If the cell is round and incapable of producing its own food, it is most likely a type of animal cell rather than a plant cell. Therefore, the organelle it must have is the plasma membrane, which is essential for all types of cells as it regulates what enters and exits the cell.
The central vacuole and cell wall are primarily found in plant cells, and chloroplasts are involved in photosynthesis, which is associated with food production. Thus, the correct answer is plasma membrane.