<b>A Gram-negative bacterial flagellum</b>. 
<p>A flagellum (plural: flagella) is a long, slender projection from the cell body, whose function is to propel a unicellular or small multicellular  organism. The depicted type of flagellum is found in bacteria such as <i>E. coli</i> and <i>Salmonella</i>, and rotates like a propeller when the bacterium swims.
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The bacterial movement can be divided into 2 kinds: <i>run</i>, resulting from a counterclockwise rotation of the flagellum, and <i>tumbling</i>, from a clockwise rotation of the flagellum.
<a href="//commons.wikimedia.org/wiki/User:LadyofHats" title="User:LadyofHats">LadyofHats</a>
2007-11
<span class="int-own-work" lang="en">Own work</span> (<span lang="en" dir="ltr">Original text: <i><bdi lang="">self-made<br>References: <a rel="nofollow" class="external autonumber" href="http://www.talkdesign.org/faqs/img/fig1.gif">[1]</a>,<a rel="nofollow" class="external autonumber" href="http://www.talkdesign.org/faqs/img/fig2.gif">[2]</a>, <a rel="nofollow" class="external autonumber" href="http://ourworld.compuserve.com/homepages/dp5/flagellum.jpg">[3]</a> (main 3), <a rel="nofollow" class="external autonumber" href="http://www.arn.org/docs/mm/flag_labels.jpg">[4]</a>, <a rel="nofollow" class="external autonumber" href="http://www.biophysj.org/cgi/content/full/91/10/3640">[5]</a> (propeller rotation), <a class="external mw-magiclink-pmid" rel="nofollow" href="//www.ncbi.nlm.nih.gov/pubmed/17142059?dopt=Abstract">PMID 17142059</a> (bend).</bdi></i></span>)