Marian Crespo, age 9, of San Jose, California, for her question:

How do fish breathe under water?

If a fish could think, he might wonder how people manage to breathe in the air. We could tell him that we breathe air through our noses and it goes doom into our lungs. There it gets trapped inside hundreds of spongy pockets. The walls of these pockets have very very thin skin and lots of very very tiny blood vessels come close to the surface. The little red blood cells grab the oxygen we need from the air, right through these thin walls.

The fish also needs oxygen. But his oxygen is dissolved in the water. Instead of lungs, he has a pair of gills, just about where you would expect to find his ears. The gills also have tiny pockets with thin walls and lots of. tiny blood vessels. He opens his mouth and streams of water flocs back through his gills. They can take oxygen from water, just as our lungs can take oxygen from the air.