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# An experiment to investigate how the effect of varying concentrations of salt solutions play on the movement of water in a potato.

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Introduction

PRELIMINARY EXPERIMENT AN EXPERIMENT TO INVESTIGATE HOW THE EFFECT OF VARYING CONCENTRATIONS OF SALT SOLUTIONS PLAY ON THE MOVEMENT OF WATER IN A POTATO. AIM The aim of this experiment is to try and find out how different concentrations of salt solutions affect the osmotic activity in a potato tissue. Thus we will be able to find out if the mass of the potato has increased or decreased in the different concentrations of salt solution. APPARATUS > A Single Fresh Potato > McCarthy Bottles = x 5 > Corks = x 5 > Water = 20cm3 x 5 > 2 Molar Salt Solution = 150cm3 > Test Tube Rack to hold 5 test tubes > Pipette > Scalpel - To cut the potato tubes into cylinders > Weight Measuring Scales > Ruler - To measure the potato cylinders accurately to 2cm long. > Cork Borer > Cutting Board - Where the potato can be placed and cut safely > Marker Pen will be used to write on the test tubes so that I will be able to distinguish between the potato cylinders and determine which salt solution is in which test tube. DETAILED INFO ON HOW TO PREPARE THE SOLUTIONS REQUIRED Just like my final experiment, in this preliminary experiment I increased the concentration in my five bottles by 0.5 moles, until it reaches 2 molar. 1 mole in 1 litre requires 58.5g of salt to be dissolved in it. Therefore as 1 litre is 1000 cm3, I was thus able to take these into account and do my measurements. 0 Moles = Pure Water 0.5 MOLES in 20 cm3 of water = 58.5/ 125 = 0.468g of SALT 1 MOLES in 20 cm3 of water = 58.5/100 = 0.585g of SALT 1.5 MOLES in 20 cm3 of water = 58.5/75 = 0.78g of SALT 2 MOLES in 20 cm3 of water = 58.5/50 = 1.17g of SALT DIAGRAM Cork Potato Cylinder (0 Molar Solution) ...read more.

Middle

to a region of high concentration (low water potential), the pure water will move into the potato cells, causing an increase in mass. I also believe that when the potato cylinders are put in higher the concentration of water in the solution, i.e. lower in concentration of salt in salt solution; the change in mass would be greater. However the change in mass would depends on the cell sap of the potato cells. The molarity of the cell sap in the potato cells is fixed for a single potato. It has a very weak concentration and so when it is placed in a higher concentration of salt solution of, for example, 1.5 M the potato cell sap acts as the hypotonic solution. This is because since the salt solution has a higher concentration, this means it has lower water potential as there are a greater number of solute molecules and so there is less number of freely moving water molecules, as they form clusters around the solute therefore it would increase in mass. Also the lower the concentration of water in the solution the more the potato cells will shrink and decrease in mass and length volume as water molecules will leave them by osmosis - from the high concentration (inside the potato) into the low concentration. FACTORS AFFECTING OSMOSIS (ADVANCED BIOLOGY - PETER SANG) There are certain factors affecting the process of osmosis. These factors are as follows: - Temperature - Concentration gradient - Size of the molecules - Permeability of the membrane I will now explain the effects of each of these factors on the process of osmosis in brief. Temperature: Osmosis is merely a process where the water molecules from the dilute solution diffuse past a semi permeable membrane to a concentrated solution. By increasing the temperature, this rate of diffusion can be increased and thus, the process of osmosis is faster. ...read more.

Conclusion

With a decrease in temperature, then the rate of osmosis also decreases and so perhaps the temperature was not kept at a constant during the entire experiment. Now, in order to keep the temperature constant, I will keep the Mc Carthy bottles containing the potato cylinders inside a stored area, where the temperature is kept constant always; this will prevent the chance of any change in the rate of osmosis and thus will prevent any inaccuracies in the mass readings. I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. Perhaps I could have used a burette. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g. Though my experiment is suitable and appropriate, it can be improved further more my using a more range of concentrations of salt solution to better reveal the change in mass of the potato cylinders when placed in these solutions but more importantly to reveal the exact concentration of the potato cell sap. Thus, in this case, it may perhaps be better to use an interval of concentrations of 0.25M. Thus, this will help to narrow down the exact concentration of the cell sap. To investigate osmosis even further numerous experiments can be done: 1) You could do an investigation into how changing surface area and the amount of solution affects the rate/how long it for osmosis to occur. 2) You could do an investigation into how osmosis is affected when it occurs it different conditions, i.e. how osmosis occurs under high or low temperatures. 3) You could investigate osmosis further by seeing the effect of concentration of different types of potatoes or using entirely different plants, vegetables, fruits etc. This would test how different semi-permeable membrane could affect osmosis and the movement of water out and into organisms. FAHIM TALUKDER 11TS ...read more.

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## Here's what a teacher thought of this essay

4 star(s)

This is an extremely detailed investigation that shows a good understanding of the scientific process.
1. The preliminary test is conducted well.
2. The introduction section is very well researched and extremely well written, although the sources should be referenced.
3. There has been a great deal of care taken in sections such as the variables, method and safety.
4. The analysis of the results needs to be readdressed and anomalous results left out.
5. The evaluation shows a good understanding of the scientific process.
7. There is a great deal of repetition in this report that should be removed.
****(4 stars)

Marked by teacher Luke Smithen 08/05/2013

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