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# Isotonic Point

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Introduction

Biology Lab Report Aim: To find the isotonic point of a potato. Introduction: Osmosis is the movement of water molecules through a partially permeable membrane in order to spread the water molecules evenly . It occurs in three different types of solutions-hypotonic, hypertonic and isotonic. A hypotonic solution has a low concentration of solute compared to the solvent. Thus if a cell is placed in it there is a lower concentration of water inside the cell than outside. The water particles enter the cell quickly, making the cell swell. A hypertonic solution has a high concentration of solute compared to the solvent. Thus a cell has a higher water concentration inside the cell than outside. So the water particles rush out of the cell, making the cell membrane shrink. An isotonic solution is one in which the concentration of the solute is the same inside and outside the semi-permeable membrane. Thus, the solutions have equal osmotic pressure and the water particles move in and out of the cell at the same rate, keeping the cell at equilibrium. Minimum absorption occurs in such cases. Apparatus: 1. A raw potato 2. Digital Balance (�0.01g) 3. Petri dish 4. Knife 5. Salt solution of concentrations ranging from 0M to 0.8M 6. Tissue paper 7. Beakers 8. Forceps Variables: Control - 1. ...read more.

Middle

Mass before experiment (�0.01g) Mass after experiment (�0.01g) Difference between masses (g) Percentage Difference Between masses (%) Average Percentage Difference (%) 0.0 0.71 0.90 1.21 0.78 0.98 1.46 +0.07 +0.08 +0.25 +09.86 +08.89 +20.67 +9.38 0.2 1.20 0.94 1.40 1.14 0.80 1.26 -0.06 -0.14 -0.14 -05.00 -14.89 -01.00 -3.00 0.4 0.83 0.94 0.71 0.55 0.38 0.56 -0.28 -0.56 -0.15 -33.73 -59.57 -21.13 -27.43 0.6 1.08 0.73 1.05 0.72 0.53 0.76 -0.36 -0.20 -0.29 -33.33 -27.40 -27.62 -29.45 0.8 0.54 1.18 0.80 0.41 0.91 0.62 -0.13 -0.27 -0.18 -24.07 -22.88 -22.50 -23.15 Error Readings: We have identified three errors in our readings- a. The +20.67% difference reading in the 0.0M concentration solution b. The -14.89% difference reading in the 0.2M concentration solution c. The -59.57% difference reading in the 0.4M concentration solution We believe that these readings are errors due to the fact that the difference between these readings and the others two readings taken for the same concentration solution is very high. We believe these errors occurred as the potato pieces taken were not originally of the same mass and thus the difference in their masses after the experiment affected their percentages in a different manner, making the percentages higher or lower. Also the pieces were of different lengths which changed the amount of surface area to absorb water. ...read more.

Conclusion

Evaluation: We should have taken more readings for our experiment to get a more accurate result as a lot of our result were erroneous and could not be used to gain the average percentage difference. This was a random error on our part. We got wrong readings due to two reasons. Both were random errors- 1. We did not measure the length of the potato strips before the experiment to make sure that they were the same. If we had done so, the surface area of the pieces would be the same, thus allowing the same amount of water to come in contact with the potato. Also we would have known if the length of the potato would have changed as well. 2. We did not take pieces of exactly the same masses. If we had done so there would have been no need to take percentages. Also we could have been sure of the accuracy of our results. We did not measure the amount of tissue paper we used to dry the potato pieces. If we had done so then we could have been sure that excess water did not remain on any strip, thus ensuring that there was no extra mass. This was also a random error made by us. Thus there are various ways by which we can improve the accuracy of our results. ...read more.

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