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Diffusion is particles moving from a level of high concentration to a level of low concentration. Diffusion occurs through the membrane but as the cell size increases the surface area to volume ratio decreases. This means the rate of diffusion slows down, the process of diffusion is useful to cells so if they don’t get nutrients in or waste out fast enough they die.

The cell membrane expands as the cell grows bigger but when this is happenings it means the volume is increasing faster than the surface area meaning the approximate size of the surface area available to pass resources to the cell slowly decreases. Other factors that affect the surface to volume is the temperature, greater the temperature the greater the random movement of molecules meaning greater diffusion and surface area, greater the surface area, the greater the rate of diffusion, but lastly concentration is when the greater the difference in concentration the greater the rate of diffusion.

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An experiment was conducted to test the diffusion of agar cubes, in this experiment the size of the agar cubes was changed and the in the new modification to the experiment is the level of acid used is changed. This experiment is going to be conducted 3 times with 5 different strengths of acid. The links between concepts that relate to the experiment are the connection between diffusion and concentration as higher the concentration the quicker it should diffuse. The strategies that is intended to be implied so the results are consistent is to make sure the acids are measured to 50ml, we will make sure all the agar cubes are dropped at the same time and the same person will measure the cubes so the measurements are consistent to see how different the agar cubes are different in size.

Hypothesis: If 5 agar cubes are placed in different strength acids than the higher strength acid will diffuse quicker than the other because as the concentration gets higher more diffusion will occur


  1. Collect the equipment and set up the equipment
  2. Cut agar cubes 2x2x2cm
  3. With the 5 different strengths of acid put 50ml of each in 5 separate cups
  4.  Get the timer ready and drop the agar cubes in the acid at the same time
  5. Time the agar cubes for 10 minutes
  6. After the ten minutes are finished take out the agar cubes
  7. Cut the agar cubes in half
  8. Measure the diffused part of the agar cube and write it down
  9. Repeat steps 4 to 8 two more times until you have done the test 3 times (the acid can also be reused or just top it up when needed)

Risk assessment

–          If the acid spills, clean it up immediately using paper towels, and wash hands thoroughly

–          If the glass dish breaks, alert the teacher and clear the area

–          If the newspaper is on fire, alert the teacher and assist in putting out fire

–          When handling acid wear Safety goggles


Trial 1

Hydrochloric acid strength Surface area cm2 Volume cm3 SA:Vol Diffusion rate mm3
0.02 23.2 7.6 23.2:7.6 21
0.1 20.88 6.48 20.88:6.48 33
0.5 22.4 7.2 22.4:7.2 48
1 20.08 6.08 20.08:6.08 43
2 17.32 4.896 17.32:4.896 38

Trial 2

Hydrochloric acid strength Surface area cm2 Volume cm3 SA:Vol Diffusion rate mm3
0.02 23.2 7.6 23.2:7.6 0
0.1 20.88 6.48 20.88:6.48 24
0.5 22.4 7.2 22.4:7.2 41
1 20.08 6.08 20.08:6.08 48
2 17.32 4.896 17.32:4.896 46

Trial 3

Hydrochloric acid strength Surface area cm2 Volume cm3 SA:Vol Diffusion rate mm3
0.02 23.2 7.6 23.2:7.6 0
0.1 20.88 6.48 20.88:6.48 19
0.5 22.4 7.2 22.4:7.2 39
1 20.08 6.08 20.08:6.08 46
2 17.32 4.896 17.32:4.896 47


Hydrochloric acid strength

0.02 0.1 0.5 1 2
7 25.3 42.7 45.7 131












The action of diffusion was tested by concentration of different hydrochloric acids in an experiment where more diffusion occurred as the acids got higher in concentration. The reaction to the acids increased as the concentration of the acids increased meaning more diffusion. It was hypothesised that as the acids got higher in strengths the diffusion would be more affective but one acid was misread and was much slower than the others. In the experiment we changed the concentration of the acids, after we set everything up the agar cubes were put in 5 different acids (one in each) at the same time and started the timer and waited 10 minutes. After the 10 minutes we took the agar cubes out of the acid and cut the cubes in half to see how much it had diffused, the diffused part of the agar cube was measured and the results were recorded. This was repeated 2 more times until we got 15 results in total. In the last trial one of the acids was not filled enough and the agar cube didn’t diffuse properly and it was uneven.  One of the acids used was very weak and it was supposed to be 0.2 but as the experiment was occurring we released that the acid could have been 0.02 so we concluded that the acid was 0.02 not 0.2. Some other improvements for the future is to check the acid after each trial and make sure there is enough acid for the next trial so there is no anomalies. An improvement that can occur for future experiments is when we were conducting the results we waited for 10 minutes but instead of doing that we could have waited until the agar cubes had finished diffusing instead.


In conclusion there are quite a few things that contribute to diffusion some of them being the surface area to volume ratio, temperature and concentration. Concentration is what was tested in the experiment for diffusion of agar cubes with different strength acids. So overall the experiment was a success with one thing that could change in the experiment for next time is instead of waiting 10 minutes wait until the agar cubes are finished diffusing and seeing how long it took for that to happen.


  • The world of cells, the problem of size. (2019, June 3). Retrieved from BIOdotEDU:
  • What is Diffusion. (2019, June 3). Retrieved from bbc:
  • What is the importance of diffusion in biology? (2019, June 3). Retrieved from Quora:

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