What unit I am choosing to do for the next experiment?
I chose mass, because on the results table it shows that the % change in mass is far more obvious than the % change in length. In the % change in length table, we can see that in two out of three test tubes, the % change in length is zero. The unit mm is still far too big for this experiment. As for the % change in mass table, we can see that all three test tubes have a more accurate and clear number to show the difference between how it started, and how it ended. The unit mass is detailed and precise enough for the experiment, and makes our result more obvious. Therefore, for the next experiment I am choosing change of mass in a plant cell in osmosis to do as a study.
Also, on the next experiment I will use 7 different solutions: water, sucrose solution 0.2M, 0.4M, 0.6M, 0.8M, 1.0M and 1.5M since it seems enough to make a graph showing the trend of the change in mass of a potato due to osmosis.
Hypothesis
According to my results, I predict that in the next experiment, when potato chips are put in weak solutions, they will gain mass and become turgid because that was what happened with distilled water and weak sugar solution. A gain of mass occurred because of osmosis there. The very weak solutions had high water potentials as the potato has low water potentials. The water molecules diffuse from a high water potential to a low water potential. The water from the solution has travelled through the partially permeable membrane into the potato cell, thus making the potato gain mass as the cytoplasm and vacuoles have swollen.
On the opposite, I predict potatoes in concentrated solutions will lose mass due to osmosis because the very concentrated solutions have lower water potentials than the potato cells. Also, plant cells plasmolyse in concentrated solutions. On my results above, it shows that in strong sugar solution the potato cell has lost mass, which proves this statement true. The potato cell has lost water as it has diffused out of it through the partially permeable membrane into the solution, hence the cytoplasm and vacuole shrinks and the cell becomes flaccid.
Osmosis Plant Cell Experiment
Aim
I will be investigating the effect of osmosis using different concentrations of glucose solution on plant cells. (A potato for example in this case)
Apparatus:
Potato
Test Tube
Knife to cut potatoes
Ruler to measure potatoes (mm)
Scale (to weigh potato chips in grams)
Measuring cylinder
Beaker
Test tubes
Sucrose solutions (Mol) 0.2M, 0.4M, 0.6M, 0.8M, 1.0M, 1.5M
Water
Variables
Controlled Variables: type, size & length of chip/potato, volume of solution, time. Factors to keep it a fair test
-use same type of potato (preferably the same potato to keep fair test as it will have the same concentration)
-use a borer is used to make the chips into the same diameter.
-use a ruler to measure all their lengths in millimetres (rather than cm, because it is more precise) to make sure they are the same length which is 20mm. Keeping the length and diameter approximately the same will help ensure that the mass weighed later would all be within a range.
-pour 80 ml amount of water or sucrose solutions (using a measuring cylinder) into each test tube to make they contain the same volume of solution.
-leave chips in the solutions for 60 minutes using a clock. (no need for something as precise as stop watch, as the chips are to be leaved for around 60 minutes which is long enough to be a fair test)
-keep potatoes in the solutions at room temperature (23°C)
Independent Variables: The solutions
-pour different solutions: water, and 6 other different concentrations of sucrose concentrations in Mols: 0.2M, 0.4M, 0.6M, 0.8M, 1.0M, and 1.5M. (This is so that I can compare with how osmosis affects a plant cell, from weak to strong. Also, there are 7 different solutions, which gives me a range big enough to plot onto a graph and show the trends enough clearly.)
Dependent variables: Measurement of mass of the potatoes
-weigh the chips on a scale before putting in solutions.
-weigh in grams, all into two decimal places as it is precise enough, and only the most precise the scale used can get.
- weigh potato chips again and it will change according to how effectively the different solutions have acted upon it through osmosis. (I cannot control this as this is depending on the independent variables.)
Method:
-Make potatoes same diameter with a borer
-Cut 21 pieces of potato chips to all the same length in millimetres (20mm)
-Weigh all the potato chips on a scale using grams (g) to 2 decimal places
-Record the masses
-Pour the same amount of 7 different solutions (0.2M, 0.4M, 0.6M, 0.8M, 1.0M, 1.5M sucrose solution & 1 water) into 7 test tubes using a measuring cylinder (8 millilitres). All the solution’s temperature are kept the same (room temperature, 23°C) to keep fair test
-Put 3 chips in one group, each marked with an individual mark in the group to help later identify which potato is which (There will be 7 groups of 3)
-Put a group of 3 chips into each test tube with a different solution
-Leave for a few hours, all the same time to keep it a fair test
-Weigh on scale and record the final mass using grams (g) to 2 decimal places
Analysis
According to my results, osmosis did occur. Evidence is shown on my results and seen clearly with my graph, as there is a trend. The higher concentration the sucrose solution is, the more mass the potato chips lose hence becoming flaccid. The more water potential in solution, the less mass the potato chip loses, and mass is even gained where the water potential was very high outside the potato chip. (Water and 0.2M sucrose solution)
I can tell because on the table and results there shows a trend. The trend is that the higher concentration my solutions are, the less mass the potato was. The results and graph show that my potato cells have increased their mass as the average percentage change in mass of my final average mass and initial average mass was +10.1%. As it has gained weight, I then know that water from the beaker has transferred into my potato chip from a high water potential through the partially permeable membrane to a lower water potential: inside the potato. The cytoplasm and vacuole would swell as this happens, hence my potatoes in water were heavier and plumper looking, proving the fact they have gone turgid. The opposite, when I went to a very strong solution -1.5M sucrose solution – the mass decreased greatly; the potatoes have gone flaccid. This shows that the water in the potato, which had higher water potential than the sucrose solution outside, had diffused out and into the sucrose solution. Osmosis is when water diffuses from a place with higher potential to a place with a lower potential. In this case, that was what happened with the water in the beaker and the water in the potato. My results support this as potato put in the highest concentration 1.5M had a loss of 30.5% of its mass. The potatoes lost mass due to osmosis, as water from plant cells diffuse out when the solution is concentrated (lower water potential). The potato cells have plasmolysed, because the water has diffused out of the cytoplasm and vacuole through the partially permeable membrane.
