In my experiment I will take some safety precautions: I will ensure that I am careful when cutting the potato with a knife and I will make ensure that the solution is kept away from power sockets. I won’t need to where safety glasses, as I’m not using any hazardous chemicals.
Variables
- For the purpose of my experiment I am going to do all the experiments at room temperature.
- To keep the water potential of the potato initially will be kept the same by using the same type of potato, which have been treated in the same way, e.g. have all been cut without being washed and peeled.
- The mass of the potato is a dependent variable, and this means that it will be measured throughout the experiment. I will measure the mass in grams. The potato chip will be measured before it is put in the solution, and after. This will allow us to see whether osmosis has taken place, and to what extent.
- The volume of the solution that the potato chips are kept in must be fair. The must be totally covered in the solution, and the amount of solution will be kept the same because all the potato chips are the same size.
- I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between scales.
Experiment
Equipment:-
- 15 Pieces of Potato
- 5x Petri Dishes
- Ruler
- Knife
- Cork Borer
- Top Pan Balancer
- 0.2, 0.4, 0.6, 0.8, 1.0 molar Sugar Solutions
- 60ml Measuring Cylinder
Apparatus Set up:
- The Apparatus will be set up as shown in the diagram below.
Method:- (Repeat this process 5 times)
- Prepare 3 pieces of potato using a cork borer, each piece must be 2cm long
- Colour one piece green, another Blue and one leave blank
- Weigh pieces using balancer and record
- Fill a Petri dish with 60ml of either 0.2, 0.4, 0.6, 0.8, 1.0 molar Sugar Solution
- Mark dish showing solution
- Place the lid on and leave for 4hrs
- Remove pieces
- Dry each one off using a paper towel
- Weigh again using Balancer and record
My Prediction
Osmosis is defined as the net movement of water or any other solution's molecules from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other.
For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from a high concentration, i.e. in the water itself, to a low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations.
This diagram shows what I stated in my prediction about the facts of osmosis, the sugar particles can’t pass through the membrane but the water particles can, moving from high to low concentration.
My Results
Analysis
The Graph and curve of best fit show us that in the first two solutions the differences increase but in the 0.6, 0.8, and 1 molar solutions the difference decreases, this backs up what I said in my prediction When plant cells are placed in high concentrations of sugar solutions the liquid in the vacuole moves across the cell wall (partially Permeable Membrane) decreasing the weight of cells, this happens when in hypertonic solution. This makes the cell become Plasmolysed, meaning very floppy and therefore causing the cell membrane to come away from the cell wall. When plant cells are placed in a low concentration sugar solution liquid moves from the solution into the cells increasing their weight.
Turgid is the normal state of cells, if a cell is placed in distilled water the water moves through the cell wall and into the sugar solution in the vacuole, when this takes place the turgid cell expands and expands until it bursts, this happens when in hypotonic solution.
Overall the experiment worked, it shows us what we needed to now and links with my prediction, and we know now that the weight difference and conc. Of solution are not proportional.
Evaluation of Evidence and Procedures
The experiment was performed to the best of my ability and I did everything possible to maintain independent and dependant variables, I also made sure that my method and operating procedure were correct and effective throughout so that I had accurate results. However there were unseen problems in the method of the experiment and the apparatus used.
- The colouring of the potato didn’t really work, only the purple was visible and I had to use my common sense to work out which piece was the one that had been coloured green as it was washed off.
- When drying the pieces I should have made sure the pieces were free of excess solution to maintain fair conditions.
- Next time I'd make sure the pieces in the Petri dishes were in the same amount of sunlight as this could alter the temperature and affect the rate of osmosis.
- When placing the pieces in individually I should have made sure the pieces were not touching and that my fingers didn’t touch the pieces already in the solution.
Overall I think the experiment was a success, I feel that my results were accurate; there are always anomalous results in all experiments.
