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  • Level: GCSE
  • Subject: Science
  • Essay length: 2224 words

What effect different solutions, with the same water potential, have on potato and cucumber strips (by mass).

Extracts from this essay...

Introduction

Jessica Rossi What effect different solutions, with the same water potential, have on potato and cucumber strips (by mass). Plan Introduction Plants in the soil have their roots in a dilute solution of various mineral ions. Sometimes, the soil they are planted in gets flooded with sea water (which has an average of 0.3 sodium chloride concentration). In these cases the roots are observed to wilt and become flaccid. In my experiment, I will simulate this situation using potato and cucumber strips, placing them in different solutions (sodium chloride, glucose and sucrose) at different molar concentrations. A substance dissolved in water is called a solute. A solvent is a liquid that is able to dissolve another substance, a solute, to form a solution. Water potential is a measure of the ability of a solution to give out water. Water potential (y) can be expressed as the sum of the solute potential (ys) and the pressure potential (yp). (y) = (ys) + (yp) The water potential of pure water is zero and all other solutions have a negative water potential. The greater the solute concentration, the more negative is the value for water potential. Background Information The water content of plants depends on environmental conditions. In land plants, water plays a vital role in structural support and mineral transport, thus, the lack of water may lead to wilting or possibly death.

Middle

[image006.jpg] * Place the correct quantity of pure distilled water into a beaker, measured using a different measuring cylinder. * Place all test tubes in test tube rack. * Place 20cm of each solution into each of the test tubes, so that all 30 test tubes will be holding each a different concentration of any solution. * Place 20cm of distilled water in another two test tubes, these will be used as the control in order for the test to be fair. * Cut 16 potato cores and 16 cucumber cores and place them on a ceramic tile. Using a scalpel and ruler (calibrated in millimeters) cut the cores at 50mm, taking care that no peel is left and that all the cores are accurately cut at the nearest millimeter. * The cores will be individually weighed on a top pan balance to an accuracy of 0.01grams. * Each of the cores will then be placed into one of the 32 test tubes for 2 hours, timing kept by a stopwatch. * After 15 hours the cores will be removed from the solutions, blot-dried on top of a filter paper, and weighed straight away. * After the experiment has been completed, all apparatus has to be washed and properly placed away, and all organic material should be disposed of.

Conclusion

However, this was impossible to do as 48 plant tissue samples were needed for each vegetable. * A variety of other similar plant roots could have been placed through the same procedure in order for comparison of different tissues. * A larger cucumber should have been used, in order to cut the chips out of the same tissue, and trying to exclude the seeds and placenta, as this could have lead to inaccuracy in the experiment. [image008.jpg] * Some results could have been inaccurate due to not allowing excess solution on the external surface of the cores from draining away before placing it onto the top pan balance. This superficial water would be measured as extra mass by the sensitive weighing scales, even if the cores have been blot-dried on filter paper beforehand. * Once the cells have been plasmolysed, it is possible that some of the solution has entered the cell between the cell wall and the cell membrane, given that the cell wall is fully permeable. This could lead to inaccuracy of results, as part of the mass in the plasmolysed plant cores would be caused by this intake of water, which has not been caused by osmosis. [image010.jpg] * The experiment was also lmited by the accuracy of the top pan balance, which showed mass in grams to one decimal place.

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