48. Helper T cells play a central role in coordinating adaptive immunity. Which of the following is NOT an outcome after a naive helper T cell is activated by an antigen-presenting cell? (A) Cytotoxic T cells are activated and subsequently destroy infected cells. (B) B cells are activated and subsequently differentiate into memory B cells and antibody-secreting plasma cells. (C) Activated helper T cells secrete cytokines and undergo clonal expansion. (D) Natural killer cells are activated and subsequently destroy infected cells. (E) Clonal helper T cells secrete cytokines that activate other immune cells.

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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