complexes in the inner mitochondrial membrane, generating a proton gradient that is used to produce ATP. The intracellular membranes, specifically the inner mitochondrial membrane, play a crucial role in facilitating this electron transfer and ATP production.

Explanation

Oxidative phosphorylation is the correct answer because it is the metabolic process that occurs in the mitochondria and is closely associated with intracellular membranes. This process involves the transfer of electrons through a series of protein complexes in the inner mitochondrial membrane, generating a proton gradient that is used to produce ATP. The intracellular membranes, specifically the inner mitochondrial membrane, play a crucial role in facilitating this electron transfer and ATP production.

56. How many molecules of carbon dioxide (CO₂) would be released from the complete aerobic respiration of a molecule of sucrose (C₁₂H₂₂ O₁₁), a disaccharide?

2

3

6

12

38

Sucrose is a disaccharide composed of 12 carbon atoms. During aerobic respiration, each carbon atom in the sucrose molecule is converted into a carbon dioxide (CO2) molecule. Therefore, the complete aerobic respiration of a molecule of sucrose would result in the release of 12 molecules of carbon dioxide.

Explanation

Sucrose is a disaccharide composed of 12 carbon atoms. During aerobic respiration, each carbon atom in the sucrose molecule is converted into a carbon dioxide (CO2) molecule. Therefore, the complete aerobic respiration of a molecule of sucrose would result in the release of 12 molecules of carbon dioxide.

57. Which of the following statements about the light reactions of photosynthesis are true?

The splitting of water molecules provides a source of electrons.

Chlorophyll (and other pigments) absorb light energy, which excites electrons.

ATP is generated by photophosphorylation.

Only A and C are true.

A, B, and C are true.

The light reactions of photosynthesis involve several processes. Firstly, the splitting of water molecules provides a source of electrons, which are essential for the production of ATP. Secondly, chlorophyll and other pigments absorb light energy, which excites electrons and initiates the electron transport chain. Finally, ATP is generated through photophosphorylation, a process that uses the energy from the excited electrons to add a phosphate group to ADP. Therefore, all statements A, B, and C are true.

Explanation

The light reactions of photosynthesis involve several processes. Firstly, the splitting of water molecules provides a source of electrons, which are essential for the production of ATP. Secondly, chlorophyll and other pigments absorb light energy, which excites electrons and initiates the electron transport chain. Finally, ATP is generated through photophosphorylation, a process that uses the energy from the excited electrons to add a phosphate group to ADP. Therefore, all statements A, B, and C are true.

58. Assume a thylakoid is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will have the most direct effect on which of the following processes?

The splitting of water

The absorption of light energy by chlorophyll

The flow of electrons from photosystem II to photosystem I

The synthesis of ATP

The reduction of NADP+

If a thylakoid is punctured and the interior of the thylakoid is no longer separated from the stroma, it will directly affect the synthesis of ATP. This is because the thylakoid membrane is responsible for the generation of a proton gradient, which is used to power ATP synthesis through chemiosmosis. If the thylakoid is punctured, the proton gradient will be disrupted, and ATP synthesis will be impaired. The other processes mentioned, such as the splitting of water, absorption of light energy, flow of electrons, and reduction of NADP+, are all part of the overall process of photosynthesis, but they are not directly affected by the punctured thylakoid.

Explanation

If a thylakoid is punctured and the interior of the thylakoid is no longer separated from the stroma, it will directly affect the synthesis of ATP. This is because the thylakoid membrane is responsible for the generation of a proton gradient, which is used to power ATP synthesis through chemiosmosis. If the thylakoid is punctured, the proton gradient will be disrupted, and ATP synthesis will be impaired. The other processes mentioned, such as the splitting of water, absorption of light energy, flow of electrons, and reduction of NADP+, are all part of the overall process of photosynthesis, but they are not directly affected by the punctured thylakoid.

59. Which of the following statements about NAD⁺ is false?

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

NAD+ has more chemical energy than NADH.

NAD+ is reduced by the action of dehydrogenases.

NAD+ can receive electrons for use in oxidative phosphorylation.

In the absence of NAD+, glycolysis cannot function.

NAD+ is actually the oxidized form of NADH. During glycolysis and the citric acid cycle, NAD+ is reduced to NADH by accepting electrons. This means that NADH has more chemical energy than NAD+. Therefore, the statement that NAD+ has more chemical energy than NADH is false.

Explanation

NAD+ is actually the oxidized form of NADH. During glycolysis and the citric acid cycle, NAD+ is reduced to NADH by accepting electrons. This means that NADH has more chemical energy than NAD+. Therefore, the statement that NAD+ has more chemical energy than NADH is false.

