The best answer would be:
The vacuole
Here is more about your question:
Unicellular organisms have a food vacuole. A paramecium for example, would draw food to itself and when the food enters the body a vacuole will encapsulate it. It is in the vacuole where the food will be slowly digested. The vacuole will travel around the cell and at the same time diffuse the nutrients needed by the cell.
