The Effect of Concentration on Osmosis

The Effect of Concentration on Osmosis
Osmosis is the diffusion of water molecules that occurs only when there is a movement of water molecules from a region of higher concentration to a region of lower concentration through a partially permeable membrane. The process ends only when the two concentrations are equal or the cell is unable to take any more water because the cell is turgid. For osmosis to take place a partially permeable membrane is required to allow water movement to take place and to prevent such a transfer between other molecules. If a cell is in contact with a solution of lower water concentration than its own contents, then water leaves the cell by osmosis, through the cell membrane. The living contents of the cell contracts and eventually pulls away from the cell wall and shrinks, this is known as plasmolysis. If you put a plant cell in water, water enters by Osmosis, and then swells up. However, the cell will not burst. This is due to the fact that the cell walls are made from cellulose, which is extremely strong.
Eventually, the cell stops swelling, and when this point is reached, we say the cell is turgid. [image] Plan for Pilot experiment Apparatus: 300cm3 1 Molar sucrose solution Distilled water A potato ? White potato preferred No. 6 cork borer ? or other with diameter of 1 centimetre 6 plastic cups Scalpel Labels Measuring cylinder Ruler Marker Cling film A range of sugar solutions will be prepared with concentrations from 0.0 M to 1.0, in intervals of 0.2, by adding varying amounts of distilled water. Sections of potato will be cut using a cork borer and scalpel to an equal length of 1.5 centimetres. For each concentration there will be 3 plastic cups to compensate for anomalies with the use of an average, it will be in these plastic cups where the potato tubers will be placed. 50cm3 will be poured into each cup. Placing three potato cylinders in one cup would involve the potatoes sharing the same environment with the same impurities within the solution. The cups will be wrapped in cling film so no human intervention takes place as well as change in atmosphere. These will be left for 23 hours in an incubator which will be kept at a constant of 20OC .Then the potato pieces will be removed by the use of tweezers and then placed on a paper towel and measured. As it is difficult to get the cut potato pieces to the same mass it was decided that monitoring the percentage difference in length would be best suited. Controls I will keep temperature as a controlled variable because I know that temperature can affect the rate of osmosis therefore the cups will be kept in an incubator regulated at 20OC. I will try to ensure that the concentration will be accurate; however, this uncontrolled variable will comprise impurities that would inhibit accurate results. The change in size of the potato cylinders would be dependent on the independent variable of the concentration of the sucrose solution because the amount of osmosis that takes place would depend on water potential. Hypothesis I predict that as the concentration of the sucrose solution increases, the weight and length of the potato cylinder will decrease. I think that the reason behind this, is that the higher the concentration of sucrose in a solution, the lower the concentration of water. When the potato cylinder is put into the solution it will lose some of its water due to osmosis and the water will diffuse into the solution of sucrose causing the potato to lose water, thus decreasing its size. In this case the potato would have a greater water potential and moves down the gradient to the solution causing the decrease in length. However, I believe that a potato cylinder placed in distilled water will increase in size because a potato cannot have a higher water potential than water itself. Therefore water will move from the solution to the potato, increasing the size of the potato. I also predict that from the 0.4 M solutions the length of potato will decrease because I think that the potato has the same water potential as the solution as a 0.4 solution. From previous knowledge of water potential, I know that when the water potential is the same between the two parties no diffusion of water will take place therefore the potato would remain the same size. Results ? For Pilot experiment Concentration of sucrose solution / M Length of potato cylinders / cm Percentage difference in length / % 1st reading 2nd reading 3rd reading 0.0 0.2 0.4 0.6 0.8 1.0 1.8 1.6 1.5 1.3 1.4 1.2 1.6 1.6 1.5 1.4 1.2 1.2 1.6 1.6 1.6 1.4 1.3 1.3 20.00 6.67 6.67 -8.89 -11.11 -17.78 The highlighted data in the table are anomalies because these cylinders had one face covered with potato peel. The potato peel affected the amount of osmosis that took place in the 23 hours because the potato peel is not partially permeable membrane therefore osmosis cannot take place in those regions with the potato peel still in place. Potato cylinder [image] [image] Shaded area indicates potato peel [image][image][image]Length 1.5 cm The total surface area of potato cylinder = 6.283185307 cm2 Surface area of potato peel = 0.785398163 cm2 Percentage of potato peel = 12.5% The fact that 12.5% of the potato?s surface area was inactive in the process of osmosis can be demonstrated by comparing the results for the potato cylinders with peel and those without peel. For example: For the distilled water the length of the potato without peel was 1.8cm whereas with peel it was 1.6cm. Percentage difference for 1.8cm potato cylinder (without potato peel) New length ? Original length X 100 = Percentage difference Original length 1.8 ? 