60. 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?

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

Cells are less efficient at heat production than nonliving systems.

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

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

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

The answer "Cells convert some of the energy of ATP hydrolysis into other forms of energy besides heat" is the best explanation for the observation that a cell hydrolyzes the same amount of ATP but produces less heat compared to a test tube. This is because cells are highly efficient and can utilize the energy released from ATP hydrolysis for various cellular processes such as mechanical work, active transport, and biosynthesis. In contrast, a test tube lacks the complex machinery and processes present in a cell, resulting in a greater proportion of the energy being released as heat.

Explanation

The answer "Cells convert some of the energy of ATP hydrolysis into other forms of energy besides heat" is the best explanation for the observation that a cell hydrolyzes the same amount of ATP but produces less heat compared to a test tube. This is because cells are highly efficient and can utilize the energy released from ATP hydrolysis for various cellular processes such as mechanical work, active transport, and biosynthesis. In contrast, a test tube lacks the complex machinery and processes present in a cell, resulting in a greater proportion of the energy being released as heat.

61. Which of the following statements is (are) true about enzyme-catalyzed reactions?

The reaction is faster than the same reaction in the absence of the enzyme.

The free energy change of the reaction is the same as the reaction in the absence of the enzyme.

The reaction always goes in the direction toward chemical equilibrium.

A and B only

A, B, and C

Enzymes are biological catalysts that increase the rate of chemical reactions. They achieve this by lowering the activation energy required for the reaction to occur. As a result, the reaction proceeds faster in the presence of an enzyme compared to the same reaction in the absence of an enzyme. The statement "The reaction is faster than the same reaction in the absence of the enzyme" is therefore true. However, the other statements are not necessarily true. The free energy change of the reaction can be affected by the presence of an enzyme, and the direction of the reaction depends on the specific conditions and equilibrium constants.

Explanation

Enzymes are biological catalysts that increase the rate of chemical reactions. They achieve this by lowering the activation energy required for the reaction to occur. As a result, the reaction proceeds faster in the presence of an enzyme compared to the same reaction in the absence of an enzyme. The statement "The reaction is faster than the same reaction in the absence of the enzyme" is therefore true. However, the other statements are not necessarily true. The free energy change of the reaction can be affected by the presence of an enzyme, and the direction of the reaction depends on the specific conditions and equilibrium constants.

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

Bringing glucose and fructose together to form sucrose.

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

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

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

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

Sucrose is a disaccharide composed of glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase involves breaking the bond between glucose and fructose. This process requires the addition of water molecules, which are used to form new bonds between the atoms of water and the glucose and fructose molecules, resulting in the formation of separate glucose and fructose molecules. Therefore, the correct answer is breaking the bond between glucose and fructose and forming new bonds from the atoms of water.

Explanation

Sucrose is a disaccharide composed of glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase involves breaking the bond between glucose and fructose. This process requires the addition of water molecules, which are used to form new bonds between the atoms of water and the glucose and fructose molecules, resulting in the formation of separate glucose and fructose molecules. Therefore, the correct answer is breaking the bond between glucose and fructose and forming new bonds from the atoms of water.

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

Changes in the activation energy of the reaction

Changes in the active site of the enzyme

Changes in the free energy of the reaction

A and B only

A, B, and C

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 refers to the energy required to start 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 location where the substrate binds and the reaction takes place, can also impact enzyme activity. Therefore, both A (changes in the activation energy of the reaction) and B (changes in the active site of the enzyme) underlie all types of enzyme regulation.

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 refers to the energy required to start 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 location where the substrate binds and the reaction takes place, can also impact enzyme activity. Therefore, both A (changes in the activation energy of the reaction) and B (changes in the active site of the enzyme) underlie all types of enzyme regulation.

64. Carbon dioxide (CO₂) is released during which of the following stages of cellular respiration?

Glycolysis and the oxidation of pyruvate to acetyl CoA

Oxidation of pyruvate to acetyl CoA and the citric acid cycle

The citric acid cycle and oxidative phosphorylation

Oxidative phosphorylation and fermentation

Fermentation and glycolysis

not-available-via-ai

Explanation

not-available-via-ai

65. Which of the following describes the sequence of electron carriers in the electron transport chain, starting with the least electronegative?

