Osmoregulation and osmotic balance are important body functions. Osmosis is the diffusion of water across a membrane in response to osmotic pressure caused by an imbalance of molecules on either side of the membrane. Nurses need to have an understanding fluid and particle movement across cellular membranes, as this dynamic process is crucial for life and homeostasis. Most water in the ground is not pure water. It usually contains dissolved mineral salts. Animals and plants need these salt compounds (which include calcium, magnesium, potassium, and the sodium you might be familiar with in table salt) to grow, develop and stay healthy. Different water sources carry different amounts of these salts. Nature wants to balance a system that is not balanced. So if you mix water with two different salt concentrations, the salts do not stay separated but spread out evenly through the solution until the salt concentration is the same throughout. You will find a similar reaction if you separate two salt solutions with a semipermeable membrane. A semipermeable membrane is a type of barrier that only lets certain particles pass through while blocking others. This type of membrane usually lets water pass through but not the salts that are dissolved in the water. In this situation, because only water can move through this membrane, the water will start moving from the area of lower salt concentration (which has more water and less salt) to the area of higher salt concentration (which has less water and more salt). This water movement will only stop once the salt and water concentration on both sides of the membrane is the same. The process of moving water across a semipermeable membrane is called "osmosis." Plants use this process to their advantage for water uptake. They create an environment of high salt concentration in their root cells that are in contact with the soil. The cell walls act as a semipermeable membrane and only let water through. Because the water outside the root cells has a lower salt concentration, water starts moving into the root cells due to osmosis. The water entering the plant fills up the cells and can travel to the rest of the plant. Osmosis, however, works in both directions. If you put a plant into water with a salt concentration that is higher than the concentration inside its cells, water will move out of the plant to balance out the concentration difference. As a result, the plant shrinks and eventually dies. You will see this effect with your own eyes in this activity using potatoes and different saltwater solutions. Materials Distilled water Measuring cup [preferably marked with milliliters (mL)] Table salt 3 plastic cups or glasses Measuring spoons in 1/2 and 1/4 teaspoon (tsp) sizes Page 2 of 2 2022. Grand Canyon University. All Rights Reserved. Spoon At least 3 potatoes Cutting board Knife Ruler Paper 2 different colored pens or pencils Timer Paper towels Graphing paper (included at the end of the document) or student may create a graph using Excel. 1 additional firm vegetable (enough for 3 equal pieces) of student's choice (e.g., carrot, sweet potato, yam, beet) 1 additional firm fruit (enough for 3 equal pieces) of student's choice (e.g., apple, pear) Preparation To prepare three different saltwater solutions first, obtain three cups and create labels for them: "0 teaspoons," "1/4 teaspoon" (metric equivalent: 1.2 mL), and "1/2 teaspoon" (metric equivalent: 2.5 mL). To each of the cups add 100 mL of distilled water (U.S. equivalent: 0.4 cups). Measure out 1/4 teaspoon of table salt, and add it to the cup labeled "1/4 teaspoon." Then measure out 1/2 teaspoon of table salt, and add it to the cup labeled "1/2 teaspoon." Use a spoon to mix the solutions until all the salt is dissolved. Convert the teaspoon values for salt quantities into mL and write the information in Table A: Potato below. Use a knife and cutting board to prepare at least three potato core pieces from each potato. NOTE: Please use caution when handling cutlery. Knives can cause serious injury if not handled properly. Ideally, you will be able to prepare nine matching core pieces at least one-half inch thick and two inches long (so you can test three pieces in each solution to compare the results thoroughly). Use a knife to carefully remove any potato skin from your cores, and rinse the cores quickly with water. Use a ruler to ensure each potato piece belonging to a cup is the same size (ideally to the millimeter). Carefully use a knife to trim any pieces as needed. Measure the initial dimensions (length and diameter/width) of each potato piece in millimeters, calculate their averages and write the information in Table A: Potato below. Procedure Put at least one potato core piece (or three if you made nine pieces) into each of the cups. As you do that, feel the potato pieces with your fingers and try to flex them a little bit. Answer question A on the data sheet. Start your timer for 30 minutes. Let the potato pieces sit in the different solutions for the whole time. Answer question B on the data sheet. After 30 minutes inspect the potato pieces inside the solutions. Answer question C on the Page 2 of 2 2022. Grand Canyon University. All Rights Reserved. data sheet. Take the potato piece(s) out of the "0 teaspoons" cup and place on a paper towel. While doing that feel the potato piece(s) again and try to bend them slightly. Answer question D on the data sheet. Use the ruler to measure the exact length and diameter or width (in millimeters) of each of the potato pieces, calculate their averages and write the results in your table. Answer question E on the data sheet. Next take the potato pieces from the "1/4 teaspoon" cup," and place them on a paper towel; as you do this feel them again. Measure