The pentose phosphate pathway is chiefly important to the cell because it supplies ________.
Answer: B
Correct answer: NADPH and pentose sugars for biosynthesis
The pathway generates NADPH for reductive biosynthesis and ribose-5-phosphate for nucleotide and nucleic acid synthesis. Its role is anabolic rather than energetic, which is why its ATP yield is negligible.
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A facultative anaerobe is an organism that ________.
Answer: B
Correct answer: grows with or without oxygen, but better with it
A facultative anaerobe respires aerobically when oxygen is present and switches to fermentation or anaerobic respiration when it is not. Escherichia coli is the standard example, and in a thioglycolate tube such organisms grow throughout while clustering near the top.
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What is the net yield of ATP from the glycolytic pathway per molecule of glucose ?
Answer: A
Correct answer: 2
Glycolysis consumes 2 ATP in its preparatory phase and produces 4 in the payoff phase, leaving a net gain of 2 ATP along with 2 NADH. Because none of this requires oxygen, glycolysis serves aerobes and anaerobes alike.
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The enzyme catalase protects a cell by breaking down ________.
Answer: C
Correct answer: hydrogen peroxide
Catalase converts hydrogen peroxide into water and oxygen, which is why a drop of peroxide bubbles on a catalase-positive colony. Superoxide dismutase handles the separate task of converting superoxide radicals into peroxide and oxygen.
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An obligate aerobe is an organism that ________.
Answer: D
Correct answer: requires oxygen for growth
An obligate aerobe depends on oxygen as its terminal electron acceptor and cannot grow without it. Mycobacterium tuberculosis is a familiar example, and in a thioglycolate tube such organisms form a band at the oxygen-rich surface.
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What serves as the terminal electron acceptor in aerobic respiration ?
Answer: D
Correct answer: Oxygen
Oxygen accepts the electrons at the end of the chain and is reduced to water. Anaerobic respiration substitutes another inorganic acceptor such as nitrate or sulphate, and because these have lower reduction potentials they yield less energy.
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Chemolithotrophs obtain their energy from ________.
Answer: B
Correct answer: the oxidation of inorganic compounds
Chemolithotrophs oxidise inorganic substances such as ammonia, hydrogen sulphide, ferrous iron or hydrogen gas. Nitrifying and sulphur bacteria are the familiar examples, and their activity drives much of the nitrogen and sulphur cycling in soil.
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The Entner-Doudoroff pathway differs from glycolysis chiefly in that it yields ________.
Answer: B
Correct answer: only 1 net ATP per glucose
The Entner-Doudoroff pathway produces a net 1 ATP, along with 1 NADH and 1 NADPH, per glucose. Despite the lower yield it is the main route in Pseudomonas and several other Gram-negative genera, and its distinctive intermediate KDPG is used to identify it.
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The proton motive force generated by the electron transport chain is used chiefly to ________.
Answer: B
Correct answer: synthesise ATP through ATP synthase
Electron transport pumps protons out, creating a gradient of both charge and pH across the membrane. Protons flowing back in through ATP synthase drive the enzyme, and the same gradient also powers flagellar rotation and some membrane transport.
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What is the end product of glycolysis ?
Answer: B
Correct answer: Pyruvate
Glycolysis splits glucose into two molecules of pyruvate. What follows depends on conditions: pyruvate enters the Krebs cycle by way of acetyl-CoA when a terminal electron acceptor is available, and is reduced to fermentation products when one is not.
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