Objective: Calculate SA:V ratio, Show the effect of SA:V ratio on rate of diffusion Hazards: Be wary when using HCL as if it gets into your eyes it could cause damage. It is also an irritant so ensure eye protection and lab coats are worn. When cutting the agar cubes to size, be carefl to not cut yourself using the scalpel. To ensure this, cut away from yourself to minimize risk. Equipment list:
Firstly, cut the agar cubes into different sizes (sides of length 2,4,6,8,10mm) and place them each in their own separate test tubes. Then add the syringe of HCL and start the stopwatch when the syringe is empty. When the dye has fully diffused out into the HCL, stop the stopwatch and record the time taken. I predicted that cubes with a larger SA:V ratio would lose their colour faster than those with a smaller SA:V ratio. Results: As one might expect, the smaller the ratio the longer it takes for the dye to diffuse into the HCL. The table above clearly shows that the cube with the SA:V ratio of o.6:1 takes the longest time (446 seconds) to lose its pigmentation, whereas the cube with a SA:V ratio of 1:3 takes the shortest amount of time (32 seconds). Unfortunately, this experiment has many limitations. For example, Dye is not the most realistic substance to observe diffusion on and may have different properties to that of oxygen. Not only this but an agar jelly block doesn't possess a cell membrane, made up of a phospholipid bilayer which would also affect the rate of diffusion.
In order to increase reliability of my results, I would repeat the experiment 3 or more times for each size of block and use these extra readings to dismiss any anomalous readings, thus giving a more accurate representation of the relationship between surface area and volume. A stopwatch giving time to a more accurate degree e.g. 2 decimal places would also increase accuracy of results. A more precise cutting tool could be used to make sure the edges are straight, for example a larger blade or a wire. As the SA:V ratio increases, the rate of diffusion also increases, showing a positive correlation between the two. This means that small living organisms such as amoeba are able to rely on diffusion for gas exchange/respiration, and therefore do not need specialised breathing apparatus.
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