Quiz: Bioenergetics and ATP — 24 questions

1. Regarding the Bioenergetics Exam Framework, which statements are correct?

A. Theoretical maximum estimates of 36 or 38 ATP can appear in bioenergetics calculations.

B. Bioenergetics questions commonly combine pathway locations with ATP and electron-carrier accounting.

C. The realistic ATP yield from glucose is fixed at exactly 36 ATP in human cells.

D. Bioenergetics questions generally separate pathway location from input and output analysis.

E. The realistic ATP yield from one glucose molecule is approximately 30–32 ATP.

Answer: (A), (B), (E)

Explanation

Bioenergetics questions commonly integrate where pathways occur with their inputs, outputs, and energy-carrier accounting. The realistic ATP yield is approximate because efficiency and NADH transport costs vary, rather than being a fixed theoretical maximum.

2. A student reports both 38 ATP and approximately 30–32 ATP per glucose. Which statements correctly interpret these values?

A. Variation in NADH transport costs contributes to differences from theoretical estimates.

B. The approximate yield of 30–32 ATP reflects realistic cellular conditions.

C. A yield of 30–32 ATP indicates that glycolysis occurs in mitochondria.

D. A fixed yield of 36 ATP is the standard realistic value for every human cell.

E. The value of 38 ATP represents a theoretical maximum estimate.

Answer: (A), (B), (E)

Explanation

Theoretical values of 36 or 38 ATP represent maximum estimates. Actual yield is approximately 30–32 ATP because efficiency and NADH transport costs vary.

3. Concerning the locations of major energy-producing pathways, select the correct statements:

A. The Krebs cycle occurs in the mitochondrial matrix.

B. Glycolysis takes place in the mitochondrial matrix.

C. Glycolysis takes place in the cytoplasm of the cell.

D. The Krebs cycle occurs across the inner mitochondrial membrane.

E. The respiratory electron transport chain operates across the inner mitochondrial membrane.

Answer: (A), (C), (E)

Explanation

Glycolysis occurs in the cytoplasm, the Krebs cycle in the mitochondrial matrix, and the electron transport chain across the inner mitochondrial membrane. These locations are distinct and form a common framework for pathway questions.

4. Regarding ATP structure and recycling, which statements are correct?

A. The bonds linking ATP’s second and third phosphates are peptide bonds.

B. ATP hydrolysis is favourable because ADP and inorganic phosphate are more stable.

C. ATP is hydrolysed to ADP and inorganic phosphate during cellular work.

D. Phosphoanhydride bonds link ATP’s second and third phosphate groups.

E. ADP is re-phosphorylated using energy obtained from food breakdown.

Answer: (B), (C), (D), (E)

Explanation

Phosphoanhydride bonds link ATP’s second and third phosphate groups. Hydrolysis is favourable because ADP and inorganic phosphate are more stable than ATP, and ATP is continually regenerated after use.

5. A cell repeatedly uses and regenerates ATP. Which statements correctly describe this process?

A. ATP functions as a rapidly recycled energy currency in cells.

B. ATP hydrolysis converts ADP and phosphate into stored glucose.

C. Glucose, glycogen, and fat are directly re-phosphorylated into ATP molecules.

D. ATP hydrolysis produces ADP and inorganic phosphate during cellular work.

E. Energy from food breakdown supports ADP re-phosphorylation.

Answer: (A), (D), (E)

Explanation

ATP hydrolysis produces ADP and inorganic phosphate to drive cellular work. Energy from food breakdown then re-phosphorylates ADP, allowing ATP to be continuously recycled.

6. Concerning exergonic and endergonic reactions, which statements are correct?

A. An endergonic reaction requires free-energy input to proceed.

B. An exergonic reaction requires energy input because its products are higher in free energy.

C. An exergonic reaction releases free energy during the reaction.

D. Exergonic products have lower free energy than the reactants.

E. Endergonic products have lower free energy than the reactants.

Answer: (A), (C), (D)

Explanation

An exergonic reaction releases free energy because its products have lower free energy than its reactants. An endergonic reaction has the opposite energy relationship and requires input.

