What best describes organ systems?

A group of organs that work together for a single function provides the best description of organ systems. In biological organisms, organ systems consist of multiple organs that collaborate to perform a specific physiological function. For example, the digestive system includes organs such as the stomach, intestines, and liver, all of which interact to break down food and absorb nutrients. This collaboration is essential for the organism's overall functioning and homeostasis.

The other choices do not accurately capture the definition of an organ system. While tissues and cells are important components of biological organization, they are not the defining characteristic of an organ system. Option A suggests that tissues work independently, which is not the case in organ systems, where organs rely on each other. Option B incorrectly implies that organ systems are merely collections of small organs without emphasizing their functional interdependence. Lastly, option D describes cellular organization rather than focusing on the unique assembly and cooperative function of multiple organs within a system.