the lines of evidence that symbiotic prokaryotes were the ancestors of eukaryotic ribosomes. See cyclohexa- mide, endosymbiont theory, ribosome, ribosomes of organelles, serial symbiosis theory, translation.
Chlorella vulgaris a species of green algae exten-sively used in studies of photosynthesis and its ge-netic control. See Appendix A, Protoctista, Chloro-phyta. chlorenchyma tissue possessing chloroplasts. chlorine an element universally found in small amounts in tissues. Atomic number 17; atomic weight 35.453; valence 1-; most abundant isotope 35Cl; radioisotopes 33Cl, half-life 37 minutes, 39Cl, half-life 55 minutes, radiation emitted—beta parti- cles. chlorolabe See color blindness. chloromycetin chloramphenicol (q.v.). chlorophyll a group of pigments that mediate photosynthesis. These include chlorophyll a and b,
the green pigments found in the chloroplasts of plants. The structural formula for the chlorophyll a molecule and the appropriate dimensions of the por- phyrin ring and phytol chain are illustrated below. The chlorophyll b molecule differs from chlorophyll a in that the CH3 indicated by the arrow is replaced by a CHO group. Other chlorophylls include chlo- rophyll c (found in the brown algae and some red algae), chlorophyll d (found in the red algae), and the bacteriochlorophylls (found in the green sulfur bacteria). See anthocyanins, Cyanobacteria. chlorophyte any protoctist that belongs to the Chlorophyta.
This phylum contains green algae that have undulipodia at some stage of their life cycle. Green land plants presumably arose from a chloro- phyte lineage. See Mesostigma viride, undulipodium. chloroplast the chlorophyll-containing, photosyn- thesizing organelle of plants. Chloroplasts are thought to be the descendants of endosymbiotic cyanobacte- ria. A typical chloroplast is illustrated on page 67.
Each is surrounded by a double membrane and con- tains a system of internal thylakoid membranes. These form stacks of flattened discs called grana in which chlorophyll molecules are embedded. Chloro- plasts contain DNA and can multiply. Replication of chloroplast DNA occurs throughout the cell cycle. Chloroplasts contain 70S ribosomes and in this re- spect resemble bacterial ribosomes rather than those of the plant cytoplasm (see ribosome). The repro-