Over time animals have evolved internal adaptations which allow them to carry out necessary life functions and maintain homeostasis. A trend with evolution/life is that the more primitive an animal is, the simpler the body design. For example, look at the heart found in the three classes of vertebrates.

Color in the blood vessels in each of the three pictures Color in the blood vessels in each of the three pictures. You will need red, blue and purple colored pencils. The vessels on the left of each picture (light gray) should be colored blue- this represents deoxygenated blood. Color the right half of each picture red. This represents oxygenated blood. The areas where the oxygenated and deoxygenated blood mix (where the light gray meets with dark gray) should be purple.

Along with the complete separation of oxygenated blood from deoxygenated blood, the evolutionary development of a four- chambered heart also allowed these organisms to generate their own body heat. This is called endothermy (or endothermic). The old term used for endothermic was warm blooded. Two classes of animals that are endotherms are: Birds and mammals

Why is having a complete separation of oxygenated and deoxygenated blood so beneficial to animals with a 4-chambered heart? Only allows blood with oxygen to circulate through the body therefore allowing for more efficient respiration. Allows them to be endothermic

Some animals are ectothermic which mean they rely on the environment to warm their body. The old term for ectothermic was cold blooded. The three classes of animals that are made up of ectotherms are: Fish Amphibians Reptiles