Plasmolysis exposes the central vacuole in onion cells

Steps:

• Onion epidermal cells soaked in solution X undergo plasmolysis if hypertonic, losing water.
• Cytoplasm shrinks and pulls away from the cell wall, creating a gap.
• The large central space Y remains as the shrunken vacuole.
• This identifies Y as the vacuole, not other structures.

Why C is correct:

• Plant cells like onion epidermis contain a large central vacuole that occupies most of the cell volume and becomes visible as an empty space after water loss in plasmolysis.

Why the others are wrong:

• A. Air: No air enters; the space forms from water efflux, not gas.
• B. Cytoplasm: Cytoplasm is the dense peripheral layer, not the empty center.
• D. Solution X: Solution remains outside the intact cell wall.

Final answer: C