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Determining the water potential of potato cortex cells.

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Introduction

Determining the water potential of potato cortex cells An experiment to investigate the effect of different sucrose concentrations on potato tissues. Biological Background knowledge: Biological background knowledge on osmosis: Osmosis is a special form of diffusion, which involves the movement of solute molecules. Osmosis can be defined as the passage of water from a region where it is highly concentrated to a region where its concentration is lower, through a partially permeable membrane. Biological background knowledge on water potential: Water potential is a measure of the free kinetic energy of water in a system, or the measure of the tendency of water to leave a solution. The more concentrated the solution the more negative will be its water potential. Water diffuses from a region of higher to a region of lower water potential. The water potential of a system is the difference between the chemical potential of the water in the system and the chemical potential of pure water under standard conditions. The water potential of pure water is zero. Water molecules move randomly. When water is enclosed by a membrane, living or artificial, some of the moving water molecules will hit the membrane, exerting pressure on it. ...read more.

Middle

Results: Molarity Mass before Mass after Mass change % Change in mass 0 1.47 1.82 0.35 23.8% 0.1 1.19 1.31 0.12 10.1% 0.2 1.52 1.59 0.07 4.6% 0.3 1.88 1.91 0.03 1.6% 0.4 1.78 1.87 0.09 5.1% 0.5 1.69 1.61 - 0.08 - 4.7% 0.6 2.25 1.99 - 0.26 - 11.6% 0.7 2.03 1.66 - 0.37 - 18.2% 0.8 2.33 1.87 - 0.46 - 19.7% 0.9 2.28 1.77 - 0.51 - 22.4% 1.0 2.00 1.55 - 0.45 - 22.5% From my results I can plot a graph showing the percentage change in mass compared to the molarities. This will show me how the molarity affects the percentage change in mass: this will be graph 1. I can also convert the molarities into values for pressure and plot a graph for it. This will help me to determine the water potential of my potato tissues: this will be graph 2. Molarity of sucrose solution Solute potential (k Pa) 0.10 -260 0.20 -540 0.30 -820 0.40 -1120 0.50 -1450 0.60 -1800 0.70 -2180 0.80 -2580 0.90 -3010 1.00 -3510 Analysis: In graph 1, there is a pattern: the line declines as the concentration of sucrose increases; this shows me that as the concentration of the sucrose solution increases, the percentage change in mass of the potatoes decrease. ...read more.

Conclusion

Evaluation: It is evident that there were sources of error within my experiment. These is due to the following factors: 1. The surface area of the potato discs: Although we aimed to get each potato disc 2mm thick, we cannot be sure that we cut them to that exact measurement, this means that the surface area on each potato disc was different and was not a fair test. 2. Other factors that affect the rate of osmosis: There are other factors that affect the rate of osmosis occurring and could therefore have affected the results. Temperature, an increase in temperature increases the kinetic energy that the particles have and this means that the rate of osmosis will increase. We did not monitor the temperature of our experiment, although this would not have dramatically affected our results, if we were to redo the experiment and make sure it was fair then we need to consider this. Ethical Implications: The potato that was used was not a rare species, it is commonly found. Risk Assessment: Care must be taken when using the cork borers and the razors to cut up the potato discs. Disposal Methods: All waste that was disposed of did not cause any threat to the environment; potatoes are biodegradable and could be thrown in the bin. No chemicals were used in this experiment. ...read more.

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