What is the term for a group of similar cells working together?

The correct term for a group of similar cells working together is "tissue." In anatomy, tissues are defined as collections of closely related cells that perform a specific function. They're categorized into four primary types: epithelial, connective, muscle, and nervous tissue. Each tissue type has unique characteristics and functions that enable the body to work efficiently. For instance, muscle tissue is specialized for contraction and movement, while nervous tissue is essential for transmitting signals throughout the body.

Other options such as "organ" refer to structures composed of multiple tissues working together to perform complex functions, while "system" refers to a group of organs that work together to accomplish a broader set of activities. The term "species" pertains to a group of organisms that can interbreed and is not relevant to cellular structure or function. Therefore, "tissue" is the most precise answer for a collection of similar cells collaborating for a specific purpose.