Shrink a Potato with Osmosis

Potato strips are soaked in salt solutions of different concentrations to observe size and flexibility changes caused by osmosis across cell membranes. Measurements before and after soaking reveal whether water moved into or out of the potato cells.

1. Prepare three cups with 100 mL distilled water each and label them 0 g, 2 g, and 4 g salt; dissolve the measured salt in the latter two cups.
2. Cut uniform potato strips or cores (about 2 inches long and ≥½ inch thick); remove skin, rinse, and trim all to identical length.
3. Record initial length and width/diameter for each strip in a data table (make triplicates if possible).
4. Gently feel and try to bend the strips to note initial texture.
5. Place one strip (or set of three) into each cup; start a 30-minute timer.
6. After 30 minutes, observe the strips in each cup; remove the 0 g strips, blot briefly, note flexibility, and remeasure length and width; record data.
7. Repeat for the 2 g and 4 g cups, recording measurements and qualitative observations.
8. Compare changes among concentrations; identify which strips swelled or shrank and by how much.

Shrink a Potato with Osmosis – STEM activity - Science Buddies:

the potato experiment - osmosis lab - Scientist Cindy:

📄 Shrink a Potato with Osmosis! - Science Buddies: https://www.sciencebuddies.org/stem-activities/potato-osmosis

• Weigh strips before and after soaking to track mass change alongside size change.
• Test additional salt levels (for example, 1 g, 3 g, 5 g per 100 mL) to better locate the isotonic point.
• Extend soak time to 1 hour or overnight and compare with 30-minute results.
• Graph final length (or mass) vs. salt concentration and find where the curve crosses the starting value (estimated isotonic concentration).
• Try other produce (carrot, apple) and compare responses.

• Use care with sharp tools (apple corer/knife); cut on a stable cutting board under adult supervision.
• Keep the workspace dry to prevent slipping; clean up spills promptly.
• Do not eat experimental materials; compost potatoes after use and wash hands.

• Why did strips in pure water get longer or firmer? (Pure water is hypotonic to potato cells, so water enters cells by osmosis, increasing turgor.)
• Why did strips in higher salt shrink or feel floppier? (Those solutions are hypertonic; water leaves cells by osmosis, reducing turgor.)
• What does it mean if a strip’s size does not change? (The solution is isotonic with the cells—no net water movement.)
• How would using tap water instead of distilled water affect results? (Dissolved salts in tap water could shift the effective concentration, slightly reducing swelling.)
• Which measurement—length, width, or mass—is most sensitive to osmosis here? (Mass usually shows the largest percent change because it directly tracks water gain/loss.)