Given that the cell is round and incapable of producing its own food, the most appropriate organelle you would assume the cell must have is the plasma membrane.
The plasma membrane is essential for all cells, as it regulates what enters and exits the cell, providing a boundary and maintaining homeostasis. The other options have specific implications:
- Cell wall: Typically found in plant cells and some prokaryotes, but not in all types of cells.
- Central vacuole: Primarily found in plant cells and some fungi; not a requirement for all cells.
- Chloroplast: Involved in photosynthesis and found only in plant cells and some protists, which means a cell that cannot produce its own food would not have chloroplasts.
Therefore, the plasma membrane is the only organelle that is universally present in all types of cells, including non-photosynthetic ones.