Osmosis & Diffusion In Depth

-Potato Lab

Review of Osmosis and Diffusion

• Osmosis is the movement of water across a cell membrane from an area of higher concentration to an area of lower concentration.

• Diffusion is the movement of molecules other than water across a membrane from an area of higher concentration to and area of lower concentration.

Water Potential

http://www.neosci.com/demos/10 1041_cell%20processes/Presentation.html

Getting the Info!

• Complete osmosis worksheet for background info!

• • Sodium/Potassium Pump and Osmosis… http://nutrition.jbpub.com/resources/animat ions.cfm?id=27&debug=0 • Ion pumps worksheet!

Can a potato be used to demonstrate osmosis and diffusion?

• Potatoes are composed of cells.

• Potato cells have cell membranes.

• Potato cells have some water and some salt inside the cells.

Design the Experiment

• What can we observe that would be evidence of osmosis and diffusion?

• What can we measure to see if a change takes place?

• What is the process that will cause a change?

• What is the variable? What is the control?

Materials

• 2 Potato slices • 2 beakers • 1 teaspoon of salt • Water • Balance

Hypothesis and Method

• Discuss a method with your group and formulate a hypothesis!

Sample Data Box

Condition Initial Mass Final Mass Change in mass

Potato in tap water

Texture change

Potato in salt water Does osmosis explain the changes? Why?

Predictions

• What do expect to see tomorrow?

• What will each potato feel like on tomorrow?

• What will each potato look like on tomorrow?

• What will happen to the mass of each potato when you measure it tomorrow?

Extension…Sports Drinks!

• • •

Hypernatremia & Hyponatremia Can you drink yourself to death??

Should the tonicity of a fluid replacement drink be isotonic, hypertonic or hypotonic???

Lab Take-Up Slides

Hypothesis

• •

Distilled Water

-Water will move from the cup into the potato because water outside the cell will be in higher concentration than water inside the cell. This is an example of hypotonic solution.

Salt Water

- Salt will move into the cell from the cup and water will move out of the cell into the cup because of a difference in concentration. This is a hypertonic solution.

Procedure

1. Label one beaker water. Label the other beaker salt water.

2. Measure the mass of both potato slices. Record the mass.

3. Add the same amount of water to each beaker so that the potato slices are covered with water.

Procedure

4. Add 1 teaspoon of salt to the beaker labeled salt water. Make sure that the salt dissolves.

5. Add slices and let both cups sit at least overnight.

6. Measure the mass of each slice.

Sample Data for Quiz Review

Condition Initial Mass

Potato in tap water 12 grams

Final Mass Change in mass

14 grams +2 grams

Texture change

More rigid, firmer Potato in salt water 11.5 grams 10 grams -1.5 grams Less rigid, softer Does osmosis explain the changes? Why?