Re: Grapsing the size of an average human cell

Hi Joan,

This is an interesting excerise. First of all, I should correct one point in your calculations, 20 microns is actually 1/50 of a millimeter, since 1 millimeter = 1000 microns. This means that 20 microns = 0.000787401575 inches, and that there are about 1270 cells (at an average of 20 microns each) per inch.

So, rather than having your students try to divide an inch into 1270 equally sized fractions, I can suggest using a very small item (see below) that students are familliar with, and then comparing that to a very large item that students are familliar with, and explaining to the students that if the large item were 1 inch long, the small item would be the size of a cell.

Lets start with a golf-ball as your small item. A golf-ball is about 1.68 inches in diameter. 1270 of them laid end to end would be about 59 yards long. One of the structures in your school might be about 59 yards long, so you could explain to the students that if the structure was 1 inch long, a cell would be the size of a golf ball in comparison to the structure.

Or, you could start with a 1/4 inch long grain of rice or a lentil. 1270 of these laid end to end would be about 26.5 feet long. The cargo section of the longest U-Haul truck is about 26 feet long, or you might be able to lay out a 26.5 foot long piece of tape on the floor of your classroom, and again explain that if the piece of tape represented 1 inch of length (or 1/2 inch long if you could only manage 13.25 feet of tape), the lentil would be the size of a cell.

I hope this helps you; if not, please feel free to submit another question.

Cheers!