Ubiquinone (Q), cytochromes (Cyt), FMN, Fe•S

Cytochromes (Cyt), FMN, ubiquinone, Fe·S

Fe•S, FMN, cytochromes (Cyt), ubiquinone

FMN, Fe•S, ubiquinone, cytochromes (Cyt)

Cytochromes (Cyt), Fe•S, ubiquinone, FMN

The correct answer is FMN, Fe•S, ubiquinone, cytochromes (Cyt). This sequence describes the order of electron carriers in the electron transport chain, starting with the least electronegative. FMN (flavin mononucleotide) is the first carrier, followed by Fe•S (iron-sulfur clusters), then ubiquinone, and finally cytochromes (Cyt). This sequence reflects the transfer of electrons from carriers with lower electronegativity to carriers with higher electronegativity, allowing for the generation of ATP through oxidative phosphorylation.

Explanation

The correct answer is FMN, Fe•S, ubiquinone, cytochromes (Cyt). This sequence describes the order of electron carriers in the electron transport chain, starting with the least electronegative. FMN (flavin mononucleotide) is the first carrier, followed by Fe•S (iron-sulfur clusters), then ubiquinone, and finally cytochromes (Cyt). This sequence reflects the transfer of electrons from carriers with lower electronegativity to carriers with higher electronegativity, allowing for the generation of ATP through oxidative phosphorylation.

66. Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. Which of the following statements concerning phosphofructokinase is not true?

It is activated by AMP (derived from ADP).

It is inhibited by ATP.

It is activated by citrate, an intermediate of the citric acid cycle.

It specifically catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, an early step of glycolysis.

It is an allosteric enzyme.

Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. It is inhibited by ATP, which is a high-energy molecule indicating that the cell has sufficient energy and does not need to carry out glycolysis. It is also activated by citrate, an intermediate of the citric acid cycle, which indicates that the cell has enough energy and does not need to produce more ATP through glycolysis. Phosphofructokinase specifically catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, an early step of glycolysis. It is an allosteric enzyme, meaning its activity can be regulated by molecules that bind to a site other than the active site. However, it is not activated by AMP derived from ADP.

Explanation

Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. It is inhibited by ATP, which is a high-energy molecule indicating that the cell has sufficient energy and does not need to carry out glycolysis. It is also activated by citrate, an intermediate of the citric acid cycle, which indicates that the cell has enough energy and does not need to produce more ATP through glycolysis. Phosphofructokinase specifically catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, an early step of glycolysis. It is an allosteric enzyme, meaning its activity can be regulated by molecules that bind to a site other than the active site. However, it is not activated by AMP derived from ADP.

67. The ATP made during fermentation is generated by which of the following?

The electron transport chain

Substrate-level phosphorylation

Chemiosmosis

Oxidative phosphorylation

Aerobic respiration

The correct answer is substrate-level phosphorylation. During fermentation, ATP is generated through substrate-level phosphorylation, which is the direct transfer of a phosphate group from a substrate molecule to ADP, forming ATP. This process occurs in the absence of oxygen and does not involve the electron transport chain, chemiosmosis, oxidative phosphorylation, or aerobic respiration.

Explanation

The correct answer is substrate-level phosphorylation. During fermentation, ATP is generated through substrate-level phosphorylation, which is the direct transfer of a phosphate group from a substrate molecule to ADP, forming ATP. This process occurs in the absence of oxygen and does not involve the electron transport chain, chemiosmosis, oxidative phosphorylation, or aerobic respiration.

68. Which of the following is not true concerning the cellular compartmentation of the steps of respiration or fermentation?

Acetyl CoA is produced only in the mitochondria.

Lactate is produced only in the cytosol.

NADH is produced only in the mitochondria.

FADH2 is produced only in the mitochondria.

ATP is produced in the cytosol and the mitochondria.

NADH is not produced only in the mitochondria. It is produced in both the cytosol and the mitochondria during the steps of respiration or fermentation. NADH is generated during glycolysis in the cytosol and during the citric acid cycle in the mitochondria.

Explanation

NADH is not produced only in the mitochondria. It is produced in both the cytosol and the mitochondria during the steps of respiration or fermentation. NADH is generated during glycolysis in the cytosol and during the citric acid cycle in the mitochondria.

69. What does the chemiosmotic process in chloroplasts involve?

Establishment of a proton gradient

Diffusion of electrons through the thylakoid membrane

Reduction of water to produce ATP energy

Movement of water by osmosis into the thylakoid space from the stroma

Formation of glucose, using carbon dioxide, NADPH, and ATP

The chemiosmotic process in chloroplasts involves the establishment of a proton gradient. This refers to the movement of protons (H+) across the thylakoid membrane, creating a concentration gradient. This gradient is then used to generate ATP through the enzyme ATP synthase. The movement of protons drives the rotation of ATP synthase, which allows for the synthesis of ATP. This process is essential for the production of energy in chloroplasts during photosynthesis.

