Investigation:Osmosis In Plants

Method

* First I will cut a potato into chunks weighing approximately 1g, I will weigh the chunks to make sure they are close to this weight.

* Using a syringe I will then put 10ml of the correct concentration of salt solution into a test tube and drop the potato in.

* I will leave the potato in there for 15min, which I will time using a stop clock.

* When the 15 minutes have passed I will use some tweezers to take the potato out.

* I will take off any excess liquid with a paper towel.

* Then I will weigh the potato and record the change from what it weighed before.

* I will then repeat this for each of the concentrations.

We repeated this process twice so that our results would be reliable.

Apparatus

* Scalpel, for cutting the potato into chunks.

* Syringe, for measuring the 10ml of salt solution.

* Test tube, to conduct the experiment in.

* Tweezers, for getting the potato chunks out of the test tube after the experiment.

* Stop clock, to time the 15 minutes that the chunks would be left in for.

* Weighing scales, to weigh the chunks of potato.

Fair Test

I made sure that it was a fair test by making sure that the only variable that I changed was the concentration of the salt solution, which was what I was investigating. I made sure that the size of potato was approximately 1g, and I made sure that I always used the same volume of salt solution, which was 10ml. I also made sure that I only kept the potato in the solution for 15 minutes.

Conclusion

These result show that my prediction is generally correct, as the general trend of the results is for the weight change to start off as a gain with the low concentration of salt solution, and to gain less as it gets closer to 0.5, then to start losing weight after there, until losing it's most weight when the concentration was 1. The trend of the graph is that as concentration increases the change in weight goes from a gain to a loss. There are two anomalies at concentrations, 0.2 and 0.6. At 0.2 there is a average loss of 0.1g and at 0.6 there is an average gain of 0.05g. I think that these were the results because of the principal of osmosis. When the concentration of salt was high, and consequently the concentration of water was low the piece of potato lost weight. This happened because in osmosis the water always moves from where there is a high concentration of water to where there is a lower concentration, when there is a low concentration outside the water moves from inside the cells to outside, so the potato loses weight. And when the concentration of salt is low the opposite happens, this explains the general trend shown by the graph and is what I expected to happen.

Evaluation

I think that my investigation was quite good, although I think it would have been better to take three sets of results I am happy with the two sets of results that I got. I also would of liked to have taken more results, such as the concentration between the ones I took, 0.1, 0.3 etc. I used a syringe to measure the amount of salt solution I used, so I feel this was accurate. As I was measuring the change in weight it was not essential to make the pieces of potato exactly the same size, so I cut it into similar sized chunks and weighed them to make sure they were roughly the same. I used a stop clock to measure the amount of time I left the potato in the salt solution for, I think that this was accurate enough as we were leaving them in the solution for a long period of time so a small variation would make little differences. I repeated the results twice to make sure they were accurate. Most of my repeated results we're close to each other, although the results at concentration 0.2 show quite a large gap between my to tries. I think this may have been caused by an error when reading the stop clock. If I was to do the experiment again, I would change several things. Firstly I would want to take three sets of results to make sure they were more reliable. I would also want to leave the pieces of potato in the solution for longer so any changes would be greater and the results more conclusive.