What is the primary composition of a flagellum?

The correct response is focused on the fact that flagella are primarily composed of proteins, specifically a protein called flagellin in many bacteria. These proteins are organized in a complex structure that enables the flagellum to function as a whip-like appendage, providing motility to the cell. The arrangement of flagellin proteins forms a helical structure, which is key to the flagellum's movement capabilities.

In the context of cellular biology, proteins are crucial macromolecules that serve various functions, including structural roles, and the flagellum exemplifies this by being made predominantly of protein. The movement provided by flagella is essential for many microorganisms, aiding in their locomotion toward nutrients or away from harmful substances.

Other molecular components like carbohydrates, lipids, and nucleic acids do play critical roles in cellular functions and structures, but they do not constitute the primary building blocks of the flagellum. For instance, carbohydrates are often found in the cell wall or as energy sources, lipids form membranes, and nucleic acids are involved in genetic information storage and transfer. However, they are not the fundamental components that make up the flagellum's structure or its ability to generate movement.