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Unformatted text preview: Origin of Eukaryotes: Protists Locomotion in Protists • Amoeboid motion: is a sliding movement; it is accomplished by streaming of pseudopodia • Swimming: via flagella or cilia • Float : Requires ATP, and interactions between actin and myosin in the cytoplasm Cilia: short and numerous Flagella: long and few in number Flagella and Cilia • eukaryotic flagella and cilia : structure consists of microtubules • more complex than prokaryote flagella Reproduction Asexual reproduction : eukaryotes: bacteria, archaea: Offspring: Sexual reproduction: Offspring: *** evolved in protists, and ranks among the most significant innovations found in eukaryotes Sexual versus Asexual Reproduction • Sexual reproduction provides individuals with many new combinations of genes • The genotypes of many parasites and pathogens evolve very quickly, so natural selection favors host individuals with new genotypes that may be able to resist them ***Many biologists view sexual reproduction as an adaptation … Variation in Life Cycles Compare prokaryotes with protists life cycle: describes the sequence of events that occurs as individuals grow, mature, and reproduce alternation of generation: alternation of the multicellular haploid and diploid phases in the life cycle Life Cycles Vary Widely among Protists A life cycle dominated by haploid cells (species shown here is the dinoflagellate Gynodinium fuscum ) ASEXUAL REPRODUCTION (offspring produced by mitosis) ( n ) ( n ) SEXUAL REPRODUCTION (offspring produced by meiosis) Mature cel ( n ) Zygote (2 n ) Diploid Haploid MEIOSIS F E R T IL IZ A T IO N M IT O S IS Fig. 29.20 Life Cycles Vary Widely among Protists A life cycle dominated by diploid cells (species shown here is the diatom Cyclotella meneghiniana ) Mature cel (2 n ) Zygote (2 n ) Gametes ( n ) (2 n ) MEIOSIS ASEXUAL REPRODUCTION (offspring produced by mitosis) SEXUAL REPRODUCTION (offspring produced by meiosis) M IT O S IS M ITO S IS GROWTH F E R T IL IZ A T IO N Fig. 29.20 Variation in Life Cycles • alternation of generations: many multicellular protists have one phase of their life cycle that is based on a haploid...
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This note was uploaded on 02/01/2012 for the course BIOLOGY 153 taught by Professor Dr.arts during the Fall '10 term at University of Toronto- Toronto.
- Fall '10