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Exam_2_key-1 - Name BIOLOGY 325H Genetics Spring 2010 Exam...

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Name ___________________ 1 BIOLOGY 325H Genetics Spring 2010 Exam 2 Before you do anything else , please: check to make certain that your copy of the exam is complete, i.e. 5 pages. print your name legibly in the space provided at the top of every page. _______________________________________________________ 1. [10 pts] A. Mammals regulate their body temperature when exposed to varying environments. What term is used to describe animals which have this capability? Technically the answer to this question is 'endotherm', but I will also accept 'homeotherm' since mammals also fit that narrower definition. B. The metabolic rate of a resting mammal is lowest when the animal is exposed to temperatures in the range 28-35 ° C (= 82-95 ° F). Explain why the metabolic rate is increased at both higher and lower temperatures. A resting mammal has its lowest or 'basal' metabolic rate within a range of temperatures called the thermoneutral zone. At environmental temperatures below this range, the mammal must expend additional energy in order to generate more body heat. At environmental temperatures above this range, it must expend additional energy on behaviors ( e.g. sweating) that help it to release body heat to its environment. 2. [5 pts] Fish and birds use the phenomenon called 'countercurrent exchange' to maximize the exchange of respiratory gases with their environment. What feature of the human respiratory system prevents us from taking advantage of countercurrent exchange? Countercurrent exchange requires that two fluids - in this case, the respiratory medium and the blood - flow continuously in opposite directions. This is not possible in humans because air enters and leaves the respiratory system through the same opening ('tidal breathing'), and therefore reverses direction from inhalation to exhalation.
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Name ___________________ 2 3. [20 pts] For a human being at sea level, the P O2 in the plasma of oxygenated blood leaving the lungs is 100 mm Hg. Answer the questions below based on the O 2 :hemoglobin binding curve at the right. A. If the deoxygenated blood returning to the heart from the kidney has lost 20% of its original O 2 content in the lung, what is the P O2 of that blood? ____ __ 45 mm Hg ___ B. If the deoxygenated blood returning from a muscle has P O2 = 15 mm Hg, what is the O 2 saturation of its hemoglobin? ____ __ 20% ____ _ __ C. What feature of hemoglobin accounts for its S-shaped binding curve? For full credit, you must correctly name this feature and explain how it works. Cooperativity. Hemoglobin is a tetramer with four O 2 binding sites. When the first O 2 molecule binds to hemoglobin, it induces a conformational change in the protein that increases the O 2 affinity of the other three binding sites. This accelerates the slope of the binding curve, such that the highest slope falls in the middle.
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