organisms develop systems for exchanging materials. During the development of a multicellular organism, cells differentiate so that they can perform

organs systems are that perform a particular function. The system is one example of a system.
The digestive system includes:
glands, such as the pancreas and salivary glands, which produce digestive juices
the stomach and small intestine, where digestion occurs
the liver, which produces bile
the small intestine, where the absorption of soluble food occurs
the large intestine, where water is absorbed from the undigested food, producing faeces