Imagining a virus April 27 2020, 1 Comment

We are all making major adjustments as the novel coronavirus runs around the globe. I would like to have some magic to work on the problems of teaching remotely and sudden, forced homeschooling, but the only magic I know is the wonder of nature. I’ll give you some lesson ideas to help deliver wonder to children.

The present situation calls for explorations of viruses. These tiny entities are hard to understand without some good illustrations and models. You can start with a math lesson about their size. You will need a meter stick or other way to measure a meter, and a ruler or a meter stick that is marked in millimeters. Children can observe a meter and then a millimeter (mm). Note that a millimeter is one-thousandth of a meter. One millimeter is about the diameter of the head of a pin. The smallest known vertebrate, a frog named Paedophryne amanuensis, is about 8 mm long.

Next, children and adults have to use their imaginations. The smallest thing that we can see using only our eyes is about a tenth of a millimeter. We need to go much smaller than that. The unit that is one-thousandth of a millimeter is a micrometer (officially spelled “micrometre” outside the US and abbreviated μm). The micrometer is useful for measuring bacteria, organelles in eukaryotic cells, and the shorter wavelengths of infrared radiation. Most animal cells range from 10-30 μm across.  

While a few of the giant viruses are in the 0.5 micrometer range, most viruses are much smaller. (Yes, there are such things as giant viruses, but they don’t infect humans.) To measure the diameter of most viruses, we need to go a thousand times smaller than a micrometer, down to the nanometer (abbreviated nm). The nanometer is one-thousandth of a micrometer. The wavelengths of visible light range from about 400-700 nm. The DNA helix is about 2 nm across, and common viruses range from 20-300 nm in diameter.

The highest magnification in a light microscope is 1000X. We can see bacteria and the giant viruses with this magnification, but to see anything smaller, we must use an electron microscope. For detailed pictures of a virion (a single particle of virus) like the one below, biologists use computer illustrations based on the molecules that make up the particle.

This website,, from the University of Utah has a great illustration of viral size vs. other objects. There is a slider underneath the illustration that allows one to see at increasing magnification down to the size of the carbon atom. The journey helps put viruses into perspective.

My booklet, “What is a virus?” has information on the structure of viruses, their replication, and how biologists image them. See (If you have the second edition of my book, Kingdoms of Life Connected, you already have most of this booklet.) This booklet includes a pattern for making a scale model of an adenovirus. To design this model, I took the measurements of the virion in nanometers and scaled them up to millimeters. I used two-ply baby yarn for the viral DNA. The model is 1,000,000 times larger than the real viral particle; it is about the size of a baseball.

If you want to make a coronavirus model, you can use a roughly spherical object that is about 10 cm in diameter and add 1 cm spikes on the outside. This gives you a virus model that is 120 mm across. The viral particle itself is 120 nm across. If you want to show the RNA inside, your model needs to be transparent or have a flap that opens to show what’s inside. A single strand from baby yarn is the right diameter to model the virus's RNA at this scale.

Try calculating how tall you would be if you were a million times larger. If you want to do it the easy way, use a unit converter on the Internet. Enter your height and then add six zeros. To give you an idea of the answer, if an average height woman were a million times taller, she would be about 1000 miles or 1600 kilometers tall!

You may wonder how something so small as a virus can change our world in such major ways. There are many people trying to figure that out right now.