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DETERMINING THE WATER POTENTIAL OF A POTATO TUBER CELLS USING THE WEIGHING METHOD.

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Introduction

TABLE OF CONTENTS Table of Contents 2 Determining The Water Potential of a Potato Tuber Cells Using The Weighing Method. 3 Aim: 3 Background Theory 3 Osmosis: 3 Water potential 3 Plasmolysis: 4 Incipient Plasmolysis 5 Pressure Potential: 5 Solute Potential 6 Osmotic Potential 6 Prediction 7 Variables 8 Dependant Variable 8 Independent Variable 8 Control Variables 8 Preliminary Investigation 9 Evaluation of Preliminary Investigation 9 Accuracy 9 Relevance to Real Experiment 9 Evaluation of Secondary Data 10 Data on Potato Tissue from US School 10 Marilyn Biology Lab Technician 11 Apparatus 13 Method 16 Precaution 18 Risk Assessment 18 Bibliography 19 Table of Figure 19 DETERMINING THE WATER POTENTIAL OF A POTATO TUBER CELLS USING THE WEIGHING METHOD. AIM: The aim of the investigation is to see in what solution the weight of the potato tuber not changes after being put in solutions with different concentrations in order to determine the water potential of the potato tissue BACKGROUND THEORY When a plant cell is bathed in a solute of the same water potential, its mass and volume will remain the same, because water enters the cell and leaves at the same rate. OSMOSIS: 1Osmosis is the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. Plant cells always have a strong cell wall surrounding them. When the take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises, 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. Turgidity is very important to plants because this is what make the green parts of the plant "stand up" into the sunlight. ...read more.

Middle

However there were problem with the experiment such as the accuracy, relevance to the real experiment, the equipment, method e.t.c. ACCURACY * In the experiment, to find the solute potential of the onion cells, you must find a concentration of sucrose or salt that causes incipient plasmolysis. You do this by mounting a layer of onion cells in varying strengths of sucrose solution, and count the % of plasmolysed cells. You cannot actually see 'incipiently plasmolysed cells - they do not look any different to unplasmolysed cells, but you count incipient plasmolysis as the point where 50% of the cells are plasmolysed and 50% are not. You are unlikely to get a sugar conc. which causes exactly 50% plasmolysis so you draw a graph of conc. against % plasmolysis and read off the conc. that would cause 50% plasmolysis. Whatever concentration this is, its solute potential will be the same as that of the cells. * It is difficult to count 20 cells using a microscope and then say which cells are plasmolysed and which cells are not plasmolysed. In a situation like this many people are likely to rely on demand characteristics. The person carry out the experiment will want his/her results to collaborate with their prediction so they make the number to suit the prediction not the right numbers while others just can not be bothered therefore they give wrong outright answers. * Also, in the real experiment it would be difficult for me to put a potato tuber under a microscope so I will be using an electronic scale to check the weight of the potato tuber and then find the point at which there is no change in mass. This will be used because this method is more accurate than using a microscope to look and count. The potato tuber is thicker than an onion cell. * When this experiment was carried out, already made sucrose solution was used. ...read more.

Conclusion

If required wear rubber gloves * Only enter a laboratory when told to do so by a technician . * Do not rush or round and most importantly do not panic. * Keep your bench and nearby floor clear, with bags and coats well out of the way * You should not carry out practical work unless supervised by a member of staff. * Follow instructions precisely * Check bottle labels carefully and keep tops on bottles except when pouring liquids from them; * Only use equipment and materials required for the experiment * Never remove anything from the laboratory without permission. * Wear eye protection, a lab coat and protective gloves when told to do so. You should continue to wear them until all practical work is finished and cleared away. * When using electrical equipment, ensure that mains plugs are fully inserted into the socket before switching on at the socket. * Ensure that your hands and the working area are dry before operating any electrical equipment. Do not use equipment with frayed or damaged cables. * When using a Bunsen burner, make sure that ties, hair etc. are tied back or tucked away. * Do not taste anything or put anything in your mouth in the laboratory. If you get something in your mouth spit it out at once and wash your mouth out with lots of water. Get help immediately. * Always wash your hands carefully after handling chemicals, and plant material. * Report any accident or breakage to your technician immediately. * Report broken glassware to a member of staff. Broken glass should be disposed of in a special container and not in the bin. * Never put waste solids in the sink. Put them in the bin unless your technician tells you otherwise. * Report all spills to your technician immediately. * Most importanly if unsure about any thing ask your teacher or the technician. ...read more.

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