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Surface are to volume ratio is an important concept that you need to understand.
Essentially, it is area of an object that is exposed to the external environment (surface area), compared to the amount within an object (volume).

Therefore an elephant has a lower surface area to volume ratio than a mouse.

The smaller an object is the greater its surface area to volume ratio.


Surface area = Length x height x number of sides

Volume = Length x height x width

SA:V = Surface area ÷ Volume  

Surface area: 1 x 1 x 6

        = 6

      Volume:1 x 1 x 1

        = 1

      SA/V: 6 ÷ 1

        = 6

This cube has a surface area to volume ratio of 6

Surface area: 4 x 4 x 6

        = 96

      Volume:4 x 4 x 4

        = 64

      SA/V: 96 ÷ 64

        = 1.5

This cube has a surface area to volume ratio of 1.5

Small cube Large cube

A high surface area to volume ratio, allows objects to diffuse nutrients and heat at a high rate.

You will often see small mammals shirving constantly, because they are quickly loosing body heat to the enviroment and need to generate more heat to survive.

This is also why we have over 1,000,000 small cells, instead of 5 large cells.

As you can see, the large an object becomes, the smaller its surface area to volume ratio is.

The video to the left uses sugar cubes and sulphuric acid.

Observe the amount of time for the reaction to take place.

Now observe the video to the right.

In this experiment, we are using sugar powder instead of cubes.

Notice how much faster the reaction occurs. This is due to the increase in surface area.

The cubes above, have a much smaller SA:V ratio than the powder.

Continue to  Diffusion and osmosis SA:V activity


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