NUMS — Medical & Dental Entry Test

NUMS Biology — Bioenergetics (Set 1)

Take the NUMS Biology — Bioenergetics (Set 1): 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 Ruben and Kamen's experiment, algae given water labelled with ¹⁸O released ¹⁸O₂. This showed that:
- A. The oxygen released in photosynthesis comes from water ✓
- B. Glucose oxygen comes from water
- C. The oxygen released comes from carbon dioxide
- D. Light splits carbon dioxide
Answer: A. The oxygen released in photosynthesis comes from water
Explanation: Labelled oxygen in H₂O appeared in the released O₂, proving photolysis of water is the source of oxygen.
Q2. A plant is supplied with ¹⁴CO₂ for a few seconds in light. The first stable compound to become radioactive in a C₃ plant is:
- A. Oxaloacetate
- B. 3-phosphoglycerate (PGA) ✓
- C. Ribulose bisphosphate
- D. Glyceraldehyde-3-phosphate
Answer: B. 3-phosphoglycerate (PGA)
Explanation: RuBisCO fixes CO₂ to RuBP, which splits into two molecules of 3-carbon PGA, the first stable product.
Q3. If the light supply to an actively photosynthesising C₃ plant is suddenly switched off, which change occurs first in the Calvin cycle?
- A. Both PGA and RuBP increase
- B. CO₂ fixation increases
- C. PGA accumulates and RuBP decreases ✓
- D. RuBP accumulates and PGA decreases
Answer: C. PGA accumulates and RuBP decreases
Explanation: Without ATP and NADPH, PGA cannot be reduced and RuBP cannot be regenerated, while CO₂ fixation continues briefly using remaining RuBP.
Q4. If CO₂ supply to an illuminated C₃ plant is suddenly cut off, the levels of RuBP and PGA would:
- A. RuBP falls, PGA rises
- B. Both remain constant
- C. RuBP rises, PGA falls ✓
- D. Both fall
Answer: C. RuBP rises, PGA falls
Explanation: RuBP continues to be regenerated but is not consumed by carboxylation, so it accumulates; PGA formation stops while it is still being used.
Q5. Which products of the light-dependent reactions are used in the Calvin cycle?
- A. NADH and FADH₂
- B. Glucose and O₂
- C. O₂ and ATP
- D. ATP and NADPH ✓
Answer: D. ATP and NADPH
Explanation: ATP and NADPH from the thylakoid reactions drive reduction of PGA and regeneration of RuBP in the stroma.