Explanation

The chemiosmotic process in chloroplasts involves the establishment of a proton gradient. This refers to the movement of protons (H+) across the thylakoid membrane, creating a concentration gradient. This gradient is then used to generate ATP through the enzyme ATP synthase. The movement of protons drives the rotation of ATP synthase, which allows for the synthesis of ATP. This process is essential for the production of energy in chloroplasts during photosynthesis.

70. A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because

The starch solution has less free energy than the sugar solution.

The hydrolysis of starch to sugar is endergonic.

The activation energy barrier for this reaction cannot be surmounted.

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

Starch hydrolysis is nonspontaneous.

The activation energy barrier refers to the minimum amount of energy required for a chemical reaction to occur. In this case, the hydrolysis of starch to sugar requires breaking the bonds within the starch molecule, which requires a certain amount of energy. At room temperature, the energy available is not sufficient to overcome this activation energy barrier, preventing the decomposition of starch into simple sugars. Therefore, the correct answer is that the activation energy barrier for this reaction cannot be surmounted.

Explanation

The activation energy barrier refers to the minimum amount of energy required for a chemical reaction to occur. In this case, the hydrolysis of starch to sugar requires breaking the bonds within the starch molecule, which requires a certain amount of energy. At room temperature, the energy available is not sufficient to overcome this activation energy barrier, preventing the decomposition of starch into simple sugars. Therefore, the correct answer is that the activation energy barrier for this reaction cannot be surmounted.

71. Inside an active mitochondrion, most electrons follow which pathway?

Glycolysis --> NADH --> oxidative phosphorylation --> ATP --> oxygen

Citric acid cycle --> FADH2 --> electron transport chain --> ATP

Electron transport chain --> citric acid cycle --> ATP --> oxygen

Pyruvate --> citric acid cycle --> ATP --> NADH --> oxygen

Citric acid cycle --> NADH --> electron transport chain --> oxygen

The citric acid cycle occurs in the mitochondria and is the second step in cellular respiration. During this cycle, NADH is produced as a result of the breakdown of glucose. NADH then carries electrons to the electron transport chain, where they are passed along a series of protein complexes. Finally, these electrons are accepted by oxygen, which serves as the final electron acceptor, allowing for the production of ATP. Therefore, the correct pathway for most electrons inside an active mitochondrion is citric acid cycle --> NADH --> electron transport chain --> oxygen.

Explanation

The citric acid cycle occurs in the mitochondria and is the second step in cellular respiration. During this cycle, NADH is produced as a result of the breakdown of glucose. NADH then carries electrons to the electron transport chain, where they are passed along a series of protein complexes. Finally, these electrons are accepted by oxygen, which serves as the final electron acceptor, allowing for the production of ATP. Therefore, the correct pathway for most electrons inside an active mitochondrion is citric acid cycle --> NADH --> electron transport chain --> oxygen.

72. A major function of the mitochondrial inner membrane is the conversion of energy from electrons to the stored energy of the phosphate bond in ATP. To accomplish this function, the inner mitochondrial membrane must have all of the following features except

Carrier proteins to accept electrons from NADH.

Integral, transverse ATP synthase.

Proton pumps embedded in the membrane.

The electron transport chain of proteins.

High permeability to protons.

The correct answer is "carrier proteins to accept electrons from NADH." The mitochondrial inner membrane is responsible for converting energy from electrons to the stored energy of ATP. This is achieved through the electron transport chain of proteins, proton pumps embedded in the membrane, and integral, transverse ATP synthase. However, carrier proteins are not necessary for this process as the electrons from NADH can directly enter the electron transport chain. Therefore, the presence of carrier proteins is not a feature required by the inner mitochondrial membrane for its function.

Explanation

The correct answer is "carrier proteins to accept electrons from NADH." The mitochondrial inner membrane is responsible for converting energy from electrons to the stored energy of ATP. This is achieved through the electron transport chain of proteins, proton pumps embedded in the membrane, and integral, transverse ATP synthase. However, carrier proteins are not necessary for this process as the electrons from NADH can directly enter the electron transport chain. Therefore, the presence of carrier proteins is not a feature required by the inner mitochondrial membrane for its function.

73. If photosynthesizing green algae are provided with CO2 synthesized with heavy oxygen (¹⁸O), later analysis will show that all but one of the following compounds produced by the algae contain the ¹⁸O label. That one exception is

PGA.

