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Unformatted text preview: Note: You may not print this exam or download the file to your computer. Exam 3 - ANSWERS BISC 220L – General Biology: Cell Biology and Physiology April 7, 2006 9 am Version
1. Answer all 18 of the questions. READ EACH CAREFULLY BEFORE ANSWERING! 2. Note that questions have different point values. In all, 140 points are possible. 3. Write your answer within the box provided for each question. Material written outside these spaces will not be graded. 4. You have 50 minutes for this exam. 5. Manage your time wisely. Good luck! WRITE YOUR NAME ON EACH PAGE
Your Name: _____________________________________________________________ Student ID Number: _______________________________________________________ Please check the box next to your TA’s name: Gorjana Bezmalinovic Tami Brown Silvana Constantinescu Jason Hoskin Anne Jokiaho Xinwen Liu Xuecong Liu Jianwei Lu Bo Zhou Rui Zhu NAME_______________________________________ 1. (4 pts.) Low levels of glucose in the plasma stimulate ___________________________ cells in the pancreas to secrete _____________________________. High levels of glucose in the plasma stimulate ______________________________ cells in the pancreas to secrete ___________________________. ANS: alpha (α); glucagon; beta (β); insulin 2. (10 pts.) List the hormones that are known to affect appetite in humans. For each hormone, list a) the cell, tissue, or organ that secretes the hormone, and b) the main effect of the hormone.
Answer in box ANS: 1) Leptin is released by fat cells (adipocytes) and it suppresses appetite by inhibiting neurons in the feeding center in the hypothalamus. 2) PYY is released by the small intestine and it suppresses appetite by inhibiting the feeding center. 3) Insulin is released by β-cells in the pancreas and it suppresses appetite by inhibiting the feeding center. 4) Ghrelin is released by the stomach and it stimulates appetite by exciting the feeding center. 3. (4 pts.) Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank (do not mark with T or F). ANS: a-T, b-T, c-F, d-F ________ a. In birds, blood pumped out of the right ventricle is deoxygenated. ________ b. In fish, blood flows directly from the respiratory organ to the body without passing through the heart. ________ c. The lumen of all blood vessels is lined with endothelial cells, except for the chambers of the heart. ________ d. The combined cross-sectional area of all the arteries is greater than that of the capillaries. Page 2 of 7 Points on this page_____________ NAME_______________________________________ 4. (12 pts.) Elephantiasis is a painful and disfiguring condition in which fluid-filled swellings develop in the limbs, genitalia, and other body parts. It is caused by filarial worms which lodge within and block lymph vessels and nodes. Explain where this fluid comes from, where it normally goes to prevent swelling, and the physical forces that create it.
Answer in box ANS: The fluid is lymphatic fluid, which is normally conveyed out of tissues back to the large veins near the heart via the lymph vessels and nodes. Filtration pressure, contractions of surrounding muscles, and one-way valves normally assure adequate flow to prevent swelling. Lymphatic fluid is created because blood pressure within capillaries, which forces fluid out of the plasma into surrounding tissues, is slightly greater than the osmotic pressure of the blood within the capillaries, which causes fluid to leave tissues and re-enter the blood. Thus, there is a net leakage of fluid into the tissues. 5. (4 pts.) Sympathetic nerves release _____________________________ in the heart, which __________________________ the heart rate. Parasympathetic nerves release __________________________ in the heart, which _________________________ the heart rate. ANS: norepinephrine; increases; acetylcholine; decreases 6. (5 pts.) In pneumonia, the alveolar epithelium and capillaries become abnormally permeable so that fluid accumulates within the alveoli. Given this, why is breathing typically rapid in patients with pneumonia? (d) a. The level of CO2 in the pulmonary arteries is decreased. Answer in box b. Bacterial or viral infection causes release of cytokines which stimulate contraction of the diaphragm. c. Fluid loss from alveolar capillaries reduces blood pressure. d. The thickened alveolar fluid impairs gas exchange, and the resulting buildup of CO2 stimulates the respiratory control center. Page 3 of 7 Points on this page_____________ NAME_______________________________________ 7. (9 pts.) Briefly explain why exercise tends to lower the pH of the blood, and how the respiratory system acts to counteract that change in pH.
