Free Bioenergetics MCQs with Answers

• A. diffusing freely through both mitochondrial membranes
• B. being carried in by shuttle systems that transfer its electrons
• C. being converted into FADH2 first
• D. being broken down and never entering the mitochondrion

Explanation: The inner mitochondrial membrane is impermeable to NADH itself, so shuttle mechanisms transfer its electrons inside, sometimes at the cost…

• A. photosynthesis gives off heat
• B. the seed coat is an insulator
• C. cellulose decomposes spontaneously
• D. respiration releases part of glucose's energy as heat

Explanation: Only a fraction of the energy released in respiration is trapped in ATP; the rest escapes as heat, which germinating seeds in bulk can…

• A. addition of hydrogen atoms to it
• B. removal of oxygen from it
• C. loss of electrons and hydrogen from it
• D. gain of electrons by it

Explanation: Biological oxidation is the removal of hydrogen, whose electrons are passed to NAD or FAD, so dehydrogenation and oxidation are the same…

• A. glucose is only partially oxidised, leaving energy locked in products such as lactate
• B. glycolysis does not occur without oxygen
• C. oxygen directly destroys ATP molecules
• D. the enzymes of respiration denature without oxygen

Explanation: Without oxygen as the final acceptor, the Krebs cycle and electron transport chain stop, so products such as lactate or ethanol still hold…

• A. 2
• B. 4
• C. 6
• D. 8

Explanation: Two CO2 come from the oxidative decarboxylation of the two pyruvate molecules and four from the two turns of the Krebs cycle, giving six…

• A. split water molecules
• B. pump hydrogen ions across the inner mitochondrial membrane
• C. reduce carbon dioxide
• D. phosphorylate glucose

Explanation: Three carrier complexes use the energy of falling electrons to pump H+ from matrix to intermembrane space, building the gradient that ATP…

• A. 2 ATP are invested early and 4 ATP are produced later
• B. 4 ATP are invested and 2 ATP are produced
• C. only two of glucose's six carbons can be oxidised
• D. glycolysis occurs twice per glucose molecule

Explanation: Two ATP prime the pathway by phosphorylating glucose and its split products, and four ATP are later formed by substrate level…

• A. 36 ATP
• B. 2 ATP and 2 CO2
• C. 6 NADH
• D. 1 ATP, 3 NADH, 1 FADH2 and 2 CO2

Explanation: Per acetyl group the cycle turns out one ATP by substrate level phosphorylation, three reduced NAD, one reduced FAD and two CO2.

• A. Cytoplasm
• B. Mitochondrial matrix
• C. Inner mitochondrial membrane
• D. Outer mitochondrial membrane

Explanation: The Krebs cycle (citric acid cycle) occurs in the mitochondrial matrix.

• A. 2
• B. 4
• C. 36-38
• D. 40

Explanation: Aerobic respiration yields approximately 36-38 ATP per glucose: 2 from glycolysis, 2 from Krebs, and ~32 from ETC.

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

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

• 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.

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

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

• 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.

• 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.

• 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.

• 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.

• 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…

• 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…

• A. Chemosynthesis
• B. Photosynthesis
• C. Phosphorylation
• D. Chemiosmosis

Explanation: Chemiosmosis synthesizes ATP by using the flow of protons through ATP synthase down their electrochemical gradient, which drives…