Given the information that the cell is round and incapable of producing its own food, the most logical organelle it must have is the plasma membrane.
The plasma membrane is essential for all cells, as it controls the movement of substances in and out of the cell and protects the internal environment.
The other options can help differentiate cell types:
- Central vacuole is typically found in plant cells and aids in storage and maintaining cell turgor pressure, but it's not essential for all cells.
- Cell wall is characteristic of plant cells and provides structural support; it wouldn't be found in all types of cells, particularly animal cells.
- Chloroplast is an organelle involved in photosynthesis, which is not applicable since the cell cannot produce its own food.
Therefore, the plasma membrane is the most critical organelle common to all cells, including a round, non-autotrophic cell.