Sheryl Ford, age 9, of Sharyn. Massachusetts, for her question:
Why don't fish drown?
Mother Nature has made arrangements for fish to breathe water, just as we breathe air. Both you and the fish need oxygen to keep the body processes going. Breathing is taking in oxygen and giving off waste carbon dioxide.
Perhaps you thought that oxygen was a gas found only in the air. As a matter of fact, oxygen is one of the most plentiful elements on earth, Most rocks contain oxygen combined with other elements, Water is composed of oxygen and hydrogen. There is also a lot of free oxygen gas present in most water. And this free oxygen is what the fishes breathe,
We take in air through the nose to the lungs. The lungs are two spongy bags where blood vessels finer than a hair come close to the surface. The surface wells are so thin that the blood can grab the oxygen from the air as it passes through the lungs. At the same time, the blood also gives up its waste carbon dioxide in the same way. We take in a breath of air containing oxygen when we breathe in. We let out a breath of air containing carbon dioxide when we breathe out.
A fish breathes in oxygen and. breathes out carbon dioxide just as we do. However, he has no lungs. Instead, he has a pair of gills where you would expect his ears to be. The gills are covered by round strong plates which you might mistake for ears.
The gills of a fish are .fringed. its in our lungs, they have finer‑thanhair blood vessels which come close to the surface. However, gills cannot take in dry oxygen from the air. They can take in oxygen only when it is dissolved in water. i`it the same time, they give out waste carbon dioxide into the water, just as we breathe it out into the air.
Our job is to keep breathing clean fresh air to supply our lungs with oxygen, The job of the fish is to keep a steady supply of water flowing through his gills. He takes this water in through his mouth. Watch him and he seems to be swallowing water all the time. Actually very little if any of this water is swallowed. It is sent back through the mouth to flow through the gills, From there it flow: out through the gill slits, which are at the back of the gill covers.
Creatures with lungs cannot breathe oxygen from water. So don't try breathing like a fish underwater. Animals with gills cannot take oxygen from the dry air. Mother Nature has arranged. to have air breathers and water breathers, so that the entire earth is well populated. Only e very, very few exception creatures can take in their oxygen from both air and water.