Modern eukaryotic cell arose in several steps Chapter 20 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 Diatoms possess rows of tubular hairs on longer of their two flagella 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 Oomycetes all multicellular and some extremely large almost exclusively marine develop specialized structure holdfast that holds them to rocks 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 thin stiff pseduopods and glassy exoskeleton lobeshaped pseudopods for locomotion Radiolarians Amoebozoans Loboseans consist of single amoeboid cell most predators parasites and scavengers of bodies of water Plasmodial slime molds single plasma membrane Cellular slime molds reproduce by mitosis and fission maintain identity form fruiting structures Asexual reproductive processes during vegetative feeding nonreproductive stage is a coenocyte many nuclei enclosed in a 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 not