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OCR AS Biology Planning Exercise 2003

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Introduction

OCR Biology Planning Exercise 2003 The effect of Time on the Firmness of Potato Chips Aim/Problem The aim of this project is to investigate the correlation between the age of a piece of potato and its 'firmness' when fried as a chip. I would like to find a plausible explanation as to why older pieces of potato form what can be described as 'limp and soggy' chips, whereas newer potatoes make 'hard and firm' chips. Hypothesis I think that the older a potato is when it is cut to make a chip, the soggier the chip becomes. The main factor that causes this is differing water potential within the cells of the potato. Osmosis is the diffusion of water through a cell wall or membrane or any semi-permeable barrier from a solution of low solute concentration to a solution with high solute concentration, up a solute concentration gradient.[1] In this definition, the term 'low solute concentration' can also be written as 'negative water potential' and 'high solute concentration' can be phrased as 'more negative water potential'. Water potential decreases when solute in a solution increases. Therefore a concentrated solution can be seen as having a lower water potential than a weak solution. Pure water has a water potential of zero, so all water potentials are negative. ...read more.

Middle

Control Variables: - The size of the slice of potato - The concentration of solution used -Time potato is left in solution for Safety * Normal lab precautions (tying hair back, stools under desks etc.) should be observed * The experiment would involve water, which is easily spilt. Therefore, you should be careful when moving around the lab as there could be spillages in the floor which you could slip on. * You should be careful when using a scalpel to slice the potato, as they are sharp and you could cut yourself with it. * We'll be using glass beakers which could be smashed, so you should be careful not to cut yourself on shards of class if this happens. Apparatus * Distilled water * Six large test tubes * A test tube holder * A ruler * A 10cm2 syringe - it is easier to use one syringe to measure out the 10cm, than it is to use a 5cm syringe twice * A scalpel * An electronic balance - the readings are more reliable than an analogue balance * Small pieces of paper * Potatoes of different ages * A stopwatch Method 1. Get six samples of potatoes, one should have been stored for each of the following times: 1 day, 2 days, 5 days, 7 days, 10 days and 14 days. ...read more.

Conclusion

The two will be in equilibrium. From my results, many calculations would be able to be carried out. You could work out the approximate change in mass per day, and see if this is a linear change or not. You could also work out where the equilibrium is. Evaluation Overall, I think my experiment is quite precise. The apparatus is class B, and although you could get more precise measurements from class A apparatus, I think the results that you could get are good enough for this experiment. I have chosen to use electronic equipment in a couple of places (balance, stopwatch) as these are more accurate. Although, the stopwatch could be a problem as it is impossible to add the potato and start the stopwatch at the same time which could cause a slight delay and leave the potato in the water for slightly longer than one minute. The experiment is valid, as it measures change in mass which directly correlates to change in water potential, which is what I said I would investigate in this experiment. To make the results reliable you could repeat the experiment more than twice. Overall however, I think my experiment is reliable enough and quite fair. There are variables beyond our control, of course (such as air temperature or pressure) which could affect the rate of osmosis, and the experiment would have to be carried out in a sealed environment to rectify this. ...read more.

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