Osmosis in Plants

Osmosis in Plants
Outline: To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given size. Definition ? Osmosis: Movement of a solvent (liquid) through a semi-permeable membrane separating solutions of different concentrations. The solvent passes from a less concentrated solution to a more concentrated solution until the two concentrations are equal. All cell membranes behave as semi permeable membranes, and osmosis is a vital mechanism in the transport of fluids in living organisms for example, in the transport of water from the roots up the stems of plants. Further relevant information on potato plant cells: Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting.
Plant cells become ?turgid? when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant ?stand up? into the sunlight. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become ?flaccid.? This is the exact opposite of ?turgid?. The contents of the potato cells Shrinks and pulls away from the cell wall. These cells are said to be plasmolysed. When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. ?Incipient? means ?about to be?. Plant cell structure: Plant Structure: How does Photosynthesis Work?: The chloroplasts in the leaf cells convert sunlight into energy for the plant. Carbon dioxide + water = Sugar + Oxygen 6CO2 + 6H2O = C6H12O6 + 6O2 Water movement in plants: Xylem cell: Root cell: The water is absorbed by the root calls and travels up the xylem cells to all the parts of the plant. Water is needed to make very important chemical processes happen, they also support the plant. Reaction rate theory: The theory is that different solutions can affect the way plant cells osmoses e.g. A sugar water solution increases the extent of osmosis compared to just water. Variables in the test: These variables can affect the extent of osmosis: - Heat:heating up the potato chip in the sugar will speed up the reaction and may increase the extent of the osmosis. Concentration of sugar in solution: The concentration of sugar in the solution is a key factor in increasing or decreasing the extent of osmosis in the plants the more sugary the solution, the greater the extent of osmosis. The more sugar, the smaller the vegetable and the greater the amount of osmosis will occur. Stirring: stirring the solution will speed up the rate of osmosis. If you leave the solution to react without stirring it will take a lot longer as the cell walls are weakened more with the molecule collisions that would occur. Increasing surface area: if the potato chip had a larger surface area the extent of osmosis would increase largely. In the experiment the pieces of potato have to be the same size (length, width and even weight). Other Vegetables: by using other vegetables you can observe how the rate of osmosis differs between them. Age:by using fresh vegetables instead of old vegetables the extent of osmosis will be greatly affected as the cell walls would be stronger and newer. preliminary Choosing a variable: It was decided that the concentration of the sugar in the solution was the best variable to use to see what affected the extent of osmosis in plants, so an experiment was set up in order to research whether our predictions were correct. Safety: To make the test safe we used goggles where necessary, we used blunt but effective corers to remove the potato pieces and we tucked all stools and bags under tables to make the environment we worked in safe. Equipment:
Sugar solution
Water
7 Pyrex beakers ? to hold the water and the sugar solution
A potato
A corer ? to extract the potato pieces
A Set of electronic scales ? to measure the potato pieces before
and after the experiment
Prediction: I predict that the higher the concentration of sugar solution, the lighter and smaller the potato piece will become. Method: A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar, 1 molar and 2 molar. This will be done by adding varying amounts of distilled water to varying amounts of sucrose solution (sugar solution). Sections of potato will be cut using a scalpel and will be weighed using scales. This part of the preparation must be done very accurately as a change in the weight may allow more or less osmosis to occur. Three chips will be placed in each beaker at the same time so an average can be taken from each tube. I will use 10 ml of each concentration of sugar solution and once in the test tubes they each will be labelled. The potato pieces will then be placed in the different beakers and then left for 45 minutes/1 hour. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed. then if time is free afterwards the test will be repeated, as to obtain a second (real)set of results. This will hopefully produce more accurate results from which I will be able to draw a more accurate conclusion. Results: Preliminary 0m 0.2m 0.4m 0.6m 0.8m 1m 2m chip 1 2.7g 2.7g 2.3g 2.0g 2.0g 2.3g 2.1g chip 2 2.6g 2.3g 2.5g 2.3g 2.0g 2.0g 2.0g chip 3 2.8g 2.6g 2.5g 2.0g 2.3g 2.0g 2.4g average 2.7g 2.5g 2.4g 2.1g 2.1g 2.1g 2.2g Fair test: We made the test fair by: -
Making each piece of potato the same weight (they were weighed on
accurate, electronic scales)
The amounts of sugar in the solution were precise.
