Animals differ in their abilities to regulate body temperature (thermoregulation). We sometimes use the terms "cold-blooded" or "warm-blooded." Most reptiles feel cold to the touch, while mammals and birds often feel warm.

Somewhat more precise descriptions can be made by using the terms poikilothermic and homoiothermic. The body temperature of poikllotherms is relatively variable, while that of homeotherms is relatively constant.

Even more useful terms are Ectothermic or Endothermic, which suggest two different mechanisms of thermoregulation. Ectotherms generally obtain heat from their external surroundings. Their body temperature varies, corresponding at any time with the temperature of their external environment.

Endothermic animals, on the other hand, have relatively constant body temperatures. Their body temperature is independent of that of their external environment. Monkeys and walruses, for example, both have body temperatures of about 38„aC, despite living in very different habitats.

However if body temperature rises above its optimum level (usually around 40„aC in mammals) then the enzyme rate inside the body will go into

In all Endotherms, including polar bears, thermoregulation is controlled by the tuber cinereum of the hypothalamus. If this small downward projection at the base of the brain were to be removed the animal would lose the ability to regulate its temperature and essentially becomes 'cold blooded.'

„h Sweating occurs and the evaporation of the water from the skin cools the skin and blood.

The creamy white fur of the polar bear is especially dense and each of the individual hairs is hollow and contain insulating air spaces. This heavy fur and a large fat layer helps to retain body heat even while the animal is swimming in the coldest arctic weather. The fur does not absorb water so once the animal has climbed out of the water it merely has to shake itself dry. It has plantigrade feet (heel and sole touching the ground), with five sharp claws for gripping the ice. Long hair between the pads protects the bear's feet from the cold and provides traction on the ice.

Some common words found in the essay are:
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Approximate Word count = 1418
Approximate Pages = 6 (250 words per page double spaced)