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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In a prokaryotic cell, where does the Krebs cycle take place ?
Answer: C
Correct answer: The cytoplasm
Bacteria have no mitochondria, so the Krebs cycle enzymes are dissolved in the cytoplasm. The electron transport chain, by contrast, is embedded in the plasma membrane, which is the prokaryotic counterpart of the inner mitochondrial membrane.
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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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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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Complete oxidation of glucose in aerobic respiration can yield a net output of _____ATP.
Answer: C
Correct answer: 38
Complete aerobic oxidation yields about 38 ATP in the classical accounting: 4 from substrate-level phosphorylation, and the rest from reoxidising 10 NADH and 2 FADH2 through the electron transport chain. Modern measurements put the real figure nearer 30, because the proton gradient also pays for transport across the membrane.
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Psychrophiles would be expected to grow:
Answer: C
Correct answer: at refrigeration temperatures
Psychrophiles are cold-loving, growing best below about 15°C and often at 0°C. Their enzymes and membranes are adapted to stay flexible in the cold, which is why they spoil refrigerated food while mesophiles cannot.
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