Stephen McRinney, age 11, of Dallas, Texas, for his question:
How do cold blooded and warm blooded animals differ?
We tend to think that most of the earth's. children are warm blooded animals but this is far from true. All earthlings Were cold blooded creatures throughout most of the long story of life. The warm blood ed ones were later arrivals, and they are far outnumbered.
Of all the creatures on our planet only the birds and mammals can be called warm blooded animals. The reptiles and the insects, the fishes and almost all the sea dwellers are cold blooded creatures so are the snails and frogs, the worms and the swarming microscopic creatures. We do not know when the first warm blooded earthlings arrived. It may have been about l00 million years ago, when the ancestors of the birds and the mammals shared the world with the dinosaurs. At any rate, cold blooded earth creatures already had been at home here for millions of years.
Body heat is created when as animal transforms its food into energy. The food is fuel that burns in a slow form of combustion. A cold blooded animal has no way to conserve this heat. He depends for his warmth upon his surroundings. As a rule, he is no warmer than the air or the ground he touches. However, his body needs warmth to function and in cold weather he becomes slow and logy. He survives the long cold of winter in the motionless coma of hibernation.
A warm blooded animal has a number of built in devices to adjust his body temperature. He has automatic operations that perform to keep his body heat from escaping when the weather is cold and others to cool his body when his surroundings get too hot for comfort. The human body has such automatic devices and they are operated by a sort of thermostat center in the brain.
Perhaps you have wondered why you shiver in the cold and sweat in the heat. These goings on are automatic adjustments to the temperature. evaporating moisture steals heat from its surroundings. On a hot day your sweat glands pour out perspiration and as it dries it takes heat from the skin and cools the body. At the same time surface blood vessels expand to let more body heat escape by radiation.
Muscular activity creates extra body heat. On a cold day a brisk walk tends to keep you warm, but if you refuse to exercise your muscles generate extra heat by shivering automatically. At the same time surface blood vessels shrink to conserve heat loss by radiation.
The normal temperature for the human body is around 98.6 degrees Fahrenheit. For most mammals it is some point between 98 and l03, and for a bird it is some point between l03 and l08 degrees. Warm blooded creatures must stay within a narrow temperature range or perish, but cold blooded creatures can survive greater heat and cold. A basking lizard may be comfortable at ll0 degrees and a fish can endure for weeks while frozen in solid ice.