* Unicellular organisms are single-celled: They don't have specialized cells like multicellular organisms.

* All functions happen within one cell: The single cell in a unicellular organism is responsible for *everything*, including taking in food, processing it, getting rid of waste, and reproducing.

So, the answer is one. The single cell in a unicellular organism is responsible for all of its functions, including taking in food.

Let me know if you have other questions about unicellular organisms!