Free Bioenergetics MCQs with Answers

51. The final electron acceptor in the electron transport chain is

• A. NAD+
• B. FAD
• C. Oxygen
• D. CO2

Explanation: Oxygen is the final electron acceptor, combining with electrons and H+ to form water.

52. Which of the following is NOT a product of anaerobic respiration in yeast?

• A. Ethanol
• B. CO2
• C. ATP
• D. Lactate

Explanation: Yeast undergoes alcoholic fermentation producing ethanol and CO2, not lactate. Lactate is produced in animal muscles.

53. The link reaction converts pyruvate to

• A. Lactate
• B. Ethanol
• C. Acetyl CoA
• D. Glucose

Explanation: Pyruvate dehydrogenase complex converts pyruvate to acetyl CoA, releasing CO2 and producing NADH.

54. Substrate-level phosphorylation occurs in

• A. Only glycolysis
• B. Only Krebs cycle
• C. Glycolysis and Krebs cycle
• D. Only ETC

Explanation: Substrate-level phosphorylation (direct ATP synthesis) occurs in glycolysis and Krebs cycle, not in ETC.

55. The respiratory quotient (RQ) for carbohydrates is

• A. 0.7
• B. 1.0
• C. 0.9
• D. 0.8

Explanation: RQ = CO2 produced/O2 consumed. For carbohydrates, RQ = 1.0; for fats ~0.7; for proteins ~0.9.

56. Which enzyme catalyzes the conversion of pyruvate to lactate?

• A. Pyruvate dehydrogenase
• B. Lactate dehydrogenase
• C. Pyruvate kinase
• D. Hexokinase

Explanation: Lactate dehydrogenase reduces pyruvate to lactate using NADH, regenerating NAD+ for glycolysis to continue.

57. Chemiosmosis involves

• A. Active transport of electrons
• B. Passive diffusion of protons
• C. Proton gradient driving ATP synthesis
• D. Direct phosphorylation of ADP

Explanation: Chemiosmosis uses the proton gradient across the inner mitochondrial membrane to drive ATP synthesis through ATP synthase.

58. The most primitive respiratory process occurring in a living cell is:

• A. Lactic acid fermentation
• B. Alcoholic fermentation
• C. Glycolysis
• D. Krebs's cycle

Explanation: Glycolysis occurs in the cytoplasm of every living cell, needs no oxygen and no organelle, and is common to bacteria, plants and animals alike, which marks it as the oldest of these pathways, dating from before the atmosphere contained oxygen. The two fermentations are add ons that merely regenerate NAD so glycolysis can continue. The Krebs cycle is later still, since it requires a mitochondrion and oxygen further down the chain.

59. An active athlete has more stamina of running compared to an officer of same age with physically inactive lifestyle. Which of the following organelles has greatly increased in the muscle cells of athlete?

• A. Nucleus
• B. Mitochondria
• C. Golgi bodies
• D. Smooth endoplasmic reticulum (SER)

Explanation: Endurance training increases the number and size of mitochondria in muscle fibres, so more ATP can be produced aerobically and the athlete relies less on anaerobic respiration and accumulates lactate more slowly. This is one of the main measurable adaptations to training. The number of nuclei and the extent of the Golgi are not what limits stamina.