Donna Wooding, age 10, of Sarasota, Florida, for her question:
Do frogs have lungs or gills?
The life story of the frog is astounding. During his kindergarten days, he wears a fringe of feathery gills where his neck should be. Later, he exchanges his fishy gills for a pair of lungs in his chest. During his lifetime he has both gills and lungs, but not both at the same time.
A grown frog spends his time in and out of the water. He sits for hours beside his swimming pool, enjoying the warm sun and using the lungs in his chest to breathe in and breathe out. Suddenly he leaps up in a fancy high dive and plunges down into the pond. After a few splendid swimming strokes under water, he may decide to settle for awhile on the bottom. And there he squats for five minutes, ten minutes or even an hour. Surely he cannot be holding his breath all this time. No, he is not. He is getting a constant supply of oxygen from the water.
Lungs, of course, are made for taking oxygen from the air and under water they are useless. Fishes and many other animals have gills made specially to sift oxygen from the water. Perhaps the frog has a pair of gills tucked away somewhere. Maybe he uses his lungs in the air and his secret gills when he goes under water. Certainly he had a pair of fishy gills when he was a water dwelling tadpole. In fact, at the time he had no lungs at all and could not breathe in the air.
But the answer is no. A grown frog has lungs,but no gills. When he exchanged his tadpole gills for a pair of lungs, he lost those gills forever. But he is an amphibian, a land and water animal. And Mother Nature was extra generous to the amphibians. She gave them special skins in place of their baby gills. The wondrous skin of the amphibian can absorb oxygen from the water.
True, it is not a pretty, petal smooth skin. It is a coarse, bumpy skin covered with pores and pimples. Fine blood vessels come close to the surface and the walls of the living cells in the skin are very thin. The blood cells can absorb molecules of oxygen right through the surface of the skin. A frog stops using his lungs when he stays below the water. But he continues to get the oxygen he needs by absorbing it right through his amphibian skin.
Water, of course, is made of hydrogen and oxygen. But fishes and frogs do not extract their oxygen from water molecules. Water tends to absorb the bases of the air. There is a lot of dissolved air in ponds and rivers, lakes and seas, especially near the surface. And a lot of it is dissolved oxygen. A salt water fish uses his gills to take these unattached molecules of oxygen from the sea. A frog lets his skin absorb this dissolved oxygen from his swimming pool and also from the dewy moisture on the ground.
Nature, it seems, makes us pay for her special gifts. The talented skin of the amphibian comes with a handicap. Dry air is disastrous to it and it must be kept damp. It has special built in cells that ooze out slippery mucus. This is why a frog feels moist and clammy. In the shade, the skin provides enough sweaty moisture to keep itself damp, but not enough to stay moist in hot, dry air. A few hours in desert sunshine shrivels up the skin of a frog and proves fatal.