Justification of hypothesis: -
I am sure that my hypothesis is correct because if there was no sugar solution and only distilled water, the cells of the potato will become turgid as the water diffuses into the cells. If there is more sugar than water i.e. higher concentrated sugar solution, the water in the cells will diffuse out as the cells tries to keep both its internal and external conditions the same. As osmosis is the net diffusion of water molecules, sugar molecules will not be able to move out or in to the cells. The term flaccid means that the cell looses water so there is less pressure pushing upon the cell wall so the cell is said to be plasmolysed. The term turgid means that there is more water inside the cell which is pushing upon the cell wall. The cell does not burst as it has a cell wall.
I have arrived to all these conclusions from reading the textbook Longman GCSE biology and also researching on various websites on the Internet.
This is what a turgid cell looks like. This happens when there is a higher concentration of water and a low concentration of sugar solution.
This is what will start happening to the cell when there is a higher glucose concentration outside and a low water concentration. This is the start of the process where the cell becomes flaccid.
This is what the cell will look like when it has become flaccid. When this happens it is said to be plasmolysied.
APPENDIX 1: -
Preliminary Work:-
Earlier on I carried out a preliminary study to find out a few things that would help me decide what I am going to use in my main experiment. Below is a list of things I used this study to find out: -
- How much time I needed to let the experiment go on
- Decide what concentrations of sugar solutions I am going to use
- How I am going to measure the mass of the potatoes
- The temperature
- The type of potato I would like to use
- Equipment I use to make the experiment a fair test
In my study I used only two different glucose concentrations. I used a 10% glucose concentration and a 1% glucose concentration. I timed the experiments for 10 minutes. I found that in both cases the mass of the potato cell reduces. The table below shows the results I got.
From the results on this table we can see that with a 10% solution the mass loss of the potato cylinder is greater than the mass of the potato cylinder from the 1% solution.
Bibliography-
Book Name: - Longman GCSE biology
Authors: - Bradfield, Phil & Potter, Steve
Page no. 134 – 135
Edition: - 2003
Method
To investigate the effects of glucose concentration on osmosis in potato cells:
Apparatus list: -
- Potato
- Blade
- Cork borer (5 mm)
-
Stop watch (100th of a second)
- Glucose solution (0.001%, 0.01%, 0.1%, 1%, 10%)
-
50cm3 Measuring cylinder (to the nearest cm3)
-
Electronic Balance (scale in grams)(to the nearest 100th of a gram)
-
Five 200cm3 beakers
- Forceps
- Labels
- Water bath (40 degrees)
- Ruler (to the nearest mm)
Actual Method: -
I carried out the experiment according to my plan. Using my cork borer, I cut 5 different holes in the potato to obtain potato cylinders. I used the electronic balance to measure the mass of the potatoes and noted the masses down in a table similar to the one show in the plan. Using the measuring cylinder I measured 20cm3 of sugar solution and found it to be too little, so had to measure 30 cm3 more to make the sugar solution to 50cm3. Got the stopwatch ready to time and slipped the potato cylinders into the beakers and started the stopwatch and then took the beakers to the water bath. I had planned to keep the water bath at the temperature of 35 degrees but as many other people in the class were doing the experiment I had to use 40 degrees. According to the plan I timed the experiment for 15 minutes. After 15 minutes I removed the solutions from the water bath and then removed the potato cylinder from the beakers one by one using the forceps. I wiped off the excess sugar solution off the potato cylinders using paper towels. I then measured the mass of each potato cylinder and noted down the masses on the table. I then calculated the mass differences of each experiment.
For the second time, I had to use a different potato as I was doing it on another day. I repeated the same process I had used for the previous day. After I had noted down the masses after the experiments I calculated the change in mass of the experiment. After doing that I drew another table and filled in the results neatly and this time I calculated the percentage change in mass which I got by dividing the change in mass over the original mass multiplied by hundred. After doing so I drew a graph of percentage change in mass against percentage sugar solution.
Changes from Planned Method
- Instead of using 2%, 4%, 6%, 8%, and 10% sugar solutions as planned, I had to use 0.001%, 0.01%, 0.1%, 1%, and 10% sugar solutions, as they were not available.
