Scale in Biology

Written by Christina Wilson Bowers; Amherst College; Massachusetts, USA

Tell your students to practice closely observing one of the images in this series. Have them draw a sketch of a single detail from a zoomed-in image. Create a class gallery of these images, with captions. Make a board listing questions for further exploration. For advanced classes, include scale bars on the sketches.
Connect with the HHMI BioInteractive activity module “What van Leeuwenhoek Saw,” which includes scale calculations and unit conversions.
Look at pond water and hunt for rotifers! Consider using Foldscopes – inexpensive, handheld paper microscopes developed in the lab of Stanford University bioengineer Manu Prakash; these are an accessible tool for hunting rotifers.
There is no shortage of life forms your students can observe with their naked eye alone. Try visiting a patch of outdoor space – life thrives everywhere. Stay a while and observe. What evidence of life is visible?
How big are the creatures you can see outdoors, in comparison to those in this series of images? How big are they compared to the palm of an average human hand?
Compare the DNA sequences of a series of organisms with extended evolutionary distances.