Understanding Surface Area to Volume Ratio (A-level Biology)
Understanding Surface Area to Volume Ratio
Exchange Surfaces
Surface Area to Volume Ratio (SA:V)
In order to calculate a surface area to volume ratio, we must first understand what is meant by the surface area and volume respectively.
The surface area can be defined as the “area of material it would take to cover an object completely”. In gas exchange, the surface area of the cell is the total area of the cell membrane.
For a cube, this can be found by multiplying the hight by the length and then by the number of sides (6 in the case of a cube!)
The volume is defined as “the amount of space that is enclosed within a container”.
For a cube again, this can be found by multiplying the height by the length and then by the depth of the object:
For a cell, the volume can be approximated by calculating the volume of a sphere:
Calculating the Ratio
The rate of exchange is determined by the surface area to volume ratio. The ratio is measured by dividing the surface area by the volume:
The greater the surface area to volume ratio, the greater the efficiency of exchange. A
s the size of the cells grow, their surface area to volume ratio decreases, decreasing their efficiency of exchange. In order to overcome this, cells can divide into two new cells, where the new cells have a greater surface area to volume ratio.
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