Welcome to Brainstuff from how Stuff Works dot com where smart Happens. Hi Am Marshall Brain with today's question. If water is made up of hydrogen and oxygen, then why can't we breathe underwater? One thing about chemicals is that once they react in certain ways, they form compounds that are often nothing like the original elements. For example, if you react carbon, hydrogen and oxygen together one way, you get glucose. If you react them together another way, you
get vinegar. If you react them together in another way, you get fat. If you react them in another way, you get ethanol. Glucose, Fat, ethanol, and vinegar are nothing like each other, but they are all made from the same elements. In the case of hydrogen and oxygen gas, if you react them together one way, you get liquid water. The reason we can't breathe liquid water is because the oxygen used to make the water is bound to two hydrogen atoms, and we cannot breathe the resulting liquid. The
oxygen is useless to our lungs. In this form, the oxygen that fish breathe is not the oxygen in H two O. Instead, the fish are breathing O two oxygen gas that's dissolved in that water. Many different gases dissolve in liquids, and we can see an example all the time in carbonated beverages. In these beverages, there's so much carbon dioxide gas dissolved in the water that it rushes out in the form of bubbles. Fish breathe that dissolved oxygen out of the water using their gills. It turns
out that extracting the oxygen is not that easy. Air has something like twenty times more oxygen in it than the same volume of water, plus water is a lot heavier and thicker than air, so it takes a lot more work to move it around. The main reason why gills work for fish is the fact that fish are cold blooded, which reduces their oxygen demands tremendously. Warm blooded animals like whales breathe air like people do because it
would be hard to extract enough oxygen using gills. Humans can't breathe underwater because our lungs don't have enough surface area to absorb enough oxygen from water, and the lining of our lungs is adapted to handle air rather than water. However, there have been experiments with humans breathing other liquids like flora carbons. Flora carbons can dissolve enough oxygen, and our lungs can draw that oxygen out. It's just that that first breath where you suck in the flora carbons to
your lungs is not very pleasant. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com and be sure to check out the brain stuff blog on the how stuff works dot com homepage