The specific enzyme/(s) of the glyoxylate cycle is/are
Answer: C
Correct answer: both (a) and (b)
The two enzymes unique to the glyoxylate cycle are isocitrate lyase, which splits isocitrate into succinate and glyoxylate, and malate synthase, which joins glyoxylate to a second acetyl-CoA. Between them they bypass the two decarboxylation steps of the TCA cycle, which is what conserves the carbon.
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To digest cellulose in its environment, a fungus produces a/an
Answer: B
Correct answer: exoenzyme
Cellulose is a huge insoluble polymer that cannot cross the cell membrane, so the fungus secretes an exoenzyme to break it down outside the cell and then absorbs the sugars released. Endoenzymes work within the cell.
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In aerobic respiration, the terminal electron acceptor is
Answer: A
Correct answer: oxygen
In aerobic respiration the electron transport chain passes electrons down a series of carriers and finally to oxygen, which is reduced to water. Oxygen’s high reduction potential is what makes the drop in free energy so large, and so allows aerobic respiration to yield far more ATP than fermentation or most anaerobic respirations. Nitrate is the acceptor in anaerobic respiration by denitrifiers.
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An obligate halophile requires high:
Answer: C
Correct answer: salt
Halophile means salt-loving, and an obligate one cannot grow without a high salt concentration - the extreme haloarchaea require several molar NaCl and lyse in fresh water. Their cytoplasm is kept osmotically balanced by accumulating potassium ions or compatible solutes.
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Energy in biological systems is primarily
Answer: B
Correct answer: chemical
Living systems run on chemical energy - energy held in bonds, and moved about in compounds such as ATP. Radiant energy matters only where photosynthesis captures it, and it is converted to chemical form at once.
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Substrate-level phosphorylation refers to the formation of ATP by ________.
Answer: C
Correct answer: direct transfer of a phosphate group from a phosphorylated compound to ADP
Here an enzyme moves a phosphate straight from a high-energy intermediate onto ADP, as happens twice in glycolysis. It requires no membrane and no electron transport chain, which is why fermenting organisms depend on it entirely.
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In order to get inorganic phosphorous into organic compounds, the phosphate ion is incorporated via
Answer: C
Correct answer: both (a) and (b)
Inorganic phosphate is drawn into organic combination by both mechanisms: substrate-level phosphorylation, where a phosphate is transferred directly from a high-energy intermediate, and oxidative phosphorylation, where ATP synthase condenses ADP and Pi using the proton gradient. From ATP the phosphate then passes to every other phosphorylated compound.
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An enzyme ______ the activation energy required for a chemical reaction.
Answer: C
Correct answer: lowers
An enzyme lowers the activation energy - the barrier a reaction must climb before it can proceed - by binding the substrate in a way that stabilises the transition state. What it does not change is the equilibrium or the overall free energy change: it makes the reaction faster, not more favourable.
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Active transport of a substance across a membrane requires:
Answer: B
Correct answer: the expenditure of ATP
Active transport moves a substance against its gradient, which cannot happen spontaneously, so it must be paid for - directly by hydrolysing ATP, or indirectly by coupling to an ion gradient that ATP maintains. Needing a favourable gradient is the mark of passive transport, not of this.
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DNA replication is semiconservative because the ______strand will become half of the ________molecule.
Answer: B
Correct answer: template, finished
Each parental strand serves as the template for a new partner and is then retained as half of the finished duplex. That is what “semi-conservative” means - half of each daughter molecule is conserved from the parent - and it is what Meselson and Stahl demonstrated.
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