UT Arlington BIOL BIOL 3427 - ch19 (21 pages)

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ch19



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ch19

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Pages:
21
School:
University of Texas at Arlington
Course:
Biol Biol 3427 - Plant Science
Plant Science Documents

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ALGAE AND THE ORIGIN OF EUKARYOTIC CELLS Chapter 19 Life began about 3 5 billion years ago in the oceans with the appearance of prokaryotes The oldest reliable date for the appearance of the eukaryotes is about 1 9 billion years ago when the first members of a group of unicellular organisms called acritarchs appear in the fossil record in China Acritarchs Are probably the remains of a group of ancient eukaryotes Were plankton Some resemble dinoflagellates while others resemble green algae Their relationship among living organisms is uncertain http www ucl ac uk GeolSci micropal acritarch html http www geo arizona edu palynology ppacrtrc html Eukaryotic cells came into existence probably by a process called endosymbiosis Mitochondria arose first as an early eukaryotic cell engulfed but did not digest a bacterium capable of aerobic respiration The two organisms lived together one inside the other and both benefited Fungi plants and animals are all probably derived from protists Fungi and animals are eukaryotes organisms that lack plastids Another line of evolution one that had mitochondria entered another endosymbiosis with a photosynthetic cyanobacterium which later evolved into a chloroplast This line gave rise to algae including green algae which in turn produced true plants the embryophytes Several clades exist that still have some extant members whose plastids have numerous prokaryotic characters Chloroplasts of red algae especially resemble cyanobacteria The kingdom Protista contains eukaryotes that cannot be assigned with certainty to other kingdoms The kingdom Protista is an artificial grouping and classification does not represent evolutionary relationships This kingdom is also known as Protoctista Protists covered in this course are those photosynthetic organisms that function like plants in ecosystems They are the grass of the ocean Protists to be studied include 1 Algae photosynthetic organisms studied by phycologists 2 Slime molds and oomycetes



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