Potato Osmosis Lab

Max Wiebe, Nick Acosta, Steven Weeks

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Problem

Do different molarities of sucrose solutions affect the rate of osmosis in potatoes?

Hypothesis

If we place equal-sized pieces of potato in a sucrose, then the water potential of the solutions with the highest sucrose concentration will increase the rate of osmosis.

Manipulated Variable

Concentration of Sucrose in Solutions
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3 Constant Factors

1. Solvent (Sucrose)

2. Potato Size

3. Submersion Time

Materials

- potato

- cutting instruments

- triple-beam balances

- metric rulers

- cups

- thermometers

- color-coded sucrose solutions of different, but unlabeled, concentrations prepared by our teacher

- graduated cylinder

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Procedure

  1. Cut the potato into 6 equal shapes of equal mass and size (preferably cubes). Make sure potato skin is peeled.

  2. Measure the mass (g) on triple beam balance

  3. Measure the volume of the solutions (with graduated cylinder)

  4. Put a potato cube in each sucrose solution.

  5. Leave the experiment to sit for 48+ hours

  6. Take out the potato cubes

  7. Measure the potatoes’ mass

  8. Calculate the difference in water potential of the solutions (calculate molarity)

Observations

After allowing the experiment sit over the weekend, we notice that some potatoes have shrunk considerably. Also, some of the solutions appear to have risen or dropped in level.

Results

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Analysis

It appears that solutions contain a great concentration of sucrose caused more water to be expelled out of the potato. It also appears that the solutions with little to no sucrose did caused water to be drawn into the potato. The greater the molarity of the solutions, the more negative its water potential was. Therefore, water moved from an area of high water potential to an area of low water potential.

Conclusion

(1) To measure the rates of osmosis in the potatoes, it was most accurate to analyze their difference in mass. (2 & 3) We calculated the water potential of the potato using the potato that experienced the least difference of mass. After using the water potential formula, the water potential for our potato came out to be -4.89 psi. (4) The water potential of the plants are nearly the same because of their equal mass, but the rate of osmosis between the plants and their different solutions differed. (5) If our potato, was placed in a dry environment, moisture from the potato would move out of the potato and into the atmosphere (high water potential to low water potential). (6) When potatoes are in the ground, they do not swell with water. Instead, their roots absorb water and nutrients, and they grow. Also, water will try to maintain homeostasis by being distributed evenly among different areas. This is an advantage because the plant cells in potatoes can only hold a certain amount of water before their cells threaten to lyse.