Which of the following statements is true for all organisms?
Answer: B
Correct answer: they require inorganic nutrients
Every organism needs inorganic nutrients - water, and sources of nitrogen, phosphorus, sulfur, potassium and the trace metals. The other three are not universal: autotrophs need no organic carbon, many organisms make all their own growth factors, and anaerobes are poisoned by oxygen.
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When acetate is the sole source of carbon for some microorganisms, the cycle which is used, is called
Answer: C
Correct answer: glyoxylate pathway
On acetate as the only carbon source, a cell would lose both carbons as CO2 in each turn of the TCA cycle and never accumulate anything to build with. The glyoxylate cycle bypasses the two decarboxylation steps, using isocitrate lyase and malate synthase, so that each two turns yield a four-carbon molecule for biosynthesis.
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The glyoxylate cycle is used by some microorganisms when___________ is the sole carbon source.
Answer: A
Correct answer: acetate
On acetate alone the ordinary TCA cycle would oxidise both carbons to CO2, leaving nothing for biosynthesis. The glyoxylate cycle skips the two decarboxylations, so that each pair of acetate molecules yields a four-carbon compound the cell can build from.
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ATPase
Answer: D
Correct answer: carries out each of the reactions indicated in (a) and (b)
ATPase is reversible, and which way it runs depends on the proton gradient. When the gradient is strong, protons flow inwards through it and the energy is used to make ATP. When the gradient is weak, the enzyme hydrolyses ATP and pumps protons out to restore it - which is how a fermenting cell maintains its membrane potential.
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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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Assimilatory sulfate reduction involves the nucleotide __________ during the incorporation of H2S in the production of __________ .
Answer: B
Correct answer: ATP; cysteine
Sulfate is chemically inert, so the cell must first activate it: ATP converts it to adenosine phosphosulfate (APS) and then to PAPS, at the cost of two high-energy bonds. The activated sulfate is reduced to H2S, which is then attached to O-acetylserine to give cysteine - the entry point for sulfur into all the cell’s organic compounds.
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A reduced compound is
Answer: C
Correct answer: NADH
NADH is the reduced form - NAD+ that has accepted two electrons and a proton. NAD and FAD as written are the oxidised forms, and ADP is a nucleotide of energy transfer, not of redox.
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