Question: is there more bacteria on a round surface or a flat surface?

Joanna Buckley answered on 13 Jun 2010:

Good question Georgia! I like random ones like these, keep ’em coming!

Bacteria can grow on both. In fact, bacteria can grow on just about anything and can survive extremes. I look at how the element silver kills bacteria and hope to stop the spread of hospital superbugs, such as MRSA.

I think for this question, we have to turn to our old friend geometry. I know, I know… it’s not my absolute favourite either but I’m afraid we have no choice. We’re talking surface areas, so the amount of exposed surface. The bigger the surface, the more bacteria will live on it (that’s if you mean that both the round and flat surface are made of the same material).

For a hemisphere or dome, the area of a sphere is 4 x pi x r^2. The area of a hemisphere will be half that or 2 x pi x r^2. As pi is 3.142, this works out at roughly 6 r^2.

The surface area of a flat surface which is as wide as the diameter of the hemisphere (2 x r) will have an area of 4 x r^2.

This means the round surface is about 1.5 times bigger then the flat surface and therefore will have more bacteria on it.