Free Bioenergetics MCQs with Answers
1,378 Bioenergetics MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Cellular respiration explains how cells release energy from glucose through glycolysis, the link reaction, Krebs cycle and electron transport chain. It includes ATP production, substrate-level and oxidative phosphorylation, aerobic versus anaerobic respiration, and the roles of mitochondria, oxygen and fermentation in energy transfer.
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- A. 6CO2 + 6H2O + energy
- B. C2H5OH + 6CO2 + energy
- C. 2C3H6O3 + energy only
- D. 6CO2 + energy only
Explanation: Complete oxidation of glucose yields six molecules each of carbon dioxide and water with the release of energy, largely captured as ATP.
Correct answer: 6CO2 + 6H2O + energy- A. glucose
- B. ATP
- C. glycogen
- D. NADH
Explanation: ATP releases a small, manageable packet of energy when one phosphate is hydrolysed, so it can power single reactions without waste.
Correct answer: ATP- A. adenine, ribose and three phosphate groups
- B. adenine, deoxyribose and three phosphate groups
- C. guanine, ribose and two phosphate groups
- D. adenine, glucose and three phosphate groups
Explanation: ATP is a nucleotide: the base adenine joined to the sugar ribose and a chain of three phosphates.
Correct answer: guanine, ribose and two phosphate groups- A. 0.7 kcal of energy
- B. 73 kcal of energy
- C. 700 kcal of energy
- D. 7.3 kcal of energy
Explanation: Each terminal phosphate bond of ATP yields about 7.3 kcal per mole on hydrolysis, a packet of energy well matched to the needs of single…
Correct answer: 7.3 kcal of energy- A. hydrogen atoms and electrons removed from the substrate
- B. carbon dioxide released by the Krebs cycle
- C. oxygen from haemoglobin
- D. phosphate groups for ATP synthesis
Explanation: Dehydrogenase enzymes strip hydrogen from intermediates and hand it to NAD or FAD, which carry the electrons to the electron transport…
Correct answer: hydrogen atoms and electrons removed from the substrate- A. glycolysis of glucose
- B. oxidative decarboxylation of pyruvate
- C. electron transport chain
- D. phosphorylation of ADP
Explanation: Glycolysis only splits glucose into pyruvate without releasing any CO2; the first decarboxylation happens when pyruvate is converted to…
Correct answer: oxidative decarboxylation of pyruvate- A. Glycolysis
- B. The Krebs cycle
- C. Oxidative phosphorylation in the electron transport chain
- D. The conversion of pyruvate to acetyl CoA
Explanation: Glycolysis nets 2 ATP and the Krebs cycle 2 more directly, but the reoxidation of NADH and FADH2 by the electron transport chain yields…
Correct answer: Oxidative phosphorylation in the electron transport chain- A. cytoplasm
- B. outer membrane of the mitochondrion
- C. intermembrane space
- D. matrix of the mitochondrion
Explanation: The soluble enzymes of the cycle sit in the mitochondrial matrix, while the electron transport chain that the cycle feeds is embedded in…
Correct answer: matrix of the mitochondrion29. The anaerobic respiration of yeast is economically useful because the carbon dioxide it releases
- A. preserves fruit juices
- B. makes bread dough rise
- C. kills contaminating bacteria
- D. sweetens the final product
Explanation: In baking, the CO2 of alcoholic fermentation inflates the dough while the ethanol evaporates, and in brewing it is the ethanol that is…
Correct answer: makes bread dough rise- A. the extra oxygen needed after the race to oxidise accumulated lactate
- B. the oxygen permanently lost from haemoglobin
- C. the oxygen stored in myoglobin
- D. the oxygen needed for the Krebs cycle during the race
Explanation: During intense effort lactate builds up because oxygen supply lags behind, and afterwards heavy breathing continues until the lactate is…
Correct answer: the extra oxygen needed after the race to oxidise accumulated lactate- A. using oxygen as the final electron acceptor
- B. that yields 38 ATP per molecule
- C. occurring only in the mitochondria
- D. without oxygen, yielding an incompletely oxidised organic product
Explanation: Fermentation is anaerobic and leaves energy locked in products such as ethanol or lactate, so it yields only the 2 ATP of glycolysis.
Correct answer: without oxygen, yielding an incompletely oxidised organic product- A. no ATP at all
- B. 4 ATP per glucose
- C. 2 ATP per glucose
- D. 24 ATP per glucose
Explanation: Only glycolysis runs without oxygen, giving a net gain of 2 ATP, while the Krebs cycle and electron transport chain need oxygen to…
Correct answer: 2 ATP per glucose- A. the Krebs cycle
- B. glycolysis alone
- C. oxidative phosphorylation
- D. the electron transport chain
Explanation: Red blood cells have no mitochondria, so they can only run glycolysis and produce lactate.
Correct answer: glycolysis alone34. The respiratory quotient of glucose, the ratio of carbon dioxide produced to oxygen consumed, is
- A. 1.0
- B. 0.7
- C. 0.5
- D. 1.4
Explanation: For glucose, six CO2 are released and six O2 consumed, so the quotient is exactly one.
Correct answer: 1.0- A. Krebs cycle, glycolysis, link reaction, electron transport chain
- B. electron transport chain, glycolysis, Krebs cycle, link reaction
- C. link reaction, glycolysis, Krebs cycle, electron transport chain
- D. glycolysis, link reaction, Krebs cycle, electron transport chain
Explanation: Glucose is first split in the cytoplasm, pyruvate is then decarboxylated to acetyl CoA, the acetyl group is oxidised in the Krebs cycle…
Correct answer: glycolysis, link reaction, Krebs cycle, electron transport chain- A. lipids that store electrons
- B. carbohydrates that carry oxygen
- C. iron containing proteins that pass electrons along by changing valency
- D. enzymes that fix carbon dioxide
Explanation: Each cytochrome carries a haem group whose iron alternates between Fe2+ and Fe3+ as it accepts and passes electrons, releasing energy in…
Correct answer: iron containing proteins that pass electrons along by changing valency- A. NAD, forming NADH
- B. oxygen directly
- C. ATP
- D. carbon dioxide
Explanation: NAD acts as the hydrogen acceptor in glycolysis, keeping the pathway going by removing electrons and carrying them onwards.
Correct answer: NAD, forming NADH- A. ethanol and carbon dioxide
- B. lactate only, with no carbon dioxide
- C. lactate and abundant carbon dioxide
- D. ethanol and lactate together
Explanation: Human muscle cells reduce pyruvate straight to lactate, releasing no CO2, whereas yeast decarboxylates pyruvate to ethanol and CO2.
Correct answer: lactate only, with no carbon dioxide- A. more glucose stored in the blood
- B. more lactate produced per second
- C. a greater supply of the final electron acceptor to the muscles
- D. a higher concentration of ATP in the lungs
Explanation: More red cells and haemoglobin mean more oxygen reaches the electron transport chain, where oxygen is the final acceptor, so more aerobic…
Correct answer: a greater supply of the final electron acceptor to the muscles40. Which two stages of aerobic respiration generate ATP directly by substrate level phosphorylation?
- A. Glycolysis and the electron transport chain
- B. The link reaction and the Krebs cycle
- C. The Krebs cycle and oxidative phosphorylation
- D. Glycolysis and the Krebs cycle
Explanation: In glycolysis and the Krebs cycle a phosphate is transferred straight from a substrate to ADP, giving 4 ATP total per glucose.
Correct answer: Glycolysis and the Krebs cycle