Which word best fits the idea of a functional assembly composed of multiple units?

• A. Organism
• B. Cell
• C. System
• D. Biomolecule

Answer: (C)

The concept here is a system—a functional assembly made up of multiple parts that interact to perform a shared function. In biology, a system isn’t a single piece; it’s a coordinated set of components—such as organs, tissues, or cells—working together, with signaling and feedback that allow the whole to operate. The function arises from the interaction of parts, not from any one component alone. For example, the circulatory system relies on the heart, blood vessels, and blood to move circulation, and its effectiveness comes from how these parts work together. In contrast, a cell is a single unit, a biomolecule is one molecule, and an organism is an entire living being composed of multiple systems. Therefore, the best word for a functional assembly of multiple units is system.