eInvestigating water potential of swede The aim of our experiment was to investigate the water potential of swede and then use our results to help us determine the water potential of plant tissue. This overall flow of water from a dilute area of high water potential to a more concentrated solution of low water potential across a partially permeable membrane is called osmosis.
I predicted that the swede cylinders which are put in a test tube with a low potential of sucrose solution would become turgid because the water molecules that are present in the swede will move away from an area of higher potential of water molecules to an area that has a lower potential of water molecules, this means that the swede sample will gain mass and become full almost to an extent where it is ready to burst.
The swede samples that are going to be put in a test tube with a high potential of sucrose solution will become flaccid because the swede cylinder will have a higher potential of water molecules and so these molecules will diffuse into the sucrose solution as it has a lower water potential, this means that the potato sample will shrivel and loose mass. Equipment * Plant tissue such as swede * 1M sucrose solution * Distilled water * Boiling tubes * Cork borer size No. 5 or 6 * Scalpel, white tile and ruler * Boling rack tube to hole six tubes * Measuring cylinders * 10cm cubed syringes Chemical balance * Tweezers * Labels or Chinagraph pencil/OHP pen * Bungs to fit boiling tubes * Paper towel for blotting To ensure that our experiment gave us the best possible outcome of results and to make sure that we carried out the experiment safely we were extra cautious with the type of equipment we used and how we used it. If we used more than one swede we made sure that the swede was of the same brand and roughly the same size this helped to reduce any errors in our results. We took care with any glassware and cutting equipment that we used to reduce the risk of anyone getting injured.
There were quite a few factors in the experiment that we controlled, for example we put stopper caps on the test tubes to stop the solution from evaporating. Also we used a syringe when measuring the amount of sucrose solution to make sure that we put the exact amount that we needed in each test tube. A top pan balance to 2. d. p was used which meant that our results were more accurate. We also made sure that our experiment was fair by only changing one variable which was the concentration of the sucrose solution and then keeping every other variable the same. ) Prepare a series of six sucrose solutions using 1. 0M sucrose and distilled water to give a range of 0. 0 – 1. 0M 2) Measure 25cm cubed of each sucrose concentration into separate boiling tubes and label with the appropriate molarity 3) Cut six cylinders from a swede using the cork borer. Trim to remove any skin and cut to the same length. 4) Dry the swede cylinders by rolling in a paper towel – the same number of times for each cylinder. For each of the six sucrose bathing solutions, weigh a cylinder on the top pan balance. In a suitable table record its mass against the appropriate solution molarity. ) Using forceps place each cylinder into the correct sucrose concentration and insert the bung 6) Leave the swede cylinders in the test tube for an hour 7) Remove each cylinder from the tubes in the same order that they were put in. Roll each cylinder in a paper towel – the same number of times as in step 4. Reweigh and record the new mass in your table against the correct bathing solution 8) Calculate the change in mass for each cylinder 9) Draw a graph of your processed results showing the intercept. Now work out the water potential value using a calibration table or curve. Join the points with straight lines and do not extrapolate
M| Water (ml)| Measurements before (g)| Measurements after (g)| Overall % change| 0. 0| 25| 2. 09| 2. 28| 9. 09| 0. 1| 22. 5| 2. 00| 2. 15| 7. 50| 0. 25| 18. 75| 1. 89| 2. 05| 8. 47| 0. 5| 12. 5| 2. 09| 2. 18| 4. 31| 0. 75| 6. 25| 1. 90| 1. 90| 0| 1| 0| 2. 16| 2. 03| -6. 02| Our results show us that there is negative correlation between the potential of sucrose solution and the mass of the swede samples decreases, we know this because on our graph we can see that overall the gradient of the line is decreasing which shows that as the potential of the sucrose solution gets higher the average mass of the swede sample decreases.
An explanation as to why some swede samples gained mass and others lost mass is because if the swede samples are placed in a test tube with a low potential of sucrose solution then the water molecules in the sucrose solution will pass through a partially permeable membrane to the swede sample and if the potato samples are placed in a test tube with a high potential of sucrose solution then they will do the opposite and the water molecules in the swede sample will move to the sucrose solution.
There may be some limitations with our results because the recommended time to leave the swede cylinders in the test tube with the sucrose solution was for an hour but we were unable to leave them in there for that long and so that may be the reason why there are some anomalies in our results.
If I was to make improvements to the experiment then I would have took a few more mass measurements for each sample so that my results are more reliable, I would also carry out the experiment on two different substances for example eggs and courgettes so that I am able to study whether osmosis takes place in the same way and I would compare where the two different equilibrium points are.
From my results I can say that my hypothesis was correct because my results show me that the swede cylinders which were put in sucrose solution that was of a low potential became flaccid because the water molecules in the swede moved into the sucrose solution and the swede cylinders that were placed in sucrose solution of a high potential became turgid because the water molecules in the sucrose solution moved to the potato. In the future to study osmosis further i will keep the concentration of sucrose solution the same but place the test tubes in different environments to see whether this will affect how osmosis will take place.