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Efeects of Osmosis in Plant Cells

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Introduction

Aim: To Investigate The Effect Of The Movement Of Water By Osmosis In Plant Cells I will use potato chips as the plant cells in the experiment to show the movement of water by osmosis in and out of plant cells by measuring the mass change, of identical chips, in different concentration solutions of sucrose. Hypothesis Prediction: I predict that the higher the concentration of water surrounding the potato cells the higher the percentage increase in mass and that the lower the concentration of water surrounding the potato cells the higher the percentage decrease in mass of the potato cells. Also, I predict that, when the potato cells are placid in a concentration of water that is Isotonic to the cell vacuole contents, there will be no change in mass of the potato cells. I further predict that unless the plant cell is turgid there will be a percentage change in mass and in the uptake of water into or out of the potato cells wall inversely proportional to the concentration of sucrose. I f the cells are turgid or placid there will be no further increase or decrease in the mass of the plant potato. Scientific Reasons For Hypothesis Water molecules will move by osmosis from an area of high concentration of water (hypotonic) through a partially permeable membrane until the concentration of water molecules on either side of the partially permeable membrane is the same. Plant cells have a partially permeable membrane surrounding the cytoplasm and beneath the cellulose cell wall. A cellulose cell wall is fully permeable i.e. it will allow any sized molecule to pass through it. A cell membrane contains pores formed by spaces between protein molecules, which will only allow small molecules to pass through e.g. water molecules however larger molecules such as sucrose or salts will not pass through the cell membrane. When a plant cell is placed in a solution that has a higher concentration of water then that present inside the vacuoles inside the plant cell, which contains a solution of starch salts. ...read more.

Middle

The potato cylinders will be left for 24 hours and then each of them will be dried carefully, again with paper towels and re-weighed. However, it is very important to dry the potato cylinders before weighing them to ensure that any change in the mass of the potato is due to a change in the water content inside the potato cells, not due to any sucrose solution on the outside of the cylinder. When the potato cylinders are re-weighed I will record the final mass in my results table. Once I have got both sets of results, the weights of the potato cylinders both before and after the experiment, and I have found out the averages I will then find out the percentage change in mass. I will then plot a graph of percentage change in mass against the concentration of sucrose solution. Variables I Would Keep The Same * Length of the Potato Cylinder - If I altered the length of the potato cylinder it would change the surface area of potato exposed to sucrose solutions. This will affect the rate of osmosis. I will maintain the length of all the potato cylinders by using a scalpel and ruler to cut and measure lengths. * Diameter - again, a change would alter the surface area of all the cell membranes exposed to sucrose solutions in turn affecting the rate of osmosis. I will make sure all the potatoes have equal diameter by using a cork borer. * Time - the length of time will be a factor that will affect the amount of water molecules that can diffuse into or out of potato cell membranes. * Temperature - the higher the temperature, the higher the kinetic energy of the water molecules, therefore the higher the rate of diffusion in or out of the potato cell membranes. * Volume of Sucrose - If the potato cells are not fully covered in sucrose solution, it will affect the rate at which they can diffuse in or out of the potato cells. ...read more.

Conclusion

However, the downside of this is that it is very time consuming. 6. A range of six solutions doesn't provide sufficient evidence to make a firm conclusion. To provide more evidence to help make a firm, valid conclusion, a wider range of solutions with reduced intervals in between the sucrose solutions would need to be used. For example, a range of sucrose solutions of the following concentrations could be prepared: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 moles/litre. 7. Measuring the change in the diameters of the potato cylinders, as well as the percentage change in mass of the potato cylinders could provide more evidence. 8. I would repeat the experiment more than three times, as this would also provide me with additional evidence to make a firm conclusion. 9. The shape of my graph is similar to my predicted graph and most of the plotted points are close, if not on the best-fit line, indicating accurate and therefore reliable results. However, I cannot make a firm conclusion about the affect of osmosis in plant cells since I have only investigated the affect of osmosis in potato cells. I cannot assume that all plant cells will behave in the same way as potato cells. To make a more valid conclusion, I need to repeat the experiment using other plant tissues e.g. carrot, lettuce or celery cells. I could also extend my investigation by looking at the degree of plasmolysis in plant epidermal cells such as beetroot, onion and rhubarb, in which the epidermis is stained with iodine. I could take the epidermis of these plant tissues and then place them in a range of sucrose solutions (0.1, 0.2, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 moles/litre). After the tissues have been in the range of sucrose solutions and if necessary they have been stained, I would then observe and estimate the degree of plasmolysis on the cells by viewing them under a microscope. Biology Coursework By Petar Radjenovic page 1 ...read more.

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