Surface Area to Volume Ratio (AQA A Level Biology)

What is Surface Area to Volume Ratio?

• 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

Maths Skill: Calculating SA:V Ratio

How to calculate surface area to volume ratio

• The surface area : volume ratio calculation differs for different shapes (these shapes can reflect different cells or organisms)

       Step 1: Rearrange the equation to find the radius

r² = surface area/4π

       Step 2: Sub in relevant figures

r² = 10.12 ÷ 12.56 = 0.805

       Step 3: Find the square root of r²

Square root of 0.805 = 0.897

       Step 4: Find the diameter from the radius

D = 2r

2(0.897) = 1.794

       Step 5: Round to three significant figures

1.79 mm