Answer in box ANS: There is an increase in metabolism in muscles, in order to meet the energy demands of exercise. The waste product of this metabolism, CO2, combines with water in body fluids to form carbonic acid, which in turn dissociates to form H+, thus lowering pH. In response to the rise in PCO2 (or drop in pH), the respiratory control center in the brain stimulates an increase in the rate and/or depth of breathing. Excess CO2 is blown off into the environment and this raises pH back to normal levels. 8. (5 pts.) Which one of the following statements about insects is correct? (b) a. Blood is contained within a system of tubes called tracheae. Answer in box b. Insects have hearts and blood vessels. c. Exchange of respiratory gases occurs between body cells and nearby, air-filled tracheae. d. Hemolymph transports respiratory gases between the tracheal system and body cells. e. Throughout the body, blood is separated from interstitial fluid by endothelial cells. 9. (5 pts.) In which one of the following situations would you expect hemoglobin to have the highest binding affinity for O2? (d) Answer in box a. in actively exercising skeletal muscle b. in the liver when you are breathing normally c. in the liver when you are holding your breath d. in the alveolar capillaries e. in the skin 10. (5 pts.) Which one of the following is not involved in the process of inflammation? (e) a. dilation of arterioles Answer in box b. an increase in osmotic pressure in the extracellular fluid c. release of prostaglandins from activated macrophages d. increased delivery of O2 to the inflamed area e. reduced volume of interstitial fluid in the inflamed area Page 4 of 7 Points on this page_____________ NAME_______________________________________ 11. (12 pts.) Explain the mechanism by which a dendritic cell activates a helper T-cell. (Note that I am not asking what a helper T-cell does after it is activated, so don’t include that in your answer).
Answer in box ANS: In tissues, dendritic cells are phagocytes that ingest bacteria. As bacterial proteins are degraded within the dendritic cell, antigenic bacterial peptides bind to MHC class II molecules that the dendritic cell continually synthesizes, inserts in its plasma membrane, and later internalizes and degrades. Therefore, MHC class II molecules can present bacterial antigens to helper T-cells. Receptors on helper T-cells bind to the antigens thus presented. When this binding is stabilized by binding to the MHC class II molecule and by a helper T-cell protein called CD4, the helper T-cell is activated. The dendritic cell also activates the helper T-cell by secreting a cytokine (interleukin-1). 12. (10 pts.) Briefly explain the cellular mechanisms by which the immune system “remembers” prior exposure to a pathogen, such that the second exposure to the pathogen provokes vigorous immune defenses. Answer in box ANS: When helper T-cells, cytotoxic T-cells, and B-cells are activated, they proliferate by mitosis to form two types of progeny, effector cells that carry out the functions of the specific lymphocyte, and memory cells that remain dormant like the original naïve lymphocytes, but are much more numerous. When the pathogen presents itself a second time, these large numbers of memory T- and B-cells carry out vigorous and specific defenses. Page 5 of 7 Points on this page_____________ NAME_______________________________________ 13. (4 pts.) Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank (do not mark with T or F). ANS: a-T, b-T, c-F, d-T ________ a. Complement proteins kill cells that have antibodies bound to their surfaces. ________ b. The clonal selection theory explains how antigens activate specific lymphocytes. ________ c. IgG molecules in milk allow some of the mother’s immunity to be passed on to the nursing infant. ________ d. Agglutination of bacteria facilitates phagocytosis. 14. (4 pts.) Indicate whether each of the following statements is true or false by writing the word “True” or “False” in the blank (do not mark with T or F). ANS: a-F, b-T, c-F, d-F ________ a. Urine is conveyed from the renal pelvis to the bladder by the urethra. ________ b. Dilation of the afferent arteriole of the nephron would cause an increase in the net filtration pressure. ________ c. In order for epithelial cells in the proximal tubule of the nephron to power the reabsorption of Na+ ions, their Na/K pumps must be located in the membrane facing the lumen of the tubule. ________ d. Eating salty food would tend to increase the volume of urine produced. 15. (12 pts.) Briefly explain the mechanism by which interstitial fluid in the inner medulla of the kidney comes to have a much higher concentration of NaCl than interstitial fluid in the cortex of the kidney. Focus your answer on the creation of this osmotic gradient, not its maintenance or function.
Answer in box ANS: The steep gradient of NaCl concentration in the inner medulla is created by the extrusion of salt from the ascending limb of the loop of Henle. The descending limb of the loop of Henle is permeable to water, so as the tubular fluid descends, water moves out by osmosis. As the fluid moves up the ascending limb, NaCl moves out, passively in the inner half of the ascending limb, and by active transport in the outer half of the ascending limb. Thus, salt accumulates in the interstitial space. Page 6 of 7 Points on this page_____________ NAME_______________________________________ 16. (5 pts.) Central diabetes insipidus is a disease in which damage to the hypothalamus or pituitary produces a deficit in secretion of antidiuretic hormone. Which one of the following is characteristic of this condition? (b) a. a high concentration of Na+ in the urine Answer in box b. producing large amounts of dilute urine c. overproduction of ADH d. high production of aldosterone e. high production of angiotensin II 17. (8 pts.) In the kidney, glucose is continually lost from the plasma into the tubular fluid, yet there is normally no glucose in the urine. How is glucose reabsorbed?
Answer in box ANS: Glucose is reabsorbed by active transport across the tubular epithelium into peritubular capillaries. 18. (2 pts.) In general, a signal molecule which conveys messages between neighboring cells without having to be transported by the blood is called a _______________________________________. One specific example of such a molecule is ____________________________________. ANS: paracrine hormone/agent or local regulator; many possible answers for second part, e.g., histamine, cytokines, chemokines, growth factors, nitric oxide, prostaglandins, etc. Page 7 of 7 Points on this page_____________ ...
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