1.5 X 100 = 20% increase 1.5 Percentage difference for 1.6cm potato cylinder (with potato peel) 1.6 ? 1.5 X 100 = 6.7% increase (to 1dp) 1.5 With peel difference ? Without peel difference = The influence of peel 20% ? 6.7% = 13.3% The loss of a possible 13.3% increase for a potato cylinder with peel can be due to the deficit of 12.5% of the partially permeable membrane. This could mean that the surface area is directly proportional to the amount of osmosis that takes place. However, this is only in theory because there are other environmental factors that affect the amount of osmosis that takes place, such as the concentration and purity of the sucrose solution. Final experiment Apparatus: 300cm3 1 Molar sugar solution Distilled water A potato No. 6 cork borer ? with diameter of 1 centimetre 6 plastic cups Scalpel Labels Measuring cylinder Ruler Marker A range of sugar solutions will be prepared with concentrations from 0.0 M to 1.0, in intervals of 0.2, by adding varying amounts of distilled water. Sections of potato will be cut using a cork borer and scalpel to an equal length of 1.5 centimetres. For each concentration there will be 3 plastic cups to compensate for anomalies with the use of an average, it will be in these plastic cups where the potato tubers will be placed. 50cm3 will be poured into each cup. Placing three potato cylinders in one cup would involve the potatoes sharing the same environment with the same impurities within the solution. The cups will be wrapped in cling film so no human intervention takes place as well as change in atmosphere. These will be left for 23 hours in an incubator which will be kept at a constant of 20OC .Then the potato pieces will be removed, the surface solution removed by the use of tweezers and placed on a paper towel and measured. As it is difficult to get the cut potato pieces to the same mass it was decided that monitoring the percentage difference in length would be best suited. The biggest change I made after the preliminaries was to ensure that no potato cylinders had potato peel. In addition I made sure that the potato rods were straight therefore guaranteeing a surface are that could be shared by all rods. I decided to repeat each concentration 3 times in order to gain an average and to allow me to distinguish whether I had any anomalous results, which could influence my hypothesis and conclusion. I also chose to use the same concentrations because it was simply easier to mix these concentrations and would make it easier for the difference of length to be indicated on a graph. When I took out the potato cylinders after the 24 hours and I had begun to measure the cylinders I began to notice their structure. The cylinders, which had increased in length became turgid and were very hard around the edges and possessed a strong as well as straight posture. Whereas the rods placed in high concentrations of sucrose were very bendy and were rather wilted. The reason for the change in structure was probably caused by the movement of the water particles from the sucrose solution and the potato. Results ? For experiment Concentration / M Potato Chip No. Starting Length (cm) Final Length (cm) Change in Length (cm) Average Change in Length (cm) 2dp Percentage Change in Length (%) 2dp Average Percentage change in Length (%) 2dp Increase /Decrease 0 1 1.5 1.7 0.2 0.17 13.33 11.11 Increase 2 1.5 1.6 0.1 6.67 3 1.5 1.7 0.2 13.33 0.2 1 1.5 1.6 0.1 0.10 6.67 6.67 Increase 2 1.5 1.6 0.1 6.67 3 1.5 1.5 0 0 0.4 1 1.5 1.5 0 0.1 0 6.67 Increase 2 1.5 1.5 0 0 3 1.5 1.6 0.1 6.67 0.6 1 1.5 1.3 -0.2 -0.13 -13.33 -12.22 Decrease 2 1.5 1.4 -0.1 -6.67 3 1.5 1.4 -0.1 -6.67 0.8 1 1.5 1.3 -0.2 -0.2 -13.33 -13.33 Decrease 2 1.5 1.3 -0.2 -13.33 3 1.5 1.3 -0.2 -13.33 1 1 1.5 1.2 -0.3 -0.27 -20.00 -18.89 Decrease 2 1.5 1.3 -0.2 -16.7 3 1.5 1.2 -0.3 -20.00 [image] Analysis Looking at the graph which I have produced to demonstrate how the concentration affects osmosis the line of best fit is negative. This shows that the potato cells increase in length in solutions with a higher water potential and decrease in size in solutions with a low water potential. This was not surprising as in earlier experimens and from past knowledge I am aware that osmosis occurs down the gradient. Osmosis with low sucrose concentration Osmosis moving down gradient Text Box: Sucrose solution (high water potential) Losing water [image] Potato (low water potential) Gaining water [image] Osmosis with high sucrose concentration Potato (High water potential) Losing water [image] Text Box: Sucrose solution (Low water potential) Gaining water [image] However, I believe that there is a limit to how much water can be lost after a higher concentration of sucrose due to the fact that the cells has been completely plasmolysed. Evaluation During this investigation it was very difficult for a person to be accurate. For example, cutting the potato cylinders accurately to 1.5 centimetres was demanding task and even then accuracy wasn?t assured because the rules used could only measure to the nearest millimetre. In addition to this measuring the change in length was hindered by measuring with a rule since many rods happened to be bendy not straight.

The Effect of Concentration on Osmosis 8.5 of 10 on the basis of 2506 Review.