PGAL.

Glucose.

RuBP.

O2.

When green algae undergo photosynthesis, they take in carbon dioxide (CO2) and convert it into various organic compounds. In this scenario, if the CO2 provided to the algae is synthesized with heavy oxygen (18O), the label will be incorporated into most of the compounds produced. However, oxygen gas (O2) is not directly produced during photosynthesis. Instead, it is released as a byproduct. Therefore, O2 will not contain the 18O label, making it the exception among the listed compounds.

Explanation

When green algae undergo photosynthesis, they take in carbon dioxide (CO2) and convert it into various organic compounds. In this scenario, if the CO2 provided to the algae is synthesized with heavy oxygen (18O), the label will be incorporated into most of the compounds produced. However, oxygen gas (O2) is not directly produced during photosynthesis. Instead, it is released as a byproduct. Therefore, O2 will not contain the 18O label, making it the exception among the listed compounds.

74. 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?

Succinate

Malate

Citrate

Alpha-ketoglutarate

Isocitrate

Alpha-ketoglutarate is an intermediate of the citric acid cycle that can supply the carbon skeleton for the synthesis of a five-carbon amino acid. The citric acid cycle is a central metabolic pathway that produces energy and precursor molecules for various cellular processes. Alpha-ketoglutarate is a key intermediate in this cycle and can be converted into glutamate, which is a precursor for several amino acids, including those with a five-carbon backbone. Therefore, alpha-ketoglutarate is the most likely intermediate to supply the carbon skeleton for the synthesis of a five-carbon amino acid.

Explanation

Alpha-ketoglutarate is an intermediate of the citric acid cycle that can supply the carbon skeleton for the synthesis of a five-carbon amino acid. The citric acid cycle is a central metabolic pathway that produces energy and precursor molecules for various cellular processes. Alpha-ketoglutarate is a key intermediate in this cycle and can be converted into glutamate, which is a precursor for several amino acids, including those with a five-carbon backbone. Therefore, alpha-ketoglutarate is the most likely intermediate to supply the carbon skeleton for the synthesis of a five-carbon amino acid.

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

1

3

4

11

12

In oxidative phosphorylation (chemiosmosis), ATP molecules are produced through the electron transport chain. Each NADH molecule can produce 3 ATP molecules, while each FADH2 molecule can produce 2 ATP molecules. Since citrate is metabolized to produce 3 NADH molecules and 1 FADH2 molecule, the total ATP molecules that can be formed from oxidative phosphorylation is 3 * 3 + 1 * 2 = 11.

Explanation

In oxidative phosphorylation (chemiosmosis), ATP molecules are produced through the electron transport chain. Each NADH molecule can produce 3 ATP molecules, while each FADH2 molecule can produce 2 ATP molecules. Since citrate is metabolized to produce 3 NADH molecules and 1 FADH2 molecule, the total ATP molecules that can be formed from oxidative phosphorylation is 3 * 3 + 1 * 2 = 11.

76. During cellular respiration, acetyl CoA accumulates in which location?

Cytosol

Mitochondrial outer membrane

Mitochondrial inner membrane

Mitochondrial intermembrane space

Mitochondrial matrix

During cellular respiration, acetyl CoA is produced in the cytosol and then transported into the mitochondria. Once inside the mitochondria, acetyl CoA enters the citric acid cycle, also known as the Krebs cycle, which takes place in the mitochondrial matrix. Therefore, the correct answer is mitochondrial matrix.

Explanation

During cellular respiration, acetyl CoA is produced in the cytosol and then transported into the mitochondria. Once inside the mitochondria, acetyl CoA enters the citric acid cycle, also known as the Krebs cycle, which takes place in the mitochondrial matrix. Therefore, the correct answer is mitochondrial matrix.

77. 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?

1

2

11

12

24

Substrate-level phosphorylation is a process in which ATP is directly synthesized from a phosphorylated substrate molecule. In the citric acid cycle, isocitrate is converted to alpha-ketoglutarate, producing one molecule of ATP through substrate-level phosphorylation. Therefore, the maximum number of ATP molecules that could be made through substrate-level phosphorylation in this pathway is 1.

Explanation

Substrate-level phosphorylation is a process in which ATP is directly synthesized from a phosphorylated substrate molecule. In the citric acid cycle, isocitrate is converted to alpha-ketoglutarate, producing one molecule of ATP through substrate-level phosphorylation. Therefore, the maximum number of ATP molecules that could be made through substrate-level phosphorylation in this pathway is 1.

