Principles of SA:V
- Surface area and volume are both very important factors in the exchange of materials in organisms
- The surface area refers to the total area of the organism that is exposed to the external environment
- The volume refers to the total internal volume of the organism (total amount of space inside the organism)
- As the surface area and volume of an organism increase (and therefore the overall ‘size’ of the organism increases), the surface area : volume ratio decreases
- This is because volume increases much more rapidly than surface area as size increases
As size increases, the surface area : volume ratio decreases
The surface area:volume ratio calculation differs for different shapes (these shapes can reflect different cells or organisms)
Examiner Tip
You are expected to be able to calculate the SA:V ratio for a cube, cuboid or cylinder and explain how the increasing size of an organism affects the SA:V ratio.
