For this experiment I will be changing the concentration of sucrose to find out roughly what concentration is inside the cells. The rest will stay the same bar the mass which will vary for each chip but won’t effect the experiment because all I need to do is work out the average mass for three experiments.
Preliminary experiment.
Before starting my experiment I needed to sort out what size chip I would need and what range of concentration I would use. In did this by setting up an experiment and then putting the results into a table and using that information to answer my questions. I left the chips in for thirty minutes. These were the results:
Therefore I will be using big chips because in the above results they showed a better increase and decrease in solution, which will be better to see a difference with when it comes to the actual experiment. I will be using 0M and 1M as the highest and lowest concentration because they show very different changes in mass with 0.2M, 0.4M, 0.6M and 0.8M being the other concentrations because these will show how the mass will change between the highest and lowest points.
Apparatus.
We used this apparatus because it helped us do our experiment.
Method.
- 6 fat chips were cut to exactly 4 cm long using a sharp scalpel on a white tile.
- 20 cm3 of each of the following solutions were measured using a clean syringe for each one: 0M, 0.2M, 0.4M, 0.6M, 0.8M, and 1M.
- The solutions were then put into 6 labelled boiling tubes.
- Using a set of top pan balance scales the 6 chips were weighed separately and the mass for each one was recorded.
- Each chip’s mass was written onto a solution/boiling tube, to know what the mass change was when the chips came out.
- The chips were then put into the boiling tubes and the stop clock was started.
- The chips were then taken out after 27 hours and the chips were then cleaned and then the new mass of each chip was recorded.
- This experiment was then repeated another 2 times to get 3 sets of results in total to get a suitable range of answers.
For prediction please turn to next sheet.
Prediction.
The pink line above the concentration line shows that the mass of the potato chips has increased at each point but as the concentration increases the amount in which the mass increases declines. The chip is fully turgid at the highest point meaning it can’t take any more solution in. This means that the concentration of the solution was higher (or weaker than the concentration of the solution inside the potato chips.
The purple line below the concentration line shows that the mass of the chip has decreased more as the solution increases but starts to curve towards the bottom because it won’t be able to loose any more mass because only the sucrose is taken out but the bulk of the chip still remains. The chip is plasmolysed at the lowest point on the graph meaning it has very little to no solution left in it.
The circled point where the two coloured lines cross the concentration line is where the chip won’t change mass and the sucrose solution is even in and out of the cell.
Results.
Conclusion.
The graph starts at a high point on 0M but as the concentration of the sucrose solution increases the percentage change in mass decreases, the mass then starts going into the minus numbers just before 0.4M according to the results recorded, meaning that 0.2m is still in the plus percentages but is a decrease in percentage from 0M showing that overall the mass decreases as the concentrations increase then the mass starts to level out at the bottom because the mass can’t decrease any more.
At the first point of 0M, the percentage change is 19.75% above 0% meaning that the mass has increased in the chip because the sucrose solution (0M/water) is a weaker solution than the cell sap meaning that the sucrose is diffusing into the cells to put more water into them. The increase in percentage for 0.2M is less then the increase in mass for 0M by 12.95%, meaning that this solution is a closer concentration to the cell sap meaning the cells haven’t taken in as much solution. But 0.4M is the closest because it is the nearest percentage to the concentration line, which is where the line would cross 0% meaning that the chip would loose no mass and therefore the concentration on the line of best fit that goes through the concentration line is the same concentration as the cell sap. On my graph this concentration is about 2.7M.
My prediction agrees with my results almost perfectly. The only difference is that I put it curved at the top as well as the bottom on my prediction graph but apart from that the lines have similar structures. Also the scale and the point at which the line crosses the concentration line has changed slightly but I had foreseen that because I had done the prediction so that it went through the middle like it was a perfect example of what I expected to see.
Evaluation.
The pink and green results highlighted in the results table are anomalous or inconsistent with the other results. The pink results is wrong most probably because I didn’t clean the excess sucrose off the chip before weighing it, therefore giving it more mass because of excess sucrose. The green result is the exact opposite in that I probably squeezed the chip too tight and compressed it so much that solution from in the chip came out, then I cleaned it making the mass less than the others. The other odd result highlighted on the graph is anomalous because it is much further away from the line of best fit than the results that are virtually touching the line.
My results were overall very reliable and this can been proven by two things:
- By looking at the closeness of each set of three results – if most of the results are close together then this is a sign that it is reliable.
- By looking at the closeness of averages to the line of best fit.
Now if you look back at my results table you can see that I have only two anomalies and the rest are close together showing that this is reliable data. Then if you look back at my graph you will see that there is only one major anomaly that is quite far away from the line of best fit again showing the data’s reliability.
The method was flawed in the way that all the chips got slightly different times in the solution and different treatment when they were taken out e.g. cleaned differently, like being squeezed or not being cleaned of excess sucrose well enough. Also, because it was I who cut the chips with the scalpel and ruler it may not have been accurate enough and not exactly the same size and shape because of the difficulty of the equipment. Another thing would be the measuring of the solution where a syringe was used, for a syringe is not very accurate and can be off.
If I could redo the experiment I would use more stop clocks (one for each solution) and dry the chips more carefully and more ‘in depth’ by dabbing it until it doesn’t make a water mark on the paper towel. I would also use a sharp knife instead of a scalpel because it is longer and can cut more chips at one time. I would also use more rulers around the chips like to box them in so as to make the chip’s size more accurate and when measuring the solutions I would use a more precise measuring instrument like a mm measuring cylinder that leaks the solution through bit by bit.
This would mean that the results would be more reliable in the way that the chips masses would be more accurate to start with and at the end too. It would also make the average percentage change in mass more accurate because the chips would be more similar and not almost similar.
By changing the variable form concentration to something else you would get different results for a different prediction because it wouldn’t be to see what the concentration is in the potato chip. Here is an example; for this example I will change the time in the solution to see how long before the potato chip couldn’t diffuse any more of its solution. In this experiment I would set up 10 or so beakers of one fixed concentration and set them off at the same time but take the chips out of the beakers at different times. I would then repeat this several times and then do the same write up as above changing the correct pieces to make sense of the experiment.
