Minute 1: The red onion cells start off on an isotonic solution before salt water is introduced. Being bathed in a hypertonic solution (the salt water) causes osmosis (the diffusion of water) from inside of the cell to the outside of the cell. As a result, the cell shrinks. This is called plasmolysis.
After Minute 1: Distilled water is introduced, which would be hypotonic in relation to the cell. This will cause the osmosis of water into the cell, causing it to expand.
This video has been sped up to 4x speed to emphasize the change.
