81. In quantitative RT-PCR for SARS-CoV-2 detection, two patient samples are analyzed. Sample A has a Ct value of 22, while Sample B has a Ct value of 30. Assuming equal amplification efficiency, which statement best describes the relative viral loads in these samples? (A) Sample A has approximately 2-fold higher viral load than Sample B (B) Sample A has approximately 8-fold higher viral load than Sample B (C) Sample B has approximately 100-fold higher viral load than Sample A (D) Sample A has approximately 256-fold higher viral load than Sample B (E) Viral loads cannot be compared using Ct values

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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