David Vozencroft, Age 10, Of Berea, Ohio, for his question:
How does a frog breathe underwater?
By August most of the year's baby tadpoles have lost their fishy tails and became long legged frogs. If you watched them grow up, you know that the tadpoles swapped their fishy gills for air breathing lungs. But the adult frogs still can breathe underwater when they wish.
Most animals must take their oxygen from the air or from the water. A few thousand creatures, however, can do both, and almost all of them are the frogs and their amphibian relatives. A grown frog has a pair of little lungs high in his chest. He has a pair of small. Nostrils on his nose and an opening in his throat to carry air to his lungs.
Mr. Frog uses his nostrils and lungs to breathe air when sitting on a lily pad of his pond or basking on the bank. When he croaks, he closes his big mouth and fills up with a breath of air through his nostrils. He adds his note to the night chorus again and again by passing this air back and forth over his vocal cords. He has a special method for taking his breathing oxygen from the water, but he can croak only in the air.
As he squats on the floor of his pond, his little round nostrils are sealed shut. His mouth is closed in a froge;y smile and no water passes into his lungs. Undervater he depends upon his clammy skin to take in the oxygen he needs. On the dry land, this moist skin sometimes leads to trouble. Its surface is covered with slimy mucus given off by tiny glands. The skin of the frog must be kept cool and moist and never allowed to become dried up in the heat of the day.
But in the pond this special skin takes over the duties of the lungs and nostrils. It dissolves the free oxygen in the water and lets it filter into tiny blood vessels. These blood vessels at the surface of the skin connect with others that circulate the blood throughout the frog's entire body. The oxygen rich blood from the skin is punped by his little heart to wherever it is needed. Mr. Frog comes out of the water when he wants to, but not to get a breath of air. With the help of his amazing skin he can breathe just as was in the water as he can on the land.
The hardest breathing problem in the animal world was so1ved by the remote ancestors of our frogs. This was almost 300 million years ago when these brave creatures left the ancient seas for life on the land. Until this time they had taken their oxygen only from the water. But the froggy ancestors had to tackle the hard ,job of taking their oxygen from the air. They succeeded, but they also kept one of their old. Skills for taking oxygen from the water.