Which protozoan structure is involved in forming the food vacuole?

The structure involved in forming the food vacuole in protozoa is the gullet. The gullet is a specialized part of the protozoan cell that assists in ingesting food particles. It acts as an indentation or channel through which food enters the cell. Once food particles are engulfed by the cell through the gullet, they are enclosed in a membrane-bound food vacuole where they can be broken down and digested.

In contrast, the cytostome also plays a role in feeding, but it specifically refers to the mouth-like structure that facilitates the intake of food, and it may not directly form the food vacuole itself. Flagella are primarily involved in locomotion, providing movement for the organism, while the pellicle is a protective outer covering that helps maintain the shape of the organism but does not contribute to the formation of food vacuoles. Thus, the gullet is directly involved in the intake of food leading to food vacuole formation, making it the correct answer.