Unlike plants, animals cannot produce their own food. Neither do they absorb nutrients like fungi or bacteria do. Instead, animals take in food and digest it inside their bodies. Animals have their cells divided into highly developed tissues and organs to carry out bodily functions, as do many plants. However, animals also have advanced systems for sensing and motion.
Members of the animal kingdom are divided into two groups: invertebrates and vertebrates. Invertebrates include animals from the simple sponges to the advanced insects and sea urchins. Vertebrate animals have internal skeletons characterized by a backbone and spinal cord. Vertebrate animals includes fishes, amphibians, reptiles, birds and mammals (including humans).