What actually powers the act of breathing -- what muscle does most of the work?
AThe lungs themselves
BThe heart
CThe diaphragm
DThe stomach
The diaphragm is a dome-shaped muscle located below the lungs. When it contracts, it flattens and pulls downward, creating more space in the chest cavity. This drop in pressure causes air to rush into the lungs (inhalation). When it relaxes, it pushes upward, compressing the lungs and pushing air out (exhalation). The lungs themselves have no muscles -- they expand and contract passively.
Question 2 True / False
The air you exhale is 100% carbon dioxide.
TTrue
FFalse
Answer: False
The air you inhale is about 21% oxygen and 0.04% carbon dioxide. The air you exhale is still about 16% oxygen and about 4% carbon dioxide. Your lungs extract only a portion of the available oxygen from each breath. This is why mouth-to-mouth resuscitation works -- exhaled air still contains enough oxygen to help someone who isn't breathing.
Question 3 Short Answer
Why do your lungs contain millions of tiny alveoli instead of just being two big hollow sacs?
Think about your answer, then reveal below.
Model answer: Millions of tiny alveoli create an enormous total surface area (about the size of a tennis court) compared to what two large sacs would provide. More surface area means more oxygen can pass into the blood and more carbon dioxide can pass out simultaneously, making gas exchange much more efficient.
This is the same principle as crumpling a piece of paper: the total surface area of all the folds and creases is much greater than the flat sheet. The alveoli provide about 70 square meters of surface area -- roughly 40 times the surface area of your skin. This massive area is necessary because your cells demand a constant, large supply of oxygen.