We must first of all understand what ectothermic and endothermic animals are. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Animals differ in their ability 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. Slightly more precise descriptions can be made 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 thermoregulation mechanisms. Ectotherms generally obtain heat from the external environment. Their body temperature varies, corresponding at all times to the temperature of the external environment. Endothermic animals, on the other hand, have relatively constant body temperatures. Their body temperature is independent of that of the external environment. Monkeys and walruses, for example, both have a body temperature of around 38°C, despite living in very different habitats. However, if the body temperature exceeds its optimal level (usually around 40°C in mammals), the rate of enzymes within the body will decrease dramatically. . This is because enzymes are proteins and they denature. One of the first organs to be affected is the brain. Since the brain controls breathing and circulation, increased body temperature disrupts the normal functioning of these important systems. If your body temperature drops dramatically (hypothermia), this will slow metabolic activity and impair brain function. Here is a graph to show the relationship between body temperature and environmental temperature for a cat (endotherm) and a lizard (ectotherm). We also need to clarify what is meant by extreme climate. In this investigation I will use two different climates, the desert and the Arctic. When an endotherm is subjected to severe cold it is susceptible to losing thermal energy, but this can be counteracted in several ways; It may lift the hairs into a more vertical position by contracting the arrector pili muscles. Air can then become trapped in the spaces between the hair and, being a poor conductor of heat, acts as an insulating layer around the animal. This is an involuntary response caused by the nervous system. The arterioles leading to the surface capillaries narrow and as a result blood flow to the skin surface is significantly reduced (vasoconstriction). This is caused by the sympathetic nervous system and is useful in uncovered regions such as the ears where the surface-to-volume ratio is particularly high and therefore particularly sensitive to cold. The metabolic rate can be increased thus heating the inside of the body. A general increase in metabolism is caused by the hormones adrenaline and thyroxine, which are produced in large quantities during cold days. There then occurs a general increase in muscle tone, which is then followed by spasmodic contractions (chills). The response to high temperature is substantially inverse to the processes described above; that is, the hairs are flattened against the body. Arterioles dilate (vasodialation), allowing blood to flow back to the surface of the skin so that heat can be lost through diffusion. Sweating occurs, and evaporation of water from the skin cools the skin and blood. Panting occurs. In some animals there are no sweat glands except in the paw pads. In this way they pant,accelerating evaporation from the lungs, pharynx and other moist areas, helping to cool the blood. The metabolic rate decreases, so less energy is generated by the bodyArctic polar bears (Thalarctos maritimus)Polar bears have successfully adapted to one of the most inhospitable climates in the world and remain active throughout the harsh winter. They are found on Arctic sea ice throughout the North Pole Basin. The polar bear's creamy white fur is particularly dense, and each of the individual hairs is hollow and contains insulating air spaces. This heavy fur and large layer of fat help retain body heat even as the animal swims in the colder Arctic climate. The fur does not absorb water so once the animal comes out of the water it simply has to shake itself to dry itself. It has plantigrade feet (heel and sole touching the ground), with five sharp claws for grasping ice. The long fur between the pads protects the bear's feet from the cold and provides traction on the ice. Another adaptation is in the thickness of the subcutaneous fat. Animals that live in cold climates, such as polar bears and seals, have a particularly thick layer of subcutaneous fat. In seals and other marine mammals such as whales, the blubber is called blubber. 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 removed, the animal would lose the ability to regulate its temperature and become essentially "cold-blooded." The tuber cinereum is stimulated by nerve impulses from cold receptors in the skin or by direct cooling. It is sensitive and reacts to temperature changes of only a few tenths of a degree. If the body temperature is too cold, the thermoregulator stimulates thyroid secretion, which increases the rate of metabolism. If the body temperature continues to drop, the work of internal organs such as the liver may increase and muscle activity in the form of shivering may begin, since muscle activity is the main source of heat available to animals. Camels (Camelus) Camels are large animals native to the desert regions of Asia and northern Africa. There are two types; the one-humped dromedary and the two-humped blight camel. Humps are reserves of meat and fat that are absorbed as nutrition when food is scarce. What makes the camel survive so well in the desert is its ability to go for many days without water. However, there is no evidence that camels store water in their stomachs. Desert vegetation can provide a camel with enough water for several months, and a thirsty camel can consume up to 30 liters of water at a time to replenish its reserves. Additionally, camels' metabolism may allow them to drink the salt water available in their habitat. A camel's body temperature can increase by up to 6aC - 8aC to minimize sweating, further aiding in water conservation. The thick, wide pads of the sole and the thick calluses on the joints of the legs and on the chest, on which he rests in a kneeling position, allow him to withstand the heat of the desert sand. Furthermore, its nostrils can be closed against flying dust, and its eyes are protected by very long eyelashes and a third eyelid. Horned Toad (Phrynosoma cornutum) These are short-tailed, short-legged lizards from the iguana family. Found primarily in dry regions of the western United States and Mexico. They can control their temperature by varying their heart rate and the speed of their body metabolism. Reptiles Although reptiles are..