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INVESTIGATING OSMOSIS AND WATER POTENTIAL IN POTATO CORES

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Introduction

INVESTIGATING OSMOSIS AND WATER POTENTIAL IN POTATO CORES WRITTEN BY SARA KHAN AIM: The aim of the experiment is to investigate osmosis and water potential of potato cores using different concentrations of sucrose solutions. INTRODUCTION: Plant cells contain a cell wall and a cell membrane. The cell wall is a permeable layer whilst the membrane is a selectively permeable membrane, this means that it will only allow certain molecules to pass through it and keep out others. An example of this is water and sucrose; water is a small molecule that can pass through the selectively permeable membrane, whilst larger molecules such as sucrose are unable to. Root hairs of plants contain within them many different substances. The way in which plant root cells take up water is by using this selectively permeable membrane to allow 'osmosis' to take place. Osmosis is a specific type of diffusion concerning only water molecules; it is the net movement of water molecules from a region of high concentration to a region of low concentration. When plant root cells take up water, water from the soil is passed across the selectively permeable they move from a high concentration in the soil to a region of low concentration inside the cell. The effect of dissolving solute molecules in pure water is to reduce the concentration of water molecules and hence to lower the water potential. All solutions therefore have lower water potentials than pure water. How much lower the solution is than pure water is known as solute potential. ...read more.

Middle

3. Distilled water- the pure water is needed because pure water is required to make up each concentration of sucrose and also for the control experiment. 4. Water bath- water bath is required to regulate the temperature. 5. Sucrose solution- the solution will be 30 cm3 for every set of potato tubes. 6. Syringe - this will allow equal volumes of each solution to be put in each test tube. 7. 15-test tubes- these will provide the container in which the solution and potato tissues are to be placed in. METHOD: 1. Label the test tubes with the concentration of the sucrose solution that will be placed in them. (Each concentration will be done three times including the control). 2. Set bath water to 25 degrees Celsius. 3. Take the syringe and extract 30cm3 of distilled water and place it in the test tube. (Make sure the syringe is clean). 4. Take a potato borer and a potato and use the potato to obtain a cylindrical piece of potato. 5. Weigh the potato cores using a top pan balance and record this weight. All cores should have the same mass. 6. Measure the diameter and length using the 15cm ruler. 7. Now place the potato tissues in the test tubes and leave in test tube rack for 3 hours. After this take out the potato tissue and measure its mass, length and diameter. 8. Record these results. 9. Repeat the experiment twice more and then record an average to have reliable results. ...read more.

Conclusion

Errors such as those mentioned would have made the conclusion reached invalid and therefore they could not be used as preliminary work for another experiment or as a basis for another investigation. The effect of these errors can be said to be minimal and thus resulting in a reliable experiment. The experiment that was carried out was reliable. This is mainly because of the steps that were taken whilst carrying out the investigation. These include the use of precision instruments, which meant the results were accurate and also reliable. The repeated readings are very close together and this shows that no large errors took place because this would have been noticed like the one anomalous result was seen on the graph. The apparatus used were to a high degree of accuracy but there are modifications, which could have been made to improve the experiment. These are all listed below: MODIFICATIONS: 1. Further test can be done for higher concentrations such as 50% sucrose solution. By having at least 10 different sucrose solutions this would give a more accurate graph from which more deductions can be made. 2. The use of a digital balance accurate to 0.001g could be used to gain increasingly more accurate results. 3. The readings can be repeated more than three times to increase the accuracy. 4. More precise instruments could be used to get all the potato cores to be of exactly the same length before placing them in the experiment to make it a fairer test. The modifications listed above would help in eliminating sources of error and also increase the reliability of the results. The modifications also suggest further work that can be done. ...read more.

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