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Osmosis Coursework

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BIOLOGY INVESTIGATION-OSMOSIS IN A PLANT CELL AIM To investigate the effect on osmosis in a plant cell consequent to a change in the concentration of its surroundings. BACKGROUND INFORMATION OSMOSIS Osmosis is diffusion but it is specialised diffusion that can only involve the movement of water molecules across a semi-permeable membrane. It is defined as "the passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a partially permeable membrane. Water potential is measured in units of pressure (usually kiloPascals). It is the pressure created by water and, under room temperature and standard pressure (25c and 100kPa), pure water has a potential of zero. Therefore, changes in certain conditions would mean the water potential would change. Some key points to take into account are: * The addition of a solute (e.g. salt) to a solvent (e.g. water) will lower the water potential. The addition of a solute to a solvent will produce a solution. * It follows that the water potential of a solution is always under zero. * The more solute that is added, the lower the water potential. * Water will always move from an area which has higher water potential (i.e. it has more solute e.g. salt) to an area with lower water potential (i.e. which has less solute e.g. salt) Osmosis can only occur through a partially permeable membrane and only when there are different concentrations of solute in each region. The following terms apply to the different state of the solutions: * Hypotonic - this is when the solution has less solutes, ...read more.


I will weigh the potato chips with electric scales, record the mass and which solution it is going into. I will Label the test tubes with the respective solutions and leave them for approximately 20 hours. After 20 hours, I will take each potato chip out of the solution and with a length of blotting paper, place each chip on one end of the paper. Then I will fold over the other end press down gently once on each chip, drying them all simultaneously. Then, I will weigh each chip again and record the new mass. Record the results and calculate the percentage change in mass. RESULTS SOLUTION (M) ORIGINAL MASS(g) MASS AFTER 20HRS (g) CHANGE IN MASS (g) PERCENTAGE CHANGE IN MASS (%) 0.00 0.91 1.02 0.11 12.09 0.20 0.96 0.96 0.00 0.00 0.40 0.94 0.80 -0.14 -14.89 0.60 0.87 0.66 -0.21 -24.14 0.80 0.90 0.55 -0.35 -38.89 1.00 0.92 0.62 -0.30 -32.61 CONCLUSION I will use 2cm lengths of potato chips with a diameter of 6mm. 7ml will be sufficient to cover the potato chip. I will use solutions ranging between 1M and 4M and those solutions with more accurate divisions will be used in order to investigate the osmotic point further. MAIN EXPERIMENT METHOD 1. Using a potato borer, I will remove about 3 potato chips from the potato. 2. Then, using the knife and on the cutting tile, I will cut each chip into smaller chips each of 2 cm in length. 3. I will ensure that there are 15 two centimetre chips when finished. ...read more.


If the results had been too anomalous, I do not think they would have been satisfactory to support my conclusion and therefore to prove my prediction. The anomaly that was present could have been produced due to number of factors. The sucrose solution was not seen prior to the experiment and all the preparation was carried out by a technician. As a result, there is a chance that the solution could have been contaminated in some way prior to use. The method I used to dry the potatoes before they were weighed for the second time was not very technical. Blotting paper and was used by placing the potato chips on one end and then folded over the other end. This meant that different potato chips could have lost more water than others and this would result in a change in the real mass. It is also possible that some of the potato cells may have been damaged when taking out the chips and putting them into the test tubes. This would have meant that some part of the semi-permeable membrane could have been damaged allowing other substances in and out of the cells. This would alter the mass of the chips. I believe that my results were extremely accurate and therefore extremely reliable. There were very few anomalies and this enabled me to carry out the experiment and form conclusions with little trouble. I would carry out the experiment again differently to enable more reliable evidence. I would have used more concentrations of sucrose solution with smaller division (i.e. 2.0, 2.25, 2.5 etc). This would enable me to investigate the osmotic point further. However, these divisions were not available to use for this experiment. ...read more.

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