their lengths and diameters or widths, calculate their averages. Write your results in the table. Answer question F on the data sheet. Repeat the same measurement steps with the potato pieces in the "1/2 teaspoon" cup. Write your results in the table. Answer questions G and H on the data sheet. Compare the results in your table. Respond to question I. Leave the potato pieces in the solutions overnight. Respond to question J. Repeat measuring steps 47 to complete the data table. Utilize the graphing paper included below, or using Excel, make a graph of your potato results with the salt concentration on the horizontal x-axis and the potato piece length or diameter after soaking on the vertical y-axis. Draw two different colored lines to make your graph. For the first, connect each of the data points you found. For the second, draw a horizontal line across the graph which starts at the point on the vertical axis that shows the original length of your potato piece. How does the activity work with other vegetables or fruit? Select one additional vegetable sample (3 equal pieces) and one additional fruit sample (3 equal pieces) and repeat the experiment. Record your results in Tables B and C. ConclusionThe shrinking and expanding of the potato strips is due to osmosis. Potatoes are made of cells, and their cell walls act as semipermeable membranes. The "0 teaspoons" solution contains less salts and more water than the potato cells (which have more salts and less water). To balance out these concentration differences, the water from the cup moves into the potato cells. The incoming water in the potato cells pushes on the cell walls and makes the cells bigger. As a result, the whole potato strip gets bigger. The opposite is the case in the higher concentration salt solutions. If the salt concentration in the cup is higher than inside the potato cells, water moves out of the potato into the cup. This leads to shrinkage of the potato cells, which explains why the potato strips get smaller in length and diameter. Due to the shrinking of the potato cells the potato strips also become less rigid. If you bent the potato strips, you should have noticed that those that had been in the solution with the highest amount of salt were much easier to bend than the potato strips in the water without salt. After graphing the data, it should be noted that there is a salt concentration at which the potato strip neither expands nor shrinks. This should be where your data curve and your start length line intersect. At this point the salt concentration inside the potato cells and inside the cup are the same. Because the concentrations are already balanced, or isotonic, no water moves. Page 2 of 2 2022. Grand Canyon University. All Rights Reserved. CleanupDiscard the saltwater solutions down the sink drain. Throw the potato pieces into the compost or waste basket, and clean up your workspace. You can cook with the other pieces of unused potato. Lab Data Sheet Observations and Hypothesis How do they feel? Are they easy to bend? Click or tap here to enter text. What do you think will happen to the strips in each of the cups? Click or tap here to enter text. Page 2 of 2 2022. Grand Canyon University. All Rights Reserved. Data Table A: Potato Salt (NaCl) Quantity V of salt in mL Concentration: Volume/Volume % Average Initial Length Average Initial Diameter/Width Average 30 Min Length Average 30 Min Diameter/Width Average Final Length Average Final Diameter/Width 0 teaspoon teaspoon teaspoon Table B: Additional Vegetable Type of Vegetable Used: Click or tap here to enter text. Salt (NaCl) Quantity V of salt in mL Concentration: Volume/Volume % Average Initial Length Average Initial Diameter/Width Average 30 Min Length Average 30 Min Diameter/Width Average Final Length Average Final Diameter/Width 0 teaspoon teaspoon teaspoon Page 2 of 2 2022. Grand Canyon University. All Rights Reserved. Table C: Fruit Type of Fruit Used: Click or tap here to enter text. Salt (NaCl) Quantity V of salt in mL Concentration: Volume/Volume % Average Initial Length Average Initial Diameter/Width Average 30 Min Length Average 30 Min Diameter/Width Average Final Length Average Final Diameter/Width 0 teaspoon teaspoon teaspoon Results and Analysis Based on your graph can you find a salt concentration at which the potato strip length should not change at all? Click or tap here to enter text. Do you see any changes? Did your potato strips shrink or expand? Click or tap here to enter text. How do they feel? Are they easier or more difficult to bend than before? Click or tap here to enter text. What do you notice about the potato piece measurements? Click or tap here to enter text. What changed about these potato strips? Click or tap here to enter text. Are your results for these similar or different compared with the potato samples in the other salt concentrations? Click or tap here to enter text. How did the feeling of the pieces compare based on what solution they were in? Why do you think this is? Click or tap here to enter text. How did the length and diameter or width of the potato pieces change in each cup? What about Page 2 of 2 2022. Grand Canyon University. All Rights Reserved. the weights if you took them? Can you explain your results? Click or tap here to enter text. How many hours did you let the potatoes soak? Click or tap here to enter text. Describe the appearance of the potatoes after you let them soak in the saltwater overnight? Click or tap here to enter text. Describe the differences that you see in all three food items tested. Did one type of food item experience a greater change than the others? Using your knowledge of osmosis and concentration, how can you explain your results? Click or tap here to enter text.