The other 25 questions

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Q6. In non-cyclic photophosphorylation, the electrons lost by photosystem II are replaced by electrons from:
- A. Photosystem I
- B. Photolysis of water
- C. Carbon dioxide
- D. NADPH
Q7. Cyclic photophosphorylation differs from non-cyclic in that it:
- A. Involves both photosystems and water splitting
- B. Produces NADPH but no ATP
- C. Occurs in the stroma
- D. Produces ATP but no NADPH or O₂
Q8. Chlorophyll a absorbs light most strongly in which regions of the spectrum?
- A. Orange and infrared
- B. Green only
- C. Blue-violet and red
- D. Green and yellow
Q9. Accessory pigments such as carotenoids benefit the plant by:
- A. Splitting water molecules
- B. Absorbing wavelengths chlorophyll a misses and protecting against photo-oxidation
- C. Acting as the reaction centre of PSII
- D. Fixing carbon dioxide directly
Q10. Protons are pumped into which compartment during the light reactions, creating the gradient used by ATP synthase?
- A. Intermembrane space of the chloroplast envelope
- B. Cytoplasm
- C. Stroma
- D. Thylakoid lumen
Q11. Photorespiration reduces the efficiency of C₃ plants because RuBisCO:
- A. Combines with O₂ instead of CO₂ at high temperatures and O₂ levels
- B. Fixes CO₂ into oxaloacetate
- C. Is destroyed by light
- D. Requires NADH instead of NADPH
Q12. C₄ plants such as maize avoid photorespiration largely because:
- A. They lack RuBisCO entirely
- B. They carry out photosynthesis only at night
- C. PEP carboxylase fixes CO₂ in mesophyll cells and concentrates it in bundle-sheath cells
- D. Their stomata are always closed
Q13. Glycolysis takes place in the ______ and produces a net gain of ______ ATP per glucose.
- A. Cytoplasm; 4
- B. Cytoplasm; 2
- C. Mitochondrial matrix; 2
- D. Inner mitochondrial membrane; 36
Q14. During vigorous exercise, human muscle converts pyruvate to lactate. The main benefit of this step is that it:
- A. Releases carbon dioxide
- B. Supplies oxygen to mitochondria
- C. Regenerates NAD⁺ so that glycolysis can continue
- D. Produces large amounts of ATP
Q15. Alcoholic fermentation in yeast differs from lactic acid fermentation in humans because yeast:
- A. Releases CO₂ and produces ethanol from pyruvate
- B. Produces more ATP per glucose
- C. Does not carry out glycolysis
- D. Uses oxygen as the final electron acceptor
Q16. How many molecules of CO₂ are released when one molecule of pyruvate is completely oxidised through the link reaction and Krebs cycle?
- A. Three
- B. Six
- C. One
- D. Two
Q17. Acetyl CoA (2C) combines with which compound to form citrate (6C) at the start of the Krebs cycle?
- A. Oxaloacetate (4C)
- B. Succinate (4C)
- C. Pyruvate (3C)
- D. α-ketoglutarate (5C)
Q18. Which is the final electron acceptor in the mitochondrial electron transport chain?
- A. Oxygen, which is reduced to water
- B. Pyruvate
- C. Cytochrome c
- D. NAD⁺
Q19. Cyanide poisoning is fatal because it blocks cytochrome oxidase. Which immediate consequence follows in the mitochondria?
- A. Glycolysis stops completely
- B. Oxygen consumption increases sharply
- C. Electron flow stops and ATP synthesis by oxidative phosphorylation ceases
- D. More NAD⁺ becomes available for the Krebs cycle
Q20. An uncoupler like dinitrophenol makes the inner mitochondrial membrane leaky to protons. The expected result is:
- A. Oxygen consumption stops completely
- B. ATP synthesis increases sharply
- C. Electron transport continues but ATP synthesis falls and more heat is produced
- D. Glycolysis is blocked
Q21. Oxidation of one NADH through the electron transport chain yields approximately how many ATP, compared with one FADH₂?
- A. About 36 ATP for each
- B. About 1 ATP for each
- C. About 2 ATP for NADH and 3 ATP for FADH₂
- D. About 3 ATP for NADH and 2 ATP for FADH₂
Q22. In the chemiosmotic theory of mitochondria, protons are pumped from the matrix into the:
- A. Cytoplasm
- B. Outer membrane
- C. Thylakoid lumen
- D. Intermembrane space
Q23. The respiratory quotient (RQ) of a seed respiring mainly fats is about 0.7. This indicates that:
- A. More CO₂ is produced than O₂ consumed
- B. Respiration is fully anaerobic
- C. Less CO₂ is produced than O₂ consumed
- D. Equal volumes of CO₂ and O₂ are exchanged
Q24. Which statement about ATP is correct?
- A. It contains deoxyribose sugar
- B. It is formed only in chloroplasts
- C. Hydrolysis of its terminal phosphate releases about 7.3 kcal/mol for cellular work
- D. It stores energy for long periods like starch
Q25. Substrate-level phosphorylation occurs when:
- A. NADH donates electrons to oxygen
- B. Light energy drives ATP synthesis
- C. A phosphate group is transferred directly from a substrate to ADP
- D. ATP is made using a proton gradient
Q26. Which process is common to both aerobic and anaerobic respiration?
- A. Oxidative phosphorylation
- B. Krebs cycle
- C. Link reaction
- D. Glycolysis
Q27. In the link reaction, pyruvate is converted to acetyl CoA. Which of the following is also produced?
- A. ATP and O₂
- B. FADH₂ and water
- C. CO₂ and NADH
- D. Lactate and NAD⁺
Q28. A leaf is kept at its light compensation point. Which statement is true?
- A. Respiration has stopped completely
- B. The rate of photosynthesis equals the rate of respiration, so there is no net gas exchange
- C. Photosynthesis has stopped completely
- D. The plant shows maximum growth
Q29. At low light intensity, increasing CO₂ concentration has little effect on the rate of photosynthesis. This is because:
- A. RuBisCO has been saturated by oxygen
- B. Light intensity is the limiting factor
- C. CO₂ is toxic to chloroplasts
- D. Temperature is too high
Q30. Where exactly in the chloroplast does the Calvin cycle occur?
- A. Stroma
- B. Thylakoid lumen
- C. Outer envelope
- D. Thylakoid membrane