3. Which of the following statements about histone modification is NOT correct? (A) Histone modifications change gene expression patterns without altering the actual nucleotide sequence of the DNA. (B) The addition of methyl groups to histone tails always leads to the immediate activation of the nearby gene by opening the chromatin structure. (C) Acetylation of histone tails generally neutralizes their positive charge, loosening the bond between histones and DNA to make the template more accessible for transcription. (D) Histone modifications occur primarily on the flexible N-terminal "tails" of the histone proteins that protrude outward from the core of the nucleosome. (E) Certain histone modifications can be inherited by daughter cells during mitosis, allowing a specific cell type to maintain its identity through successive cell divisions.

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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