Taking a look the trend shown on my graphs, the higher the concentration of sucrose, the more water has been lost inside the potato according to my graph as the line goes down below the x-axis becoming negatives, after the water solution. The line on my graph starts to level slightly as the concentration goes higher. (The gradients in between each other start decreasing) This is because the potato cells seemed to have plasmolysed, so they lose the water that’s remained inside slower than when they are filled with water. Plasmolysis is when water of plant cells in concentrated solutions has diffused out. When water is lost, the cytoplasm and vacuole shrinks. The cell wall does not shrink as much because it is very stiff. As the cytoplasm and vacuole continue to shrink more towards the centre of the cell, the cell wall will be left behind. My results prove this because the difference between each solution starts to decrease. From water to 0.2M there is about 10% difference, but from 1.0M to 1.5M there only seems to be about 2% difference.
Also, on my graph it shows that the % change in mass is about zero around sucrose solution 0.2M, as the line has crossed the x-axis, meaning that there are no net gain or loss of mass. It is isotonic, which helps me find out approximately the concentration of the potato. I would need more concentrations to find more accurately at which level of sucrose solution is the potato is isotonic, hence finding the concentration of the potato.
In conclusion, my graph proves that osmosis did occur because the water moved from high water potential outside the potato to a lower water potential inside the potato causing the potato to increase in mass. In strong sucrose solution, the high water potential is in the potato, which then diffuses out of the potato into the lower water potential outside the potato. This caused a decrease of mass in the potato.
My results support my prediction, as I predicted that in water, the potato would gain mass, and the potato chips in water had increased by +10.1%. In the strong sucrose solution, (1.5M) there was a -30.5% loss of mass in the potato, as the water had moved out of it. Therefore, I showed the effect of osmosis, as plant cells do not burst in pure water but become turgid as there is an increase in mass, and plant cells lose mass or even plasmolyse in concentrated solutions. (From a high water concentration in the potato to a low water concentration outside the potato)
Evaluation
My experiment was fairly accurate, though it could have been more accurate than it was. I tried making the factors of the controlled variables, such as making the potato chips the same size hence mass as accurate I could, but I didn’t as time was very limited, so I did not have the time to cut and measure all of eh potato chips until they were the very same mass. The good thing was, the potato chips were made the same diameter using a borer, which ensures me that the surface areas will be the same for all potatoes, so I had only had the worry of measuring the length of my potatoes accurately enough. If I had more time, I could have done so hence making this experiment more accurate. However, I did make the decisions of my units well, because using weight in terms of grams to see if osmosis occurred is much more effective than having to measure my potatoes’ length using millimetres. 100th of a gram is quite accurate compared to length in millimetres.
Looking at the result, there doesn’t seem to be any anomalies in particular, but looking at the graph of my line of best fit, there seems to be a point that is further way from the line than others. The existence of this small anomaly may be that there was too much water that I didn’t wipe off the potato when I took it out of the solution. However, all my points besides the 0.6 one seem really close to the line, so this increases the reliability since it follows the trend of osmosis and different concentrated solutions. My graph starts with a point well above the x-axis, showing that the potato has gained mass due to osmosis. As the sucrose solutions got more concentrated, the mass decreased and the line goes rather steep, but from 0.2M to 1.5M there is a slight levelling of the line showing that plasmolysis is occurring. Between 0.2M-1.5M, all the points are very close to line except for 0.6M. It should have lost more mass, but it was probably because I did not dab off enough liquid when I weighed it after putting it in the solution.
Having three potatoes for each solution also makes this experiment more reliable because I can find an average from it.
Improvements:
The potatoes were not all the same mass due to limit of time. I could improve this issue next time if I were to have more time. I also did not dab off enough water, so next time I should carefully dab each to make sure all liquid are off.
Timing was not exact as I put all the chips in different times. I don’t feel that I shall need to improve this next time as the duration of the experiments is hours long, so having a few seconds in difference will not affect my results very much at all.
If I were to take this experiment again next time, I could have more concentrations to improve my work, specifically in the area where the potato chip would be isotonic. To do this, I would put more sucrose concentrations in between 0.15M to 0.25M, as the line on my graph seems to cross the x-axis somewhere near 0.2 M sucrose solution. (The line through the x-axis means it would be isotonic, no net gain or loss of mass) Using 0.15M, 0.175M, 0.25M sucrose concentrations would help me find almost precisely where the potato would have no net gain or loss of mass. When the potato chip is isotonic, I could therefore find out its concentration too, hence developing my experiment into a higher level.
Furthermore, I could also carry the experiment on other fruits and vegetables such as a pear or an apple. An apple or banana for example, would have a much different result as it has more sugar in it than a potato does.