Larry Hug, age 11, of Omaha, Nebraska, for his question:

How can a frog, stay under water?

When a frog graduates from his tadpole stage of life, he swaps his fishy gills for a pair of air breathing lungs. He spends hours leaping through the grass and squatting beside his pond. So we know that a grown frog can take his oxygen from the air. And naturally we expect an air breathing animal to drown in the water. But the frog is full of surprises. He can dive in and spend a long time squatting under water on the floor of his pond.

Surely a frog cannot breathe in the air and also under water. In a way he can. He has a pair of lungs that breathe oxygen from the air, more or less as our lungs do. He also has a remarkable skin that can absorb molecules of dissolved oxygen in the water. There are tiny blood vessels very close to the surface of his skin. They grab oxygen from the water and circulate it through his blood stream.