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Introduction

Mr Chips: Investigation to find an isotonic solution for potatoes Introduction Investigation aimed to find out the amount of grams of salt solute needed to create an isotonic solution to prevent osmosis in fresh cut potato chips. Osmosis is the movement of water molecules through a selectively-permeable membrane down a water potential gradient. More specifically, it is the movement of water across a selectively permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration). The water molecules will continue to move through the semi-permeable membrane until both sides have reached a state of equilibrium. Isotonic solution is a solution in which its solute concentration is the same as the solute concentration of another solution with which it is compared In plant cells when water moves into the vacuole it increases in size and pushes the cell membrane against the cell wall, this causes the cellulose cell wall to stretch slightly and when it can stretch no further it becomes taut and firm. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. At this point the cell wall prevents the cell from bursting and is said to be fully turgid. ...read more.

Middle

Hypothesis The prediction for this experiment is that as the concentration of the solutions increase the mass of the potato chips will decrease. Equipment * NaCl (salt) * Distilled water * Potatoes * Potato peeler * Cork borer * Knife * Safety blade * Measuring cylinder * 18 Boiling tubes * Marker for labelling * 3 Racks * Para film, 18 squares * Stop clock * Cutting tile * Top pan balance * Paper towels Method 1. Collect all materials listed above 2. Make up 100cm3 of each of the salt solutions using information from table 1 below 3. Label three boiling tubes 0.0% 4. Repeat step three for each of the other concentrations 5. Measure out 25cm3 of 0.0 solution and pour into the labelled boiling tube, repeat for the remaining two tubes labelled 0.0% 6. Now repeat the previous step for each of the remaining concentrations 7. Peel the two potatoes 8. Cut 18 cylinders of potatoes and trim to five millimetres in diameter and 40 millimetres in length 9. Weigh one cylinder and note its mass in grams, record in table labelled initial mass, place into the boiling tube labelled 0.0%, repeat twice for the remaining tubes labelled 0.0% 10. Repeat step nine for each of the remaining concentrations 11. Seal all the boiling tubes with para film and leave for two hours at room temperature 12. ...read more.

Conclusion

Also the potato may be a little out of season at the time of the experiment thus influencing the sugar content. A further experiment with a variety of potatoes may help put this debate to rest. The potatoes were cut into cylinders, not chips, giving a different volume to surface area ratio; rigid cut slender chips may give better results, though this could give rise to human error. Scales used for weighing potato could be more modern or accurate. Time of insertion and extraction of each chip to and from each boiling tube is near impossible to be carried out simultaneously, an unfortunately difficult problem to resolve. With excess water on the potatoes, paper towels were used to dab of the excess. However, in doing this water could have been removed that was not excess, and altered the results. Alternatively, a quick shake to remove excess drips of water and then weigh. Conclusion As the concentration of the solutions increased the mass of the potato chips decreased. At the point of 0.43% concentration equilibrium was met with the solute and the potato cell contents. The amounts of grams required are 4.3g Sodium Chloride plus 995.7cm3 of water to make a litre of solute. ?? ?? ?? ?? 1 | Page Biology Module One Practical Investigation: Mr Chips Elizabeth McKnight 1 | Page ...read more.

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