Jimmy Robinson, age 14, of Santa Maria, California, for his question:
How can a worm breathe underground?
This problem requires some imagination, plus a magnifying glass or a helpful hand lens. We are used to a world filled with objects that human eyes can see and other human senses can perceive. The earthworm lives in a world of smaller proportions and we must use our imaginations to share his point of view. By magnifying his worm sized surroundings, we see that his problems come in much smaller sizes than ours.
When we walk around on the ground, we tend to assume that the whole thing is made of dense, solid material. And, indeed, much of the earth's crust is made of dense solid rock. But the earthworm does not live inside solid rock. He lives in the earth, in the crumbly soil which is made of solid particles and porous pockets. And all those tiny pockets are filled with air, the very same air that we breathe above the surface.
Actually, one needs to magnify a sample of ordinary soil with a lens to get a true picture of the numerous air pockets mixed with the crumbs of dirt. Maybe to an underground earth¬worm, the soil seems like a room partly filled with a lot of bouncy balloons. There is plenty of air around for him to breathe. What's more it is the most, shady air that his sensitive skin requires.
Naturally, his body plan is designed to make the very best use of his earthy environment. His breathing system does not require a nose or even lungs, for he absorbs dissolved oxygen straight through the surface of his skin. The catch to this convenient system is moisture. His skin must remain moist to dissolve the oxygen he needs.
The earthworm is tinted pink by countless tiny blood vessels that come to the surface of his skin. There they absorb the dissolved oxygen through the thin surface and, with the help of five pairs of simplified hearts, his circulatory system pumps his bloodstream throughout his body. Along the way, his bloodstream gathers up waste carbon dioxide from his living cells. This is exchanged for fresh oxygen when the tiny capillaries bring it back to the surface.
True, the worm's breathing system is very simplified. But it works and there are plenty of air pockets in the soil to supply his worm sized needs. However, the whole system depends on keeping the skin moist, and for this he does not depend entirely upon the dew. His skin is riddled with mucus glands and more moisture is added from pores, especially between the segmented rings.
Other land animals have tougher skins, but they have lost the earthworm's talent for breathing through the skin. He can, in fact, live for months submerged in water. But a dried out skin is fatal to him. This is why he shuns the dry air and spends the daylight hours in his shady burrow, surrounded by plenty of pockets of breatheable air.
Marie Thomason, age 8, of Sioux City, Iowa for her question: Does a whale get the bends? A big whale may dive down more than half a mile and stay below for an hour. Then he comes up to breathe the stale air from his lungs and fill up with fresh air. This may take about ten minutes. Then down he plunges to the depths again with no trouble at all. Human divers, as we know, cannot do this sort of thing. If they go down deep and hurry back up, they get a horrible sickness called the bends.
Water is heavy and when a human diver goes down deep, the weight of the water presses in on every side. It causes bubbles of nitrogen gas to form in the blood and the flesh. If the diver comes up slowly, in very easy stages, the trouble goes away. But if he comes up fast, he suffers from the bends. Whales do not have this problem because their bodies are used to life in deep water. They have built in ways to cope with the heavy pressure and a complicated chemical system that stops the nitrogen bubbles from forming. So whales don't get the bends.