NUMS — Medical & Dental Entry Test

NUMS Biology — Bioenergetics (Set 3)

Take the NUMS Biology — Bioenergetics (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review. Covers 30 NUMS…

What this test covers

30 NUMS Biology

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. In the light reactions, the photolysis of water supplies:
- A. electrons to replace those lost by photosystem II ✓
- B. ATP directly to the stroma
- C. NADP⁺ to photosystem I
- D. carbon dioxide for the Calvin cycle
Answer: A. electrons to replace those lost by photosystem II
Explanation: Water is split at PSII: 2H₂O → 4H⁺ + 4e⁻ + O₂; the electrons replenish the reaction-centre chlorophyll.
Q2. The oxygen released in photosynthesis originates from:
- A. carbon dioxide
- B. glucose
- C. RuBP
- D. water ✓
Answer: D. water
Explanation: Experiments with ¹⁸O-labelled water and CO₂ showed that O₂ comes from H₂O.
Q3. If a plant is supplied with CO₂ labelled with ¹⁴C, in which compound does the label appear first?
- A. 3-phosphoglycerate (PGA) ✓
- B. RuBP
- C. Glucose
- D. NADPH
Answer: A. 3-phosphoglycerate (PGA)
Explanation: CO₂ is fixed by RuBP to give two molecules of 3-PGA, the first stable product in C₃ plants.
Q4. How many turns of the Calvin cycle are needed to synthesise one molecule of glucose (6 carbons)?
- A. 2
- B. 12
- C. 6 ✓
- D. 3
Answer: C. 6
Explanation: Each turn fixes one CO₂; six carbons need six turns (18 ATP, 12 NADPH).
Q5. How many ATP and NADPH molecules are used in the Calvin cycle to make one glucose?
- A. 18 ATP and 12 NADPH ✓
- B. 36 ATP and 24 NADPH
- C. 12 ATP and 18 NADPH
- D. 6 ATP and 6 NADPH
Answer: A. 18 ATP and 12 NADPH
Explanation: Per CO₂: 3 ATP and 2 NADPH. For 6 CO₂: 18 ATP and 12 NADPH.

The other 25 questions

Take the timed test (free, no sign-up) to see your score and the answer and explanation for every question.

