Create motion with salt! Learn exactly how plant cells manage water with an activity you can see--and feel. Credit: George Retseck
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Key ConceptsBiologyOsmosisCellsChemistryConcentrationWater transport

IntroductionHave you ever wondered exactly how plants "drink" water from the soil? Water absorb in plants is rather complicated. A procedure called osmosis helps the water move from the soil right into the plant roots—and then into the plant"s cells. In this task you will watch for yourself exactly how you deserve to make water relocate with osmosis!

BackgroundMost water in the floor is not pure water. It usually has dissolved mineral salts. Animals and plants need these salt (which include calcium, magnesium, potassium and the sodium you could be acquainted with as table salt) come grow, develop and also stay healthy. Different water sources carry different quantities of this salts. Nature desires to balance a mechanism that is no balanced. For this reason if you mix water with two different salt concentrations, the salt don"t stay separated however spread out evenly with the equipment until the salt concentration is the exact same throughout.

You"ll uncover a similar reaction if you different two salt remedies with a semipermeable membrane. A semipermeable membrane is a type of obstacle that just lets certain particles pass v while impede others. This kind of membrane usually allows water pass through but not the salts that are dissolved in the water. In this situation, since only water can move v this membrane, the water will start moving from the area of reduced salt concentration (which has much more water and also less salt) come the area of greater salt concentration (which has actually less water and much more salt). This water movement will only stop as soon as the salt and also water concentration top top both sides of the membrane is the same.

The process of moving water throughout a semipermeable membrane is referred to as osmosis. Plants use this procedure to their advantage for water uptake. They create an atmosphere of high salt concentration in their root cell that room in contact with the soil. The cell walls act together a semipermeable membrane that only let water through. Because the water outside the source cells has a lower salt concentration, water start moving right into the source cells because of osmosis. The water beginning the tree fills up the cells and can take trip to the remainder of the plant. Osmosis, however, functions in both directions. If you placed a plant into water with a salt concentration that is higher than the concentration within its cells, water will relocate out of the plant to balance out the concentration difference. Together a an outcome the tree shrinks and also eventually dies. Friend will see this result with your very own eyes in this task using potatoes and different saltwater solutions.


Distilled waterMeasuring cup v milliliters (mL)Table saltWeight scale with gram measurementsThree plastic cup or glassesSpoonAt the very least three potatoesApple corer. (Alternatively, you have the right to have an adult assist you usage a cutting board and knife.)Knife (and an adult helper to assist you usage it)RulerPaperPen or pencilTimerPaper towelsGraphing record (optional)Other vegetable(s) or fruit (optional)


Prepare three various saltwater solutions. Create labels because that the 3 cups: "0 grams," "2 grams" and also "4 grams."To each of the cups include 100 mL of distilled water.Weigh out 2 grams of table salt, and include it come the cup that says "2 grams." Then weigh out 4 grams of table salt, and include it come the cup labeling "4 grams." usage a spoon to mix the remedies until all the salt is dissolved.Draw a table in which you can enter the starting measurements (length and diameter or width) and also end measurements of each potato piece for every salt concentration (0, 2 and 4 grams).Prepare at least three potato cores. Closely push the corer all the method through the potato, and also remove the core very closely so the potato piece stays intact. (Alternatively, you have the right to have one adult assist cut the potato right into strips the all have actually the very same dimensions.) The potato pieces must be at least one-half customs thick and two inch long. (Ideally girlfriend will be able to prepare nine equivalent cores or strips therefore you deserve to test 3 pieces in each solution to compare the results thoroughly.)Use a knife to very closely remove any type of potato skin from your cores, and also rinse the cores easily with water.Use a ruler to ensure every potato item is the exact same size (ideally to the millimeter). Very closely use a knife to trim any type of pieces as needed.Measure the dimensions (length and also diameter or width) of each potato piece in millimeters, and write the details in the table.Optionally, friend can also weigh each potato piece and record their weights.


