An electron micrograph of a thin longitudinal section of the Yellow mutant of the unicellular green alga Chlamydomonas. Unlike cells grown in the light, the chloroplast appears fragmented and lacks the typical paired thylakoid membranes. The chloroplast still retains a prominent pyrenoid. Also seen is the central nucleus and Golgi complexes. Image made available by James D. Jamieson and the Department of Cell Biology, Yale University School of Medicine.