Page 1 BISC 307, Exam 1 Answers Spring 2015 1. Which one of the following is the most accurate statement of the hygiene hypothesis? (d) a. Excessive use of antibiotics has favored the evolution of antibiotic-resistant bacteria. b. Natural selection will favor mutations that significantly improve reproductive success early in life even if they increase the risk of death later in life. c. Greater virulence is bad for pathogens because it kills the host too quickly, thus many pathogens evolve toward low or intermediate levels of virulence, which are better strategies to maximize transmission to other hosts. d. Humans co-evolved with their intestinal microbiota and parasitic worms – they manipulate our immune systems to survive, and we minimize our inflammatory responses to limit damage to ourselves. Medicine and cleanliness removes some of these symbionts & parasites, resulting in inappropriate immune reactions. e. Humans evolved mechanisms to survive despite frequent scarcity of food. The modern abundance of high calorie foods has created a mismatch between our metabolic abilities and our dietary environment, causing the current epidemics of obesity, diabetes type 2, and cardiovascular disease. 2. Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank. Do not write T or F. ANS: a-F, b-T, c-F, d-T ___________ a. The more we expose bacteria to antibiotics, the harder they will try to adapt. ___________ b. Mutations occur commonly, but evolution only occurs when mutations are passed from generation to generation and spread through a population, usually driven by natural selection. ___________ c. A mutated gene that predisposes people to diabetes type 2 has recently been identified. Based on the large number of mutations that have accumulated in this gene, it is estimated that it began diverging from the wild type gene about 800,000 years ago – long before we emerged as a species. Therefore, it is likely that our hominin ancestors also suffered from diabetes type 2. ___________ d. Pesticide-resistant head lice are now very common. The first of the following explanations for this is more likely than the second: 1) Genes for pesticide resistance were present before pesticide-containing shampoos were widely used. Lice carrying these genes became more common as the shampoos were used. 2) Frequent exposure to pesticide-containing shampoos caused mutations that allowed lice to become more resistant. 3. Imagine two aqueous solutions, A and B, that are separated by a membrane that is permeable to K+ but not to Cl- or H2O. Solution A is 100 mM KCl, and solution B is 1 mM KCl. Which one of the following statements is most likely to be true? (d) a. Over time, osmosis will increase the volume of solution A and decrease the volume of solution B. b. K+ ions will diffuse from solution A to solution B until the [K+] of both solutions is 50.5 mM. c. K+ ions will diffuse from solution B to solution A until the [K+] of both solutions is 50.5 mM. d. Solution A is electrically negative with respect to solution B. e. Solution B is hyperosmotic compared to solution A.Page 2 4. From an evolutionary point of view, menopause is puzzling in that it appears to reduce lifetime reproductive success. Humans are almost the only mammal that continues living for an extended time after menopause. Which of the following hypotheses to explain menopause is plausible? (g) a. If the probability that a mother dies in childbirth, or a child dies in infancy, increases with aging of the mother, then there will come a point where natural selection will favor mothers who stop reproducing in order to ensure survival of their last child. b. Menopause evolved to free grandmothers from raising their own infants so that they could help their daughters rear grandchildren. c. Female fetuses are endowed with several million oocytes, but the vast majority of these are defective. During oocyte maturation, defective oocytes are detected and killed by apoptosis. Due to this massive attrition, the supply of healthy oocytes is simply depleted by the frequent ovarian cycles. d. Both a & b are plausible. e. Both a & c are plausible. f. Both b & c are plausible. g. All three (a, b, c) are plausible. 5. Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank. Do not write T or F. ANS: a-F, b-T, c-F, d-T ___________ a. If the erythrocyte membrane is permeable to urea, and erythrocytes were suspended in an isosmotic solution of urea, then the erythrocytes would shrink in volume. ___________ b. To a close approximation, a solution composed of 20 mM KCl and 260 mM glucose would be isosmotic to a 150 mM solution of NaCl. ___________ c. The Na+/K+ pump transports 2 Na+ ions into the cell and 3 K+ ions out of the cell for every molecule of ATP it hydrolyzes. ___________ d. During embryonic and postnatal development, declining expression of Na/K/2Cl transporters in neuronal membranes would lead to a drop in intracellular [Cl-] in these cells. 6. The bacterium Bordetella pertussis secretes pertussis toxin (PT). When PT is taken into body cells, it enzymatically modifies the -subunit of inhibitory G proteins (Gi), preventing Gi from binding to G protein-coupled receptors in the plasma membrane. Which one of the following statements is most likely correct? (c) a. Exposure to PT should inhibit adenylyl cyclase activity. b. Exposure to PT should cause an increase in GTP-bound -subunits. c. Intracellular concentration of cAMP should increase after exposure to PT. d. After exposure to PT, splitting of Gi proteins into  and - subunits should increase. 7. Supplements of the steroid hormone estrogen can be taken via several different routes, for example, orally (as a pill), transdermally (as a patch), or vaginally (gel, tablet, ring). In contrast, the only practical way of administering the protein hormone insulin is by subcutaneous injection with a hypodermic needle. Briefly explain this difference in terms of the physical/chemical properties of the two hormones. ANS: Because it is a non-polar (lipophilic) molecule, estrogen easily permeates plasma membranes. Thus, it is readily absorbed into many different tissues. In contrast, insulin is a large, polar, hydrophilic molecule that does not permeate membranes at all. It is a protein, so would be digested by the stomach and intestine if