In DNA, adenine is the complementary base for _____, and cytosine is the complement for ______.
Answer: C
Correct answer: thymine, guanine
The pairing is fixed by hydrogen bonding: A with T through two bonds, and C with G through three. Uracil replaces thymine in RNA, so it plays no part in DNA.
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Superoxide ion is toxic to strict anaerobes because they lack:
Answer: C
Correct answer: dismutase
Oxygen chemistry produces the superoxide radical, and the enzyme that disposes of it is superoxide dismutase, which converts it to hydrogen peroxide and oxygen. Strict anaerobes lack it, so superoxide accumulates and destroys their cell components - which is why oxygen is lethal to them. (Catalase then removes the peroxide, and most anaerobes lack that too.)
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ATP synthase complexes can generate ____ATPs for each NADH that enters electron transport.
Answer: C
Correct answer: 3
Each NADH delivers its electrons at the top of the chain, and their passage down it pumps enough protons to drive roughly 3 ATP through ATP synthase. FADH2, entering lower down at coenzyme Q, yields about 2. (Measured values are closer to 2.5 and 1.5, since the gradient also pays for transport across the membrane.)
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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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Which of the following is responsible for phosphate solubilization?
Answer: C
Correct answer: Bacillus
Bacillus species are among the best-known phosphate solubilisers: they secrete organic acids that release phosphate bound in insoluble mineral form, which is why they are used as biofertilisers alongside Pseudomonas.
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The essential function of fermentation is to ________.
Answer: A
Correct answer: regenerate NAD+ so that glycolysis can continue
Glycolysis needs a supply of oxidised NAD+, and without a terminal electron acceptor the cell cannot regenerate it through the electron transport chain. Fermentation solves this by reducing pyruvate or a derivative, so the ATP yield stays at the 2 from glycolysis.
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Chemoautotrophs can survive on ______alone.
Answer: C
Correct answer: minerals and CO2
A chemoautotroph takes its energy from oxidising an inorganic compound such as ammonia, nitrite, sulfide or ferrous iron, and its carbon from CO2. So it needs minerals and CO2 and nothing organic at all - which is what lets such organisms colonise bare rock and deep-sea vents.
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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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Energy is carried from catabolic to anabolic reactions in the form of _______
Answer: B
Correct answer: ATP
ATP is the cell’s energy currency. Catabolism captures released energy by phosphorylating ADP, and anabolism spends it by hydrolysing ATP back to ADP and phosphate at the point where work must be done. Coupling the two through a common intermediate is what lets one pathway pay for another.
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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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