Answer to Critical Thinking Activity - Chapter 15

1. Below 100 meters the body finds itself in a very unusual situation and becomes rather desperate. Collapsed lungs must be prevented and this is the only way of doing it. Like all body processes and mechanisms, this one must have a genetic base. If this genetic ability did not exist, the world record breathold dive would be much shallower.

2. Except for being a mammal, humans are not particularly related to the marine mammals. Since humans show the Blood Shift, obviously this ability is not limited to the marine mammals. Therefore, it is reasonable to suppose that most or all mammals would do so under the right circumstances.

3. Studies have shown that Sudden Death Syndrome (by heart attack) happens most among out of shape males over 30 who smoke, and who may have minor heart ailments.

4. The ultimate answer is that, if they weren,t, there would be no fish. Water is the medium in which fish live. It is 800 times more dense than air. Air is normally about 20% or 200,000 parts per million oxygen. Water generally is only around 10 parts per million oxygen and under poor conditions can be much lower. To best absorb the available oxygen, a fish has several means available. 1. The gill tissue separating the water from the fish,s blood is extremely thin, about as thin as possible to facilitate diffusion of gases back and forth. 2. Naturally, blood is constantly moving through the circulatory system of the fish and therefore through the gills. There is no stoppage. 3. There is no stoppage of water moving across the gills, either, but a constant flow. In humans, at the end of each inhalation and exhalation the air ceases to move across the surface of our lung tissue for a few moments. Compared to a fish, this is very inefficient.

5. A lizard has only a three chambered heart. Blood is not pumped directly from the heart to the lungs, thus when a lizard runs, the entire heart and blood capacity of the animal is used to circulate oxygen around the body. Therefore, breathing is of no value. Of course, this cannot be kept up for long runs, but you never see a lizard make a long, unbroken run. Humans have a four chambered heart and do pump blood directly to the lungs. Even so, in a short sprint of 100 yards there is, as with the lizard, probably more energy available for running if one doesn't breathe.