7. A biochemical reaction produces molecules with higher free energy than its starting molecules. Which statements correctly apply?

A. An exergonic reaction would instead produce lower-free-energy products.

B. The reaction proceeds because its products are more stable than its reactants.

C. The reaction is endergonic because its products have higher free energy.

D. The reaction is exergonic because higher-energy products release free energy.

E. The reaction requires an input of free energy to proceed.

Answer: (A), (C), (E)

Explanation

Endergonic reactions require free-energy input because their products have higher free energy than their reactants. Exergonic reactions instead release free energy, so they do not have the stated endergonic energy relationship.

8. Regarding ATP-mediated energy coupling, which statements are correct?

A. ATP coupling lowers the substrate’s free energy before an endergonic reaction.

B. Phosphate transfer temporarily increases the substrate’s free energy.

C. ATP hydrolysis drives cellular work without involving a substrate intermediate.

D. ATP’s terminal phosphate may be transferred to a substrate.

E. ATP hydrolysis can be coupled to an endergonic cellular reaction.

Answer: (B), (D), (E)

Explanation

ATP hydrolysis is coupled to an endergonic cellular reaction by transferring ATP’s terminal phosphate to a substrate. This temporary phosphorylation raises the substrate’s free energy and helps drive the reaction.

9. Regarding redox reactions and electron carriers, which statements are correct?

A. NAD⁺ accepts two electrons and two protons overall to form NADH plus one released proton.

B. Oxidation involves the loss of electrons, whereas reduction involves their gain.

C. Oxidation and reduction occur together within a redox reaction.

D. FAD accepts two hydrogen atoms to form FADH₂ and later transfers their electrons.

E. NADH accepts electrons from NAD⁺ during the reduction of the carrier.

Answer: (A), (B), (C), (D)

Explanation

Oxidation involves electron loss, whereas reduction involves electron gain; these paired processes occur together in redox reactions. NAD⁺ accepts electrons and protons to form NADH while releasing one proton into solution; FAD instead accepts two hydrogen atoms and later transfers their electrons to the electron transport chain.

10. Concerning the reduction of electron carriers, select the accurate statements:

A. FAD becomes FADH₂ after accepting two hydrogen atoms.

B. NADH is converted into NAD⁺ by accepting electrons from the surrounding solution.

C. NAD⁺ accepts two electrons and two protons overall during its reduction.

D. NADH is the reduced carrier that delivers electrons to later reactions.

E. NAD⁺ becomes NADH while releasing one proton into solution.

Answer: (A), (C), (D), (E)

Explanation

NAD⁺ is reduced when it accepts two electrons and two protons overall, producing NADH and releasing one proton. NADH is the reduced carrier, whereas FAD accepts two hydrogen atoms to become FADH₂ and later delivers their electrons.

11. The main features of glycolysis include which of the following?

A. Glycolysis directly converts glucose into two acetyl-CoA molecules.

B. Glycolysis proceeds through ten enzyme-catalysed steps.

C. Glycolysis takes place in the mitochondrial matrix when oxygen is available.

D. One glucose molecule is split into two three-carbon pyruvate molecules.

E. Glycolysis occurs in the cytosol without requiring oxygen.

Answer: (B), (D), (E)

Explanation

Glycolysis takes place in the cytosol, does not require oxygen, and converts one six-carbon glucose into two three-carbon pyruvate molecules through ten enzyme-catalysed steps. Fermentation is associated with pyruvate’s later fate when oxygen is unavailable, not with the oxygen requirement of glycolysis itself.

12. For the link reaction associated with one glucose molecule, select the accurate statements:

A. The link reaction occurs once because glucose forms one pyruvate molecule.

B. Two acetyl-CoA molecules are formed per glucose.

C. The link reaction occurs twice because one glucose produces two pyruvate.

D. Two NADH molecules are produced per glucose.

E. Two carbon dioxide molecules are released per glucose.

Answer: (B), (C), (D), (E)

Explanation

One glucose produces two pyruvate, so the link reaction occurs twice and yields two acetyl-CoA, two carbon dioxide, and two NADH. The two pyruvate molecules arise from one six-carbon glucose molecule, not from two starting glucose molecules.

