Posted by: salamandercandy | July 12, 2007

Scale in Biology

I’ve spent another week here at Vanderbilt, studying antimicrobial peptides from frogs and their effects on different microbes. A lot of biology lab work involves measuring out liquids, moving liquids between tubes, mixing them, heating them to particular temperatures for particular lengths of time, etc. You can’t actually see your tiny objects of study, so conducting very different types of research can look superficially the same. I’m used to working with DNA and enzymes, biological molecules that are too small to see even with a microscope, and in practice it just looks like I study small plastic tubes containing clear liquid. Similarly, the microbes I’m studying here can’t be seen with my naked eyes, so it’s just liquids in tubes all over again.

However, the volume of the liquids is different. In molecular biology, almost all of your time is spent manipulating volumes between a microliter (a cubic millimeter) and a milliliter (a cubic centimeter). Working with DNA, I never use a pipette tip that can hold more than a milliliter. Working with cells, though, I often measure out tens of milliliters. It’s because cells are so enormous compared to molecules; a microliter can easily hold billions of molecules, but to store billions of cells, you usually need many milliliters. And since cells actually can be seen under the microscope, that adds a whole new activity to my routine.

This got me thinking about biological scale in practice. Not the size of proteins versus cells versus organisms, but the scale at which scientists actually work when they study different levels of biology. Here’s a list of your basic options for the scale of your work:

(<0.001 meter)3: Nanobiology (individual molecules). You can’t easily manipulate a volume of less than a microliter with your hands, so studying biology at this scale (for example, dotting a miniscule volume of a gene or peptide onto a chip) requires complex robotic equipment.

(0.001-0.01 meter)3: Molecular biology (populations of molecules). The scale at which I am most comfortable. Equipment: small tubes and small plastic pipette tips holding clear liquids.

(0.01-0.1 meter)3: Cellular biology. From bacterial populations to blood samples. Equipment: large tubes and large glass pipettes holding frequently colorful and/or aromatic liquids, as well as microscopes.

(0.1-1 meter)3: Multicellular anatomy and physiology. Looking at the whole animal or plant, be it alive or be it dead, or major organs of large organisms (your brain is bigger than a liter, for example). Equipment: dissecting knives and stethoscopes.

(1-10 meter)3: Multicellular behavioral and population biology. Give the organism some space and see what it does, or set a few of them loose and watch them multiply. Equipment: a room with a video camera.

(10-100 meter)3: Ecology. Many species interacting with each other and the abiotic environment in a particular habitat. Equipment: boots, buckets, nets, shovels.

(>100 meter)3: Macroecology. Broad sweeping trends over vast tracts of the Earth’s surface, from the stratosphere to the deepest ocean depths. I suspect many macroecologists sit at computers and look at GIS and other data, so this only refers to those who actually go outside and travel from one study site to another. Equipment: a car or airplane.

Of course, this list is an oversimplification, and lots of biology takes place at multiple levels. In fact, one reason why I like population genetics so much is because you get to collect samples in the field on a macro scale, and then work with them in the lab on a micro scale. It’s also why I like biology in general more than other sciences: only biological systems are complex enough to have so much to study on so many levels of scale.


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