Bioenergetics

Biology, SSC-Punjab Class 9. This chapter is split into 26 topics and has 626 practice questions. The topics covered are listed below, followed by 10 free sample questions from the chapter.

Topics in this chapter

1. Cellular respiration: aerobic respiration overview 24 questions
2. ATP: structure and the cell's energy currency 25 questions
3. Photosynthesis: dark reactions (Calvin cycle) 24 questions
4. Mechanism of respiration: electron transport chain and ATP yield 24 questions
5. Photosynthesis: definition, equation, and light reactions 27 questions
6. Anaerobic respiration and fermentation 27 questions
7. Mechanism of respiration: glycolysis and the Krebs cycle 27 questions
8. Comparison of photosynthesis and respiration 22 questions
9. The ATP-ADP cycle and energy release 24 questions
10. Role of chlorophyll in photosynthesis 22 questions
11. Use of respiratory energy and comparison of aerobic and anaerobic respiration 24 questions
12. Learning outcomes and key points of Bioenergetics 23 questions
13. End-of-chapter exercise: select the correct answer 24 questions
14. ATP structure and energy calculations 24 questions
15. Photosynthesis equation and raw materials 25 questions
16. Light reactions: electrons, water splitting and NADPH 24 questions
17. Calvin cycle: carbon counting and figure details 24 questions
18. Pigments and light absorption scenarios 22 questions
19. Aerobic and anaerobic respiration: features and reasoning 24 questions
20. Fermentation: equations, organisms and applications 25 questions
21. Glycolysis, link reaction and Krebs cycle: counting molecules 27 questions
22. Electron transport chain and total ATP from glucose 23 questions
23. Uses of respiratory energy: scenarios and list items 23 questions
24. Photosynthesis and respiration: finer comparisons 24 questions
25. Bioenergetics: odd-one-out, true-false and reasoning items 20 questions
26. Glossary terms related to Bioenergetics 24 questions

Sample questions: Bioenergetics

10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.

Q1. Arrange the following key events of the light reactions (Figure 8.3) in the correct order:

• A. Water is split -> NADPH is formed -> chlorophyll absorbs light -> the electron transport chain begins
• B. Chlorophyll absorbs light and releases high-energy electrons -> electrons pass through the electron transport chain, producing ATP -> water is split, releasing oxygen and hydrogen ions -> NADP is reduced to NADPH(correct answer)
• C. NADP is reduced to NADPH -> water is split -> chlorophyll absorbs light -> ATP is produced
• D. ATP is produced -> chlorophyll absorbs light -> water is split -> electrons enter the transport chain

Answer: B.The light reactions begin with chlorophyll absorbing light and releasing high-energy electrons, which pass through the electron transport chain to produce ATP, while water is split releasing oxygen and hydrogen ions, and finally NADP is reduced to NADPH using the electrons and hydrogen ions.

Q2. Arrange the following steps of the Calvin Cycle (Figure 8.4) in the correct order:

• A. 3-C carbohydrates form first, before any CO₂ enters the cycle
• B. 5-C compounds regenerate first -> then CO₂ combines with 6-C compounds -> then glucose splits into 3-C compounds
• C. Glucose forms first -> then 3-C carbohydrates form -> then 6-C compounds form -> then CO₂ is released
• D. CO₂ combines with 5-C compounds -> unstable 6-C compounds form and split into 3-C compounds -> 3-C compounds are reduced to 3-C carbohydrates using ATP/NADPH -> carbohydrates form glucose or regenerate 5-C compounds(correct answer)

Answer: D.The Calvin Cycle proceeds from CO₂ combining with 5-carbon compounds, forming unstable 6-carbon compounds that split into 3-carbon compounds, which are then reduced to 3-carbon carbohydrates using ATP/NADPH, finally forming glucose or regenerating the 5-carbon compounds.

Q3. Assertion: The dark reactions can, in principle, continue for a short time even immediately after light exposure stops. Reason: The dark reactions rely on ATP and NADPH that were already produced during the preceding light reactions. What is the correct relationship?

• A. Both assertion and reason are true, and the reason correctly explains the assertion(correct answer)
• B. The assertion is true, but the reason is false
• C. Both are true, but the reason does not explain the assertion
• D. The assertion is false, but the reason is true

Answer: A.Since dark reactions use previously produced ATP and NADPH rather than directly requiring light, they could, in principle, continue briefly using any existing supply of these molecules even after light exposure stops, correctly explaining the assertion.

Q4. How does the chapter's description of aerobic respiration's two phases relate to the more detailed mechanism of cellular respiration described later in the chapter (glycolysis, Krebs cycle, electron transport chain)?

