Exam 1 Answers 1 Exam 1 Answers, BISC 307L, Spring 2012 1. Which one of the following is not an example of homeostasis? (b) a. Increased blood pressure in the aorta stimulates a reduction in the strength of the heartbeat. b. A rise in estrogen during the menstrual cycle stimulates an increase in the number of progesterone receptors in the uterus. c. A rise in [Ca2+] in the plasma triggers release of a hormone that stimulates bone formation. d. A rise in [glucose] in the plasma triggers release of a hormone that stimulates liver cells to synthesize glycogen. e. A decrease in body temperature stimulates neurons in the hypothalamus to initiate heat-conserving behavior. 2. Indicate whether each of the following statements is true or false by writing “True” or “False” in the blank. Do not just write “T” or “F.” ANS: a-F, b-F, c-T, d-T __________ a. The strains of E. coli spread between patients by hospital workers are likely to be less virulent than strains of E.coli spread between students by preschool teachers. __________ b. Coughing is a pathological condition which should always be suppressed. __________ c. The majority of people alive today do not express the lactase gene after early childhood. __________ d. It is likely that obesity is a direct result of a mismatch between our modern nutritional environment and our evolved metabolic abilities. 3. If the left ventricle is weakened by disease, it may be difficult for it to pump out the blood it receives from the right ventricle, resulting in chronic distension (over-inflation) of the left ventricle. The resulting stretching of the walls of the left ventricle make it even weaker, creating a downward spiral that ends in death caused when massive failures in the circulatory system. If natural selection operates to maximize survival and reproductive fitness, how could evolution have produced a system that is so prone to heart failure of this sort? ANS: Heart failure of the type described most commonly occurs in middle and advanced age, well after the reproductive phase of life. Over most of time we have existed as a species, lifespan was much shorter than in modern times. Thus, it is likely that the mechanisms that cause heart failure would not have a negative effect on fitness during human evolution. 4. Solutions A and B are separated by a membrane that is permeable only to K+, and nothing else. Solution A is 100 mM KCl, and solution B is 1 mM KCl. Which one of the following statements is correct? (d) a. K+ ions will diffuse from solution A to solution B until the [K+] of both solutions is 50.5 mM. b. Water will diffuse from solution B to solution A until the [K+] of both solutions is 50.5 mM. c. KCl will diffuse from solution A to solution B until the [K+] of both solutions is 50.5 mM. d. K+ ions will diffuse from solution A to solution B until a membrane potential develops, with solution A negative with respect to solution B. e. None of the above statements is correct. 4 pts. 4 pts. 6 pts. 4 pts.Exam 1 Answers 2 5. A rare genetic disease is caused by mutations in the SLC5A1 gene. This gene codes for the one of the most abundant forms of SGLUT protein. In persons with the disease, the SGLUT protein is non-functional. Briefly explain why persons with this disease would be expected to show malnutrition, severe diarrhea, and dehydration. ANS: The SGLUT protein is an important Na+-dependent transporter in the apical membrane of intestinal epithelial cells. SGLUT is responsible for the absorption of glucose (and galactose-not necessary) from the lumen of the intestine into the blood. The lack of functional SGLUT would impair glucose absorption and thus lead to malnutrition. Normally, transport of Na+ and glucose (and Cl-) out of the lumen creates an osmotic gradient that also drives the reabsorption of water. Without functional transporters, glucose cannot be reabsorbed and so it accumulates in the lumen, which draws water out of the body, causing diarrhea 6. A neuron has an intracellular [Na+] of 14 mM and an extracellular [Na+] of 140 mM. What would be the membrane potential if the membrane were only permeable to Na+? (b) a. +81 mV d. 0 mV g. -81 mV b. +61 mV e. -41 mV h. insufficient information is given c. +41 mV f. -61 mV 7. Refer to the diagram below. 8. Indicate whether each of the following statements is true or false by writing “True” or “False” in the blank. Do not just write “T” or “F.” ANS: a-T, b-F, c-F, d-T __________ a. Progesterone can affect cells by binding to specific receptors on the plasma membrane. __________ b. Inhibiting phospholipase C is likely to block the synthesis of all eicosanoids. __________ c. The hormone carbon monoxide (CO) is released from CO-secreting cells by exocytosis. __________ d. In the blood plasma, most lipophilic hormones are bound to carrier proteins. a. One would not expect to find aquaporin channels in the membranes of reabsorptive epithelial cells. b. One would expect intracellular [Na+] to be lower than extracellular [Na+] in both the secretory and reabsorptive epithelial cells. c. CFTR Cl- channels are located in the apical membranes of secretory epithelial cells. d. In reabsorptive epithelial cells, one would expect to find Na+/K+ pumps only in the apical membrane. 9 pts. 4 pts. 3 pts. This diagram shows a typical sweat gland in human skin. The secretory coil fills the lumen with a NaCl solution that is isotonic with the blood plasma. As this solution moves upward through the reabsorptive duct, NaCl is reabsorbed into the blood, such that the sweat that is secreted onto the skin surface is hypotonic. Assume that along its entire length, the walls of the sweat gland consist of a single layer of epithelial cells joined by tight junctions. Which one of the following statements about this system is false? (d) 4 pts.Exam 1 Answers 3 9. Which one of the following statements is false? (d) a. Lowering extracellular [K+] makes the potassium equilibrium potential more negative. b. Raising extracellular [K+] would depolarize most neurons. c. If the chloride equilibrium potential is less negative than the membrane potential, then one would expect that opening Cl- channels would generate an inward current. d. If nothing else changes, raising extracellular [Na+] would cause the peak of the action potential to occur at a less positive potential. 10. Luteinizing hormone (LH) binds to LH