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

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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.

Uncertainty: 1% error (50ml measuring cylinder)

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Conclusion:

We can see for the table that as the block of gelatin goes from 5*5*2.5mm to 10*10*10mm the volume is increasing at a faster rate than the surface area. That is why we see that the surface area to volume ratio decreases as size increases. As the gelatin block grows it needs to carry out more and more reactions with the hydrochloric acid in order to turn fully pink.  

We can deduce the following information from the graphs:

  • As surface area increases so does the time for the acid to penetrate.
  • As volume increases so ...

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