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1. Describe gas exchange in the lungs, naming the structures involved and explaining why the exchange occurs.

2. What changes occur in the blood if one were to hold ones breath for a period of time? If one were to breathe rapidly and deeply for a period of time?

3. Trace the pathway taken by a molecule of oxygen from the time it enters a nostril until it enters a red blood cell.

4. Why are gills poorly adapted for life on land?

5. How do amphibians compensate for their low efficiency of lung ventilation?

6. How do reptiles, birds and mammals improve the efficiency of lung ventilation over that of amphibians?

7. Often people who appear to have drowned can be revived, in some cases after being underwater for as long as half an hour. In every case of full recovery after extended submergence, however, the person has been submerged in very cold water. Is this observation consistent with the fact that oxygen is twice as soluble at 0C as it is at 30C?

8. Can you think of a reason why a circulatory system has not evolved in which oxygen is actively transported across respiratory membranes, in place of the passive process of diffusion across these membranes that is universally employed?

9. If by accident your pleural membrane were punctured, would you be able to breathe?

10. Trace the path of a drop of blood from the left ventricle to the big toe and back to the left ventricle, naming the vessels and structures encountered during the trip.

11. Name the one artery in the body that does not carry oxygenated blood. Explain why it does not carry oxygenated blood.

12. How does lymph differ from blood?

13. Why are valves needed in veins but not in arteries?

14. Oxygen-transport pigments are found in crustaceans, but not in insects. Explain this difference.

15. Citrate ions (C6H5O7-3) combine with calcium ions (Ca2+) to form an insoluble product,

2C6H5O7-3 + 3Ca2+ Ca3(C6H5O7 )2. Why do you suppose that a small quantity of sodium or potassium citrate is added to blood collected for storage in blood banks?

16. General edema is characteristic of extreme cases of protein deficiency. Can you account for this?

17. Why is it difficult to see platelets in stained blood slides?

18. Summarize the various mechanisms by which our circulatory system adjusts to the demands of strenuous exercise.

19. Why have mammals not improved the efficiency of their circulation by evolving hearts larger that 0.6% of their body mass?

20. Instead of evolving an entire second open circulatory system, the lymphatic system, to collect water lost from the blood plasma during passage through the capillaries, why havent vertebrates simply increased the level of serum albumin in their blood?

21. Starving animals often exhibit swollen bodies rather than emaciated ones, in early stages of their deprivation. Why?

22. The hearts of the more advanced vertebrates pump blood entirely by pushing action. Why do you suppose hearts have not evolved that act like suction pumps, drawing blood into the heart as it expands, rather than pushing it out as the heart contracts?