Transmission electron microscope image, showing an example of green algae (Chlorophyta).  <br><br><i>Chlamydomanas reinhardtii</i> is a unicellular flagellate used as a model system in molecular genetics work and flagellar motility studies.  <br><br>This image is a thin x-section cut through the isolated axoneme. <i>Chlamydomonas</i> flagella have the "9+2" structure characteristic of all eukaryotic cells. The axoneme has a central unit containing two single microtubules and nine peripheral doublet microtubules (known as the "9+2"). Dynein sidearms project from the A tubule of each doublet. Also visible in this image are the radial spokes and the inner sheath.
Dartmouth Electron Microscope Facility, Dartmouth College
Source and public domain notice at <a rel="nofollow" class="external free" href="http://remf.dartmouth.edu/imagesindex.html">http://remf.dartmouth.edu/imagesindex.html</a>, derived from <a href="//commons.wikimedia.org/wiki/File:Chlamydomonas_TEM_17.jpg" title="File:Chlamydomonas TEM 17.jpg">Image:Chlamydomonas TEM 17.jpg</a>.