An organ is a collection of different tissues that carries out a particular function (e.g. liver). An organ system is a collection of organs that functions to carry out a specific task in the organism (e.g. digestive system). At each level of organization, the structure helps determine the function.
Our bodies consist of a number of biological systems that carry out specific functions necessary for everyday living. The job of the circulatory system is to move blood, nutrients, oxygen, carbon dioxide, and hormones, around the body.
