# What are some examples of surface area to volume ratio?

##### 1 Answer

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.