What is defined as a collection of body parts working together for a common purpose?

The correct answer is the organ system. An organ system is defined as a group of organs that work together to perform complex functions for the body. Each organ within the system contributes to the overall purpose of maintaining homeostasis, supporting growth, and enabling movement among other functions. For example, the respiratory system includes the lungs, trachea, and diaphragm, which all work together to facilitate breathing.

The other terms, while they describe groups of biological elements, do not represent a collection of body parts working together at the same level as an organ system. Tissue refers to a group of similar cells working together to perform a specific function, but it is not made up of multiple types of organs. A cell is the basic unit of life, and while it is part of tissues, it does not signify a collaboration of multiple parts. An organ is a single structure made of tissues that performs a certain function, but it does not encompass the broader collaboration of multiple organs that an organ system represents.