Posted February, 2014 for the last of 6 lectures on March 3, 2014: Lectures for Senior University Georgetown

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"Big have little fleas upon their backs to bite 'em; and little fleas have littler fleas, and so ad infinitum."

For this final lecture, I'll paraphrase Shakespeare, (i.e., near the end of the little speech "The Seven Ages of Man," in Shakespeare's play, As You Like It, Act 2 Scene 7), where the character Jacques finishes up by saying, "the last scene of all that ends this strange, eventful history..."--- and in this present scene, really simply the last of this series of lectures---there will be more---I introduce not an age of man, but another phenomenon: We are made of cells, we humans. No one in Shakespeare's time knew anything about this invisible world (I spoke about Shakespeare last session). But that's not the weird part. There are animals that live somewhat self-sufficient life and they do all their life functions within the bodies of a single cell! Now how do they do that. We have billions of cells that make up our various parts, our mouth parts, our skin---and they're all specialized. Those tiny little one-celled animals do it all within their one-celled body, though admittedly with different parts of that one cell---which I'll be describing. Astonishing!

Relative Size

Protozoa are for the most part bigger than bacteria and smaller than tiny complex animals, but the biggest protozoa are bigger than tiny animals---and indeed, the bigger eat the smaller. Sometimes a pack of little ones attack and eat a slightly larger one. All this goes on in the size of a speck of dust. Interestingly, A speck of dust is halfway between the size of the whole planet earth and an atom. Below on a logarithmic scale is the range of smaller and larger critters with protozoa sort of in the middle.

It should be noted that some one-celled animals are smaller than blood cells---such as malaria--- and a few are just visible to the naked eye or bigger. This throws into question what it means to be one "celled."

Also, protozoa range widely in size! Some are tiny, some are humungous. They range between about 2 to 800 millionths of a meter, most being in the 30 to 200 millionths size---a "micron" being that size, marked by the sign µm.

The Microscopic Realm

As discussed elsewhere on this website, Anton van Leeuwenhoek invented the microscope and made observations. Size comparisons are on a linked website.

Bibliography

Prager, Ellen. (2011). Sex, drugs and sea slime: the oceans' oddest creatures and why they matter. Chicago: University of Chicago Press.
   A few good pages (2-5) on the place of the protoctists radiolaria and foraminifera in the big picture.





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