Q6. A plant is placed in the dark after being in light. Calvin cycle activity soon falls because:
- A. glucose accumulates and blocks stomata
- B. ATP and NADPH are no longer being supplied
- C. RuBisCO is lost from the stroma
- D. CO₂ stops diffusing
Q7. Cyclic photophosphorylation produces:
- A. ATP only
- B. O₂ only
- C. ATP, NADPH and O₂
- D. NADPH only
Q8. Where in the chloroplast is the proton concentration highest during photosynthesis?
- A. Outer membrane
- B. Inner membrane space
- C. Thylakoid lumen
- D. Stroma
Q9. Chlorophyll a and b absorb little light of one colour, which gives a trough between the blue and red peaks in the action spectrum for photosynthesis. Which colour is it?
- A. Blue
- B. Violet
- C. Red
- D. Green
Q10. In a chromatography experiment on leaf pigments, the pigment that travels furthest is:
- A. carotene
- B. chlorophyll b
- C. xanthophyll
- D. chlorophyll a
Q11. On a very hot dry day, the stomata of a C₃ plant close. Which result is most likely?
- A. Photorespiration increases
- B. O₂ is depleted inside the leaf
- C. Photosynthesis rises due to higher CO₂
- D. RuBisCO fixes more CO₂
Q12. Which feature of C₄ plants reduces photorespiration?
- A. Stomata remain closed during the day
- B. PEP carboxylase fixes CO₂ in mesophyll cells and delivers it to bundle sheath cells
- C. RuBisCO is absent
- D. No Calvin cycle occurs
Q13. Kranz anatomy is found in:
- A. pea and bean
- B. wheat and rice
- C. cactus only
- D. maize and sugarcane
Q14. CAM plants such as cactus open stomata at night mainly to:
- A. do photolysis
- B. increase transpiration
- C. avoid light
- D. reduce water loss while taking in CO₂
Q15. A leaf disc experiment shows oxygen output doubles when light intensity is doubled but does not rise on a further doubling. The probable limiting factor at the high light is:
- A. chlorophyll b
- B. CO₂ concentration or temperature
- C. glycolysis
- D. light
Q16. Glycolysis in one glucose molecule has a net gain of:
- A. 4 ATP and 2 NADH
- B. 38 ATP
- C. 2 ATP and 4 NADH
- D. 2 ATP and 2 NADH
Q17. Which step of glycolysis is the main regulatory point inhibited by high ATP?
- A. Phosphofructokinase step
- B. Glucose diffusion
- C. Lactate synthesis
- D. Pyruvate formation only
Q18. Yeast ferments 1 mole of glucose anaerobically. How many moles of CO₂ are released?
- A. 2
- B. 1
- C. 0
- D. 6
Q19. During vigorous sprinting, muscle cells regenerate NAD⁺ by:
- A. reducing pyruvate to lactate
- B. transferring electrons to O₂ at once
- C. oxidising lactate to CO₂
- D. decarboxylating pyruvate to ethanol
Q20. The link reaction for one glucose molecule yields:
- A. 2 acetyl-CoA and 2 FADH₂
- B. 2 acetyl-CoA, 2 CO₂ and 2 NADH
- C. 2 acetyl-CoA, 6 CO₂ and 6 NADH
- D. 1 acetyl-CoA, 1 CO₂ and 1 NADH
Q21. How many CO₂ molecules are released from the complete aerobic oxidation of one glucose molecule (link reaction plus Krebs cycle)?
- A. 2
- B. 12
- C. 6
- D. 4
Q22. In one turn of the Krebs cycle, the number of NADH, FADH₂ and GTP/ATP produced is:
- A. 4, 1 and 2
- B. 1, 3 and 1
- C. 2, 2 and 1
- D. 3, 1 and 1
Q23. Cyanide poisons cells by binding cytochrome c oxidase. The immediate effect on a cell is:
- A. the Krebs cycle makes more ATP
- B. electron transport stops and ATP production falls
- C. lactate is oxidised
- D. glycolysis stops completely at once
Q24. When oxygen is absent, which reduced carrier accumulates in the mitochondrial matrix because the chain stalls?
- A. NADH
- B. ADP
- C. NAD⁺
- D. Pyruvate dehydrogenase
Q25. Dinitrophenol makes the inner mitochondrial membrane leaky to protons. Which effect would you expect?
- A. Oxygen uptake stops
- B. Oxygen uptake continues but ATP synthesis falls and heat increases
- C. ATP synthesis increases
- D. The proton gradient grows larger
Q26. The respiratory quotient (RQ) of a germinating seed that is respiring fat is about:
- A. 1.0
- B. 0.7
- C. 0.9
- D. 1.3
Q27. If a tissue releases 6 mL of CO₂ and takes up 6 mL of O₂ over the same time, which substrate is being respired?
- A. Fat
- B. Organic acid
- C. Carbohydrate
- D. Protein only
Q28. Respiration in an organism with RQ greater than 1 suggests:
- A. anaerobic respiration or oxidation of oxygen-rich substrates
- B. no release of CO₂ at all
- C. complete oxidation of protein only
- D. oxidation of pure fat alone
Q29. ATP synthase in mitochondria synthesises ATP when protons:
- A. are pumped into the matrix
- B. flow back from the intermembrane space to the matrix
- C. are pumped into the cytoplasm
- D. bind to oxygen in the intermembrane space
Q30. Photophosphorylation differs from oxidative phosphorylation because in photophosphorylation the energy for the electron flow comes from:
- A. light absorbed by chlorophyll
- B. hydrolysis of ATP
- C. fermentation
- D. oxidation of NADH