Free Cellular Respiration MCQs with Answers

• 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.

• 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.

• 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.

• 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…

• 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…

• 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…

• 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…

• 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…

• 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…

• 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…

• 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.

• 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…

• 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.

• 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.

• 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…

• 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…

• 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.

• 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.

• 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…

• 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.