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To investigate the affects of a potato in different molar solution of sucrose and water. Ultimately, I would like to find the molarity inside a potato cell.

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Introduction

Biology Coursework Helen Wilkinson 11 CHW 11set1 Aim The aim of this experiment is to investigate the affects of a potato in different molar solution of sucrose and water. Ultimately, I would like to find the molarity inside a potato cell. Diagram Hypothesis I have researched the topic of osmosis and have found out osmosis is the diffusion of water particles from a high concentration to a low concentration of water particles. This movement of water particles occurs through a partially permeable membrane. A partially permeable membrane have very small gaps which only the smaller water molecules can fit through therefore pass in and out of the object, the large sucrose molecules are unable to fit through at all. In the experiment I wish to complete, the small holes in the potato membrane will allow water to pass either into the potato tissue or into the solution around the tissue. If the solution around the potato were a weak solution (lots of water particles) I would expect the water particles from around the potato to diffuse into the potato cell by osmosis, because the water molecules are moving from a weak sugar solution to a strong sugar solution. I would expect this to continue until equilibrium is reached, this means the concentration is the same in both the tissue and the solution therefore the water molecules can pass through the membrane on both sides at a steady rate. ...read more.

Middle

* Top pan balance * Measuring cylinder * Stop watch * Sharp Knife Method I firstly must remove the skin off the potato so the skin does not affect my results. Because I don't want to stop diffusion of water particles, I will thoroughly wash my potato before it is cut it. My potato pieces must all be of an identical size, I have decided on 4cm by 1cm wide which I will use a 30cm ruler to measure. I will cut six potato pieces in this way. I will cut one extra than necessary in case one in inaccurate. I will then mix the solutions using accurate measurements; I must weigh the potatoes before submerging them in water so I can measure the increase in weight. I will then put the pieces of potato into the solutions for fifteen minutes. Once I have removed the potato I will wait for about four minutes to allow any osmosis to take place I will then remove excess water so the weight is simply based on the potato and weigh them. I will repeat this experiment twice and then take average results to ensure the accuracy of my results. Fair test * The potato pieces must be from the same potato so the experiment is fair and the potato tissues are identical * I should wait before re weighing ...read more.

Conclusion

In concentration 1,0.8,0.6 and 0.2 (which I feel is incorrect) the mass decreases as water was drawn out of the potato but in concentration 0.4 and 0 the mass increase as water was taken into the potato. Therefore, the higher the concentration of sucrose solution outside, the greater the loss of water. The lower the concentration, the greater the gain of water. This links back to my pilot test where the results firmly show this see pilot test graph. Evaluation Overall I am fairly pleased with my method and results, it was a safe investigation, but I am aware they could be better. I have noticed the anomalous results, they could have occurred for any number of reasons. I may have left some potato skin on the potato cell, which could have affected the rate of osmosis. If I performed this experiment again I would check the size and the mass of each potato is the same, I have overcome this in the experiment by working out a percentage change. I think I could have repeated the experiment several more times so I had enough results to dismiss anomalous results totally. If I were to extend my experiment I would research the rate of osmosis more closely. I would use more concentrations to give a better overall view and use potatoes that have come from different areas of land to, as the amounts of sucrose solution may be different. ...read more.

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