13. The Krebs cycle and respiratory electron transport chain are characterized by which statements?

A. The Krebs cycle turns twice for each glucose molecule.

B. The Krebs cycle produces four carbon dioxide molecules per glucose.

C. The Krebs cycle occurs in the mitochondrial matrix.

D. The Krebs cycle yields six NADH and two FADH₂ per glucose.

E. The Krebs cycle produces two acetyl-CoA molecules as its principal glucose yield.

Answer: (A), (B), (C), (D)

Explanation

The Krebs cycle occurs in the mitochondrial matrix and turns twice per glucose. Its yield per glucose is four carbon dioxide, six NADH, two FADH₂, and two ATP; the electron transport chain then uses NADH and FADH₂ to pump protons across the inner membrane.

14. Which statements correctly describe aerobic respiration after the Krebs cycle?

A. Chemiosmosis produces ATP through proton flow across ATP synthase.

B. Oxygen accepts electrons and protons to form water at the chain’s end.

C. Protons are pumped into the intercristal space during electron transport.

D. Carbon dioxide accepts the final electrons and protons to form water.

E. Electron transport chain complexes receive electrons from NADH and FADH₂.

Answer: (A), (B), (C), (E)

Explanation

The electron transport chain transfers electrons from NADH and FADH₂ through protein complexes in the inner mitochondrial membrane, pumping protons into the intercristal space. Chemiosmosis uses proton flow through ATP synthase to produce ATP, and oxygen accepts the electrons and protons to form water.

15. Regarding the role of fermentation in cellular energy production:

A. Fermentation allows glycolysis to maintain its net yield of two ATP per glucose.

B. Fermentation converts glycolytic ATP directly into additional oxidative phosphorylation products.

C. Fermentation prevents glycolysis from producing ATP when oxygen is unavailable.

D. Fermentation generates most aerobic ATP through an electron transport chain.

E. Fermentation regenerates NAD⁺ when NADH cannot be reoxidized by oxidative phosphorylation.

Answer: (A), (E)

Explanation

Fermentation restores NAD⁺ when oxidative phosphorylation cannot reoxidize NADH, allowing glycolysis to continue. Glycolysis then supplies a net yield of two ATP per glucose, while fermentation itself adds no ATP.

16. Which statements accurately distinguish lactic acid fermentation from alcoholic fermentation?

A. Lactic fermentation produces lactate in animal cells and some bacteria.

B. Alcoholic fermentation produces ethanol and carbon dioxide in yeast and some bacteria.

C. Lactic fermentation and alcoholic fermentation produce identical end products.

D. Alcoholic fermentation reduces pyruvate to lactate in animal muscle cells.

E. Lactic fermentation releases carbon dioxide while producing ethanol.

Answer: (A), (B)

Explanation

Lactic fermentation reduces pyruvate to lactate without releasing carbon dioxide, whereas alcoholic fermentation produces ethanol and carbon dioxide. These products distinguish the two pathways and their typical organisms.

17. Concerning the energetic consequences of lactic acid and alcoholic fermentation:

A. Both pathways generate additional ATP beyond glycolysis.

B. Both pathways depend on oxidative phosphorylation to produce their ATP.

C. Both pathways regenerate NAD⁺ to support continued glycolysis.

D. Both pathways preserve glycolytic ATP production without adding extra ATP.

E. Both pathways preserve a net yield of two ATP per glucose.

Answer: (C), (D), (E)

Explanation

Both fermentation pathways regenerate NAD⁺ and preserve glycolysis’s net production of two ATP per glucose. Neither pathway produces additional ATP beyond the glycolytic yield.

18. Which statements correctly describe the organization of chloroplasts and mitochondria?

A. Light-dependent reactions occur across the mitochondrial inner membrane.

B. The Calvin cycle takes place within the mitochondrial matrix.

C. Mitochondrial respiration uses the inner membrane and matrix.

D. Chloroplast thylakoid membranes are arranged into stacks called grana.

E. The chloroplast stroma surrounds and contains the thylakoid stacks.

Answer: (C), (D), (E)

Explanation

Thylakoid membranes are stacked into grana and suspended in the stroma. In contrast, mitochondria use their inner membrane and matrix for respiration, while the Calvin cycle occurs in the chloroplast stroma.

