Exploring Osmosis: How Water Travels Through Potato Cells

In this lab, students will explore osmosis, which is how water moves through a semi-permeable membrane (which is a thin layer that only lets some substances like water pass through). Students will use the potato pieces (pre-cut by teachers) and place them in different salt solutions to see how water moves from areas with a high water concentration (more water) to areas with a low water concentration (less water). The solutions will range from plain water to low salt water to high salt water.

Osmosis occurs because the water is trying to balance out of the potatoes cells. By comparing all three solutions, student will be able to contrast and see how the cells in the potatoes respond to each concentration (each plain, low salt and high salt solution). This will let students relate this lab to real life examples of osmosis. For example, fruits and vegetables shrink (lose water) in salty solutions or why fingers get wrinkled when swimming. For students to have a clear understanding of osmosis, please follow the instructions down below and try to finish the lab by using clear scientific language!

*PLEASE DO NOT EAT ANY OF THE LAB CONTENT OR DRINK ANY SOLUTIONS*

1. 3 small beakers (100 mL each)
2. 3 rectangular potato pieces (pre-cut by teachers)
3. Table Salt
4. Distilled Water
5. Scale
6. Ruler
7. 3 spoons
8. Clear Tape
9. Paper Towel
10. Black Sharpie
11. Lab Coat
12. Goggles

Use clear tape and a black sharpie to label the beakers. Beaker 1 will be labelled Plain Water, beaker 2 will be labelled Low Salt and beaker 3 will be labelled High Salt. Make sure to lay the tape on the side that will not cover the measurements of the beakers.

Grab the distilled water, 3 beakers and pour 100 mL of distilled water into each beaker. In the Plain Water beaker there will be no salt content so it will remain the same. In the Low Salt beaker, add 1 tablespoon of salt and stir until seemingly dissolved. In the High Salt beaker, add 2 tablespoons of salt and stir until seemingly dissolved as well.

Use the pre-cut rectangular potato pieces. Double check the potatoes should be around 4 cm long and 1-2 cm in width. They should all be around the same size.

Place each potato piece on the given scale and record its mass in grams (g). Take a ruler to measure the length and width of each potato pass (Note: important to measure for any expansion or reduction).

Put each potato piece into the labelled beakers and make sure it is fully submerged under each solution. In the case of the potato pieces floating to the top, gently place a spoon on the potato to weigh each piece down (Note: metal spoons will not compromise solution or results).

Leave the potatoes unsettled in the solutions for 45 minutes.

For every 15 minutes, make sure to check for size and color. Did it get bigger or smaller? Did it go through a color change? Once potato pieces are out of the solution and the time is up, check for texture, is it soft, hard or bendy?

Observation table provided above (Note: think about size, color and texture when making observations).

Line up all three potato pieces and compare how they look and feel, discuss with your lab partners.

Solution is safe to pour down the drain. Make sure to clean station with soap and water as well as cleaning all contaminated materials.

Osmosis is the movement of water through a semi-permeable membrane (a barrier that only lets some substances in and blocks the others) with a high concentration of water (excess amount of water) to an area with a low concentration of water (under average/less water). This process helps balance the concentration of solutes (e.g salt) on both sides of the membrane.

1. Plain Water: the concentration, also known as the amount of water inside and outside of the potato is around the same amount. This means there is almost no net movement of water (no water going into or out of the cell). The potato will stay firm and look the same
2. Low Salt Water: the concentration difference which is the difference in the water amount is much smaller inside the potato so a bit of water moves outside of the potato. This will cause a different in texture, feeling less hard.
3. High Salt Water: has a much lower concentration of water (less water) outside of the potato, water rushes out of the potatoes cells. This will cause the potato to become very flexible, soft, appear to have shrunk and look lighter in colour around the edges of the potato.

Please use language learned in this lab such as: semi-permeable membrane, concentration, high concentration, low concentration, osmosis, solution etc.

1. List what happened to the potato piece in the high salt water beaker and why?
2. Use your understanding of osmosis and explain the low salt water content result?
3. Why did the potato in plain water stay the same?