Osmosis in Red Onion Cells (more fun with microscopes)

Phase 1: Dry Mount Obtain a thin, purple piece of onion Place it on a slide, shiny side up No water!!! Observe and draw on low power, then find the most purple section, and observe and draw on medium power

Phase 2: Saltwater Wet Mount Add 2-3 drops of saltwater to same onion (use cover slip too) Observe 2-3 min on low power and draw Initially you’ll see changes along the perimeter, but as time passes, you’ll see changes throughout the cell Observe a noticeably affected area under medium power Draw

Prepare Slide for Phase 3 Gently place slide in freshwater to rinse (be careful not to lose the onion!) Gently dry the slide by dabbing onion tissue dry

Phase 3: Distilled Water Wet Mount Place 2-3 drops of distilled water on same onion slide (use cover slip) Watch cells for 2-3 minutes on low power and draw Should start to see changes around the perimeter Observe a noticeably affected area under medium power and draw

Questions 1. When the salt solution was added to the onion cells, where was the greater concentration (most pure) of water (inside or outside the cell membrane)? How do you know? 2. In the winter, grass often dies near the roads that have been covered in salt to remove the ice. Using what you have learned in this experiment, what do you think is the reason the grass dies?

3 minutes after distilled water