live on the blood or tissue of other organisms.
The type of teeth seen in are usually broad and flat.
Some animals have specialized cells that absorb food, break it down internally, and pass the nutrients to other cells in a process called .
have some tissues, such as cell walls, which require special structures like rumen to break down in the digestive system.
Gas exchange involves the absorption of into the bloodstream and the release of CO2 waste.
Aquatic animals have specialized structures called that allow for oxygen to be absorbed into the bloodstream directly from water as it passes through.
Insects typically have circulatory systems.
Ammonia must be converted into urea in the to be excreted later in mammals as urine.