Question 1

Aerobic respiration differs from anaerobic respiration in which of the following respects?

Accepted Answer

The final electron acceptors are different

Question 2

Which of the following is accomplished in chemiosmosis?

Accepted Answer

The oxidation of NADH

Question 3

The amount of ATP that can be obtained by complete oxidation of a glucose by a bacterium is

Accepted Answer

greater than by a yeast cell

Question 4

Suppose a eukaryotic cell had a mutation that prevented the production of cytochrome c. As a result of this mutation, which of the following processes would not occur?

Accepted Answer

Cellular respiration

Question 5

Bioenergetics of respiration — In the mitochondrial (or bacterial) electron transport chain used for aerobic respiration, what molecule serves as the final (terminal) electron acceptor at the end of the chain?

Accepted Answer

Introduction / Context:Aerobic respiration relies on a series of redox reactions in the electron transport chain (ETC) to convert the reducing power stored in NADH and FADH2 into a proton motive force and, ultimately, ATP. A defining feature of an aerobic ETC is the identity of its terminal electron acceptor—the molecule that finally accepts electrons leaving the chain. Understanding who accepts these electrons explains why oxygen is essential for maximal ATP yield and why respiration stops when the acceptor is absent.Given Data / Assumptions:NADH and FADH2 donate electrons to the ETC.Carriers such as FMN, iron–sulfur proteins, coenzyme Q (CoQ), and cytochromes pass electrons stepwise.The “final” or “terminal” acceptor is the molecule that receives electrons last, allowing water formation in aerobic systems.Concept / Approach:In aerobic organisms, molecular oxygen (O2) is the terminal electron acceptor. Electrons flow from complex to complex via carriers with progressively higher redox potentials, culminating at cytochrome oxidase (complex IV), where O2 is reduced to water. CoQ (ubiquinone), FMN, and cytochromes are intermediate carriers; they shuttle electrons but do not serve as the ultimate sink under aerobic conditions. This terminal step is what enables continuous electron flow and sustains oxidative phosphorylation through ATP synthase.Step-by-Step Solution:Trace electron flow: NADH/FADH2 → FMN/Fe–S → CoQ → cytochromes → O2.Identify the last redox couple: cytochrome oxidase reduces O2 to H2O.Conclude that oxygen is the terminal acceptor in aerobic respiration.Verification / Alternative check:Cyanide poisoning, which blocks cytochrome oxidase, halts electron transfer to O2 and collapses ATP production—direct evidence that O2 is the final acceptor in the aerobic chain.Why Other Options Are Wrong:CoQ: lipid-soluble intermediate carrier, not terminal acceptor.A cytochrome: protein carrier; passes electrons to the terminal acceptor but is not itself the final sink.FMN: initial flavin carrier at complex I; not terminal.Common Pitfalls:Confusing the last protein complex (cytochrome oxidase) with the last molecule in the overall reaction; the acceptor is O2, not the enzyme itself.Final Answer:oxygen

Question 6

Energy yields — Compared with complete aerobic metabolism of glucose, the amount of energy (calories per mole) obtained by a cell from glucose via fermentation is:

Accepted Answer

Introduction / Context:Cells extract energy from glucose through pathways that differ dramatically in ATP yield: aerobic respiration (glycolysis + pyruvate oxidation + TCA + electron transport chain) and fermentation (glycolysis followed by redox-balancing end steps). Knowing which strategy yields more energy is essential for microbiology, biochemistry, and industrial fermentation design.Given Data / Assumptions:Aerobic respiration allows complete oxidation of glucose to CO2, transferring electrons to O2.Fermentation ends with partially oxidized products (e.g., lactate, ethanol) and no electron transport chain is used.ATP yield correlates with how completely electrons are transferred to a high-potential acceptor (like O2).Concept / Approach:Aerobic respiration yields the highest ATP because the electron transport chain and oxidative phosphorylation convert redox energy into a proton gradient that drives ATP synthase. Fermentation regenerates NAD+ by transferring electrons to organic intermediates without an external terminal electron acceptor. This yields only the substrate-level phosphorylation ATP from glycolysis (typically 2 ATP per glucose), far below the ~28–32 ATP per glucose often cited for aerobic conditions in eukaryotes (bacteria may vary but remain far higher than fermentation). Therefore, energy per mole from fermentation is less than from aerobic metabolism.Step-by-Step Solution:Note fermentation ATP yield ≈ 2 ATP/glucose from glycolysis.Recognize aerobic respiration adds oxidative phosphorylation, greatly increasing ATP.Conclude fermentation energy is less than aerobic yield.Verification / Alternative check:Redox balance: fermentation products retain substantial potential energy (not fully oxidized), demonstrating why energy recovery is lower than when O2 is the acceptor.Why Other Options Are Wrong:Greater/equal: contradict the fundamental role of the ETC and full oxidation in maximizing ATP.None of the above: incorrect because “less than aerobic” is accurate.Common Pitfalls:Equating rapid growth in some fermenters with high ATP yield; growth rate also depends on flux and regulation, not ATP per mole alone.Final Answer:less than aerobic metabolism

Question 7

Catabolism of lipids — Fatty acids are broken down to acetyl-CoA predominantly by which metabolic pathway?

Accepted Answer

Introduction / Context:Cells harvest energy from lipids by converting long-chain fatty acids to acetyl-CoA, which then enters the citric acid cycle and fuels oxidative phosphorylation. Correctly naming the pathway that performs this conversion is a foundational learning objective in biochemistry and metabolism.Given Data / Assumptions:Fatty acids are catabolized stepwise by removing two-carbon units.Carbohydrate pathways (EM, ED, PPP) primarily process sugars, not fatty acids.Acetyl-CoA is the common product feeding the TCA cycle.Concept / Approach:β-oxidation repeatedly cleaves two-carbon fragments as acetyl-CoA by oxidizing the β-carbon of the acyl chain in cycles: oxidation, hydration, oxidation, and thiolysis. Entner–Doudoroff, Embden–Meyerhof (glycolysis), and the pentose phosphate pathway are carbohydrate routes that do not produce acetyl-CoA from fatty acids. Thus, β-oxidation is the correct pathway for fatty acid to acetyl-CoA conversion.Step-by-Step Solution:Recognize fatty acid catabolism uses a dedicated pathway.Recall β-oxidation cycle removes two-carbon acetyl-CoA units per turn.Exclude carbohydrate-specific pathways (EM, ED, PPP).Verification / Alternative check:Mitochondrial β-oxidation in eukaryotes and analogous processes in bacteria supply large amounts of reduced cofactors (NADH, FADH2), confirming the energy-conserving function tied to acetyl-CoA generation.Why Other Options Are Wrong:Entner–Doudoroff, Embden–Meyerhof, PPP: sugar catabolism and biosynthesis routes, not fatty-acid breakdown.Common Pitfalls:Confusing acetyl-CoA origin from pyruvate dehydrogenase (after glycolysis) with the lipid-specific β-oxidation route.Final Answer:β-oxidation

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