The correct answer is E: surrounded by a membrane.

The vacuole in a plant cell is surrounded by a membrane called the tonoplast. It is typically filled with cell sap, which contains water, nutrients, waste products, and sometimes pigments. The vacuole plays several key roles in maintaining the cell's turgidity (rigidity), storing nutrients, and aiding in the cell's growth.

- A: The vacuole is not just a "large empty space." It is filled with cell sap and is important for cellular functions.
- B: The vacuole in a plant cell is usually much larger than in an animal cell, where multiple smaller vacuoles may exist.
- C: The vacuole is not filled with air; it is filled with cell sap, as mentioned above.
- D: A vacuole is not an "ordinary vacuum"—it is a specialized organelle in plant cells.

Thus, the vacuole is surrounded by a membrane (tonoplast), making E the correct answer.