What are some examples of surface area to volume ratio?
The surface-area-to-volume ratio or SA:V, is the amount of surface area of an organism divided by its volume.
Assume that you are a spherical cell.
Your SA:V is important because you depend on diffusion through your cell wall to obtain oxygen, water, and food and get rid of carbon dioxide and waste materials.
Let's calculate SA:V for three cell sizes.
r = 1 mm:
r = 2 mm:
r = 3 mm:
Your surface area to volume ratio decreases as you get bigger.
Now let's assume that nutrients can diffuse into your cell at the rate of 0.05 mm/min. In 10 min they would reach 0.5 mm to the centre. What fraction of your cell would still be unfed after 10 min?
r = 1 mm
r = 2 mm
r = 3 mm
The bigger you get, the longer it takes for the nutrients to reach your interior.
Beyond a certain limit, not enough nutrients will be able to cross the membrane fast enough to accommodate your increased volume.
You will have to stop growing if you want to survive.