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Investigation to look at the water potential of Celeriac

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Introduction

Investigation to look at the water potential of Celeriac A-S Coursework Transport Module Joel Davies The aim of this investigation is to look discover the water potential of the root vegetable Celeriac. To do so, the effect of varying concentrations of sugar solutions on Celeriac will be observed and a conclusion reached. As preliminary work, the effects of sugar solution on potato has been investigated to give a general idea of what to expect and to discover any problems with the, method before the larger Celeriac experiment. Background research has also highlighted properties of Celeriac that are different to potato and will therefore affect the water potential of the plant. Relevant background knowledge The generalised plant cell is as in the diagram below: The vacuole and cytoplasm contain the solution that is being investigated. The cell wall is fully permeable and therefore does not effect the movement of substances into and out of the cell. It does however contain 20-40% cellulose which applies a pressure potential that is important in the water potential of the cell. The cell membrane and tonoplast (membrane surrounding the vacuole) are partially permeable, therefore allowing certain molecules through while prohibiting others. Non-polar and lipid soluble substances can pass through since they are not effected by the phospholipid bi-layer. Molecules that are polar and ions however cannot pass through the membrane unless 'carried' across by specialist proteins, large insoluble substances cannot enter and do not affect Osmosis (only soluble substances affect solute potential). Although water molecules are polar, they are not affected by the membrane due to their small size. This allows Osmosis to take place without being affected by the membrane. Diffusion is the spreading out of a substance from a high concentration gradient to a low one (without the use of energy). There are many examples of diffusion, such as orange squash - when it is added to water it all turns orange due to the 'squash molecules' dispersing throughout the water. ...read more.

Middle

* Same Celeriac plant: All the cylinders will be cut from the same plant since different plants will have grown in slightly different environments. The variation in the environments will have affected the amount of starch produced (due to photosynthesis-light and water availability) and therefore the conversion into monosaccharides and the ?s. If the ?s of all the cylinders were different it would be much harder to find a value for ?w. * Same part of the plant: The cylinders will also be cut from the same area of the cortex (as is physically possible). Different areas will have varied densities, concentrations of sugars and therefore ?w. A constant ?w makes the results obtained more accurate. Apparatus Cork borer size 4 Scalpel Tile cutting slate Ruler 30cm accurate to 1mm Electronic weighing scales accurate to 0.01g Celeriac bulb Sucrose solution 1M 1litre 2 Syringe 25ml with 1ml divisions 11 McAndrew Bottles & Tops 50ml Distilled water 1 litre Clock 12 hours accurate to 1 second Tissue paper Chinagraph pencil Experimental safety * Take care while cutting with the cork borer and the scalpel, making sure you cut away from the body on the tile * Take care not to get any of the chemicals in your eye - safety glasses should not be necessary Method 1. Using the 2 syringes, measure out the correct amounts of 1M sucrose solution/distilled water for each of the different solutions, pouring each into a different McCartney bottle. Use the table below for quantities Strength of sucrose solution Distilled water 1M sugar solution (% 1M) (ml) (ml) 0 20 0 10 18 2 20 16 4 30 14 6 40 12 8 50 10 10 60 8 12 70 6 14 80 4 16 90 2 18 100 0 20 2. Label each of the McCartney bottles using the Chinagraph pencil 3. Using the cork borer, cut out 11 cylinders (use a pencil to get the Celeriac out of the borer) ...read more.

Conclusion

This could have been due to a number of factors such as not waiting for the scales to finish calculating the weight, very inaccurate reading of the pipette or most likely a piece of Celeriac which was particularly more dense/less dense than the other cylinders. Improvements There are many improvements that could be applied to the experiment: 1. With more time the experiment could be repeating more times which would give an average results which would be far closer to the true value. This would be most noticeable in that the graph of solution concentration against percentage mass change would be a smooth curve or straight line. 2. More Celeriac plants would allow experiments on a variety of different plants which would give a more accurate reading for the water potential of Celeriac. 3. A team of scientists instead of just one. This would allow all of the chips to be cut and placed in the solutions at the same time and therefore cut out any inconsistencies in the timing of the experiment. 4. Making the 1M solution up closer to the time in which the experiment is going to take place would reduce the amount of water evaporating which increases the concentration of the solution. 5. Also mixing each solution using sucrose powder and water individually would cut out errors due to evaporating water and inaccuracies when measuring the sucrose solution in the pipettes. By calculating the ratio of sucrose powder to water for each concentration, the solutions could be prepared in each McCartney bottle. Conclusion Validity Taking into account the inaccuracies and problems mentioned above it can be concluded that although the results are not accurate enough to give a reliable figure for the water potential of Celeriac, they are accurate enough to show that it is noticeably lower than that of potato which supports the view that Celeriac brakes starch chaining down into short monosaccharides in cold weather. Biography Biology 1 OCR examining board Practical Biology for A-level Roberts, King and Reiss (p82-86) New Scientist (15 July 2000) Web sites: www.crop.cri.nz/psp/broadshe/celery.htm www.crfg.org/crfginfo.html www.britanica.com/bcom/eb/article/5/0,5716,108925+6+106179,00.html ...read more.

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