Using Potatoes for Osmosis and Diffusion Labs

• Easy materials list!

• Easy set up and clean up!

•Involves calculations and graphing!

Win!  Win!  Win!

I love labs that:

• Teach or illustrate multiple concepts
• Use simple consumable materials and readily available lab items
• Involve weighing, measuring and calculating
• Require the students to make a HAND-MADE graph
• Provide a perfect visual of the concepts I teach in the classroom
• Reinforce the use of lab equipment and proper laboratory skills
• Require the students to use critical thinking and problem solving skills
• Require students to closely examine the date in order to draw a conclusion

This lab meets all of the above requirements!!  The ideas that you are about to read about are not new.  And the teaching of osmosis and diffusion in a cell structure unit is timeless and absolutely necessary. There are so many lab activities to choose from for this topic, but what I describe below has proven to be the best for my students.  When the students in the lab are exclaiming "WOW!" as they view plasmolysis occurring in cells viewed with a microscope, you (the teacher) have succeeded in solidifying that concept in their brain.

The lab I use has two different activities.  Part A of this lab is qualitative.  Students will view plasmolysis in a living cell.  Students will observe cells under the microscope as plasmolysis takes place, and easily and excitedly view the collapse of the cell.   Cells from an onion or an Elodea leaf are subjected to a few drops of salt water and students can instantly view plasmolysis occurring in these cells.

Part B of this lab is quantitative.  (I am a big fan of quantitative!!)  Students will measure the amount of water lost (in grams) from potato slices.  Students will draw pictures and describe what they see in Part A.  Students will measure and graph their results in Part B.

In the first part of the lab, students place a small piece of onion skin, or a leaf from the Elodea (Anacharis) aquarium plant on a microscope slide, along with a few drops of distilled water.  Students view the cell, draw the cell, and describe the position of the cell contents.  Once the initial observation is complete, students use a small piece of paper toweling to draw off the water, replacing it with a few drops of 15% salt water solution.  The transformation is stunning.  The plant cells immediately undergo plasmolysis.  No student can fail to understand what has just happened.

While the first part of the lab requires only drawings and descriptions from the students, the second part of the lab will require weighing, measuring, calculating and graphing.

Purpose of this lab:
1. To observe the process of plasmolysis inside living cells.
2. To observe the effect of different types of solutions on living cells.
3. To quantitatively measure the rate of plasmolysis in potato slices.

MaterialsNeeded:  Microscopes, Microscope slides, Cover slips, 5% sodium chloride solution, Medicine droppers, Elodea plant, 10% sodium chloride solution, Distilled water, Potatoes, various sugar solutions, 100 mL beakers, Balances.

In this part of the lab, the student uses a cork borer to make 20 small cores of potato.

The potato cores are massed 4 at a time to determine their initial mass.

The 4 cores of potato are placed in solutions of different sucrose molarities.  The first beaker contains distilled water, the second contains a .2M sucrose solution, the third contains a .4M sucrose solution, the fourth contains a .6M sucrose solution and the last contains a .8M sucrose solution.

The potatoes are allowed to sit in their various solutions overnight.  After 24 hours they are weighed to determine their final mass.  The student will calculate a percent change in mass and place this data on a graph.  From the graph, the student will determine the solute concentration of the potato.  The student will decide if the potato was hypotonic or hypertonic to the solution in which it was placed.

As I stated at the beginning, these ideas are not new or unique, and you may already be doing these activities in your science lab.  I have tried many, many osmosis and diffusion labs, but this one has proven to be the most effective in getting the concepts across to my students.

My TpT store has a variety of free and paid resources to help you teach these concepts.  You might want to check out my FREE LAB, "The Effect of Concentration on the Rate of Diffusion" by clicking the red link.

Paid resources include the following:

Lab: Qualitative and Quantitative Plasmolysis

Cellular Transport Jeopardy Review Game

Lab: Diffusion Through a Non-Living Membrane

Cellular Transport Critical Thinking Worksheet