16. RED ONION OSMOSIS

INTRODUCTION: 

In this experiment we will see the process called osmosis of a red onion, with different material (distilled water, salt water and a microscope).

OBJECTIVES:

- To see what happens to the piece of onion when we put distilled water and salt water.

PROCEDURE:

A) PHASE 1: NORMAL CELLS/DRY MOUNT 

1. Carefully slice away the colored layer of cells from the red onion. This should only be the thin purple layer. Trim to get a piece about this actual size.

2. Place the thin, purple onion layer on a dry microscope slide shinny side up-do not put on water or cover slip yet.

3. Scan the entire onion tissue on low power to find and center the most purple area and focus. Set the microscope to medium power and focus the view.

4. Take a picture

B) PHASE 2: SALT WATER ENVIRONMENT/WET MOUNT 

Now that you have observed the layer of normal cells which are the subject of this lab, make a wet mount using 2 or 3 drops of salt water solution on the onion tissue then install cover slip.

5. Watch the cells for approximately 2-3 minutes or longer as you again survey the entire onion tissue on low power. You should see changes within many of the cells intially near the perimeter of the onion tissue. As time passes all or most of the cells shoulb become affected by the salt water. Find some cells that have noticeably been affected and observe them under medium power.

Obervations: We can see the process of plasmolosis.

C) PHASE 3: DISTILLED WATER ENVIRONMENT/WET MOUNT 

6. After you have colored the diagram correctly above, you need to prepare for phase 3 of this lab by putting the entire salt water wet mount in the dish of tap water to rinse off the salt water from the slide, cover slip and onion tissue layer. Dry the slide and cover-slip then gently dab the onion tissue dry.

7. Make a wet mount of the onion tissue you just rinsed using 2 or 3 drops of distilled water on the onion tissue then install cover slip. Watch the cells for approximately 2-3 minutes or longer as you again survey the entire onion tissue on low power. You should see changes within many of the cells intially near the oerimeter of the onion tissue. As tine passes all or most of the cells should become affected by the distilled water. Find some cells that have noticeably been affected by the distilled water and observe them under medium power.

Observations: The cells become more bigger because they took the water

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 know this? Explain:

Answer: Inside, because outside is the salt solution.

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?

Answer: The cells leaved water.

3. Which kinf of transport does water follow across the membrane?

Answer: Passive (membrane difussion)