What is this concept of shared work among specific cells called?

The correct answer is: tissue.

Explanation:

Humans are made of organ systems, organ systems are made of organs, and organs are made of tissues. These tissues are all composed of specific cells that work together in order to carry a particular task that is demanded by the body.

There are four basic types of tissue: epithelial tissue (found in the surface of the skin and in the inner lining of hollow organs), muscular tissue (has the ability to contract), nervous tissue (regulates and controls bodily functions), and connective tissue (connects all of the other organs).