A group of similar cells working together form a tissue. A group of different tissues working together form an organ. A group of organs working together to perform a specific function is an organ system.
Work Step by Step
For example, muscles are tissues made up of muscle cells. The heart is an organ made up of several types of tissues, including muscle tissue. The circulatory system is an example of an organ system composed of several different organs, such as the heart, that work together to perform a certain function.