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To investigate the relationship between the time taken for diffusion and cell dimension.

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Introduction

Banu Thuraisingam Aim: To investigate the relationship between the time taken for diffusion and cell dimension. Procedure: 1. Place the gelatin block on a tile or Petri dish and use a scalpel or razor blade to cut it in half, producing two cubes of 10mm sides 2. Keep on of these cubes intact and cut the other in half 3. Repeat this cutting operation until you have 4 more cubes. 4. Fill a test-tube to within 10ml of the top with dilute HCl 5. Note the time: starting with the largest block drop all the blocks into the acid in the test-tube and close it securely with a rubber bung or cork. 6. Tilt the tube to spread the gelatin blocks along its length. Hold the tube horizontally and rotate it so that you can see each block clearly and from all sides. Try not to warm the tube too much with your hands or the gelatin may dissolve. 7. Note the time taken for the acid to penetrate to the center of the block as indicated by the disappearance of the orange color. Data Collection: This is a table of results showing the time for hydrochloric acid to penetrate a gelatin block with the variance of size which includes surface area, volume and surface area to volume ratio. ...read more.

Middle

Both holding the test tube with my warm hands and holding the test tube to the sunlight could have increased the temperature of the Hydrochloric acid and thus increasing the rate of penetration. The results could have been affected due to the following reasons of human error. One place where human error takes place is when cutting the gelatin into blocks as we can never be sure if the sizes we have cut are exactly the sizes that are wanted. There are such problems as cutting in a straight line as well as measuring and handling a jelly-like substance. Another human error would be making the distinction between when the orange gelatin has become fully pink. By doing the experiment I can honestly say that it is very difficult to decide when the orange has become pink as it is a gradual change and not an immediate one. The results are based on what people perceive the color to be. There is also human error in stopping the stop watch. When you decide that the color has fully changed and you want to stop the stopwatch it takes at least a few seconds for your brain to process that and for your finger to hit the stop button. ...read more.

Conclusion

Therefore, since a cell must maintain a certain surface area to volume ratio, its size is limited. Cells make up organisms so if we think of this lab on a larger scale we can deduce more information. Organisms have to exchange substances like food, waste, gases and heat with their surroundings. These substances diffuse between the organism and the surroundings. The rate at which a substance diffuses is given by Fick's Law: Rate of Diffusion a surface area x concentration difference distance The organism's surface area that is in contact with the surroundings determines the rate of exchange of substances. The volume of the organism determines the requirement for materials. Thus the ability to meet requirements depends on the surface area to volume ratio. As organisms get bigger their volume and surface are both get bigger, however volume increases more rapidly than surface area and we can also see this in our results. There is a problem with size however. When the organisms increase in size it becomes harder for them to exchange materials with their surroundings. Thus, as mentioned earlier, this problem sets a limit on the maximum size for a single cell of about 100mm. If it is any bigger than this the materials just can't diffuse fast enough to support the reactions need to sustain life. ...read more.

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