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Osmosis in potato cells.

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Introduction

Osmosis in Potato Cells Scientific Theory Osmosis is similar to diffusion, but a little different. It is the movement of water molecules across a partially permeable membrane, from a region of high water concentration to a region of low water concentration, (along a concentration gradient). A partially permeable membrane, is a membrane with tiny holes, however these holes are so tiny that only water molecules can pass through and no other substance, for example glucose. When a substance, for instance sugar, dissolves in water it attracts the water molecules and stops them from moving freely, this actually reduces the concentration of water. In the diagram above, there are more free water molecules on the right of the membrane than on the left. Therefore water will diffuse more rapidly from right to left across the membrane, rather than left to right. The sugar molecules can diffuse from left to right across the membrane, but because they are big molecules they will diffuse more slowly than water. The effect of this is to gradually dilute the sugar solution. Osmosis also takes place in plant cells, when the cell is in a less concentrated solution. ...read more.

Middle

this way * Prepare two test tubes, A and B Fill test tube A with water, and test tube B with a twenty- percent sugar solution. Water of 20 ml * Leave the solutions for three hours * After three hours, measure and weigh the potatoes from each test tube A and B. Note the differences. Results Below are the results for the potato tubes immersed in pure water. Length of tube in cm Mass of tube in grams Length after soaking Mass after soaking Length difference (cm) Mass difference (grams) Percentage change in length Percentage change in mass 9 5.6 9.5 6.4 0.5 0.8 6 14 7 4.4 7.7 5 0.7 0.6 10 13 7 4.5 8 5.3 1 0.8 14 18 8 3.6 8.9 4.2 0.9 0.6 11 17 6.5 3 7 3.4 0.5 0.4 8 13 Average increase in length = (6+10+14+11+8)/5 = 9.8% Average increase in mass = (14+13+18+17+13)/5 = 15% Below are the results for the potato tubes immersed in a twenty- percent sugar solution. Length of tube in cm Mass of tube in grams Length after soaking Mass after soaking Length difference (cm) ...read more.

Conclusion

This may effect the amount of osmosis taking place. Also all the potato tubes were not of the same length and mass, if I had taken care of this my results would be more accurate. I also feel that potatoes from different countries may also affect the rate of osmosis, as the rate of osmosis would be according to their climate and maybe the type of soil too. I could also try an experiment with Visking tubing and compare the results to this too. However as I cannot see the membrane of the potato I will not be able to compare properly. Also some of the tubes not increasing a lot may be because in the water solution some tubes may have had more water than the rest. And in the glucose solution less decrease may be because there was less glucose and more water in that solution than the rest. I can improve the experiment by using more potato cells to get stronger correlation on the graph. However, though my experiment was not too reliable because of the method used, my experiment strongly proves that osmosis occurred and so my experiment must have a considerable amount of reliability. My results also are sufficient for me to conclude that osmosis does take place in potato cells. ...read more.

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