Figure 1. Structure of a vegetative Chlamydomonas reinhardtii cell. ; This cell has a 5-10 µm diameter (Gallaher et al., 2015). The two anterior cilia possess a 9+2 microtubule structure characteristic of motile cilia of eukaryotes. The cilia are critical for mating processes and confer motility to the cell (Harris, 2001). A single cup-shaped chloroplast occupies a large proportion of the cell's volume. This organelle houses the machinery for oxygenic photosynthesis and contains the pyrenoid, a structure in which Rubisco is concentrated; the pyrenoid is a component of the carbon concentrating mechanism (CCM) which functions to concentrate inorganic carbon in the cell against a concentration gradient (Mackinder et al., 2016). Close to the cell equator, at the edge of the chloroplast, is the eyespot. This primordial visual system allows the cells to orient their swimming toward or away from the light (phototaxis). Under hypoosmotic conditions, the cytoplasmic water content is maintained by pumping water out of the cell through contractile vacuoles positioned at the cell’s anterior (Komsic-Buchmann et al., 2014). At the base of the cilia are the basal bodies, which are responsible for ciliary assembly (Dutcher and O'Toole, 2016). Other features of the cell include a centrally located nucleus, a proteinaceous cell wall, Golgi bodies within the cup-shaped region formed by the chloroplast, and mitochondria. Image credit: Debbie Maizels.