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Osmosis investigation.

Extracts from this document...

Introduction

Planning the investigation What is osmosis? Osmosis is a special type of diffusion that only happens in water. It is the diffusion of water molecules through a semi-permeable membrane along a concentration gradient from a high concentrated solution to a diluted solution along a concentration gradient in order to lower the concentration of the solution the other side of the membrane and overall to make the solutions at equilibrium (to make the solutions at an equal concentration). A semi-permeable membrane is porous but allows water to pass through it more rapidly than dissolved substances. In layman's terms: it has lots of really small holes in, so small in fact, that in which small molecules such as water and small ions such as sodium and potassium ions may pass in either direction through the membrane, and bigger molecules such as glucose and sugars can't. It is similar to a sieve that can filter out small molecules and leave in large molecules. Key: Sugar molecule Water molecule An example of osmosis: The above picture shows us that the water molecules are moving into the concentrated sugar solution through the semi-permeable membrane. The sugar molecules are much bigger than the water and therefore are too big to fit through the little gaps in the semi-permeable membrane. Eventually more water molecules will go into the concentrated sugar solution until both solutions were of an equal concentration. Osmosis is useful for plants because it opens the stomatal guard cells (the cells that let air in and out of the plant). When there's a lack of water the stomata pores close to avoid any more water being lost. Osmosis is also important in plant cells because it gives support to green plant tissue. Animal cells don't have a cell wall and therefore can easily burst if too much water is taken in via osmosis. When a plant is well watered the cells will draw in water by osmosis. ...read more.

Middle

When weighing the cylinder of potato I will dry it on a paper towel so a to get more accurate results. To make sure I am safe whilst carrying out the experiment I will take care when handling the scalpel and borer. One important thing to consider when carrying out the experiment is the variety and source of potato must at all times be the same; this is because different variety and age of potatoes have different thickness' of cell wall. When carrying out the experiment I will use the same potato and if not possible then potatoes from the same packet as they will be the same variety and approximately the same age, therefore ensuring a fair test is in progress. Safety This may not seem like a dangerous experiment but we must bear in mind that we must always use scalpels with care, but it should be perfectly safe because the scalpels used are small and often relatively blunt. Another thing to take into consideration is that the test tubes are made up of glass, therefore I would recommend that no one run in the class while the experiment is taking place and is careful while handling the test tubes as when broken can be dangerous. One more thing to consider is that when gouging this can be messy and dangerous if the potato is missed and someone gouges his or her hand. For this reason I suggest that everyone should handle the potato gougers with care and don't boar the potatoes in your hand, use the tile or a board. Method Please note that the picture above is only using one cylinder in each test tube; in the test I will put 5 cylinders in each test tube. ? I will collect the equipment listed in the section called 'apparatus'. ? Then label each beaker with the following: 0%, 5%, 10%, 15%, 20%, and 25%. ...read more.

Conclusion

This would make the concentration of the sucrose solution inaccurate and the degree of inaccuracy would vary from region to region of solution and hence would be different for every volume taken from it. To eradicate the error caused by this the sucrose solution should be stirred before each volume is taken from it. But considering the above I think it was because the tissue sampled was also less dense than the solutions it was immersed in. This meant that the potato cylinders floated in the solution and hence a small portion of each chip was not immersed in the solution. These cells will not have been as affected as the immersed cells, although water will have diffused into or out of them through the immersed cells. The diffusion pathway is far greater than that of the immersed cells, as the water molecules have to pass through the immersed cells first, so osmosis will have occurred at a slower rate, and thus to a lesser extent over the same time period. The mass of these cells will therefore have contributed to the initial mass and remained almost constant, making the final change in mass less accurate. I think the conclusion reached was not accurate because there were many anomalous results, but the rest lay on a smooth curve, which intercepted the x-axis at a credible point. The exact value of this point may not be exactly accurate as it is calculated from a freehand curve of best fit. There are also many sources of error in the procedure. However overall the only major source of error was the balance used and possibly variability of potato tissue as most of the other major sources of error are equal for all cylinders, for example temperature. The results obtained were as accurate as possible with the apparatus that was available and the conclusion obtained is reliable for the potato used. The water potential of another potato may vary greatly from that of the one used here and therefore it is hard to calculate the inaccuracy of the value obtained. Fay Hanrahan 11DV ...read more.

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