- Instead of using just 1 potato I had to use two different potatoes as we were doing the experiment over 3 days so we did not really have a chance to use the same potato.
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Instead of using just 20 cm3 of sugar solution I had to use 50 cm3 as I found 20 cm3 to be too little.
Hypothesis
Osmosis is the net diffusion of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane. With this statement my hypothesis is that the mass of the potato cylinders will decrease because the concentration of the sugar solution outside the potato cell is higher than the one inside the potato cells. Therefore osmosis takes place and the water inside the potato cell that has a lower concentration diffuses out of the potato cell through the partially permeable membrane thus making the cell flaccid. If the amount of water particles is higher outside than inside the potato cells then the water molecules will diffuse into the cell making it turgid and thus the mass will increase.
Justification of the Hypothesis
I am sure that what I said in my hypothesis is correct because if there was no sugar solution and only distilled water, the cells of the potato will become turgid as the water diffuses into the cells. If there is more sugar than water i.e. higher concentrated sugar solution, the water in the cells will diffuse out as the cells tries to keep both its internal and external conditions the same. As osmosis is the net diffusion of water molecules, sugar molecules will not be able to move out or in to the cells. When this happens the cell becomes flaccid. The term flaccid means that the cell looses water so there is less pressure pushing upon the cell wall so the cell is said to be plasmolysed. The term turgid means that there is more water inside the cell which is pushing upon the cell wall. The cell does not burst as it has a cell wall. The mass of the potato cell would increase if the cells became turgid as they took in more water. The mass of the potato cells would decrease if the cells become flaccid, as it has lost water.
Table of Results
Below are the table of results for the experiment I carried out.
Analysis of Results
As it can be seen in the graph and the table of results, it can be seen that the percentage mass change is higher in the experiment with the weaker percentage sugar solution. This also proves that my hypothesis is correct. I believe this is because the 0.001% sugar solution contains more water particles than sugar particles. It is because of this osmosis takes place. Osmosis is the net diffusion of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane. The water molecules from the sugar solution diffuse into the potato cells. This makes the cells turgid. A cell is said to be turgid when the pressure inside the cells pushes against the cell wall of the cell making the cell turgor. It can be seen in the graph that the experiment with the 10 % sugar solution has lost mass. I believe this is because there are less water particles in the sugar solution than in the potato cell. So the water in the potato cells diffuses out of the potato and into the sugar solution. When this happens the cells become flaccid. This happens when water is lost by osmosis and the cell decrease in volume and the cytoplasm no longer pushes against the cell wall. Eventually the cell contents shrink so much that the membrane and cytoplasm split away from the cell wall and gaps appear between the wall and the membrane. When this occurs, the cell is said to be plasmolysed. I have noticed that I have two anomalous results in my graph as I had drawn the line of best fit. These anomalous results are justified in the evaluation.
Evaluation
I am fairly sure that my results are reliable as they proved my hypothesis but I had two anomalous results. I think this is because as we did the experiment over 3 days, we did not have a chance to use the same potato as I had planned to do. All potatoes do not have the same tissue structure and also concentration of sugar in different potatoes is different. I am sure that excess solution cannot be the reason for anomalous results because I wiped it off before I measure the mass of the potatoes. I believe that another reason for there to be anomalous results is that as I was the only person working on the experiment, some of the experiments stayed in the solution longer than the others. I believe this can affect the reliability of my results. Lastly I think that if I was provided with better equipment to work with than I could make this experiment more accurate and reliable. Below is a graph to compare the reliability of my results. Below is a graph comparing the results of the two experiments I carried out.
From the graph above I can see that my results are reliable as both the lines are very similar.
My results could be improved if I was able to use a larger range of concentrations and have smaller intervals with in then. I would have also liked to carry out the experiment for a longer time so that I could have larger figures to which I could work with. I could also repeat the same experiment but this time with different aged potatoes so that I could compare the result of both experiments.
Bibliography
Book Name: - Longman GCSE biology
Authors: - Bradfield, Phil & Potter, Steve
Page no. 134 – 135
Edition: - 2003
Websites: -