What is an organ composed of?

An organ is composed of a group of tissues that work together to perform specific functions within an organism. Each type of tissue contributes to the overall function of the organ by providing specific structural and functional roles. For example, in the heart, cardiac muscle tissue is responsible for contraction, while connective tissues provide support and structure. This organization allows the organ to carry out its role efficiently.

In contrast, other options do not correctly define what an organ is. An organ is not solely made of only one type of cell or a singular cell type, as this would imply a lack of complexity needed for the diverse functions that organs perform. Additionally, an organ is not simply a fluid medium; while some organs may contain fluids (like blood in the circulatory system), they are fundamentally composed of multiple types of tissues. Thus, the composition of an organ as a group of tissues is essential for its proper function and structure.