CHAPTER 16 The Origin and Evolution of Microbial Life: Prokaryotes and Protists Modules 16.18 – 16.21
Cell with nucleus and endomembrane system PROTISTS…the eukaryotes The eukaryotic cell probably originated as a community of prokaryotes—The Endosymbiotic Theory of Lynn Margulis (1970) Eukaryotic cells evolved from prokaryotic cells more than 2 billion years ago The nucleus and endomembrane system of eukaryotes probably evolved from infoldings of the plasma membrane of ancestral prokaryotes Plasma membrane Cytoplasm Endoplasmic reticulum Nucleus Nuclear envelope Ancestral prokaryote Cell with nucleus and endomembrane system Figure 16.18A
Photosynthetic eukaryotic cell Mitochondria and chloroplasts probably evolved from symbiotic prokaryotes that took up residence inside larger prokaryotic cells Evidence comes from the fact that mitochondria, chloroplasts and centrioles all have their own DNA that is similar to the DNA of bacteria. It also replicates independently of the nuclear DNA. Aerobic heterotrophic prokaryote Mitochondrion Mitochondrion Photosynthetic prokaryote Chloroplast Some cells Ancestral host cell Photosynthetic eukaryotic cell Figure 16.18B
Early protists were the ancestors of plants, animals, and fungi 16.19 Protists—unicellular eukaryotes and their close multicellular relatives—probably represent multiple kingdoms Early protists were the ancestors of plants, animals, and fungi The taxonomy of protists is in a state of flux Figure 16.19
16.20 Protozoa are protists that ingest their food They include flagellates amoebas Figure 16.20A, B
apicomplexans ciliates Red blood cell Apex Cilia Cilia Macronucleus Figure 16.20C, D Macronucleus
Most protozoa live freely in water or moist soil Some live in humans and other animals and cause disease
Slime molds are protists that may constitute a distinct kingdom 16.21 Cellular slime molds have both unicellular and multicellular stages Slime molds are protists that may constitute a distinct kingdom Amoeboid cells Sluglike colony Reproductive structure Figure 16.21