To find out the concentration of cell sap within the vacuole of a potato cell.

I think that using a 0.1 molar salt solution the weight of the chip will stay the same because the concentration of cell sap in the solution and in the potato chip will be the same so osmosis will not take place and the weight will stay the same. This will be equilibrium.

I think that using a 0.5 molar salt solution the concentration of cell sap in the potato chip will be less than in the salt solution causing the chip to lose water by osmosis therefore losing weight.

I think that using a 1.0 molar salt solution the concentration of cell sap in the potato chip will be less than in the salt solution causing the chip to lose water by osmosis therefore losing considerable weight.

I think using a 2.0 molar solution the concentration of cell sap in the potato chip will be less than in the salt solution causing it to lose a lot of weight. It will definitely become plasmolysed via osmosis removing enough water from the cells to shrink the vacuoles to their point of no return (when they cannot recover) or further. The weight at this point will be at its minimum for the chip under these conditions.

In summary I think a potato chip that is put into a stronger solution will decrease in weight more than a weaker solution because the concentration of cell sap in the potato chip will be less than in the solution causing it to lose weight (losing water) and if it is in a weak solution it will still lose water but will not shrink as much in size as the one in the stronger solution. Equilibrium will be somewhere in the middle.

This is the graph I can expect to formulate from the data I collect.

Apparatus

Measuring cylinder

5-100ml beakers

3 Potatoes

Scalpel

Cork borer (size 5)

Cutting tile

Salt Solution (0,0.1,0.5,1 and 2 molar salt solutions)

Electronic weighing scales

Stop clock

Tweezers

Diagram

Method

Firstly I took a potato and using a size 5-cork borer I extracted 5 chips from the potato. Then using a scalpel cutting on a cutting tile I cut all the chips down to 2.2g in weight measuring with some electronic scales. Then 5 beakers were set up with the following concentrations 0,0.1,0.5,1 and 2. I first poured the salt solution from a big container into a large ready set beaker and from that I poured the various solutions into a measuring cylinder and from they're poured them into the beaker. Then at the same time the 5 different chips were put into the 5 beakers and were left in the solution for 2 hours using a stopwatch to keep track of the time.

After the 2 hours was up the chips were removed from the beakers using a pair of tweezers and then using the electronic scales the chips were measured and results put into a table.

After the experiment was finished it was then repeated twice more giving me 3 sets of results. The results were averaged and then a graph was formed from that.

For a controlled experiment the things I kept the same were:

A) Temperature

All results were collected at room temperature (20-22 degrees Celsius). I kept the experiment at room temperature by doing all of my results on the same bench in the biology lab.

B) Volume of salt solution

I used a volume of 25ml of salt solution for every result I assured this by using a measuring cylinder for every volume of salt solution.

For safety I always held the scalpel away from myself and used a cutting tile so I didn't pierce the bench. I also acted sensibly with all my equipment for the experiment and never behaved irresponsible or irrational in any way.

Evaluation

Overall I think my measurements were fairly accurate but could be improved if I did the experiment again. In pouring the different concentrations of salt solution I used a measuring cylinder which was accurate to + or - 1 ml. As the measuring cylinder was used for all the concentrations in between pouring the solutions I didn't have time to wash out the measuring cylinder so the salt solution left on the side could have affected the concentration of the salt solution poured in but only slightly.

In the timing and in keeping track of the 2 hours the stop clock was accurate to 0.01 of a second. Its all well being able to keep time to 0.01 of a second but it took me 10 seconds to take out all the chips and place them on paper towels. The electronic scales were accurate to 0.01 of a gram and using the scalpel I could actually thinly cut off potato to the weight of 0.02 of a gram. On all 15 occasions all the chips were cut to 2.19, 2.20 or 2.21 grams.

I made sure that there were no chips with any skin on them and all the chips were roughly the same length but as I was measuring weight and I wasn't to conscious about the length I didn't measure the chips with a ruler. As 1/3rd of the experiments was done on 1 day and the other 2/3rds on another day (the experiment was done 3 times so 1/3rd was 1 experiment) the temperature might have not been the same. Also if the beakers were left next to an open window the draught could have affected the temperature.

I used a size 5-cork borer, which was the same for every experiment. I used 1 potato for 5 chips so differences in the potatoes could have affected some things. As I did 1 experiment on 1 day and 2 on another the potatoes used could have been grown in a different area, which had different things in the soil (higher or lower ph).

I had 1 piece of anomalous data for which I have no explanation other than the experiment was done on a different day so maybe the room temperature on those separate was different? I redid this set of results 3 more times and added the results to the table and to the graph. I have also circled the piece of anomalous data on the graph and also highlighted the data, which was redone.

If I did the experiment again I would use a more accurate measuring cylinder, which reads to 1/2 an ml. I wouldn't use a more accurate clock as taken into account the 2 hour time span a second would not really make a difference but I would use four other people to take the chips out of the beakers at the same time. Using a scalpel I don't think I could have cut the chips any more accurately so a more accurate set of scales would be of no use unless I used some sort of sophisticated machine to cut the chips. I would do all the experiments on the same day instead of doing them spread over 2 days as that caused a number of problems (temperature, different potatoes).

If I did the experiment again I would also measure the difference in length as well as weight and how temperature may affect the experiment by heating the salt solution before the potato chip was put in it. I would also try more concentrations of salt solution using more varied concentrations (e.g. 0,1,2,3,4,5...) and less varied concentrations (e.g. 0.1,0.2,0.3,0.4,0.5...).

I don't think there were many inaccuracies in my method, the only one I can think of is the removal of the chips from the beakers after 2 hours and having to do it one after another and not all together.

I am quite confident of my results as I collected them to the best of my ability under the circumstances

Analysis

In my results the mass of the chip in the 0 molar went up by 0.2 grams because the concentration of cell sap was higher in the potato chip causing the water from the 0 molar solution to move into the potato by osmosis causing its weight to increase. The 0.1 molar solution caused the chips to stay the same weight because the concentration of cell sap in the solution and in the potato chip was the same so osmosis could not take place and the weight stayed the same (therefore equilibrium is reached using a 0.1 molar solution). At 0.5 molar the chips went down by 0.7 grams but when I repeated this, as the data was anomalous the chips lost 0.5 grams in weight. This was because the concentration of cell sap in the potato chip was less than in the salt solution causing the chip to lose water by osmosis therefore losing weight. At 1 molar the chips lost 0.8 grams because the concentration of cell sap in the potato chip was less than in the salt solution causing the chip to lose water by osmosis therefore losing considerable weight.

At 2 molar the chips lost 0.9 grams because the concentration of cell sap in the potato chip was less than in the salt solution causing it to lose a lot of weight. It became plasmolysed via osmosis removing enough water from the cells to shrink the vacuoles to their point of no return (when they cannot recover) or further. The weight of the chip at this point was at its minimum for the chip under these conditions.

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Conclusion

In my experiment equilibrium was reached using a solution of 0.1 moles indicated from my graph and from the table of my results. Therefore as I have evaluated everything thoroughly I agree with this. Equilibrium is reached at 0.1 molar.