If the cell is round and incapable of producing its own food, it is likely a type of animal cell or a heterotrophic organism. The organelle that you can definitively assume the cell must have is the plasma membrane.
Chloroplasts are involved in photosynthesis and are found in plant cells and some protists, which produce their own food. A cell wall is characteristic of plant cells and some microorganisms but not animal cells. A central vacuole is typically found in plant cells as well. Therefore, the best answer is plasma membrane.