Method
- Cut potatoes with core bores so that they are 2.3cm long and 1.5cm in diameter (make sure you get rid of the peels) x15
- Dry the potatoes with paper towels and then weigh each potato to get the original mass.
- Create different solute concentrations:
- Distilled water
- 25% sucroce (12.5mL) and 75% water (37.5mL)
- 50% sucroce (25mL) and 50% water (25mL)
- 75% sucroce (37.5mL) and 25% water (12.5mL)
- Pure sucroce
- Mark 5 potatoes with red toothpicks, 5 potatoes with green toothpicks and 5 potatoes with yellow toothpicks. Mark them by sticking the toothpicks through the centre of the potato (red toothpicks : trial 1, green toothpicks : trial 2, and yellow toothpicks : trial3)
- Place 3 potatoes in each solute concentration (1 red, 1 green and 1 yellow)
- Leave potatoes in the solutions for 2 nights.
7. after a period of 2 nights, remove the surface solution using paper towels and then they will be re-weighed and re-measure in length.
8. If you have time afterwards please repeat this experiment again as to obtain a second set of results. This will hopefully produce more accurate results from which you will be able to draw a more accurate conclusion.
Data Collection
Table
The effect of concentration of sucroce on the weight (grams) and length (cm) of potatoes after two days
Data processing
Average length of potato after 2 days = 2.5cm (1dp)
Average weight of potato after 2 days = 4.50 grams (2dp)
Average length of potato after 2 days = 2.3cm (1dp)
Average weight of potato after 2 days = 4.19grams (2dp)
Average length of potato after 2 days = 2.4cm (1dp)
Average weight of potato after 2 days = 3.86grams (2dp)
Average length of potato after 2 days = 2.1cm (1dp)
Average weight of potato after 2 days = 3.44grams (2dp)
Average length of potato after 2 days = 2.2cm (1dp)
Average weight of potato after 2 days = 3.72grams (2dp)
Conclusion
We predicted that as the concentration of sucrose in water increased the mass of potato decreased making the potato flacid. Decreasing the sucroce concentration in water allowed less osmosis to occur, therefore remained more turgid than the potato that was in the higher concentration solution. Therefore our hypothesis was correct.
This happened because water moved in and out of cells depending on the relative concentrations of solutes that were dissolved in water. Osmosis is the passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration. When the potato was in a highly concentrated solution the low solute levels of the potato diffused through to the highly concentrated solute level making the potato flacid. When the potato was in a low concentrated solution the low solute levels of the solution diffused through into the potato where there was high solute concentration.
Cell membranes are completely permeable to water; therefore, the environment the cell is exposed to can have a dramatic effect on the cell.
Hypertonic solutions contain a high concentration of solute relative to another solution. When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel and become flaccid. In the case of our experiment the pure sucroce solution acted as a hypertonic solution.
Hypotonic solutions contain a low concentration of solute relative to another solution. When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode or become turgid. In the case of our experiment the distilled water acted as a hypotonic solution.
Our graph trends show that the weight of the potato decreases as the concentration of the sucroce and the water increases, but after the concentration reaches a point where it is 75% sucroce and 25% water the weight starts to increase causing a slight curve on the graph.
Our graph trends show that the length of the potato fluctuated around 2 to 2.5cm causing a zigzag pattern on the graph. Although our trend does not support the line of best fit, as the best line of best fit as the first two points on the graph are lower than expected.
Evaluation
Our experiment supported the hypothesis however; there may have been ways which we could have improved on our experiment such as:
However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen and possibly find out the saturation point of the potatoes. The range of concentrations was adequate but I would possibly create more ratios if I repeated the experiment so that I would have more varied results, i.e. 20:80, 30:70 and so on. This way would have allowed me to also find out the isotonic point far more accurately.
The cutting of the potatoes was the most difficult part of the experiment as 3 different people were cutting the potatoes to get the 2.3cm in length and 1.5cm in diameter. Each teammate could read the ruler wrong which we measured our diameter and length in, therefore causing some agitation. Next time we can improve on this by just letting one person to cut the potatoes and measuring them rather than having several teammates do the same job at once, or, I would have possibly found a machine to cut the potato as it would ensure that all potatoes would be the same weight and dimensions.
If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time because we might have spent more time drying one potato then the other therefore causing our results to vary.
We did not know how to change our ratios into concentration; therefore this is mainly the biggest error in this experiment. Next time, we can improve on this by managing the time that is given to us better, and get help from someone who has some valid knowledge on how to change ratios to concentrations. Eg: a chemistry teacher.
Class results could have been used to increase the validity of the data collection. However I think that the experiment was successful and I was very pleased with the complete comparison of my results with my initial prediction.
