What is the function of the plunger in a syringe?

The correct answer highlights the primary role of the plunger in a syringe, which is to facilitate the movement of fluid. The plunger creates a sealed environment inside the syringe; when it is pulled back, it decreases the pressure inside the barrel, allowing fluid to be drawn into the syringe through the needle. Conversely, when the plunger is pushed down, it increases the pressure and forces the fluid out of the syringe, making it essential for the administration of injections or drawing blood.

Although there are aspects related to holding the needle, preventing air from entering, and measuring fluid volume, these functions are not the main purpose of the plunger itself. The plunger's design specifically focuses on enabling the efficient transfer of liquids by utilizing changes in pressure within the syringe.