Multi cellular organisms, like people, are made up of many cells. ... At each level of organization—cells,tissues, organs, and organ systems—structure is closely related to function. For instance, the cells in the small intestine that absorb nutrients look very different from the muscle cells needed for body movement
These tissues make up organs (so for example the heart is made up of many tissues). These organs then work together forming organ systems (such as the digestive system, which is made from organs such as the stomach, intestines and rectum) to perform a particular function.
