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To determine concentration of cell sap in potato tuber cells.

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Introduction

Investigation to determine the concentration 23rd September 02 of cell sap in potato tuber cells Aim- To determine concentration of cell sap in potato tuber cells Preliminary information- I will use osmosis to investigate the concentration of cell sap in potato tuber cells. Osmosis is the net movement of water particles across a partially permeable membrane from a region of high water concentration to an area of low water concentration. Molecules in a solution move in constant random motion because they have kinetic energy. The water molecules can travel through the pores in the cell membrane of the potato cells but sucrose particles are too big to get through since they contain more atoms (C12H22O11- twelve carbon, twenty-two hydrogen and eleven oxygen as opposed to H20- two hydrogen and one oxygen). Since they are in constant random motion the water molecules eventually move across the membrane to the area with less water molecules in until the two sides are in equilibrium. When they are in equilibrium the cells have reached their osmotic point- this is when the particles are still moving in constant random motion but there is no net movement of water molecules. The changes happening inside the cell due to osmosis bring about visible changes in the plant. When a plant is placed in a less concentrated solution water flows through the cell's cytoplasm and into the vacuole the increased pressure of the water in the vacuole (turgor pressure) ...read more.

Middle

and the mass decreased when I put them in 1m sucrose solution- they became plasmolysed. This is because osmosis occurred when the water molecules moved from the regions of low concentration of water molecules through the partially permeable cell membranes to the regions of high concentration of water molecules. This is because molecules in a solution move in constant random motion because they have kinetic energy and the water molecules pass through the pores of the partially permeable cell membranes in the potato tuber cells but the sucrose molecules are to big to get through since they contain more atoms (C12H22O11 as compared to H2O). Since they are in constant random motion the water molecules eventually moved across the membrane to the area with less water molecules in (down the concentration gradient of concentration of water molecules) until the two sides were in equilibrium: there was no net movement of water molecules. My aim for this experiment was to determine the concentration of cell sap in potato tuber cells. My graph passes through the point on the x-axis of 0.328M, which tells me that is the point where no net osmosis occurs: the iso-osmotic point. Therefore that is the concentration of cell sap in the vacuoles of the potato tuber cells. My results support my prediction in general because the scientific ideas in the prediction and the results are the same. ...read more.

Conclusion

This would indicate no further decrease in mass. I will leave them for 24 hours because that is a sensible amount of time to leave a potato tuber chip for if I want osmosis to occur. I could also find out the concentration of cell sap in onion cells to see if it is the same as potato cells. To do this I would use exactly the same method as I used for the potato cells: ~ Cut 6 pieces of onion, weigh them and record their masses ~ Place each one in a test tube containing distilled water/sucrose solution and leave for 24 hours ~ Take them out and blot them on filter paper ~ Weigh them and record their masses ~ Record which piece of onion has changed the least in mass ~ Repeat experiment to improve reliability in case the first set of results were incorrect I will use exactly the same solution concentrations as I did in the potato experiment going from 0M distilled water to 1M sucrose solution in 0.1M intervals. I will plot it on the same graph as the potato cell sap concentration graph so that I can easily compare the two cell sap concentrations. The concentration of solution at which the line of best fit will cross the x-axis, where the onion is no longer losing or gaining any mass (iso-osmotic point) will be the concentration of cell sap in onion cells. Imogen Hagarty 2 ...read more.

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