29. A researcher incubates hepatocytes with 15NH4Cl and observes that 15N appears first in glutamate, then subsequently in aspartate. Which of the following best explains this sequential labeling? (A) 15NH4+ → glutamine (by glutamine synthetase) → glutamate → aspartate (by transamination) (B) 15NH4+→ glutamate (by glutamate dehydrogenase) → aspartate (by transamination with oxaloacetate) (C) 15NH4+→ carbamoyl phosphate (by CPS I) → glutamate → aspartate (via urea cycle intermediates) (D) 15NH4+ → glutamate (by glutamate dehydrogenase using succinate) → aspartate (by transamination with fumarate) (E) 15NH4+→ glutamate (by glutamine synthetase) → aspartate (by reductive amination of oxaloacetate)

29. A researcher incubates hepatocytes with ¹⁵NH₄Cl and observes that ¹⁵N appears first in glutamate, then subsequently in aspartate. Which of the following best explains this sequential labeling?
(A)¹⁵NH₄⁺ → glutamine (by glutamine synthetase) → glutamate → aspartate (by transamination)
(B) ¹⁵NH₄⁺→ glutamate (by glutamate dehydrogenase) → aspartate (by transamination with oxaloacetate)
(C)¹⁵NH₄⁺→ carbamoyl phosphate (by CPS I) → glutamate → aspartate (via urea cycle intermediates)
(D) ¹⁵NH₄⁺ → glutamate (by glutamate dehydrogenase using succinate) → aspartate (by transamination with fumarate)
(E) ¹⁵NH₄⁺→ glutamate (by glutamine synthetase) → aspartate (by reductive amination of oxaloacetate)

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統計： A(0), B(1), C(1), D(0), E(2) #3853334

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2026/04/01

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氮代謝 (Nitrogen Metabo...

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13. Suppose a person begins breathing very rapidly while resting (hyperventilating), which of the following best describes how homeostasis is restored? (A) Rapid breathing decreases blood CO2 levels, thereby raising blood pH. The frontal cortex detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate. (B) Rapid breathing increases blood CO2 levels, thereby causing the blood pH to drop. The hypothalamus detects the change and decreases stimulation of the rib muscles and the diaphragm, thereby reducing the breathing rate. (C) Rapid breathing decreases blood CO2 levels, thereby raising blood pH. The hypothalamus detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate. (D) Rapid breathing increases blood CO2 levels, thereby causing the blood pH to drop. The medulla oblongata detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate. (E) Rapid breathing decreases blood CO2 levels, thereby raising blood pH. The medulla oblongata detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate.

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