# Cell models

It's straightforward to model cells using cubes.

We can investigate the effect of increasing size on surface area to volume ratios using models based on cubes:

So, as the volume increases, the surface area does not increase at the same rate.

If a graph is drawn:

Question

What is the surface area to volume ratio of the highlighted mark?

This cube will have a surface area:volume ratio of 1.

The volume = 6 × 6 × 6 = 216

The surface area = 6 × (6 × 6) = 216

A stacked bar chart can be drawn to illustrate the proportions of surface area and volume.

In the below table scientists have estimated the surface area:volume ratios of various organisms.

OrganismSurface area in square metresVolume in cube metresSurface area:volume
Bacterium6 × 10-121 × 10-186 000 000:1
Blow fly6 × 10-41 × 10-6600:1
Whale6 × 1041 × 1060.06:1

Large organisms have:

• mechanisms to increase surface area proportionately, such as additional absorbing areas or adaptations of shape
• transport systems and keep distances for diffusion to a minimum

Organisms living in harsh environmental conditions may reduce their surface area, eg cacti, to reduce loss of water.