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Biology 103
2002 First Paper
On Serendip

Sum yourself up in a single cell

Sarah Tan

Somehow during high school, a friend of mine was watching me pack a travel bag, and based on stream-of-conscious thoughts I voiced and my overall level of high stress, she likened me to a paramecium. The comparison was based mainly on our hazy recollections from freshman year biology, which didn't involve much on paramecia. We imagined paramecia swimming around at random, bumping into things, getting disoriented, and waving their cilia in a frenzy. For some time now, I've wanted to find out how accurate this image was and therefore how accurate the comparison was, but I never had a pressing reason to look these things up. For this purpose, I was more interested in the behaviors of paramecia as opposed to their physical structure, though it turns out that the latter cannot be fully disregarded in trying to understand the former.

One of the first things I found that had never occurred to me about paramecia is that they are three-dimensional. All the pictures I'd seen before of paramecia presented a view that looked two-dimensional so that if they rotated, they'd just become a line of cilia. I realize that this couldn't reasonably be the case because it would be impossible for them to always be right side up under the microscope. They travel by rotating lengthwise on an invisible axis and moving forward or backward depending on the way the cilia beat (4). Although it seems like an unproductive use of energy, this method in fact allows the paramecia to move in direct lines despite being asymmetrical creatures. Another interesting characteristic of paramecium movement that came up in more than one source is their reaction to encountering a block in a path. When that happens, paramecia go backwards a bit at an angle, turn slightly, and try again. They repeat this trial and error process until it is successful (2). The paramecium's complexity has been discussed regarding the abovementioned navigation of obstructions, as well as recognizing dangerous situations and the apparent learning from past experiences, all done by a single cell with no nervous system, neurons or synapses (7).

The common misconception that paramecia or other single-celled organisms are simple or more primitive that multi-cellular organism is completely untrue. Paramecia, as types of ciliates are larger than the average unicellular eukaryotes, and they are arguably the most complex unicellular organisms. Because single-celled organisms must perform all functions with a single cell without the advantage that multi-cellular organisms have of specialized cells for specific functions, their structure may be much more complex than the cells of larger organisms (1). Such functions include movement, water balance, food capture, sensitivity to environment, and possibly self-defense. Defense, however, is one function where there seems to be some uncertainty as to whether paramecia have it. When they are disturbed, they rapidly shoot out trichocysts-short, thread-like structures (5). While most sources seem to agree that they are used for defense, at least one argues that the trichocysts of paramecia are seldom successful in warding off predators (3). Another source seems to describe trichocysts but calls them extrusomes (1), and the difference in what should be standard terminology is confusing.

Although paramecia are almost always described as cigar or slipper-shaped, they are not stuck in that form. They are able to change shape to squeeze through narrow passages and are therefore more versatile than I had previously realized (10). The reason they maintain their usual oval form, though, is their exterior membrane, called a pellicle, which is elastic enough for small changes but stiff enough to protect them (4). Understanding just how small they are was also enlightening, particularly when a video said that several hundred thousand paramecia could live in a single dewdrop (10).

So what about the comparison that this started out with? Up until this point, the paramecium seems rather sedate, which is not what I had hoped for. Nevertheless, I continued searching and turned up some video clips of paramecia in action under the microscope. This was where I could watch the speed at which they swam around, and I finally found evidence for our assumptions in the beginning. Given the 10,000-14,000 cilia on each cell's surface (3), looking at the speed at which they can zoom around is just fun (6), but specifically zooming in on the cilia is fascinating (9). I think that in real time, the paramecium does fit the qualities that my friend meant when she described me as a paramecium because it seems to have to independently do with one cell what most other organisms only do with many more. Additionally, the new information I learned in researching paramecia for the paper also suits my personality surprisingly well, such as dubious defense mechanisms, insisting on trying to run through brick walls, using roundabout way for everyday tasks which works well for them but perhaps not many other similar organisms.

Even if this is not a topic of great interest to the general population, or even to anyone besides my friend and I who share this joke, I think that researching paramecia has been useful to me in helping to get it "less wrong." Neither of us had biology in mind when we started this, but double checking the biological facts ensures that we are using the metaphor correctly, and we can now better explain the similarities than we could before. One problem that this method of research shows, however, is the ease with which information and data can be adopted and manipulated by someone who has a specific conclusion to prove. There are all kinds of ways to spin the supposed facts so that they show a predetermined result, and if the listener is not aware of the way in which the research was obtained, it is all too easy to be misled.

References

(1) Introduction to the ciliata

(2) Paramecium - www.101science.com

(3) Paramecium - NYU

(4) Paramecium

(5) Protist Images: Paramecium Caudatum

(6) Molecular Expressions Digital Media Gallery: Pond Life - Paramecium (Protozoa)

(7) How does a paramecium move and process information?

(8) Paramecium by phase contrast

(9) Micscape video gallery

(10) National Geographic video


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