Investingating The Cause And Effect Of Surface Area Of Diffusion

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There are several biochemical processes take place in the organisms which indispensable for the living. For instance, respiration, excretion and nutrition. These processes involve the exchange of nutrients, gases and waste products. Cells have to be small in size for expediting the diffusion rate of nutrients and gases into and out of the cells in high rate. It’s because the diffusion rate is depending on the surface area to volume ratio. The diffusion rate will be slow if cells are big as the volume is greater compared to the surface area. Moreover, if the cells continuously growing, the volume grows faster than the surface area and lead to a sparse surface area in which cells couldn’t get enough needs and might end up dying. The surface area of a cell means the area of the cells exposed to the surroundings and volume means the internal space of the cells. In this experiment, you will investigate the cause and effects of two variables, the surface area to volume ratio and the rate of diffusion by using agar jelly.

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To investigate the relationship between the size and shape of an object and the time taken for a substance to diffuse to its centre Hypothesis It was hypothesised that if the surface-area-to-volume ratio of the agar block is bigger, then the diffusion rate will be faster.


4 agar blocks

Paper towel

0.1 M sulphuric acid

4 x small beakers

Clear plastic ruler

2 x Cutting tile



Disposable gloves Procedure

Positioned the agar on the cutting tile.

Measured the length and cut the agar blocks into correct size by using the scalpel. As the following size, A 20mm x 20mm x 20mm B 12mm x 12mm x 12mm C 20mm x 30mm x 3mm D 10mm x 18mm x 10mm

Poured 25ml of sulphuric acid in each of the 4 beakers.

Slowly put the agar blocks in each cup and checked the blocks are fully covered by the sulphuric acid. Started the stopwatch once the blocks are added into the acid.

Let the process for 5 minutes then took the agar blocks out of the acid. Placed them on the paper towel for drying up.

Cut each block in half by using the scalpel. Then, measured the thickness of the coloured section.

Recorded the results in a table, as shown below


Dimensions of block Surface area (mm²) SA Volume (mm³) Vi SA:V Thickness of coloured section (mm) Volume of coloured section Vr Volume of discoloured section Vd % of block diffused with acid 20X20X20 mm 2400 8000 0.30 15 3360 4640 58.0% 12x12x12 mm 864 1728 0.50 8 515 1213 70.2% 20x30x3 mm 1500 1800 0.83 0 0 1800 100% 10x18x10 mm 920 1800 0.51 5 261 1539 85.5% A B C D This table shows the results on the rate of diffusion relatives with the surface area to volume ratio. Clearly showing that larger the SA: V, the higher the rate of diffusion. Block A with the lowest ratio and result in a lowest percentage of block diffused with acid (58%). While block C, highest ratio, 100% of block diffused with the acid and which results in 0mm of coloured section. The ratio of block D greater than block B by 0.01 and therefore result in a higher percentage of block diffusion.


There is no relationship between this two variables. It’s because the overall trend is not consistent, the largest volume has the lowest rate diffusion but the rate of diffusion of the smallest volume of the block didn’t show the highest rate of diffusion.

There is no relationship between this two variables as the comparison result is not consistent. The largest surface area results in lowest rate of diffusion but the smallest surface area didn’t lead to an utmost rate of diffusion.

The larger the surface area to volume ratio, the larger the amount of diffusion of acid. The results suggested that Block C with the largest ratio has the largest percentage of block diffused with the acid and Block A with the least ratio has the smallest percentage.

The results from the experiment supported the hypothesis. As shown in table, the overall trend of the data suggests that the larger the SA: V, the higher the percentage of block diffused with the acid.

Allowing the exchange of nutrients, gases and waste products take place efficiently. It’s because cells have large surface area to small volume and this can lead to higher rate of diffusion.

It is important to be careful with the use of scalpel as it has a sharp edge. Next, wear gloves through the whole experiment as it involving the use of acid. Also, prevent using metal spoons to take out or place the agar blocks into the beaker as there will have reaction between metal and acid. Safety procedures are essential and necessary to prevent minor or major accidents.

An improvement to the method would be measuring the temperature during the trials. It’s because the temperature is an extraneous variable which might affect the results. The higher temperature might cause a greater energy and lead to a higher diffusion rate. A more reliable way to place the blocks into the beaker could be by using the cradle to make sure the acid is fully cover the blocks. For a more reliable results, the experiment could improve by carrying out more times with the same method to prevent abnormalities during the trials. For a more comparable result, use a more different size of blocks.

For a better improvement of this experiment, experimenters could use model or machine to cut out the exact size of the agar jelly error in measurements.

In my humble opinion, I think that cell E would allow for the highest rate of diffusion. It’s because it has the largest surface area due to the villi and microvilli. Villi are tiny, vascular projections which can be found in the intestine to aid food absorption which involve the process of diffusion and active transport.

Many animals curl up tightly on cold days to prevent restraint body heat. As the body’s surface area is directly proportional to the external heat loss. When the animals curl up, surface area expose is smaller, the surface area to volume ratio becomes smaller. Therefore, less heat is lost to the surroundings and warm up the animals. In a hot climate, animals tend to stretch out to increase heat lose and cool down their body temperature. As when they stretch out, surface area exposed to the surroundings is greater and this results in greater heat loss relative to its volume.


In summary, this experiment investigated the cause and effect of surface area to volume ratio and the rate of diffusion. It can be concluded that the larger the ratio, the greater the rate of diffusion. This was shown by the findings of the experiment, Block C with the highest ratio, the colour decolourised completely by the acid while Block A with the highest ratio left with the largest volume of the coloured section. This investigate has shown that cells have to be small in size in order to get a high diffusion rate.


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