What is the definition of an organ?

The definition of an organ is accurately captured in the choice indicating that it is a group of tissues working together for a specific function. An organ is composed of different types of tissues that collaborate to perform a unique function within an organism. For instance, the heart is an organ made up of muscle tissue, connective tissue, and nervous tissue, all of which work together to pump blood throughout the body.

In comparison, a collection of similar tissues would describe a tissue type rather than an organ, as it lacks the functional collaboration needed to achieve a specific task. A group of cells with similar structures does not encapsulate the complexity of an organ, which involves multiple tissue types interacting. Finally, while a collection of organs performing different functions describes an organ system, it doesn't pinpoint the specific definition of an organ itself. Hence, the notion of tissues working together is central to understanding what defines an organ.