AQA GCSE Surface area to volume ratio (Biology)

Surface area to volume ratio.

Surface area to volume ratio can affect diffusion. Below is an image showing the calculation of the surface area to volume ratio of two cubes.

Length of side (cm)	1	2
Surface area (cm²)	1 x 1 x 6= 6	2 x 2 x 6 = 24
Volume (cm³)	1 x 1 x 1 = 1	2 x 2 x 2 = 8
Surface area:volume ratio	6:1	24:8 or 3:1

As the cube becomes larger, the surface area to volume ratio will decrease.

We can relate this to organisms, if we think of the cubes as being organisms.

The larger the organism, the smaller the surface area to volume ratio.

Surface area to volume ratio for real organisms

Below is an example of comparing a single celled bacterium to a human.

The bacterium has a surface area:volume ratio of 6 million:1

The human has a surface area to volume ratio of 28:1

This proves the point that the larger the organism, the smaller the surface area:volume ratio is.

Surface area to volume ratio for single celled organisms.

Single celled or unicellular organisms have a large surface area to volume ratio.

This is because single celled organisms rely upon diffusion to obtain nutrients such as glucose and oxygen for aerobic respiration and remove waste products such as carbon dioxide.

Their large surface area to volume ratio allows them to obtain the nutrients in sufficient quantities and remove waste products quickly enough to meet the needs of the organism.