Put one potato strip (or 3 if you made nine pieces) into each of the cups. When you execute that feeling the potato strips with your fingers and try to flex lock a little bit. How carry out they feel? space they straightforward to bend?Start your timer because that 30 minutes. Let the potato strips sit in the different solutions for the entirety time. What execute you think will happen to the strips in every of the cups?After 30 minutes examine the potato strips within the solutions. Do girlfriend see any kind of changes?Take the potato strip(s) out of the "0 grams" cup and also place on a paper towel. While doing the feel the potato pieces again and shot to bend them slightly. How execute they feel? are they simpler or more challenging to bend than before?Use the leader to measure the specific length and diameter or width (in millimeters) of every of the potato strips, and also write the results in your table. What do you notification about the potato piece measurements? Optionally you can weigh this pieces and record their weights.Next take it the potato strips native the "2 grams" cup, and place them on a document towel; as you carry out this feeling them. Measure their lengths and also diameters or widths. Create your outcomes in the table. Optionally you can weigh these pieces and also record your weights. What changed around these potato strips?Repeat the same actions with the potato strips in the "4 grams" cup. Write your results in the table. Are your results for these comparable or different contrasted with the various other ones?How walk the emotion of the strips compare based on what solution they to be in? Why perform you think this is?Compare the outcomes in your table. How go the length and also diameter or broad of the potato strips change in every cup? What around the weights if you took them? can you explain your results?Extra: If girlfriend weighed every of her strips before and also after soaking them, to compare the weights. How does the fixed of the potato strips change in each solution?Extra: leaving the potato strips in the solutions for a longer time period. How perform they watch if you let lock soak in the saltwater because that one hour or overnight?Extra: If you have graphing paper, make a graph the your outcomes with the salt concentration top top the horizontal axis and the potato strip length or diameter ~ soaking top top the vertical axis. Draw two lines to make her graph. For the first, attach each of the data points girlfriend found. Because that the second, attract a horizontal line beginning at the point on the upright axis that reflects the original size of her potato strip. Based on your graph deserve to you uncover a salt concentration at which the potato strip length should not adjust at all?Extra: How does the task work with various other vegetables or fruit? try it to uncover out!

Observations and ResultsDid your potato strips shrink and also expand? at the beginning all the potato strips need to have had actually the exact same length and also should have all felt the same. As soon as you put them right into the various solutions, however, this starts to change. Whereas the potato strips in the "0 gram" cup probably obtained larger in size, the other potato strips probably got much shorter after leaving them in the saltwater because that 30 minutes. (If friend didn"t watch any far-ranging changes ~ 30 minutes, leave the potato strips in the saltwater services longer.)

The shrinking and expanding of the potato strips is due to osmosis. Potatoes space made that cells, and also their cell wall surfaces act together semipermeable membranes. The 0 grams solution has less salts and an ext water than the potato cells (which have much more salts and also less water). To offset these concentration differences, the water from the cup moves into the potato cells. The just arrived water in the potato cells pushes ~ above the cell walls and makes the cell bigger. As a result the totality potato piece gets bigger. The contrary is the situation in the greater concentration salt solutions. If the salt concentration in the cup is greater than inside the potato cells, water moves out of the potato into the cup. This leader to shrinkage that the potato cells, which describes why the potato strips obtain smaller in length and diameter. Due to the shrinking that the potato cell the potatostrip additionally becomes much less rigid. If girlfriend bent the potato strips, girlfriend should have noticed that those that had been in the equipment with the highest possible amount the salt to be much less complicated to bend than the potato strips in the water without salt.

If girlfriend made the graph you probably noticed that there is a salt concentration in ~ which the potato piece neither expands nor shrinks. This need to be whereby your data curve and your start size line intersect. In ~ this suggest the salt concentration inside the potato cells and inside the cup are the same. Due to the fact that the concentration are currently balanced no water moves.

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CleanupDiscard the saltwater solutions in the sink. Throw the potato strips right into the compost, and also clean up your workspace. Girlfriend can chef with the various other pieces of unused potato.

More come ExploreOsmosis, indigenous Biology DictionaryDo Fish Drink? from mcgill University"s Office for Science and SocietyCucumber Chemistry: Moisture catch with Desiccants, from Scientific AmericanSuck it Up! how Water Moves through Plants, from scientific research BuddiesSTEM tasks for Kids, from scientific research Buddies