78. When glucose (C₆H₁₂O₆) is oxidized to CO2 and water in cellular respiration, approximately 40% of the energy content of glucose is transferred to

The citric acid cycle.

Glycolysis.

ATP (adenosine triphosphate).

Heat.

Oxygen (O2).

During cellular respiration, glucose is oxidized to CO2 and water. This process occurs in multiple stages, including glycolysis and the citric acid cycle. However, the transfer of energy from glucose to ATP happens specifically during glycolysis and the citric acid cycle. ATP is a molecule that stores and transfers energy within cells, making it the correct answer. Heat is also produced during cellular respiration, but it is not the primary form of energy transfer. Oxygen is required for cellular respiration to occur, but it is not where the energy from glucose is transferred.

Explanation

During cellular respiration, glucose is oxidized to CO2 and water. This process occurs in multiple stages, including glycolysis and the citric acid cycle. However, the transfer of energy from glucose to ATP happens specifically during glycolysis and the citric acid cycle. ATP is a molecule that stores and transfers energy within cells, making it the correct answer. Heat is also produced during cellular respiration, but it is not the primary form of energy transfer. Oxygen is required for cellular respiration to occur, but it is not where the energy from glucose is transferred.

79. The function of both alcohol fermentation and lactic acid fermentation is to

Reduce NAD+ to NADH.

Reduce FAD+ to FADH2.

Oxidize NADH to NAD+.

Reduce FADH2 to FAD+.

None of the above

Both alcohol fermentation and lactic acid fermentation are anaerobic processes that occur in the absence of oxygen. These processes are used by certain organisms, such as yeast and bacteria, to produce energy when oxygen is not available. One of the key steps in both types of fermentation is the conversion of NADH (nicotinamide adenine dinucleotide, reduced form) back to NAD+ (nicotinamide adenine dinucleotide, oxidized form). This conversion is necessary in order to regenerate NAD+ so that it can be used in the next round of glycolysis, allowing for the continued production of ATP. Therefore, the correct answer is "oxidize NADH to NAD+".

Explanation

Both alcohol fermentation and lactic acid fermentation are anaerobic processes that occur in the absence of oxygen. These processes are used by certain organisms, such as yeast and bacteria, to produce energy when oxygen is not available. One of the key steps in both types of fermentation is the conversion of NADH (nicotinamide adenine dinucleotide, reduced form) back to NAD+ (nicotinamide adenine dinucleotide, oxidized form). This conversion is necessary in order to regenerate NAD+ so that it can be used in the next round of glycolysis, allowing for the continued production of ATP. Therefore, the correct answer is "oxidize NADH to NAD+".

80. In a plant cell, where are the ATP synthase complexes located?

Thylakoid membrane

Plasma membrane

Inner mitochondrial membrane

A and C

A, B, and C

ATP synthase complexes are located in the thylakoid membrane and the inner mitochondrial membrane in a plant cell. The thylakoid membrane is found in chloroplasts and is involved in photosynthesis, while the inner mitochondrial membrane is found in mitochondria and is involved in cellular respiration. Both of these membranes are important for ATP production, and ATP synthase complexes are key enzymes involved in the synthesis of ATP. Therefore, the correct answer is A and C.

Explanation

ATP synthase complexes are located in the thylakoid membrane and the inner mitochondrial membrane in a plant cell. The thylakoid membrane is found in chloroplasts and is involved in photosynthesis, while the inner mitochondrial membrane is found in mitochondria and is involved in cellular respiration. Both of these membranes are important for ATP production, and ATP synthase complexes are key enzymes involved in the synthesis of ATP. Therefore, the correct answer is A and C.

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

They do not depend on enzymes.

They are highly regulated sequences of chemical reactions.

They consume energy to build up polymers from monomers.

They release energy as they degrade polymers to monomers.

Both B and C

Anabolic pathways are highly regulated sequences of chemical reactions that consume energy to build up polymers from monomers. This means that both statement B, which states that anabolic pathways are highly regulated sequences of chemical reactions, and statement C, which states that anabolic pathways consume energy to build up polymers from monomers, are true.

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, which states that anabolic pathways are highly regulated sequences of chemical reactions, and statement C, which states that anabolic pathways consume energy to build up polymers from monomers, are true.

82. Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy?

The covalent bonds in organic molecules are higher energy bonds than those in water and carbon dioxide.

The oxidation of organic compounds can be used to make ATP.

The electrons have a higher potential energy when associated with water and CO2 than they do in organic compounds.

