Below is the method that I am going to follow through my preliminary investigation.
- I will take a potato and cut it into half
- Using a hole borer I will then take one cylinder of potato tissue from the potato.
- I will then cut the cylinder into four disks and I will then weigh them using an electronic balance. In order to get accurate weights I will weigh the filter paper and the cell sap on it with the potato disk and I will then subtract the weight of the potato disk from the total reading.
- I will then put the potato disks into different tonicity of sucrose solutions.
- I will then leave the disks overnight in the solutions and weigh them again the next day and see the change in the weight.
I will be using the following the equipments.
- A knife
- A tile
- 2* pipettes
- Measuring Cylinder
- Potato
- Hole borer
- Electronic Balance
- Ruler
- Different tonicity of sucrose solution.
- 4* specimen jars
In order to obtain reliable results I will use the above equipments accurately and precisely.
I will make this investigation valid by using the right equipment and by trying and keeping the other possible variables that like the volume of the solution, time- how long I am going to keep the disk in the solution, temperature, and type of potato constant through out the experiment because these variables could affect the process of osmosis in the potato cells
In this experiment use of the equipment is really important and it could affect the results I get. For example if I was supposed to use a blunt knife to cut the potato disks, there is a huge chance that I will rupture the cell membranes of the potato. The ruptured cells of the potato will not take part osmosis Therefore I will be very careful in cutting the disks.
Below is the results table of my preliminary investigation.
Now that I know that the disks of potato has gained weight in the 0 molar sucrose solution and they have lost weight in the 1 molar sucrose solution I have decided that my range of the molarity of the sucrose solution will be between 0 and 1 molar because I want to find out at which molarity of sucrose solution the potato’s weight is unchanged.
Analysis
Although I tried and cut the disks very accurately and made sure that they are of same weight I realise that to make my results more reliable I will find out the percentage change in weight for each of the potato disk. I am going to do this by using the below formula. As I look at the results I obtained and the graph I have plotted, I found that as I increased the molarity of the sucrose solution there was a decrease in % weight gain of the potato disks.
Change * 100
Original
After I have calculated the percentage change in weight I will then plot a line graph of sucrose concentration against percentage change in mass. I will also draw a curve of best fit for this graph.
As I can see from my graph there is pattern in my results. It shows zero change at first and then as I continue to increase the molarity of sucrose solution the percentage in weight is a loss which gets bigger. My graph also shows that after 1 molar of sucrose solution the graph appears to be levelling. This is happens because a point comes when there is no water left in the vacuole because the cell loses it due to osmotic movement of the water out. This causes the protoplast to pull away from the cell wall and the protoplast no longer presses on the cell wall. This point is known as incipient plasmolysis. Any further loss of water causes the protoplast to shrink more and eventually the vacuole disappears completely. This condition is called plasmolysis and the cell is said to be flaccid because there is no water left in the cells.
My conclusion does support my prediction where I say that if the concentration of the sucrose solution is hypertonic outside the cell there will be decrease in weight and vice versa if the concentration of the sucrose solution is hypotonic outside the cell there will increase in weight of the cell and if the tonicity of the solution is isotonic at both sides then there will be no change in weight and like wise my results support my prediction too
Evaluation
The procedure that I have used to obtain the results is quite straight forward yet accurate. I think the results I obtained are reliable and accurate as there are not many anomalous points in my plotted graph and they fit the pattern very closely. I think that this investigation was carried on fair grounds and I tried and kept the controllable variable constant. To support my conclusion I have collected enough evidence, I have collected three readings for each sucrose solution and I have got an average for them. If I was to repeat this experiment again I will use different types of potato for my investigation. This will help me in understanding the osmotic movement in different types of potato.