19. Concerning the events of the light-dependent reactions, which statements are accurate?

A. Light excites electrons within the thylakoid membrane system.

B. ATP synthase produces ATP by photophosphorylation.

C. Electron transport through the thylakoid membrane pumps protons.

D. Photosystem II splits water and releases molecular oxygen.

E. RuBisCO fixes carbon dioxide during the light-dependent reactions.

Answer: (A), (B), (C), (D)

Explanation

Light-dependent reactions occur across thylakoid membranes. Photosystem II splits water, electron transport pumps protons, and ATP synthase produces ATP through photophosphorylation.

20. Regarding electron acceptance during the light-dependent reactions:

A. NADP⁺ is converted directly into ATP by ATP synthase.

B. NADP⁺ accepts electrons after their passage through the photosynthetic electron chain.

C. Reduction of NADP⁺ produces NADPH.

D. NADP⁺ serves as the final electron acceptor.

E. Oxygen serves as the final electron acceptor and is reduced to water.

Answer: (B), (C), (D)

Explanation

NADP⁺ accepts the electrons at the end of the light-dependent reactions and is reduced to NADPH. Oxygen is released during water splitting rather than serving as the final electron acceptor.

21. The Calvin cycle includes which of the following processes?

A. RuBisCO attaches carbon dioxide to RuBP.

B. Most produced G3P contributes to regeneration of RuBP.

C. The Calvin cycle takes place in the chloroplast stroma.

D. ATP and NADPH help produce G3P from three-carbon compounds.

E. The Calvin cycle splits water across the thylakoid membrane.

Answer: (A), (B), (C), (D)

Explanation

The Calvin cycle occurs in the stroma, where RuBisCO fixes carbon dioxide onto RuBP. ATP and NADPH help convert the resulting three-carbon compounds into G3P, with most G3P regenerating RuBP.

22. Which comparisons between respiratory and thylakoid electron transport chains are correct?

A. Oxygen is the final electron acceptor in respiratory electron transport.

B. NADP⁺ is the final electron acceptor in the thylakoid chain.

C. The thylakoid chain uses oxygen as its final electron acceptor.

D. Water supplies electrons to the thylakoid electron transport chain.

E. Respiratory electron transport receives electrons from NADH and FADH₂.

Answer: (A), (B), (D), (E)

Explanation

The respiratory chain receives electrons from NADH and FADH₂ and ultimately transfers them to oxygen. The thylakoid chain receives electrons from water and ultimately reduces NADP⁺ to NADPH.

23. Regarding ATP-producing pathways during glucose respiration, which statements are correct?

A. Oxidative phosphorylation produces ATP directly from glucose cleavage reactions.

B. The Krebs cycle includes substrate-level phosphorylation.

C. Oxidative phosphorylation produces most ATP derived from glucose.

D. Substrate-level phosphorylation occurs during glycolysis.

E. The respiratory electron transport chain drives oxidative phosphorylation.

Answer: (B), (C), (D), (E)

Explanation

Oxidative phosphorylation generates most ATP from glucose through the respiratory electron transport chain. Substrate-level phosphorylation makes ATP directly during glycolysis and the Krebs cycle.

24. Concerning the ATP yield from complete oxidation of one glucose molecule:

A. More than twenty ATP molecules typically arise from oxidative phosphorylation.

B. The total yield is commonly estimated at approximately 30–32 ATP rather than an exact fixed value.

C. The realistic total yield is approximately 30–32 ATP.

D. Oxidative phosphorylation contributes fewer than ten ATP molecules.

E. Direct substrate-level phosphorylation supplies most of the total ATP.

Answer: (A), (B), (C)

Explanation

A realistic glucose yield is approximately 30–32 ATP. More than twenty ATP molecules generally arise from oxidative phosphorylation rather than direct substrate-level phosphorylation.