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investigating the water potential of potato cells

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Introduction

Internal assignment: Measure water potential of a potato's cells Research question: how is water potential of potato cells differ in different sucrose concentration? Background information: Investigate the water potential of a potato's cells in different sucrose concentrations. The concentrations will be: 0.8M, 0.4M, 0.2M, 0.15M, 0.075M and 0.00M. Terminologies used in this experiment: * Hypertonic solution: solution that has higher osmosis pressure (or has more solutes) than another solution to which it is compared. * Hypotonic solution: a solution that contains less solute (more water) compared to the cytoplasm of the cell. * Isotonic solution: Solutions of equal solute concentration1 * Diffusion: the spread of particles through random motion from regions of higher concentration to regions of lower concentration. * Osmosis: movement of solvent molecules through a selectively-permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves, without input of energy, across a semi-permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations * Water potential: potential energy of water per unit volume relative to pure water in reference conditions. ...read more.

Middle

0.75 gram 1.3 Ruler +/- 0.5 mm 2 mm 25 Variables: Controlled variables: * Length of time potato put in sucrose solution * Size of potato cubes * Volume of sucrose solution in a tube (5cm3) * Initial mass of potato cubes * Temperature of experiment's environment Independent variables * Sucrose solution's concentration Dependent variables: * Potato cells' water potential Test's results: Raw data: Raw data of mass of potato tissues (gram) after 15minutes putting in Sucrose solution at different molarity. The initial mass of potato cubes was 0.75 gram exact. Molarity Tube 1 Tube 2 Tube 3 Tube 4 Tube 5 0.8 0.55 0.66 0.60 0.65 0.68 0.4 0.72 0.78 0.70 0.73 0.74 0.2 0.81 0.85 0.82 0.83 0.87 0.15 0.87 0.85 0.84 0.88 0.84 0.075 0.99 0.93 0.90 0.94 0.97 0 1.01 1.17 1.04 1.03 1.10 Quantitative data: At first, when the sucrose solution as just added to the potato cubes, all of them sank. But the cubes floated slowly in the sucrose solution. There are differences between the float of the cubes in different concentration. In the 0.8M concentration, the cubes floated the most. The float of the cubes in other tubes is proportional to the dense of the concentration. ...read more.

Conclusion

This would affect badly on the result of the whole because the water potential of different potatoes' cells is different. Two, the second error is that while putting the potato cubes on the table for a long time without any cover, the water in potato cells evaporated, which might change the water potential of it. Three, while blotting the cubes, I might have blotted them so strongly, this made the water in cells come out, which also lead to the inaccurate. Four, because the amount of potato cubes was big, and we don't have enough time so that we only estimated the size the cubes. The size might not be exact 2mm3 LIMITATION AND SUGGESTIONS Limitations Suggestions Potato cubes stick together, hence the surface of potato cubes in sucrose solution might decrease Shake the tubes contain potato cubes gently and frequently in order to make the cubes separate. Water in potato cells will be lost because of evaporation Put the potato cubes in a box with lid or Petri dish with wrap after cutting. Using different potatoes Use one potato only. If the surround of the potato is dry and turn dark brown, cut it off and use the inner parts. The sensitiveness of digital balance can cause to an imprecise in measuring the potato cubes' masses because just a touch can change the result of a measure. ...read more.

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