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19.1 Characteristics of Prokaryotic Cells Single-celled bacteria and archaeans Prokaryotes and Viruses No nucleus or membrane-bound organelles Chapter 19 Smallest, most widely distributed, numerous, and metabolically diverse organisms • Autotrophs and heterotrophs Prokaryote Cell Shapes Prokaryote Cell Structures Spheres (cocci), rods (bacilli), spirals (spirilla) Typical surface structures • • • • Cell wall Outermost protective capsule or slime layer One or more flagella Pili 1 A Prokaryotic Cell Flagella and Pili Prokaryotic Fission Prokaryotic Cell Characteristics 2 19.2 The Bacteria Food Poisoning The most common and diverse prokaryotes • Some are pathogens (cause disease in a host) Bacterial Diversity: Cyanobacteria Bacterial Diversity: Gram-Positive Bacteria Oxygen-releasing photoautotrophs Have thick walls • Chloroplasts probably evolved from ancient cyanobacteria by endosymbiosis • Endospores resist heat, boiling, irradiation, acids and disinfectants • Some are human pathogens 3 Bacterial Diversity: Chlamydias Bacterial Diversity: Spirochetes Spring-shaped Chlamydias • Live on their own or in hosts • Some are pathogens • All are intracellular parasites of animals • Obtain ATP from host cells • Some sexually transmitted diseases (C. trachomatis) Archaean Physiology Archaeans in Extreme Environments Halophiles (salt lovers), extreme thermophiles, and methanogens (methane makers) 4 19.4 The Viruses Viral Structures Viruses are noncellular infectious particles that cannot reproduce on their own Viruses infect a host cell; their genes and enzymes take over the host’s mechanisms of replication and protein synthesis Prion Infections Prions Proteins that occur naturally in the vertebrate nervous system, but can cause fatal disease when they misfold Antibiotic Resistance Use of antibiotics favors antibiotic-resistant bacteria Genes that convey drug resistance can arise by mutation, may spread among members of the same or different species by conjugation 5 20.1 An Evolutionary Road Map Protists Protists – The Simplest Eukaryotes • The simplest eukaryotes • Most are single-celled • Some are multicelled and large Chapter 20 Protist Structure Protist Evolutionary Tree Protist cells have a nucleus (eukaryotes) Most have one or more mitochondria Many have chloroplasts that evolved from cyanobacteria or from another protist Dominant stage of life cycle: Haploid or diploid 6 Key Concepts: Comparing Prokaryotes and Eukaryotes SORTING OUT THE PROTISTS Protists include many lineages of single-celled eukaryotic organisms and their closest multicelled relatives Gene sequencing and other methods are clarifying how protist lineages are related to one another and to plants, fungi, and animals 20.2 Ancient Flagellates Disease-Causing Flagellates Flagellated protozoans • Single-celled heterotrophs with flagella • Unwalled cells, pellicle retains shape Most euglenoids live in freshwater • Some have chloroplasts that arose by secondary endosymbiosis from a green alga • Contractile vacuoles expel excess water Trichomonas vaginalis Trypanosoma brucei 7 20.3 Shelled Amoebas 20.4 Alveolates Foraminiferans and radiolarians All alveolates have tiny sacs (alveoli) beneath the plasma membrane • Single-celled heterotrophs with a secreted shell • Many openings for pseudopods • All single-celled Examples: • Ciliates, dinoflagellates, and apicomplexans Ciliates Dinoflagellates Aquatic predators and parasites with many cilia Aquatic heterotrophs and autotrophs with a cellulose covering • Example: Paramecium • Photosynthetic protists cause algal blooms in nutrient-rich water 8 Apicomplexans 20.5 Malaria Plasmodium species cause malaria Heterotrophs: Parasites living in animal cells • • • • Cell-piercing structure made of microtubules Reproduce sexually and asexually in host cells Only gametes have flagella Example: Plasmodium (malaria) 20.6 Single-Celled Stramenopiles Photosynthetic Stramenopiles Two flagella, one with hairlike filaments Diatoms, coccolithophores, and golden algae Oomycotes • Heterotrophs (decomposers and parasites) that grow as a mesh of absorptive filaments • Some parasitic species are important plant pathogens • Often part of the phytoplankton • Photosynthetic cells (contain fucoxanthin) Hard parts accumulate as mineral deposits • Coccolithophores (calcium carbonate plates): Chalk and limestone • Diatoms (silica shells): Diatomaceous earth 9 Stramenopiles of the Phytoplankton 20.7 Brown Algae Multicelled, photosynthetic stramenopiles • Include microscopic strands and giant kelps (the largest protists; ecological and commercial value) 20.8 Green Algae 20.9 Red Algae Chlorophytes (most green algae) and charophytes (closest relatives of plants) Most red algae are multicelled • Have chloroplasts with chlorophylls a and b • Store carbohydrates as starch grains • Cultivated for commercial products 10 20.10 Amoebozoans Amoebas (single cells) and slime molds (“social amoebas”) Slime Molds Plasmodial slime molds • Feed as a multinucleated mass • Heterotrophic, free-living 11
