Final answer:
In a hypertonic solution, water occupies the space between the cell wall and the cell membrane.
Step-by-step explanation:
In a hypertonic solution, the substance that occupies the space between the cell wall and the cell membrane is water. When cells are in a hypertonic solution, water particles move out of the cell, causing the cell membrane to shrink and detach from the cell wall, a process known as plasmolysis.