A dog is a multicellular organism. It obtains energy from the food it eats and uses this energy to perform its vital life functions. A dog eliminates waste through panting, feces, urine, and respiration. It has a definite boundary, as its inner organs are covered by skin and fur. A dog regulates homeostasis in different ways. One way is by panting, which helps the dog maintain a stable internal temperature. Like humans, a dog has a complex organ system that grows and develops throughout its entire life. A dog reproduces and passes on genetic information to its puppies. It also senses and responds to stimuli. For example, a dog has a very astute sense of smell, and its mouth waters when it smells food.