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Skill Area P - Planning - Osmosis is a form of passive transport, and a specialised form of diffusion.

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Introduction

Skill Area P - Planning Introduction - Osmosis is a form of passive transport, and a specialised form of diffusion. It is the movement of water from a dilute solution to a more concentrated one, through a semipermeable membrane. Hence it is where water moves from a high to a low concentration. I will design an experiment to test this process on a typical example of osmosis' effect on plant cells, taking as the sample, potato. It is through osmosis and the fluctuating levels of water in the cell that the concentrations of minerals in the plant are regulated. Expt. 1 Last year, I conducted two experiments in which dialysis tubing was used to simulate the semipermeable membrane. In the first experiment a knot was tied in one end of a length of soaked dialysis tubing and a pipette was used to half fill it with a strong glucose solution. The air bubbles were expelled and a knot was tied in the other end. At this point the tubing was flaccid (limp). When it was then placed in a test-tube full of distilled water, it became turgid (firm). [See diag.1] Expt. 2 In the second experiment red-dyed sugar solution was placed in a bell-shaped piece of apparatus, with a capillary tube off it and a cellulose film over the bottom [See diag.2]. ...read more.

Middle

I will require 10 potato pieces (two for each solution). As they will be cut from a slice of potato 1 cm tall, the height is already constant. I must also ensure that the breadth of each piece is constant: 1cm. It is vital that the breadth and height are constant so that it is possible to measure any change in length. Of course, in order to measure the change, it will be necessary to ensure that the initial lengths are constant, and to ensure that I measure the same sides at the beginning as the end. To do this, I will take a tiny segment out of one side (I will measure the other). The initial lengths will be 2.5 cm. Obviously, it is hoped that the potato will have an even density, but in case it does not, the individual masses will be measured beforehand as well as afterwards. Through the use of such a precise piece of apparatus, I hope to be more accurate in my final readings. Also, this way the comparison between increase/ decrease in the lengths of potato pieces may be reinforced by a comparison between the increase/ decrease in their masses. So the readings will not only be more accurate, but also more reliable. ...read more.

Conclusion

Planned Method - First I will cut out the 10 potato pieces (10x10x25mm) on the white tile with the scalpel, taking a chunk out of one side [see diag. 4a]. Then I will measure their masses on the electric balance. Then I will measure out the volumes of the bathing solutions (20ml each) in a measuring cylinder (the measuring cylinder will be dried after each measure) [see diag. 4b]. Then I will pour the bathing solutions into the 5 boiling tubes, which I will have labelled, and two potato pieces will be placed into each boiling tube and the timer started [see diag. 4c]. 30 minutes later, I will remove the 10 potato pieces, rinse (briefly) and dry them, and measure their lengths and masses. These will then be recorded. Then the volumes of the bathing solutions will be recorded (again, the measuring cylinder will be dried after each measure). Diagrams Safety Precautions - As with all substances in a science laboratory, it is vital that I do not taste the potato, the solutions or the distilled water. I must not touch my face or licking my fingers before washing my hands, but I should attempt to avoid getting the liquids if possible, as it risks contaminating our results. Evidently, care must also be taken with the scalpel in the cutting of the potato, as it is a sharp instrument. ...read more.

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