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A Sc1 Investigation into the effect of Concentration on Osmosis:

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Introduction

A Sc1 Investigation into the effect of Concentration on Osmosis: PLANNING Aim: The aim of this investigation is to see how changing the concentration of salt in a solution will affect osmosis in potatoes. Background: All living organisms have certain requirements that must be satisfied in order for the organisms to remain alive (e.g. CO2, O2, H20 are all vital requirements). The majority of these substances are received by diffusion e.g. in gaseous exchange (in humans) O2 and CO2 diffuse into and out of the lungs. Osmosis is a special type of diffusion. Osmosis is the movements of water molecules from an area of high water potential to an area of low water potential via a semi-permeable membrane; this is a process that works in all living cells. E.g. as shown below, the water molecules move from an area of the highest water potential (HWP= a high concentration of water molecules, i.e. pure water has the highest WP) to an area of where the water molecules are in a lower concentration i.e. an area of low WP. Osmosis is similar to diffusion, this is the movement of a liquid or gas from an area of high concentration to an area of lower concentration, however, osmosis is individual because it's the diffusion of water only across a semi-permeable membrane from an area of high WP to an area of low WP. The membrane is said to be semi-permeable because it allow some but not other molecules to pass through it. In the example above the large molecules can't pass through the gaps in the membrane therefore only the water molecules can diffuse through the membrane, essentially water molecules can move through the membrane but chemicals can't. The semi-permeable membrane is vital if osmosis is to occur successfully, therefore, osmosis requires a non-disrupted membrane, e.g. if the cell membrane is exposed to too much heat osmosis can't occur because the semi-permeable membrane is disrupted. ...read more.

Middle

the variable measured) was mass/change in mass. I calculated the change in mass by weighing the potato before and after it was put in the solution, these two masses: starting mass and ending mass were then used to calculate the finishing mass: Ending Mass - Starting mass = Change in mass E.g. 21g - 13g = 8g These change in masses showed how the change in concentration had effected osmosis in the potato. However, it is difficult to compare the change in masses fairly in a graph or results table because some potatoes may have different starting masses, i.e. the data may be misleadingly represented by drawing a graph by looking at change in mass. E.g. Piece 1: Starting Mass = 50g. Change in Mass = 5g. Piece 2: Starting Mass = 10g. Change in Mass = 5g. Both pieces have the same change in mass, however, when put in context the first piece of potato has only had a 10% change in mass compared to its starting mass whereas the second piece has had a 50% change in mass compared to its starting mass. By only looking at the change in mass we can mistakenly believe that both these potatoes have had the same change in mass compared to their starting mass. To get around this problem we must process the results obtained rather than just working out the change in mass. To process the results further I found it best to process the results into a percentage change. (Ending Mass/Starting Mass) * 100 = Percentage after compared to start. ((Ending Mass/Starting Mass) * 100) - 100 = Percentage Change. By processing the results into 'percentage change' and plotting a graph from this we can gain a clear fair picture of the results obtained. Results: A Table Showing the Raw Data Recorded from an Investigation into the Effect of Concentration on Osmosis in Potato. ...read more.

Conclusion

The original results detract from the firmness of the conclusion because of the anomalous results and the fact that they reduce the reliability of the experiment. However, the conclusion can be said to be firm because both the experiments supported the statement and the repeat run firmly indicated that the conclusion was entirely true. Improvements and Further Work: There are number of alterations and improvements that could be added to the method which would allow us to investigate further into the area of osmosis in biology. -You could investigate osmosis further by seeing the effect of concentration of different types of potatoes or using entirely different plants (e.g. plants, other vegetables, fruits or a different type of potato). This would test how different semi-permeable membrane could effect osmosis and the movement of water out and into organisms. -You could investigate the time it would take for potato cells to plasmolysis. I.e. you could investigate using extremely low or high concentrations with potatoes. This would allow you to see how long it would take the potato to plasmolysis and die. -You could do the experiment using a longer period of time for osmosis to occur. By doing this you could investigate how long it takes for osmosis to fully complete. It could also be connected to the above improvement in finding how long it takes for the potato cells to plasmolysis. E.g. use a 3 hour or longer 24 hour period. -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. -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. You could also investigate the amount of heat that the semi-permeable can withstand before the membrane is disrupted. After this you could expose the potato to a certain amount of heat, a large amount (but not enough to completely disrupt the membrane) and then you could see how exposing the potato to heat beforehand affects osmosis. Basil Adamo ...read more.

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