OK, Lets get things straight. I am studying for my year 12 biology exam that's on the 11th of June. I am seriously freaking out.
The question I am about to ask is not a Homework question.

I do not understand the biology micromillimeter measurement. The one that looks like "um". I have seen in numerous amounts of times but it never seems to make much sense to me. :(
Can someone please explain it in a term that maybe I might be able to understand? :confused:
Thanks heaps, Danni

I'm sure you have looked up micromillimeter and found that it's a metric unit of length equal to one billionth of a meter. But this isn't the preferred SI unit (International System of Units). The SI unit is nanometer (nm) (= micromillimeter). The micrometer (micrometer = micron) has the symbol “um” and it is one millionth of a meter.

So a micromillimeter isn't "um".

See the Wiki SI prefix page SI prefix - Wikipedia, the free encyclopedia

From a biologist perspective a bacteria is about micrometer in size (E. coli is 1 X 2 um) while the diameter of a DNA double helix is about 2 nm

Just to slightly correct jem. The SI unit is the meter (m), but can be expressed with the SI prefix to denote meters.

As far as I'm aware, m, mm, um and nm are all equally valid (and so are the other SI prefixes).