Patricia Misencik, aged 10, of Nichols, Conn,, for her question:

How come a fish can live underwater and we can't?

A fish might ask you, How come you can live in the air? You would, of course, tell him that you need air to breathe. Your nose and lungs take oxygen from the air. Your body needs oxygen to keep going.

If you really met this talking fish, he would say, But I need oxygen too. My fishy body also uses oxygen to keep going. But, he would explain, I cannot take oxygen from the air. I do not breathe through a nose.

Chances are, your fish couldn't talk at all. So Andy will explain. The fish breathes through his gills. His gills are under little flaps dust where you would expect his ears to be. His gills take in oxygen from the water. Your lungs take in oxygen from the air.

Oxygen is taken through the body by the blood. This happens to you and also to the fish. Your blood and the fish's blood take oxygen right through thin walls of tissue. Gills and lungs are made of very much the same kind of tissue. But your lungs cannot take oxygen from the water. The fish's gills cannot take oxygen from the air. So he lives underwater because he needs air from the water to breathe. You must live in the air.