Investigating The Effect Of Osmosis On Plant Cells And Tissue

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Investigating The Effect Of Osmosis On Plant Cells And Tissue

Planning

I am going to investigate the effect of varying concentration of external sugar solutions on the amount of osmotic activity between the solution and a potato core of a given size.

To create a fair test certain aspects of the experiment will have to be kept the same, whilst one key variable is changed. If this experiment is not a fair test, I will be obtaining the wrong results which could lead me to the wrong conclusions. As I have written above, I have chosen to vary the concentration of the sugar solution.

The first and most important thing to do is to get the measurements of the solutions and the mass of the potato cores as exact and as accurate as possible. This will be done to every single potato core. I will use a ‘size 6’ cork borer (for all the potato cores taken out to make it a fair test) to get the potato cores out of the original potato. The cork borer produces almost perfect cylinders which make it a lot more accurate to work with, rather than having potato cores which aren’t the same width or aren’t similar in shape. I will be evenly cutting the potato cores with a scalpel to make them as equal in length as possible to make it a fair test. I will explain how the length will effect the effect of osmosis below.  I will also be measuring the length to the nearest millimetre. If any of the non-variables are not kept constant , it would mean it would not be fair test. If we take the potato core for instance. If the potato core was taken out with different cork borers, it would mean that the potato core would be a different width, or if one potato core was longer than another potato core, there would be an increase in surface area which would therefore mean that there is more surface area for osmosis to occur which would either mean that the potato core would be heavier than it should be or lighter than it should be.

I am going to use the same top-pan balance to weigh my potato cores. The reason being that the measurements may slightly vary between scales. I am going to place a petri dish on the scale which I will use to weigh my potato cores on. This is to prevent any contamination. Weighing the potato cores on the scale straight after each other will not be suitable seeing that there may be substances on one potato core which may pass on to another potato core, which can affect results. It will be unsuitable for me to wipe a wet cloth on a top-pan balance, but a petri dish can be easily washed and wiped clean after weighing each potatoes core.  

The potato cores fully covered in the sucrose solution is also another vital part in order to make this experiment as fair as possible. This is because if the potato core is not fully covered by the sucrose solution, the effect of osmosis will not occur to its fullest and I would get different readings (of the mass) for each potato core, which will also make the test unfair. Therefore, I will use 20dm3 of each concentration of solution for each potatoes core. Carrying out the experiments in a constant temperature environment is very important. The temperature may affect the reliability of the experiment, for example, at extreme temperatures the cells of the potato may die and at less extreme temperatures the experiment may be speeded up compared with at high temperatures.. To prevent this from happening, all the test tubes will be situated in the same location (at room temperature). However, this may not produce a constant environment, but I will try and make the test as fair as possible.

Getting and experimenting with the exact measurement of concentration of sugar solution is extremely vital to the experiment. If the volume of one solution in a test tube is higher or lower than another, it will affect the pattern of results. For example, if the volume of solution is higher than the others, it would be quite likely that there will more osmosis occurring seeing that there is more sucrose solution, whereas if there is less volume of solution in the test tube,  not as much osmosis will occur. Again, however, this may not always be true. I can always find out by actually doing an experiment where I put two potato cores of the same length in separate test tubes in the same concentration of sugar solution but with a different amount. For example, one potato core can be put in a test tube of 10ml of 1.0M of sugar solution and one potato core can be put in a test tube of 25ml of 1.0M of sugar solution.

Starting my stop watch as quickly as possible is another important factor to consider. My stop watch should start as soon at the potato cores are put inside the test tube, and stop the watch as the required time for osmosis to occur finishes. The duration of the length of osmosis to occur will be dependent on my preliminary results. Whatever I will decide, I will be leaving the potato cores inside the sucrose solutions for the same amount of time for each concentration of solution. I can ensure that each potato core will be left in their solution for the same amount of time by putting the potato cores in their solution in at the same time and leaving them for a specific period of time and then taking them out them out at the same time. Stopping the watch, talking the potato cores out and weighing their mass in less than a minute is extremely hard to do seeing the  amount of top-pan balances available. There is also too many sets to go through in such a fast time, I will therefore try my best to weigh the potato cores as quickly and as safely as possible.

Equipment Necessary For The Experiment

Scalpel-to cut the potato to equal lengths (a scalpel cuts accurately).

Cork Borer-to take out the potato cores from the original potato.

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Top-Pan balance-to weigh the potato cores.

Two potatoes to provide the potato cores, five different concentrations of sucrose solution; 0.2M, 0.4M, 0.6M, 0.8M and 1.0M. (0.0M is just dilute water). Distilled water-to make the different concentrations. .

Labels for the test tubes(18 labels)-labelling each test tube would prevent any                                                    confusion in which concentration each test                                                        tube is and which test tubes are mine.

Test tube rack for each molarity level(5 test tube racks)-This is to avoid any confusion ...

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