49. The ras and p53 genes encode key proteins that function in cell-signaling pathways. Mutations in ras occur in about 30% of human cancers, and mutations in p53 occur in more than 50%. Based on their physiological roles in regulating the cell cycle, the ras gene is classified as a(n) __________, and the p53 gene is a(n) __________. (A) proto-oncogene; oncogene (B) oncogene; tumor-suppressor gene (C) proto-oncogene; tumor-suppressor gene (D) tumor-suppressor gene; proto-oncogene (E) tumor-suppressor gene; oncogene

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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