We left the potato pieces in the solution for the same amount of
time.
We didn?t disturb or stir the beakers filled with solution.
Evaluation & Criticisms: The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen. The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine or tool to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. This would ensure that I have an accurate amount of fluid in each beaker. I could also weigh each chip on a more accurate scale, e.g. not to 0.0g but to 0.00g. There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused by my mistakes. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction. Secondary sources: The test can be proved right from many other sources from the internet or text books for example, both suggest that the test was correct and that the result that were collected were mainly correct as well. Here are some articles that prove or the results were correct: [image]The internet: I found this picture and a piece of text about it on the inter net:- ?The solvent passes from a less concentrated solution to a more concentrated solution until the two concentrations are equal?. (Found from a link on google.com) And:- ?The end result is that the plant, that was placed in the sucrose solution, will had decreased in size and its mass lessened a considerable and noticeable amount? (Found on a revision web site) real Choosing a variable: (same as preliminary) It was decided that the concentration of the sugar in the solution was the best variable to use to see what affected the extent of osmosis in plants, so an experiment was set up in order to research whether our predictions were correct. Safety: (same as preliminary) To make the test safe we used goggles where necessary, we used blunt but effective corers to remove the potato pieces and we tucked all stools and bags under tables to make the environment we worked in safe. Equipment: (same as preliminary)
Sugar solution
Water
7 Pyrex beakers ? to hold the water and the sugar solution
A potato
A corer ? to extract the potato pieces
A Set of electronic scales ? to measure the potato pieces before
and after the experiment
Prediction: (same as preliminary) I predict that the higher the concentration of sugar solution, the lighter and smaller the potato piece will become (keeping in mind the odd results will be discarded). Method: A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar, 1 molar and 2 molar. This will be done by adding varying amounts of distilled water to varying amounts of sucrose solution (sugar solution). Sections of potato will be cut using a scalpel and will be weighed using scales. This part of the preparation must be done very accurately as a change in the weight may allow more or less osmosis to occur. Three chips will be placed in each beaker at the same time so an average can be taken from each tube. I will use 10 ml of each concentration of sugar solution and once in the test tubes they each will be labelled. I could also weigh each chip on a more accurate scale, e.g. not to 0.0g but to 0.00g. The potato pieces will then be placed in the different beakers and then left for 45 minutes/1 hour, even thought the waiting time should maybe be changed to around 1 hour and 30 minutes+, we can?t though as we just don?t have the time to put this in to action. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed and the difference found between both tests (preliminary and real). Results: 0m 0.2m 0.4m 0.6m 0.8m 1m 2m chip 1 2.90g 2.90g 2.10g 1.50g 1.60g 2.10g 1.70g chip 2 2.70g 2.10g 2.50g 2.10g 1.70g 1.50g 1.70g chip 3 3.00g 2.70g 2.50g 1.50g 2.00g 1.70g 2.20g average 2.90g 2.60g 2.40g 1.70g 1.80g 1.80g 1.90g Difference between real and preliminary: 0m 0.2m 0.4m 0.6m 0.8m 1m 2m 0.20g 0.10g 0.0g -0.40g -0.30g -0.30g -0.30g Fair Test:
Making each piece of potato the same weight (they were weighed on
accurate, electronic scales)
The amounts of sugar in the solution were precise.
We left the potato pieces in the solution for the same amount of
time.
We didn?t disturb or stir the beakers filled with solution.
We did the experiment in a constant room temperature.
Evaluation & Criticisms: In my opinion the experiment was very successful. I obtained a large quantity of very accurate results, very much the same as from the preliminary results, from which It was able to create graphs showing percentage increase. I think I took enough results for the amount of concentrations that I was using, as I believe that this part of the preliminary need not be changed, I also believe that the time I left the potato chip in the solution for was enough and didn?t need shortening or lengthening. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen as it may affect the osmosis rate. The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine or tool to cut the potato as it would ensure that all potatoes would be the same weight and dimensions but no tool could be found so we had to make do with the scalpels and ruler. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. There were not many out of the ordinary results, but some were not as close to the line as others. This may have been caused by my mistakes that were not before picked up on in the preliminary. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass quite considerably. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was very successful and I was very pleased with the complete comparison of my results with my initial prediction.

Osmosis in Plants 7.1 of 10 on the basis of 4001 Review.