Table of Contents

• Prequiz
• 1: Tall (and small) tales
• 2: Metric conversions: step to the right, step to the left
• 3: 3 Worlds: Milli, Micro, Nano
• 4: Focus on the microworld
• 5: Small stuff in the microworld
• 6: Next stop... the nanoworld
• 7: End of the line... the picoworld
• 8: What to memorize

3 Worlds: Milli, Micro, Nano

We can roughly divide most phenomena of biological interest into 3 scales: the milliworld (1 meter to 1 millimeter), the microworld (1 millimeter to 1 micron), and the nanoworld (1 micron to 1 nanometer).

To get a first, rough intuition about these scales, it helps to figure out what belongs where. You already know plenty of biological phenomena that belong in the milliworld -- things like cats, mice, eyeballs, fruitflies... Notice that that's quite a range. The smaller worlds are harder to visualize because you don't see them every day.

So what's in the microworld? Starting with the biggest stuff and going down...

• protists and single-celled animals
• cells of plants or animals (eukaryotes)
• bacteria (prokaryotes)

And what's in the nanoworld? Again, starting with the biggest stuff...

• parts of cells (like mitochondria, chloroplasts, and so on) are right on the border between the micro and nano worlds
• visible light wavelength
• viruses
• cell membranes
• largish molecules (like proteins, carbohydrates, hemoglobin, etc)
• DNA double helix
• small organic molecules (like simple sugars)

I am not trying to say that there is some kind of magical division between the microworld and the nanoworld, or that the rules of physics suddenly change, or anything like that. The reason that I'm talking about microworld and nanoworld is just to give you a point of reference, to help you figure out which units will be most convenient, and which biological structures have similar sizes.

Going back to P. Bunyan for a moment, you know there are things that are convenient to measure in feet (stoves) and other things that are convenient to measure in miles (rivers). You don't mix them up, but you also know that ultimately they belong to the same continuum.