Compared with the interstitial fluid that bathes active muscle cells, blood reaching these cells in arterioles has aa. higher PO2.b. higher PCO2.c. greater bicarbonate concentration.d. lower pH.

Countercurrent gas exchange in the gills of a fisha. maintains a gradient that enhances diffusion.b. enables the fish to obtain oxygen without swimming.c. means that blood and water flow at different rates.d. allows O2 to diffuse against its partial pressure gradient

When you inhale, the diaphragma. relaxes and moves upward.b. relaxes and moves downward.c. contracts and moves upward.d. contracts and moves downward.

Explain how each parameter in Fick's law of diffusion is reflected in the structure of the mammalian lung.

Frog lungs have a smaller surface area for gas exchange than mammalian lungs. How do frogs compensate for this difference?a. Frog tissue absorbs more oxygen from the blood than mammalian tissue does.b. Frogs breathe more quickly than mammals.c. Frogs also obtain oxygen via diffusion across the skin.d. Frog lung tissue has a greater density of capillary beds than mammalian lung tissue.

Carp are fishes that thrive in stagnant-water habitats with low oxygen partial pressure. Compared with the hemoglobin of many other fish species, carp hemoglobin has an extremely high affinity for O2. Draw an oxygen–hemoglobin equilibrium curve showing separate lines for carp and a fish that lives in water with a higher oxygen partial pressure. Explain why they differ.

What is the primary feedback used by the brain to control breathing?a. heart rateb. partial pressure of O2c. blood pH, which indicates O2 leveld. blood pH, which indicates CO2 level

What are two advantages of breathing air, compared with obtaining dissolved oxygen from water? What is a comparative disadvantage of breathing air?

During exercise, the cardiovascular system must supply muscles with large amounts of oxygen and fuel and get rid of a lot of wastes. How do the cardiovascular systems of athletes respond to prolonged exercise?During athletic training, the oxygen–hemoglobin dissociation curvea. shifts to the right, unloading more oxygen to tissues.b. shifts to the right, unloading less oxygen to tissues.c. shifts to the left, unloading more oxygen to tissues.d. shifts to the left, unloading less oxygen to tissues.