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Chapter 20 Modern eukaryotic cell arose in several steps◦ flexible cell surface◦ cytoskeleton◦ nuclear envelope, which enclosed a genome organized into chromosomes◦ appearance of digestive vacuoles◦ acquisition of certain organelles via endosymbiosis Theory of endosymbiosis:certain organelles are descendants of prokarytoes engulfed, not digested, y ancient eukaryotic cells  Chloroplasts traced back to engulfment of cyanobacteria Eukaryotes classified in one of eight major clades◦ alveolates◦ excavates◦ stramenophiles◦ plants ◦ rhizaria◦ Amoebazoans◦ fungi◦ animals◦ first 5 clades are referred to as protists Alveolates◦ poses aleveoli◦ unicellular and most photosyntethic  Dinoflagellates◦ most marine and photosynthetic◦ producers of organic matte in oceans◦ have two falgella and can take on different forms◦ harmful to fihs and can, when in great numbers, both stun and feed on them Apicomplexans◦ apial complex(mass of organelles contained in apical end(tip)of cell)◦ elaborate life cycles featuring asexual and sexual reproduction Ciliates◦ numerous hairlike cilia▪ shorter but identical to eukaryotic flagella◦ Possess two types of nuclei◦ almost all are heterotrophic◦ cilia provide forward and backward locomotion in spiraling manner ◦ contractile vacuoles excrete water organisms constantly take in by osmosis Excavates◦ several groups lack mitochondria▪ lost due to evolution  Diplomonads and Parabasalids◦ unicellular and lack mitochondria◦ have falgella and cytoskeleton Heteroloboseans◦ body forms relate to loboseans(amoebozoan group)◦ 2 stage life cycle Euglenids and kinetoplastids◦ unicellular excavates with flagelltes◦ mitochondira contain disc-shaped cristae◦ flagella contain crystalline rod◦ reproduce asexually by binary fission◦ euglenids have diverse nutritional requirements◦ often photosynthetic◦ kinetoplastids unicellular parasites with 2 flagella and single large mitochondrion Stramenophiles◦ possess rows of tubular hairs on longer of their two flagella Diatoms◦ all unicellular and synthesize carbs and oils as photosynthetic products◦ lack flagella except in male gametes◦ almost all diatoms deposit silica in cell walls◦ all symmetrical either bilaterally or radially◦ reproduce both asexually an sexually brown algae ◦ all multicellular and some extremely large◦ almost exclusively marine◦ develop specialized structure,holdfast, that holds them to rocks  Oomycetes◦ nonphotosynthetic◦ consist of water molds and down mildews◦ absorptive heterotrophs(secrete enzymes that digest large food molecules into smaller molecules that can be absorbed)◦ cell walls made of cellulose◦ water molds are all quatic and saprobic(feed on dead organic mater) Rhizaria◦ 3 primary groups:cercozoans,foraminiferans, and radiolarians▪ unicellular and mostly aquatic◦ have long thin pseudopods Cerczoans◦ diverse forms and habitats Foraminiferans◦ secrete external shells of calcium carbonate◦ some species, pseudopods provide locomotion Radiolarians◦ thin,stiff pseduopods and glassy exoskeleton Amoebozoans◦ lobeshaped pseudopods for locomotion Loboseans◦ consist of single amoeboid cell◦ most predators, parasites and scavengers of bodies of water Plasmodial slime molds◦ during vegetative(feeding,nonreproductive) stage is a coenocyte (many nuclei enclosed in a single plasma membrane) Cellular slime molds ◦ reproduce by mitosis and fission(maintain identity)◦ form fruiting structures Asexual reproductive processes:◦ binary fission:splitting of one cell into two by mitosis followed by cytokinesis◦ multiple fission:splitting of one cell into multiple cells◦ budding:outgrowth of new cell from surface of old one◦ sporulation:formation of specialized cells(spores) that are caable of developing into new individuals Asexually reproduced groups of nearly identical organisms called clonal lineages Sexual behavior conjugation:two individuals line up tightly against ach other nd fuse in oral groove region of body◦ sexual process but not reproductive  Alternation of generations:multicellular diploid stage and multicellular haploid phase  Heteromorphic alternation of generations, two gen. Differ morphologically Isomorphic do


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UNLV BIOL 197 - Chapter 20

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