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Watch living plant cells change shape in real time. By adding saltwater to red onion cells, you can observe water leaving the cells through osmosis and see the cell contents pull away from the cell wall.
Materials
- Small piece of red onion
- Saltwater solution (1 teaspoon of salt in 100 mL of water)
- Distilled water
- Microscope
- Glass slides and coverslips
- Dropper or pipette
- Tweezers
- Paper towel
Instructions
- Peel a very thin, transparent layer from the inner surface of a red onion piece using tweezers.
- Place one small drop of water in the center of a clean glass slide.This helps the onion peel stick flat and prevents it from drying out.
- Lay the thin onion peel flat on top of the drop of water.
- Lower a coverslip slowly at a 45° angle to avoid trapping air.
- Start with low power, then move to high power. You’ll see neat, rectangular cells filled with reddish or purple cytoplasm that touches the cell wall.
- Without removing the coverslip, place one drop of saltwater at one edge of the coverslip.Hold a paper towel at the opposite edge to draw the saltwater through the slide.
- Observe under the microscope as the colored cytoplasm begins to shrink away from the cell wall.The water moves out of the cell into the saltier environment.
- Draw or photograph both stages (before and after saltwater) labeling cell wall and cytoplasm.
What’s going on?
- Osmosis is the movement of water across a cell membrane from low solute concentration (less salty) to high solute concentration (more salty).
- In saltwater, water moves out of the cells, making the cytoplasm shrink and pull away from the cell wall , this is plasmolysis.The red pigment in the onion makes these changes easy to see.
- This experimental setup offers an opportunity to observe and comprehend how cells react to alterations in their environment and understand osmosis as a fundamental process in living organisms.
Level
- Intermediate-Advanced
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