Effect of Osmosis on Potato
Aim: To investigate the effect osmosis has on potato pieces that are placed in different concentrations of sugar solutions in water. Hypothesis: I believe that the more saturated the solution is the lighter the potato will be, and the potato in the clear water will weigh more after being left in the solution over a 24 hour period. This is because the cell membranes in the potato act as semi permeable membranes (meaning that they only allow certain molecules through).
In the clear water the potato will gain mass because the potato will gain water from the solution around it from osmosis. This osmosis effect is the flow of water across the semi permeable membrane from a solution of higher water potential (water) to one with a lower water potential (potato). The potato will allow water into it to even out the sugar concentration between the solution and the potato.
Therefore the potato will gain mass in clear water.
As the concentration of the sugar in the water increases the potato loses more and more mass because the difference in water potential between the inside of the potato cells and the outside solution gets more and more different. This means that when the potato is placed in the higher sugar concentration solutions more water will move out of the potato from osmosis.
Independent Variable: The amount of sugar in each solution of water (4 teaspoons, 3 teaspoons, 2 teaspoons, 1 teaspoon, and no sugar) Dependent Variable: The weight of the potato after being left in the solution for 24 hours and dried out. Controlled Variables:
•Amount of water used- 150mls
•Temperature of solution- all kept in same room for similar temperature •Weight of potato- 20 grams each piece
•Type of potato- all pieces are cut from one big potato
•Type of cup- all glass
•Weighing machine- all pieces are weighed on the same machine for consistent and accurate results Materials:
•5 cups of the same type
1Collect the water and the separate sugar amounts of 1, 2, 3, and 4 teaspoons of sugar. 2Place each sugar amount in a different cup, leaving one without sugar. 3Fill all 5 cups with 150 mls of boiling water to dissolve the sugar. Clearly label each cup to recognise the amounts of sugar in each cup. 4Mix the sugar in the cups to dissolve it. Put the saturated solutions in the fridge for a while to cool them down to room temperature. 5Cut 10 potato pieces from the potato’s to the same size and shape using a cork borer for accuracy. 6Dry each piece with a paper towel to speed up the osmosis process. 7Weigh each piece to make sure they are the same weight (all are 20 grams). 8Once the solutions have cooled down take them out of the fridge and place 2 potato pieces in each of the cups for more accuracy with results. 9Place all the cups back in the same place in the fridge so that the temperature remains the same. 10Leave all the potato pieces in the solution and set timer for 24 hours. 11Once the timer has finished, remove a piece of potato, dry it with a paper towel, then reweigh it. Record the final weight. Use the same electronic scales for consistency.
Amount of sugar in solutionPotato weight after experiment:
Potato 2Average weight between both potatoes
0 teaspoons21 grams23 grams22 grams
1 teaspoon21 grams19 grams20 grams
2 teaspoons18 grams18 grams18 grams
3 teaspoons17 grams15 grams16 grams
4 teaspoons15 grams15 grams15 grams
The results show what I predicted in my hypothesis. The potato left in the clear water gained mass after 24 hours, and then as the concentration of sugar in the solution increased the potato lost more mass. The line shows a slight curve towards the end, showing that the potato will not always keep losing mass the higher the sugar concentration is. This is because the fluid inside a potato will only account for a certain amount of the potato’s weight, and once all that is gone the potato will not lose or gain any weight at all. The weight of the potato left in water with 1 teaspoon of sugar in it is the same weight as before. This is because both the solution and the potato would have had similar water potential levels, so their sugar concentrations were already even so osmosis had no effect.
When the potato was put in clear water it gained mass because the potato gained water from the surrounding solution from osmosis. Osmosis causes a flow of water across the semi permeable membrane from a solution with a high water-potential to one with a lower water potential. The potato gained water because the water had a higher water potential than the potato. When the potato was put in a solution with high sugar concentration, the potato had a higher water potential (low solute) than the surrounding solution (high solute) so the flow of water went from the potato through the semi permeable membrane to the solution, causing the potato to lose water and therefore lose mass.
My results were reasonably fair because I used a number of ways to get reliable results. I used a cork borer to make sure all the potato pieces used were almost exactly the same shape. This meant that each piece had the same surface area for the diffusion of water effect from osmosis. I also used two pieces of potato to find an average result to get more accuracy, and everything was done under the same conditions so the results will be in
the right proportion. Next time I would use more potato pieces in each cup and do the experiment twice for more accurate results.
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