Phosphate is considered to restrict the induction of
Answer: B
Correct answer: secondary metabolites
Phosphate at growth-supporting concentrations represses secondary metabolism - antibiotics, alkaloids, pigments - while primary metabolism, which the cell needs to grow, proceeds. This is why industrial fermentations are often run with phosphate deliberately limited once growth is complete.
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Free energy change (ΔG) of a reaction is referred to as the amount of energy
Answer: C
Correct answer: liberated or taken up during reaction
\(\Delta G\) is a change, and it may have either sign. A negative value means energy is released and the reaction is spontaneous (exergonic); a positive value means energy must be supplied (endergonic). The quantity itself covers both cases.
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Which of the following does not produce oxygen as a product of photosynthesis?
Answer: B
Correct answer: Purple sulfur bacteria
Purple sulfur bacteria are anoxygenic photosynthesisers: they use H2S rather than water as the electron donor, so the by-product is elemental sulfur, not oxygen. Oak trees, cyanobacteria and phytoplankton all split water and release O2.
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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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Hexose monophosphate pathway is also known as
Answer: A
Correct answer: phosphogluconate pathway
The hexose monophosphate shunt is also called the phosphogluconate pathway or the pentose phosphate pathway. Its purpose is not ATP but NADPH for biosynthesis and ribose-5-phosphate for nucleotides.
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If radioactive bicarbonate was supplied to bacterial cells, which were actively synthesizing fatty acids, it is expected to find the bulk of the radioactivity in
Answer: A
Correct answer: cellular bicarbonate
The CO2 fixed by acetyl-CoA carboxylase to make malonyl-CoA is released again at each condensation step of fatty acid synthesis. So the labelled carbon passes through the pathway and returns to the cellular bicarbonate pool rather than being built into the fatty acid chain, which is assembled entirely from acetyl units.
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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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The role of bacteriochlorophyll in anoxygenic photosynthesis is to
Answer: C
Correct answer: use light energy to energize an electron
A bacteriochlorophyll molecule in the reaction centre absorbs a photon and is raised to an excited state, from which it donates a high-energy electron to the first acceptor. Everything else - the transport chain, the proton gradient, the ATP - follows from that single act of energising an electron.
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TCA cycle functions in
Answer: C
Correct answer: amphibolic reactions
The TCA cycle is amphibolic: it works in both directions of metabolism. It oxidises acetyl-CoA for energy (catabolic), and its intermediates are drawn off as precursors - oxaloacetate and α-ketoglutarate for amino acids, succinyl-CoA for porphyrins (anabolic). Anaplerotic reactions exist precisely to replace what is withdrawn.
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Entner-Doudoroff pathway is found in
Answer: C
Correct answer: both (a) and (b)
The Entner-Doudoroff pathway is found in prokaryotes of both kinds - aerobes such as Pseudomonas and anaerobes such as Zymomonas. It is an alternative to glycolysis, yielding only 1 ATP per glucose instead of 2, and it is essentially absent from eukaryotes.
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