The esophagus, stomach, and intestine together are part of a level of organization called:

Organs. The third level of cell organization. As explained, cell is the basic unit or element in every living organism. By which, is the smallest component and when grouped forms tissues, hence when tissues are grouped they form the organs and when organs group together they form the organ system and thus, the organism. Furthermore, esophagus, stomach, intestines, and the accessory organs are all part of the system called the digestive system of a living organism. Digestive system then is responsible for absorption and metabolism of food and delivers nutrients throughout the body.