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To investigate the effects of sucrose concentration on osmosis in potato tissue.

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Introduction

To investigate the effects of sucrose concentration on osmosis in potato tissue PLANNING We have been asked to research the effects of sucrose concentration on osmosis in potato tissue. Osmosis is the spontaneous movement of a solvent (-in this case water) from a place where its chemical potential is higher to another place where it is lower, through a semi-permeable membrane (-such as a cell membrane). A cell membrane lets smaller molecules such as water through but does not allow bigger molecules to pass through. The smaller molecules will continue to diffuse across the membrane until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are in a steady state, with molecules moving in and out of the membrane, however with no net loss or gain. Plant cells always have a rigid cell wall and cell membrane surrounding them. When they take up water by osmosis the cells start to swell up, but the cell wall prevents them from bursting, (-which is what animal cells, who have no cell walls would do), the plant cell is then said to be turgid. When turgid, 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 hydrostatic pressure works against osmosis, even when the plant cell's water potential is greater than that of the outsides. ...read more.

Middle

is low. This could be called a weak or dilute solution. In a low concentration of water, the amount of solute is high. This could be called a strong or concentrated solution. When a semi-permeable membrane divides two such solutions, the water molecules will move from the area of high concentration to the area of low concentration, until both sides have reached equilibrium. Knowing that osmosis will occur between a semi-permeable membrane whenever there is a difference between the water concentrations on the two sides of the membrane, and when knowing that this happens to cells they will either become turgid if water flows into them, or plasmolysed if water flows out of it, and thus change their mass. Knowing this we can set an experiment, so that if the concentration of a solution into which a cylinder of potato is placed is greater than a certain level the cylinder will contract, and if the concentration is less then that level, it will expand. This can be shown using pure water (high water molecule concentration), the potato cell in the dilute solution will swell and increase its mass and volume/length. If places in a highly concentrated solution of sucrose, the opposite would happen and the potato will decrease in volume/length and mass. I predict that the greater the concentration of water in the external solution the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water in the external solution, the greater the amount of water that leaves the cell. ...read more.

Conclusion

This is summed up in a table. Result's table: Concentration-sucrose Amount of sucrose Starting Mass End Mass Mass difference 0% 0ml 0.90g 1.00g +0.10g 40% 2ml 0.87g 0.88g +0.01g 60% 3ml 0.92g 0.90g -0.02g 100% 5ml 0.91g 0.85g -0.06g This shows that the isotonic level is at some point just above 40% sucrose solution. I would need to repeat my experiment quite a few times to get reliable results, and to average out some inaccuracies that might have happened. Also I will need to use new dry test tubes after each experiment as to prevent contamination. Also the mixing beaker will be washed using water and dried using paper towels for the same reason, as the contamination, will affect the results, which would then display low accuracy and no repeat values. SAFETY I will have to wear goggles to prevent the sucrose liquid getting into my eyes, take care with the sharp scalpel, and to wear aprons to prevent splashes getting on my uniform. Preliminary work-shapes my understanding The preliminary work let me decided on some crucial factors: -Time for experiment: 10 minutes -Amount of solution: 5ml -Length of potato: 3cm-make sure no skin is on the potato, as it will block the osmosis happening on that part of the potato, therefore smaller surface area. -Dry potato after experiment to get rid of excess water-see reasons for this actions above - Mixing beaker will be washed using water and dried using paper towels-see reasons for this actions above -Concentrations of sucrose to be used: -0% -20% -40% -60% -80% -100% PHILIP XIU 11SK BIOLOGY COURSEWORK 1 ...read more.

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Here's what a teacher thought of this essay

3 star(s)

This is a good start to a report on this investigation.
1. The planning section has a good level of detail and includes relevant information.
2. The fair test section also has a good level of detail but lacks structure.
3. The scientific knowledge section shows good research but should be at the beginning of the report.
4. The tables of results are well presented.
5. During the method section of the preliminary test the structure breaks down. Use subheadings to divide methods and findings.
6. The report needs to be finished.
*** (3 stars)

Marked by teacher Luke Smithen 29/05/2013

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