• A. The first phase corresponds to the electron transport chain, and the second phase corresponds to glycolysis
• B. The two-phase overview has no relationship to the more detailed mechanism
• C. The first phase (glucose to pyruvic acid) corresponds to glycolysis, and the second phase (complete oxidation of pyruvic acid) corresponds to the Krebs cycle and electron transport chain together(correct answer)
• D. Both phases correspond only to the Krebs cycle, with no relation to glycolysis or the electron transport chain

Answer: C.The initial breakdown of glucose into pyruvic acid corresponds to glycolysis, while the complete oxidation of pyruvic acid (releasing all remaining energy) corresponds to the subsequent Krebs cycle and electron transport chain steps detailed later in the chapter.

Q5. If mitochondria in a cell were non-functional, but the cytoplasm remained intact, based on the chapter, the cell would most likely still be able to carry out:

• A. The electron transport chain normally
• B. Complete aerobic respiration with maximum energy yield
• C. The Krebs cycle, since it does not need mitochondria
• D. Glycolysis, since it occurs in the cytoplasm and does not require oxygen(correct answer)

Answer: D.Since glycolysis occurs in the cytoplasm and does not require oxygen or functional mitochondria, a cell with non-functional mitochondria could still carry out glycolysis, though it could not proceed to the Krebs cycle or full aerobic respiration.

Q6. Assertion: Aerobic respiration produces far more ATP per glucose molecule than glycolysis alone. Reason: The Krebs cycle and electron transport chain generate large amounts of NADH and FADH₂, which the electron transport chain converts into substantial additional ATP. What is the correct relationship?

• A. Both assertion and reason are true, and the reason correctly explains the assertion(correct answer)
• B. The assertion is true, but the reason is false
• C. The assertion is false, but the reason is true
• D. Both are true, but the reason does not explain the assertion

Answer: A.The large additional ATP yield of full aerobic respiration compared to glycolysis alone is directly explained by the substantial NADH and FADH₂ generated by the Krebs cycle, which the electron transport chain converts into most of the total 36 ATP.

Q7. Which of the following correctly summarizes why aerobic respiration is generally more advantageous than anaerobic respiration for most complex organisms?

• A. Both types of respiration are functionally identical in every respect
• B. Anaerobic respiration is always the preferred pathway, regardless of oxygen availability
• C. Aerobic respiration produces less ATP than anaerobic respiration
• D. Aerobic respiration produces far more ATP (36) per glucose molecule than anaerobic respiration (2), providing more energy for the many ATP-dependent processes in the body(correct answer)

Answer: D.Because aerobic respiration produces far more ATP (36) per glucose molecule than anaerobic respiration (2), it provides much more energy to power the body's many ATP-dependent processes, making it generally more advantageous when oxygen is available.

Q8. Considering the seven uses of respiratory energy listed in the chapter together, which general theme do they share?

• A. They are all processes that release energy rather than consume it
• B. They all represent essential cellular or bodily processes that require an input of energy (ATP) to occur(correct answer)
• C. They are all processes related only to photosynthesis
• D. They are all processes that occur exclusively in plant cells

Answer: B.The seven uses (muscle contraction, active transport, biomolecule synthesis, DNA replication/mitosis, nerve impulse transmission, temperature maintenance, and toxin elimination) all share the common theme of being essential processes that require an input of ATP energy to occur.

Q9. Reviewing the whole chapter, which sequence best reflects the logical flow of topics from the basic energy currency of the cell to the comparison of the two major energy-related processes?

• A. Cellular respiration -> comparison tables -> ATP as energy currency -> photosynthesis
• B. ATP as the cell's energy currency -> photosynthesis (light and dark reactions, chlorophyll) -> cellular respiration (aerobic/anaerobic, glycolysis, Krebs cycle, electron transport chain) -> comparison of respiration types and comparison with photosynthesis(correct answer)
• C. Photosynthesis -> comparison tables -> cellular respiration -> ATP as energy currency, in that exact reverse order
• D. Comparison of photosynthesis and respiration -> ATP as energy currency -> cellular respiration -> photosynthesis

Answer: B.The chapter logically progresses from introducing ATP as the cell's energy currency, to explaining photosynthesis (including its light and dark reactions and the role of chlorophyll), to explaining cellular respiration (aerobic and anaerobic, with its detailed mechanism), and finally to comparing respiration types and comparing respiration with photosynthesis.

Q10. Which of the following best summarizes the full set of differences between photosynthesis and respiration in type of metabolism, energy handling, capable organisms, site and time of occurrence?

• A. Photosynthesis is an anabolic, light-dependent, daytime-only process restricted to chloroplasts in certain organisms that stores energy, while respiration is a catabolic process occurring in all cells of all organisms at all times, transforming stored energy into ATP(correct answer)
• B. Photosynthesis occurs in all organisms at all times, while respiration is restricted to plants during the day
• C. Both processes are identical in metabolism type, energy handling, capable organisms, site, and timing
• D. Respiration stores bond energy, while photosynthesis transforms energy into ATP

Answer: A.Photosynthesis is anabolic, light/daytime-dependent, restricted to chloroplasts in certain organisms, and stores bond energy, while respiration is catabolic, occurs all the time in all cells (cytoplasm and mitochondria) and transforms the bond energy of food into ATP.