How is an organ defined in biological terms?

An organ in biological terms is defined as a structure made up of groups of tissues that work together to perform specific functions. The correct answer reflects this definition as it emphasizes the collaboration of multiple tissue types, each contributing to the overall function of the organ.

In a biological context, different types of tissues work together to perform unique roles; for example, in the heart, muscle tissue contracts to pump blood, while connective tissue provides support and structure. This interplay among various tissue types is essential for the organ's operation and effectiveness, illustrating the complexity of biological systems.

Other options, while discussing cells and tissues, do not accurately encompass the definition of an organ. A grouping of cells with different functions or individual cells performing specific tasks does not consider the necessity of tissues working in concert, whereas having single tissue types working independently does not represent the collaborative nature of an organ, which is defined through the interaction and integration of various tissues.