Investigating the factors that affect water uptake by potatoes

The water is stored in the vacuole in the cell of the potato chip and as that expands then so does the mass of the potato chip.

Method

The following apparatus were used:

• Scales
• Potato chip
• Water solution
• Measuring jugs + beakers
• Thermometer
• Boiling tubes
• Stop clock
• Knife
• Pipette

• Firstly, cut the potato chip to the size 35mm.
• Put the potato chip in a beaker with 30 cubed cm of water in it.
• I will measure the mass of the potato chip before and after I put it in the water.
• Record the difference in mass.
• Repeat the experiment 3 times to obtain accurate results.
• Then repeat the steps above but with salt solution using the measurements above in the table.

I will keep it a fair test by keeping the time of incubation, temperature, size of the potato chip and variety of potato chip the same. I will keep the type of potato the same so that it does not interfere with the results. I will keep the temperature the same by using a thermometer and checking the temperature of the water regularly. I will use a stop clock to keep the time of incubation the same. To keep the size of the potato chip same I will be accurate and use a measuring ruler and a sharp knife.

Trial Run

• Cut the potato chip to the size 35mm
• Measure its mass and record it
• Place potato chip in salt solution
• Leave it in the solution for two minutes
• Remove from the salt solution and record its mass
• Place back in solution and leave for two minutes again
• Repeat this process until you have done this for at least 20 minutes.

I have chosen to leave the chip to incubate for 20 minutes because it has the biggest change of mass.

Conclusion

Generally, the pattern was as the concentration of salt increased the average % change in mass decreased. This can be seen from the line of best fit on the graph. The average % change in mass decreased because of osmosis. This is the movement of water from a region of a high concentration to a low concentration of water through a selectively permeable membrane. Water is needed in plants for photosynthesis and to keep the cells turgid. A flaccid cell is where it is not full of water. In the experiment, the chips vacuole was the high concentration and the solution was the low concentration. When the water in the chips vacuole is removed, the mass of the chip decreases. The water potential of the solution inside the vacuole was 0.32m.

Evaluation

The accuracy of the results were as good as they could have been considering the circumstances and conditions of the experiment. The results were not very reliable because we did not have the time to re-do the experiment more than 3 times. The individual % changes are not very close together, but the average percent change and median percent change are close. An example is the fifth line of results (0.8m). The median is 15.38 and the average is 15.28. Generally, the results did not fit on the line of best fit. The anomalous result (2m) was a freak result. Possible sources of error for it may have been a miss calculation of the mass of the chip. If I were to redo the experiment I would make sure there were more boiling tubes and stop clocks so I could the same concentration more than 3 times. This would have made my results more accurate.