Take the NUMS Biology — Bioenergetics (Set 4): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review. Covers 30 NUMS…
The first 5 questions of this test, with the correct answer and explanation.
Q1. A muscle cell breaks down 5 mol of glucose entirely by glycolysis followed by lactate formation. How many moles of ATP are produced (net)?
Answer: D. 10
Explanation: Glycolysis nets 2 ATP per glucose (4 made − 2 used); lactate formation yields no additional ATP. 5 × 2 = 10 mol.
Q2. For one glucose molecule completely oxidised in aerobic respiration, how many molecules of NADH and FADH₂ are produced in total from glycolysis, the link reaction and the Krebs cycle?
- A. 12 NADH and 0 FADH₂
- B. 10 NADH and 2 FADH₂ ✓
- C. 8 NADH and 4 FADH₂
- D. 6 NADH and 2 FADH₂
Answer: B. 10 NADH and 2 FADH₂
Explanation: NADH: 2 (glycolysis) + 2 (link) + 6 (Krebs, 3 per turn × 2) = 10. FADH₂: 1 per turn × 2 = 2.
Q3. Three molecules of glucose are completely oxidised in aerobic respiration. How many molecules of CO₂ are released?
Answer: C. 18
Explanation: Each glucose gives 6 CO₂ (2 from the link reaction and 4 from two turns of the Krebs cycle); 3 × 6 = 18.
Q4. The Calvin cycle fixes 6 molecules of CO₂ to make one glucose. How many ATP and NADPH molecules are used (3 ATP and 2 NADPH per CO₂ fixed)?
- A. 6 ATP and 6 NADPH
- B. 12 ATP and 18 NADPH
- C. 36 ATP and 24 NADPH
- D. 18 ATP and 12 NADPH ✓
Answer: D. 18 ATP and 12 NADPH
Explanation: Per CO₂: 3 ATP and 2 NADPH; for 6 CO₂: 18 ATP and 12 NADPH.
Q5. Palmitic acid is oxidised completely: C₁₆H₃₂O₂ + 23 O₂ → 16 CO₂ + 16 H₂O. What is the respiratory quotient?
- A. About 0.70 ✓
- B. 1.0
- C. 0.90
- D. 1.43
Answer: A. About 0.70
Explanation: RQ = CO₂ produced ÷ O₂ consumed = 16 ÷ 23 ≈ 0.70, typical of fats, which contain little oxygen per carbon.
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Q6. In a respirometer, a tube without KOH shows a volume decrease of 2 mL per hour; a tube with KOH (absorbing CO₂) shows a decrease of 10 mL per hour. What is the RQ of the organism?
- A. 0.8
- B. 0.2
- C. 1.25
- D. 5.0
Q7. In a cell with high ATP and abundant citrate, the activity of phosphofructokinase falls. What is the most direct consequence?
- A. The Calvin cycle is activated
- B. Glycolysis speeds up to make more pyruvate
- C. Glycolysis slows, conserving glucose when energy is plentiful
- D. Fermentation is switched on
Q8. A student fills a flask with yeast and glucose, kept without oxygen. When 90 g of glucose (C₆H₁₂O₆ = 180) is completely fermented, what mass of CO₂ is released? (C = 12, O = 16)
- A. 88 g
- B. 22 g
- C. 44 g
- D. 90 g
Q9. Dinitrophenol (DNP) makes the inner mitochondrial membrane leaky to protons. Which combination of changes is expected in a cell treated with DNP?
- A. Oxygen consumption stops, the proton gradient is lost and ATP synthesis rises
- B. Glycolysis stops completely, the Krebs cycle speeds up and ATP synthesis rises
- C. The proton gradient increases, ATP synthesis rises and heat output falls
- D. Oxygen consumption continues or rises, ATP synthesis falls, and heat output rises
Q10. Cyanide blocks the last carrier (cytochrome oxidase) of the mitochondrial electron transport chain. What happens inside the matrix?
- A. FADH₂ is oxidised faster, so the Krebs cycle speeds up as NAD⁺ is regenerated
- B. Pyruvate is converted to CO₂ at an increased rate because ATP demand has risen
- C. Oxygen is consumed more rapidly because the electron carriers stay fully oxidised
- D. NADH accumulates and the Krebs cycle slows because NAD⁺ is no longer regenerated
Q11. During sprinting, lactate rises in a muscle and is carried to the liver. What does the liver do with it?
- A. Stores it directly as glycogen without change
- B. Oxidises it to ethanol and CO₂
- C. Converts it back to pyruvate and glucose (Cori cycle)
- D. Excretes it unchanged in bile
Q12. A mutant plant lacks photosystem II but retains photosystem I. Which statement about its light-dependent reactions is correct?
- A. It still produces oxygen by photolysis but makes no ATP in the light
- B. It cannot make any ATP in light, because only photosystem II drives ATP synthesis
- C. It can make ATP by cyclic photophosphorylation but cannot produce oxygen
- D. It can make NADPH and oxygen normally by non-cyclic photophosphorylation
Q13. A plant is given water containing heavy oxygen (¹⁸O) and normal CO₂. In which product will ¹⁸O first appear?
- A. Glucose made in the Calvin cycle
- B. Oxygen gas released in the light reactions
- C. ATP
- D. Carbon dioxide in the stroma
Q14. An action spectrum of photosynthesis of a leaf peaks in blue-violet and in red light, with a trough in green. Which inference is correct?