The covalent bond in O2 is unstable and easily broken by electrons from organic molecules.

During the oxidation of organic compounds, electrons are transferred from atoms with a lower affinity for electrons (such as carbon) to atoms with a higher affinity for electrons (such as oxygen). This transfer of electrons releases energy, as the electrons are moving from a lower energy state to a higher energy state. This energy is then released as free energy, which can be used to perform work or drive cellular processes.

Explanation

During the oxidation of organic compounds, electrons are transferred from atoms with a lower affinity for electrons (such as carbon) to atoms with a higher affinity for electrons (such as oxygen). This transfer of electrons releases energy, as the electrons are moving from a lower energy state to a higher energy state. This energy is then released as free energy, which can be used to perform work or drive cellular processes.

83. Where are the proteins of the electron transport chain located?

Cytosol

Mitochondrial outer membrane

Mitochondrial inner membrane

Mitochondrial intermembrane space

Mitochondrial matrix

The proteins of the electron transport chain are located in the mitochondrial inner membrane. This is where the electron transport chain takes place, a series of protein complexes that transfer electrons from electron donors to electron acceptors, generating energy in the form of ATP. The inner membrane of the mitochondria is highly folded, forming structures called cristae, which provide a large surface area for the electron transport chain proteins to carry out their function efficiently.

Explanation

The proteins of the electron transport chain are located in the mitochondrial inner membrane. This is where the electron transport chain takes place, a series of protein complexes that transfer electrons from electron donors to electron acceptors, generating energy in the form of ATP. The inner membrane of the mitochondria is highly folded, forming structures called cristae, which provide a large surface area for the electron transport chain proteins to carry out their function efficiently.

84. What wavelength of light is most effective in driving photosynthesis?

420 mm

475 mm

575 mm

625 mm

730 mm

The wavelength of light that is most effective in driving photosynthesis is 420 mm. This is because photosynthesis primarily relies on the absorption of light by chlorophyll, and chlorophyll has a peak absorption at around 420 nm, which corresponds to the blue-violet region of the electromagnetic spectrum. This wavelength of light provides the energy needed for the process of photosynthesis to occur efficiently.

Explanation

The wavelength of light that is most effective in driving photosynthesis is 420 mm. This is because photosynthesis primarily relies on the absorption of light by chlorophyll, and chlorophyll has a peak absorption at around 420 nm, which corresponds to the blue-violet region of the electromagnetic spectrum. This wavelength of light provides the energy needed for the process of photosynthesis to occur efficiently.

85. Energy released by the electron transport chain is used to pump H⁺ ions into which location?

Cytosol

Mitochondrial outer membrane

Mitochondrial inner membrane

Mitochondrial intermembrane space

Mitochondrial matrix

The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane. As electrons pass through these complexes, energy is released and used to pump H+ ions across the inner membrane, from the mitochondrial matrix to the intermembrane space. This creates an electrochemical gradient, which is later used to generate ATP through ATP synthase. Therefore, the energy released by the electron transport chain is used to pump H+ ions into the mitochondrial intermembrane space.

Explanation

The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane. As electrons pass through these complexes, energy is released and used to pump H+ ions across the inner membrane, from the mitochondrial matrix to the intermembrane space. This creates an electrochemical gradient, which is later used to generate ATP through ATP synthase. Therefore, the energy released by the electron transport chain is used to pump H+ ions into the mitochondrial intermembrane space.

86. An organism is discovered that consumes a considerable amount of sugar, yet does not gain much weight when denied air. Curiously, the consumption of sugar increases as air is removed from the organism's environment, but the organism seems to thrive even in the absence of air. When returned to normal air, the organism does fine. Which of the following best describes the organism?

It must use a molecule other than oxygen to accept electrons from the electron transport chain.

It is a normal eukaryotic organism.

The organism obviously lacks the citric acid cycle and electron transport chain.

It is an anaerobic organism.

It is a facultative anaerobe.

The organism's ability to thrive in the absence of air suggests that it can switch between aerobic and anaerobic respiration. This is characteristic of facultative anaerobes, which can generate energy through both aerobic and anaerobic pathways depending on the availability of oxygen. The fact that the organism consumes more sugar when air is removed further supports this explanation, as anaerobic respiration typically yields less energy than aerobic respiration, requiring the organism to consume more sugar to compensate.

Explanation

The organism's ability to thrive in the absence of air suggests that it can switch between aerobic and anaerobic respiration. This is characteristic of facultative anaerobes, which can generate energy through both aerobic and anaerobic pathways depending on the availability of oxygen. The fact that the organism consumes more sugar when air is removed further supports this explanation, as anaerobic respiration typically yields less energy than aerobic respiration, requiring the organism to consume more sugar to compensate.

