Location: Outside U.S.
Date: Winter 2012-2913
Hello. I teach General High School Biology (9-12, but I mostly have 9th & 10th graders for students). For most of my 16 years of teaching, I have done so with the understanding that Prokaryotes do not possess cilia -- That is until our last textbook adoption.
(I feel the need to state that I am NOT one of those teachers that â?oteaches out of the textbook. I also do not automatically accept, or model such behavior for my students, information just because it is printed. But I do design my class so that the students are regularly using the text as a resource for reinforcement and review, sometimes as an intro, and occasionally as a supplement.)
To continue, the textbook we are currently using (Glencoe Science Biology, McGraw-Hill 2009) not only states that Prokaryotes have cilia but they go on to distinguish it from Eukaryotic cilia by stating, Prokaryotic cilia and flagella contain cytoplasm and are enclosed by the plasma membrane. When I noticed this, it prompted me to do some internet research. Thus far, I have been unsuccessful in finding any sort of definitive answer. Mostly the sources I have reviewed either deliberately state that Prokaryotes do not have cilia, or they are ambiguous -- sometimes mentioning it as a general cell feature but not specifically mentioning whether or not both cell types possess cilia, or the source does not even address cilia at all (usually those are sources reporting on just Prokaryotes).
I also looked through some of my old college texts. The first two texts I searched mirrored my lack of success searching the internet. My Introduction to Microbiology text states, Cilia and flagella are only on some protozoa and some specialized animal cells. However, my General Biology textbook has a table that list rows of Cell Features in the far left column, including Flagella or cilia (when present). The other three columns are titled, Prokaryotic Cell, Plant Cell, and Animal Cell. For the Prokaryotic Cell the table simply lists solid, rotating in regards to Flagella or cilia (when present) -- which, as you can see, leaves the reader unsure as to whether the table is reporting that Prokaryotic cells have flagella, cilia, or both that are solid and rotating. (I know that Prokaryotic flagella rotate, so the author must have at least intended to report that fact. This ambiguity is mirrored in many sources I have reviewed.) If one flips further into the textbook to the section where Bacteria are discussed (a section that would now more appropriately be titled Prokaryotes since the group has now been separated into Bacteria and Archaea), there is no mention of cilia under Bacterial Movement. Only flagella and gliding are mentioned.
So as you can see, among the sources I have viewed there are both direct and indirect contradictions as to whether or not Prokaryotes possess cilia. That led me to wonder if perhaps some sources somehow are mixing-up opilia with cilia. But as far as I know, pili are not used for locomotion so that seems unlikely.
Sorry for the long-winded question, but I thought it was important to include the kinds of things I have come across in the last few years when trying to find clarification about whether or not prokaryotes possess cilia. I'm hoping you can add some better insight? Until then, I will continue to explain (briefly) to my students that I am unsure about whether or not cilia is actually a Prokaryotic feature
I searched the question: “do prokaryotes have cilia?” I got (among other “hits”) the answer:
This source gave an unambiguous “Yes”. The source implied that this is a fairly common characteristic of prokaryotes. I commend you on your point of view that just because it is in the text may or may not be true.
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Update: November 2011