Surface Area to Volume Ratio & Cell Size
 Cells cannot get too large. When cells get too large they must divide.
 One of the main reasons that cells divide is to take advantage of a
more efficient surface area to volume ratio.
 Normal cells will divide 50 times (mitosis)
 An example of surface area to volume ratio:
Surface Area = 2cm2
Surface Area = 1cm2
Total Surface Area = 2x2x6 = 24cm2 TSA = 1x1x6 = 6cm2
Volume = 2x2x2 = 8cm3
Volume = 1x1x1 = 1cm3
S.A. : V = 3 : 1
S.A. : V = 6 : 1
*Note that the larger cube is twice the size of the smaller cube.
 As the size of a cell increases. Its surface area to volume ratio decreases.
This means that as the cell gets larger, each cubic unit of cytoplasm
/organelles are serviced by proportionately less cell membrane. Therefore
communication within the cell and its surrounding environment is less
efficient. Nutrients and waste are not processed as quickly through the
process of diffusion.
 Why is Surface Area to Volume ratio important? (S.A. : V)
1. Cells rely on diffusion for materials such as nutrients, to get into
the cell.
2. Diffusion is the movement of molecules from an area of high
concentration to an area of low concentration. Diffusion itself is not
a highly rapid or efficient means of distributing materials over long
cellular distances.
3. A larger cell requires more nutrients and produces more waste.
Cell Size
Surface Area
Volume
S.A. : V Ratio
1mm
6mm2
1mm3
6:1
2mm
24mm2
8mm3
3:1
4mm
96mm2
64mm3
1.5 : 1
8mm
384mm2
512mm3
0.75 : 1