What term describes groups of similar cells working together to perform a common function?

The term that describes groups of similar cells working together to perform a common function is "tissues." Tissues are fundamental units within the body that consist of cells that share similar structures and functions, enabling them to work collaboratively to achieve specific tasks. For example, muscle tissue is made up of muscle cells that contract to allow movement, while epithelial tissue covers surfaces and lines cavities.

In contrast, organs are made up of different types of tissues that work together to perform complex functions, such as the heart or lungs. Systems refer to groups of organs that work together to carry out broader functions in the body, like the digestive or circulatory system. Cells are the basic building blocks of all living organisms, but they are the smallest unit of structure and do not refer to groups of cells. Thus, "tissues" accurately captures the concept of similar cells united for a specific purpose within the biological framework.