- A. Carotenoids alone drive photosynthesis, since only they absorb blue-violet and red wavelengths
- B. Chlorophylls absorb red and blue most strongly, so those wavelengths drive photosynthesis best
- C. Red light is absorbed mainly by water in the leaf, not by pigments, so it drives little photosynthesis
- D. Green light drives photosynthesis best because leaves reflect it and so it penetrates deeper
Q15. A photosynthesis rate plateaus as light intensity increases at 0.04% CO₂, but plateaus at a much higher rate when 0.10% CO₂ is supplied at the same temperature. At the first plateau the limiting factor is
- A. carbon dioxide concentration
- B. none; the process is at its biochemical maximum
- C. light intensity
- D. chlorophyll content
Q16. A leaf is kept at the light intensity at which no net gas exchange occurs. Which statement is true at this point?
- A. Respiration has stopped
- B. Photosynthesis has stopped
- C. Stomata are closed so CO₂ is not available
- D. Photosynthesis rate equals respiration rate
Q17. A steady-state algal culture is suddenly moved from light to darkness. What change in the levels of RuBP and glycerate 3-phosphate (PGA) is expected in the Calvin cycle?
- A. RuBP rises and PGA falls
- B. Both fall to zero immediately
- C. Both RuBP and PGA rise
- D. RuBP falls and PGA rises
Q18. The CO₂ supply to an illuminated algal culture is suddenly cut off. What is expected?
- A. RuBP accumulates and PGA falls
- B. NADPH is used faster
- C. PGA accumulates and RuBP falls
- D. Both PGA and RuBP rise
Q19. Why does a C₄ plant such as maize outperform a C₃ plant such as wheat at high temperature and low CO₂ inside the leaf?
- A. It lacks rubisco entirely and fixes all its CO₂ directly with PEP carboxylase in the mesophyll, with no Calvin cycle
- B. It keeps its stomata wide open at night, so more CO₂ enters and photorespiration is eliminated during the day
- C. PEP carboxylase fixes CO₂ in mesophyll cells and concentrates it around rubisco in bundle-sheath cells, reducing photorespiration
- D. It uses photosystem II only in the bundle-sheath cells, so oxygen is never produced near rubisco in the mesophyll
Q20. Which statement about photorespiration is correct?
- A. It is beneficial because it produces large amounts of ATP
- B. It occurs when CO₂ is high and O₂ is low
- C. Rubisco fixes O₂ instead of CO₂, and the process consumes ATP without producing it
- D. It occurs in mitochondria only in the dark
Q21. The pH of a cactus leaf extract is lower at dawn than at dusk. This is because
- A. malic acid accumulated in vacuoles overnight during CO₂ fixation
- B. glycolysis stops at night
- C. stomata open at noon and release acid
- D. lactic acid is made during daytime photosynthesis
Q22. During illumination of a chloroplast, which statement about protons and ATP synthase is correct?
- A. Protons accumulate in the stroma and flow into the thylakoid lumen through ATP synthase
- B. Protons flow out of the chloroplast to the cytosol, which drives ATP synthase in the envelope
- C. Protons accumulate in the thylakoid lumen and flow back to the stroma through ATP synthase
- D. ATP synthase lies in the outer membrane and is driven directly by light absorbed by chlorophyll
Q23. Which of the following is an example of substrate-level phosphorylation?
- A. ATP formation by cyclic electron flow in thylakoids
- B. ATP formation by ATP synthase in cristae
- C. Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate with ATP formation
- D. Conversion of NADH to NAD⁺ in the electron transport chain
Q24. On a paper chromatogram, a pigment spot has travelled 4.2 cm while the solvent front has moved 7.0 cm. What is its Rf value?
- A. 0.4
- B. 0.6
- C. 2.8
- D. 1.67
Q25. A lamp is 25 cm from a pond weed producing 40 bubbles per minute, with light the only limiting factor. Light intensity ∝ 1/d². How many bubbles per minute are expected if the lamp is moved to 50 cm?
Q26. A light bottle of pond water gains 6 mg O₂/L over a period, while an identical dark bottle loses 2 mg O₂/L. What is the gross photosynthetic production over this period?
- A. 12 mg O₂/L
- B. 4 mg O₂/L
- C. 6 mg O₂/L
- D. 8 mg O₂/L
Q27. In the reaction C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, which statement about electrons is correct?
- A. Both glucose and oxygen are oxidised
- B. Carbon is reduced from CO₂ to glucose
- C. Glucose is reduced and oxygen is oxidised
- D. Glucose is oxidised and oxygen is reduced
Q28. Which statement correctly contrasts the roles of NADPH and NADH?
- A. NADPH carries electrons for biosynthesis such as the Calvin cycle, while NADH carries electrons to the electron transport chain
- B. NADH is made only in the stroma of chloroplasts, where it carries electrons for biosynthesis, while NADPH is made in mitochondria
- C. NADPH is made in glycolysis and passes electrons to the electron transport chain, while NADH is made in photosynthesis
- D. Both carry electrons to the Calvin cycle, but NADPH is made only in mitochondria while NADH is made only in chloroplasts
Q29. Acetyl CoA (2 carbons) enters the Krebs cycle and combines with a 4-carbon acid. How many carbons does the first product have, and how many CO₂ are released in one complete turn?
- A. 6 carbons; 2 CO₂ per turn
- B. 6 carbons; 3 CO₂ per turn
- C. 4 carbons; 2 CO₂ per turn
- D. 5 carbons; 3 CO₂ per turn
Q30. A crop grown in magnesium-deficient soil develops yellow leaves with green veins. Which explanation is most direct?
- A. Magnesium makes up the haem group of cytochromes only, so the electron transport chain fails
- B. Magnesium is the final electron acceptor of photosystem II, so electron transport stops without it
- C. Magnesium is a central atom of the chlorophyll molecule, so chlorophyll synthesis falls
- D. Magnesium is needed to build cellulose in the walls of leaf veins, so the veins stay green