Investigate the transportation of water in living cells through the process of Osmosis

         To make this experiment a fair test, I will have to make sure the weight of the each potato will weigh the same, by weighing each chip on balance scales, 2.5grams, that the total amount of solution for each sample will be the same amount, 20ml, by measuring the solution accurately, with a syringe or measuring cylinder. The concentration of the solution in each sample will be different to a different mole. This is the only factor that needs to be changed. I am going to try and measure the weight of each chip and the amount of solution for each sample the same, to make it a fair test. I plan to make 18 measurements in total, so I’ll have to do three lots of six batches, to try and get a more accurate result. So if the two results for the 1 molar sample, had a huge range, then I can look at the third result to see which of the first two results was wrong, and if something had gone wrong during the experiment.

Hypothesis:

I predict using my own knowledge and from information that I have gathered, form textbooks, the Internet and other books, I can make a prediction of what will happen in result of the experiment that I will carry out. I predict that the solutions with a high concentration of water, the potato chip’s mass will increase. The solutions with a low concentration of water will have a decrease in mass. If left long enough, you probably would be able to see the potatoes shrivel up or swell. My graph, I predict will look similar to this, if my results are accurate.

I predict this will happen because, when the solution outside the cell is as of a greater concentration of water than the cell itself, the cell will take in water. This is called a Hypertonic Solution. The water molecules can pass through the cell membrane in both directions, in and out, but more water will come into the cell than out, making it swell or turgid in plant cells, this is good for giving support to the plant, and for opening stomata. The water molecules move in out of the cell, trying to act like it’s evening out the concentration on both sides of the membranes. The opposite happens if the solution outside the cell is as of a lesser concentration of the cell itself. This is called a Hypotonic Solution. It will shrink or become flaccid in plant cells. When the concentration inside and outside of the cell is the same. This is called an Isotonic Solution. The same amount of water moves in and out of the cell, making the cell stay the same.

Equipment:

• Balance Scales                      

• Measuring Cylinder
• Syringe
• 18 test tubes
• 4 test tube racks
• Stopwatch
• Borer Cork
• Scalpel

• Sugar solution
• Distilled water
• 3 Medium potatoes
• Tile
• Paper Towels

Table of how to make the solutions needed:

Method:

1. Label the test tubes, 1m, 0.8m, 0.6m, 0.4m, 0.2m and 0m on six of the test tubes and repeat with the other 12 test tubes, so you should have 3 sets of test tubes labelled.
2. Place the test tubes, in descending order to their molar.
3. Place the appropriate amount of sugar solution and water in each test tube according to the concentration of the wanted solution. (Look at table above) I am going to use 20ml of solution in total in each test tube. Use a measuring cylinder and syringe to measure it accurately!
4. Put the borer cork into a potato, make sure hands are well clear, from the end of the potato, which the cork is going to come out at. Take out cork, and push chip out and place on the tile.
5. Place each chip on the balancing scales in turn, and weigh each one, making sure each one weighs 2.5grams. Use scalpel to cut chips to right mass, BECAREFUL WHEN USING THE SCAPEL!
6. Place one chip in each test tube, try to make sure, you drop them in roughly at the same time.
7. Start the stopwatch and leave potatoes in there for an hour.
8. Drain the solution from each test tube and weigh each of the chips in turn and record the results.
9. Repeat steps 4-8 twice to get two more sets of results.

Results Table:

My graph shows me, that more sugar in the solution, the less water is taken from the potato. The lines on the graph are decreasing, but not dramatically, as the amount of sugar is increasing. The lines are not straight, especially towards the end.

Conclusion:

From my results and graphs I can draw up a conclusion on my experiment, that, the more sugar, the potato decreases in mass. My graph shows, as the amount of sugar increases in the solution, the mass of the potato decreases and when, the amount of sugar is less, the mass of the potato increases. As when, the solution was 0m, the mass of the potato was, on average, 2.76g, when the solution was 0.6m, the mass of the potato was 2.18g, and when the solution was 1m, the mass of the potato was 1.96m. This shows that the graph is decreasing as the mole of the solution goes up.