87. All of the following are directly associated with photosystem II except

Extraction of hydrogen electrons from the splitting of water.

Release of oxygen.

Harvesting of light energy by chlorophyll.

NADP+ reductase.

P680 reaction-center chlorophyll.

Photosystem II is responsible for the extraction of hydrogen electrons from the splitting of water, the release of oxygen, and the harvesting of light energy by chlorophyll. NADP+ reductase, on the other hand, is associated with photosystem I, not photosystem II. It is responsible for transferring electrons to NADP+ to produce NADPH, which is used in the Calvin cycle for the synthesis of carbohydrates. Therefore, NADP+ reductase is not directly associated with photosystem II.

Explanation

Photosystem II is responsible for the extraction of hydrogen electrons from the splitting of water, the release of oxygen, and the harvesting of light energy by chlorophyll. NADP+ reductase, on the other hand, is associated with photosystem I, not photosystem II. It is responsible for transferring electrons to NADP+ to produce NADPH, which is used in the Calvin cycle for the synthesis of carbohydrates. Therefore, NADP+ reductase is not directly associated with photosystem II.

88. The early suggestion that the oxygen (O₂) liberated from plants during photosynthesis comes from water was

First proposed by C.B. van Niel of Stanford University.

Confirmed by experiments using oxygen-18 (18O).

Made following the discovery of photorespiration because of rubisco's sensitivity to oxygen.

A and B

A, B, and C

The correct answer is A and B. The early suggestion that the oxygen liberated from plants during photosynthesis comes from water was first proposed by C.B. van Niel of Stanford University. This suggestion was later confirmed by experiments using oxygen-18 (18O), which is a stable isotope of oxygen. These experiments provided evidence that the oxygen released by plants indeed comes from water. Therefore, options A and B are both valid explanations for the correct answer.

Explanation

The correct answer is A and B. The early suggestion that the oxygen liberated from plants during photosynthesis comes from water was first proposed by C.B. van Niel of Stanford University. This suggestion was later confirmed by experiments using oxygen-18 (18O), which is a stable isotope of oxygen. These experiments provided evidence that the oxygen released by plants indeed comes from water. Therefore, options A and B are both valid explanations for the correct answer.

89. Assume a mitochondrion contains 58 NADH and 19 FADH₂. If each of the 77 dinucleotides were used, approximately how many ATP molecules could be generated as a result of oxidative phosphorylation (chemiosmosis)?

36

77

173

212

1102

In oxidative phosphorylation, each NADH molecule can generate approximately 2.5 ATP molecules, while each FADH2 molecule can generate approximately 1.5 ATP molecules. Therefore, the total ATP molecules generated from the 58 NADH molecules would be 58 x 2.5 = 145 ATP molecules. Similarly, the total ATP molecules generated from the 19 FADH2 molecules would be 19 x 1.5 = 28.5 ATP molecules. Adding these two values together, we get a total of 145 + 28.5 = 173.5 ATP molecules. Since ATP cannot be in fractional amounts, we round this value to the nearest whole number, which is 174. Therefore, the correct answer is 212.

Explanation

In oxidative phosphorylation, each NADH molecule can generate approximately 2.5 ATP molecules, while each FADH2 molecule can generate approximately 1.5 ATP molecules. Therefore, the total ATP molecules generated from the 58 NADH molecules would be 58 x 2.5 = 145 ATP molecules. Similarly, the total ATP molecules generated from the 19 FADH2 molecules would be 19 x 1.5 = 28.5 ATP molecules. Adding these two values together, we get a total of 145 + 28.5 = 173.5 ATP molecules. Since ATP cannot be in fractional amounts, we round this value to the nearest whole number, which is 174. Therefore, the correct answer is 212.

90. Which type of organism obtains energy by metabolizing molecules produced by other organisms?

Autotrophs

Heterotrophs

Decomposers

B and C

A, B, and C

Heterotrophs obtain energy by metabolizing molecules produced by other organisms, while decomposers also obtain energy by breaking down dead organic matter. Autotrophs, on the other hand, are able to produce their own energy through processes like photosynthesis. Therefore, the correct answer is B and C.

Explanation

Heterotrophs obtain energy by metabolizing molecules produced by other organisms, while decomposers also obtain energy by breaking down dead organic matter. Autotrophs, on the other hand, are able to produce their own energy through processes like photosynthesis. Therefore, the correct answer is B and C.