What term describes groups of tissues that perform one or more specific functions?

The term that describes groups of tissues performing one or more specific functions is "organs." Organs are structured assemblies of various types of tissues working together to execute distinct tasks in the body. For example, the heart is an organ made up of muscle tissue, connective tissue, and nervous tissue, all functioning collectively to pump blood throughout the body.

This understanding of organs as functional units is essential in anatomy and physiology since it leads to the comprehension of how different systems in the body operate. The other terms do not accurately represent this concept. Microorganisms refer to microscopic entities like bacteria and viruses, which are not composed of tissues. Systems pertain to groups of organs working together to perform complex functions (like the circulatory system), while cells are the smallest unit of life and are the basic building blocks of tissues, but they do not perform specific functions on their own as a collective group.