1. Compare the amount of oxygen needed by an animal with little movement versus an animal that moves about a lot, and discuss how the respiratory system is adapted for those needs. In particular, comparisons should be made between invertebrates (such as a hydra or an earthworm) versus flying insects, or between vertebrates such as a frog or a bird.
2. Explain why a countercurrent exchange mechanism in a fish's gills allows maximal efficiency in absorbing oxygen from the water. Mention that perhaps this same system is seen in the next chapter in the function of the kidney.
3. Consider why a bird has a complete ventilation
method but a mammal does not; consider what different metabolic
requirements might have led birds to develop their more efficient
mechanism over time.