In a study to examine the effectiveness of a new acne cream, participants were assigned to one of two groups: those who would be asked to use the cream for three months and those who would not use any treatment. Participants would be asked to keep a journal rating how bad they think their acne is on a scale of 1–10 each week. What are the well-designed aspects of this study? What are the limitations? How would you improve the design of this study to address these limitations?

Which of the following best illustrates homeostasis? (Explain your answer.)

a. Most adult humans are between 5 and 6 feet tall.

b. All the cells of the body are about the same size.

c. When the salt concentration of the blood goes up, the kidneys expel more salt.

d. When oxygen in the blood decreases, you feel dizzy.

The diaphragm is a large sheet of muscle that helps move air in and out of your lungs. Breathing is automatically controlled by the brain, but you can choose to hold your breath or breathe deeper. What kind of muscle do you suppose makes up the diaphragm? (Explain your answer.)

You read a blog that states, 'A squid's eye has been perfectly designed to see in the dark depths of the ocean.' Draft a paragraph that responds to the blog's use of the phrase 'perfect design' by citing an example discussed in this chapter.

After a long, hot run together, your friend tells you that you should dunk your head into a cooler of water to lower your body temperature more rapidly, rather than sitting and waiting to cool down. What do you think? Form a hypothesis about how the ice-cold water might affect the rate at which your body temperature returns to normal. How could you test your hypothesis?