Warm Blooded And Cold Blooded Animals (1971)

[Music] fish are cold-blooded and live in water porpoises are warm blooded and live in water too what do these words warm-blooded and cold-blooded mean well we can go to a laboratory and find out let's set up an experiment we're going to deal with the temperature of water in a flask the water in this flask has a temperature it's about 74 degrees fahrenheit which is about 23 degrees centigrade or celsius we can measure the temperature of the air around the flask with this thermometer it's also about 23 degrees centigrade now let's see what happens when we measure both air and water temperature in a refrigerator the air temperature in the refrigerator is about two degrees centigrade as you'd expect the water temperature will drop after a few hours the temperature is three degrees centigrade in the water almost the same as the air temperature we heat the flask of water and its temperature changes again this heat comes from a flame heat might also come in the form of radiant energy from the sun it might come from air that's been indirectly warmed by the sun it might come from water that's been warm by the sun but always the source of heat is outside the flask eventually the water in the flask takes on the temperature of its environment now living things are different many produce heat of their own but in one way cold-blooded animals like this fish are a little like the flask of water we've attached a special thermometer device to this fish that tells us its body temperature without hurting it right now its temperature is 25 degrees centigrade that's about the same as the temperature of the water that surrounds the fish you know what will happen when we add ice to the water the water gets cooler but not only does the water temperature change the fish's temperature changes almost as much and that's probably as good a description of cold-bloodedness as we can get a body temperature that changes with temperature outside the body at this lower body temperature the fish has trouble moving in this aquarium there's nothing this fish can do to change its temperature in a larger body of water where temperatures vary the fish can move to a region of the water where the temperature is best suited to it the temperature of water doesn't usually vary much in nature however air temperature is much more changeable think for example about cold-blooded animals that live in the desert the temperature of the desert air can change very much and the surface of the sand can get very hot its temperature can go higher than 120 degrees fahrenheit a temperature that can kill living things on the surface of the sand a cold-blooded animal on the surface of the sand must move away from such heat here a snake burrows deep into the cooler sand below the hot surface at night the temperature of the desert air on the surface sand may be near freezing a drop of some 100 degrees at this temperature some cold-blooded animals can no longer function if the temperature drops below freezing the animal may escape death by moving away from the cold it could dig down below the cold surface into the warmer sand underneath so the cold-blooded animals that live in air control their body temperature in about the same way as the cold-blooded animals that live in water to raise their body temperature they move towards sources of heat to lower it they move away from the heat perhaps into the shade but for long periods of time in some places there may not be enough heat above the ground to keep a particular cold-blooded animal active in this case it waits for the return of warmer weather in a condition something like hibernation but there are some animals whose muscles work as well in cold weather as in warm their body temperature doesn't change each time the outside temperature changes these are the animals we call warm blood mammals are warm blooded so are birds their body temperature tends to remain about the same and perhaps that's as good a description of warm bloodedness as we can get a body temperature that is more constant regardless of the temperature outside the body for example warm blooded animals may have special coverings on their bodies that help them retain their body heat let's see how animal body coverings work these three flasks are filled with a liquid at room temperature first we'll wrap one flask with the outside covering of one kind of warm blooded animal the fur of a mammal and we'll put the flask on ice the second flask is wrapped with the outside covering of the other kind of warm blooded animal the feathers of a bird that will go on ice too we leave the third flask uncovered and place it on ice now all three flasks are on ice the temperature in the uncovered flask is dropping rapidly what's happening to the temperature of the liquid in the other flasks the temperature is holding fairly steady the liquid is losing heat very slowly both feathers and fur help slow down the escape of heat to the surrounding ice they insulate the flasks why what is there about them that makes them such good insulators the closer we look at the hairs that make up the fur and the barbs that form the feathers the more alike the two animal coverings seeing their many tiny parts trap air spaces between them and these air spaces slow down the escape of heat feathers or fur are common coverings for warm blooded animals are coverings all that affect heat loss in an animal does the size of the animal make a difference let's insulate two flasks of liquid of different size with the same type of fur and put them on ice we'll see if the rate of heat loss of the liquid in them is different the temperature of the liquid in the large flask is dropping but the temperature in the small one is dropping faster the same is true of animals a smaller animal loses heat faster than a larger one to keep up its body temperature the smaller animal has to eat relatively more food for its weight than the larger one but both the larger and smaller warm blooded animals need more food than cold-blooded animals of the same size warm-blooded animals that have adapted to life in water like porpoises have developed another kind of insulation special layers of fat under the skin help slow down the escape of heat even more penguins are so well insulated that they can keep their eggs warm with the outside temperature 50 degrees below zero fahrenheit but keeping body heat up is only half the problem for too much heat will kill them as quickly as it will kill a cold-blooded animal how can warm-blooded animals get rid of extra heat moisture evaporates from the skin of some animals and from the tongue of others this evaporation helps warm-blooded animals cool off in hot weather birds may molt they lose some feathers which reduces their insulation but warm or cold-blooded all creatures of the earth have some system for dealing with heat for the most part the cold-blooded animals are the most directly affected by the temperature around them their body temperatures are changeable to cool themselves they move to a cool place warm-blooded animals on the other hand are less affected by outside temperatures their body temperatures tend to be more constant [Music] to achieve this steady temperature much food is required because of this importance of food many warm-blooded animals spend more of their time eating than many cold-blooded animals do [Music] some of both kinds of animals cold-blooded and warm-blooded managed to live in almost every part of our earth in water and in air [Music] some of both kinds live on the ground both kinds live in warm climates [Music] both kinds live in cold climates [Music] the living creatures of our earth have evolved different solutions to a common need the need to keep their bodies at temperatures at which life is possible [Music] you