Biology 2.1 Making Chips By: Biology 12B

1.What was this experiment about?

We had to cut potatoes into 3 gram pieces. We then soaked the pieces overnight in solutions of different salt concentrations. We then weighed them and recorded the difference in weight. This experiment was about the process of osmosis and was for a biology internal (2.1).

2. What were the variables?

Independent variable – The concentration of salt in the solution. (0.0, 0.1, 0.3, 0.5, 0.7 and 0.9 moL). Dependent Variable – The change in weight after a night soaked in a salt solution. Measured in grams.

3. How did you ensure reliability and validity of data?

We had many controlled variables to ensure that this was a fair test. Beginning Weight – 3 grams Amount of solution – 40mL Used same scales We also used distilled water as a controlled variable to make sure that the potatoes didn’t lose weight when soaked in water normally.

4. What results did you get? Were they expected? My results showed that when soaked in distilled water the potato pieces gained weight but when soaked in a solution that contained salt the pieces lost weight.

This was expected and was what my hypothesis predicted. However, my results also showed that as the concentration of salt became higher the amount of weight lost decreased. This I did not predict and can still not explain.

5. What is the science behind what happened? Give details.

Water wants to move from an area of high concentration to an area of low concentration to reach an isotonic state (where the amount of water is the same inside the cell and outside the cell). When the potato was soaked in distilled water, the potato contained the lower concentration of water than the solution, so was hypertonic. The water moved from the solution into the potato, resulting in the weight gained. However, when the potato was soaked in a salt solution the opposite occurred. The solution had a lower concentration of water than the potato, making the potato hypotonic. The water moved from the potato into the solution resulting in the loss of weight.

6. What went wrong?

When conducting my experiment I did not think about surface area. Some of my potatoes had a larger surface area than others which may have made my results unreliable. Cells that have a larger surface area have a larger sized cell wall/plasma membrane exposed to the environment around it. This means that water has a better chance of getting through the semi-permeable membrane by osmosis.

7. What improvements do you think you could make to this experiment? If I was going to do this experiment again I would make the amount of skin on the potato one of my controls. Some of my potato pieces had more skin than others. Potato skin cells may be less or more permeable than potato flesh cells which could have affected the process of osmosis and therefore my results.