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To find out how various concentrations of water affects osmosis in potato cells and to see if any patterns emerge that are related to osmosis.

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Introduction

Osmosis in Plant Cells Aim To find out how various concentrations of water affects osmosis in potato cells and to see if any patterns emerge that are related to osmosis. Background Information I shall begin this investigation with an explanation of what osmosis is. Osmosis is a special case of diffusion, which involves exchange of water particles across a semi-permeable membrane. Normally diffusion takes place in particles in the form of gas. Diffusion is where a high concentration of particles move over to where there is a low concentration of these particles until there is a state of equilibrium. This is when the particles have become evenly distributed within the volume in which diffusion took place. Osmosis is very similar to this principle, but will take place across a semi-permeable membrane. A semi-permeable membrane is a wall that has microscopic holes in it. Large particles (E.g. Sucrose, starch, protein etc.) are unable to fit through, as the holes are too small. Smaller particles (E.g. Oxygen, water, carbon dioxide, ammonia, glucose, amino-acids etc.) will be able to fit through these holes. A diagram below shows how this principle works. Osmosis occurs when there is a difference in concentrations of water between two sides of water solutions, which are separated by a semi - permeable membrane. Where there is a high concentration of water molecules (e.g. a higher number of available water molecules in a certain volume of solution). And where there is a low concentration of water molecules (a lower number of available water molecules in a comparable volume of solution), which is separated by a semi - permeable membrane. The dilute solution is said to have a higher osmotic potential and has more available/free water molecules in it. This will dilute the other solution, which has a lower osmotic potential and might have fewer water molecules in it, but more molecules like sugar or salt dissolved within it. ...read more.

Middle

stands for grams, (mm) stands for millimetres and (%) stands for percentage change. On the following pages are two hand drawn line graphs, which show the percentage change of the mass in sugar and salt solutions and the change in length in the sugar and salt solutions. I have drawn an approximate line of best fit for each of the results. Change & Rank Difference Between Ranks (d) Solutions Mass (%) Rank Length (%) Rank Sugar - 0.8 Molar -25.0% 1 -10.0% 1 0 Sugar - 0.6 Molar -23.1% 2 -5.0% 2 0 Sugar - 0.4 Molar -8.0% 3 -2.5% 3 0 Sugar - 0.2 Molar 13.0% 4 5.0% 4 0 Salt - 0.8 Molar -20.8% 5 -7.5% 5 0 Salt - 0.6 Molar -20.0% 6 -5.0% 6 0 Salt - 0.4 Molar -16.0% 7 -2.5% 7 0 Salt - 0.2 Molar -8.0% 8 0.0% 8 0 Distilled Water 24.0% 9 12.5% 9 0 TOTAL (d) 0 Spearmans Rank = 1 - ((6?(d2))/(N3-N)) Where d = difference and N = number of results Total (d) 1 This chart is designed to show how the change in length is linked to the change in height. By using the formula RS = 1 - ((6?(d�))/(N�-N)). This is known as Spearman's rank and is used to determine whether something has a positive or negative or no correlation. It can also determine how good the correlation is. If the result is 1, then that is a perfect positive correlation. If it is -1, then it is a perfect negative correlation. If it is 0, then there is no correlation. Below is a representative diagram showing how this law works. -1 0 1 My results come out as 1. Therefore, there is a positive correlation between change of mass and change in length, indicating that these are connected. As the length increases, so does the mass, and also the same applies when the length decreases, so does the mass. ...read more.

Conclusion

The strengths of the solutions may not have been entirely correct, however, if there was a discrepancy, it would have been too minute to tell the difference. The measurements of the solutions could have been affected by human error. I used 25cm� of solutions, but it would have been impossible for me to get the measurements the same every time. This may have been because a meniscus formed inside the measuring cylinder, so it was difficult to judge how much solution had been placed into the cylinder. However, I doubt small discrepancies would have affected the results much. Evaporation may have played a part during the experiment, as this may have reduced the final amount of solution, but this is unlikely, as all of the pots had foil lids. I did the experiment all on one day, but if I had done the experiment at another time, the temperature and therefore the volume would have changed slightly when measuring out the solutions. I only used one chip per pot, but if I had done more, I could have worked out an average change in mass and length for each solution. This would have prevented any unusual results from emerging. Only specialised computer equipment and computer controlled environments could have made the experiment a completely fair test by having identical measurements and the same environmental conditions. Although, there would be little point in doing this, as there were no anomalous results. There are no other investigations that could be used to prove the principle of osmosis. I previously mentioned the cucumber experiment, but this would not be as good as the potato experiment as, it would be too difficult to take accurate length measurements. It is only worth conducting an experiment if the results are worth gathering. The measurements are important when conducting an experiment as they help to prove any hypotheses and can show any patterns that emerge. ?? ?? ?? ?? 23/04/07 Andrew Rudhall 11H Science 1 Biology Investigation Centre No: 63203 Candidate No: 7152 Page 1 of 8 ...read more.

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