         From my graph, I can see that there are three results, which I think are wrong. I think this because, the graph should be gradually descending as it goes along, but there are two points, which see two of the lines, going up and then back down again. On the 1st batch, the 0.8m result seems to be wrong, as it went from, 2.23g to 2.31g, then back down to 1.94g, it should go down from 2.23g, then down to 1.94g. On the 3rd batch, 0.8m or the 1m results are wrong, as the line goes from; 2.10g right down to 1.75g, then back up to 2.05. So one of these results are wrong. I think that they are wrong, due to inaccurate weighing of the chips perhaps, I should have wiped the surface of the scales each time, before weighing, to get rid of any excess potato remains. There may have been an inaccurate measurement in the solutions, which might have caused these wrong results.

         My results showed that, there was an increase in mass when the solution was 0m and 0.2m, which shows me that, the less sugar there was, the potato’s mass increased. The rest of the potato’s mass decreased. The percentage increase for 0 and 0.2m was 10.4% and 4.4%. My results showed this, because of how osmosis works. When there is more water outside the potato than inside, then the potato will take in more water, making it turgid. My results showed this, the mass of the potato, where there was more water outside it than inside, did increase.

         In my hypothesis, I predicted that the potatoes in a solution with more sugar, will have a decrease in mass and the potatoes in a solution with less sugar will have an increase in mass. This is because osmosis is the movement of water through semi-permeable membrane from an area with a high concentration of water to an area with a low concentration of water. My hypothesis was correct; as this is what my results had proved to show, apart from the 3, perhaps wrong results that I had collected. Also, the 0.4m results, all 3, showed a decrease in mass. The 0.4m has less sugar than water, therefore there should be an increase in mass instead. This makes my predicament wrong, but I think it’s perhaps the amount of water and sugar was quite close in amount, in the solution, that this occurred, or perhaps, it’s because I didn’t leave them for long enough for the process to really start happening. My graph showed, that the more sugar in the solution, the mass of the potato decreased, which backs up my hypothesis.

Evaluation:

I think that my results weren’t as accurate as it could have been, this is due to the fact, that I had three results, which weren’t right and the range between some of the results were quite large, e.g. 0.13g. My measurements, I think, are quite accurate, I measured using measuring instruments and carefully measured them, but I noticed on one of the batches, that one of the test tubes, had more solution in it than the others, so I measured it again, and this time it was the same as the rest of the test tubes. To make it more accurate and to stop what I did from happening next time, I could make sure that the syringe was completely empty before adding the next lot of solution. I could make sure that the balancing scale was wiped clean, so there is no excess weight to interfere with the results. I could have weighed the potatoes at the same time, rather than weighing 1 and then leaving the others being exposed to the air, this could have an affect on the results, but this would be quite difficult to carry out, I would probably need some help from others.

         I think that my experiment was designed well enough, to bring me accurate results, though I think that my experiment wasn’t carried out well enough to bring me accurate results. I think, for the 3rd batch, I didn’t, perhaps leave the potatoes in there for long enough, as the stop watch only went up to 25 minutes and then resets itself, which meant, I lost track of time for that batch, so I had to estimate as best as I could when an hour would be over. Also, that leads me onto the next point, which is, that in my planning for the experiment, I intended to leave the potatoes in the solutions for at least two hours, but due to the time restraint, I could only leave them there for an hour.

         If I had to do this experiment again, then I would definitely leave the potatoes in the solutions for at least 2 hours, if not longer.  This would then give me a better set of results to draw up a more accurate conclusion. I would also make sure that I would get a better timer, to time how long I leave them for. I could do the experiment four times in total, to try and get a better average.

I could also have a look at how the temperature might affect the speed of osmosis. Molecules move faster at a higher temperature, therefore it could speed up the rate of osmosis. So I would have to record the surrounding temperature and do another batch somewhere with a higher/lower temperature to see if it makes any difference at all. This will then enable me to plan my experiment more carefully and to allow more accurate results. I could also see how different varieties of potatoes, grown in different surrounding environments can affect the outcome of the results. I could do a separate experiment for this, which then can lead me back to my original experiment to put these factors into perspective, so I can consider them, while doing the experiment again.

   ( Search for OSMOSIS)

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 SCHOOLS/GCSEBITESIZE/BIOLOGY 

Comptons Interactive Encyclopedia

Encarta

Nelson Balanced Science- The Living World    

Covent garden books- The Science Encyclopedia

Class notes

AQA Revision guide

CGP Biology Revision Guide