Ch28WordLectureOutline - CHAPTER 28 THE ORIGINS OF...

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CHAPTER 28 THE ORIGINS OF EUKARYOTIC DIVERSITY Introduction Protists are eukaryotes and thus are much more complex than the prokaryotes. The first eukaryotes were unicellular. Not only were they the predecessor to the great variety of modern protists, but also to all other eukaryotes - plants, fungi, and animals. The origin of the eukaryotic cell and the emergence of multicellularity unfolded during the evolution of protists. A. Introduction to the Protists Eukaryotic fossils date back 2.1 billion years and “chemical signatures” of eukaryotes date back 2.7 billion years. For about 2 billion years, eukaryotes consisted of mostly microscopic organisms known by the informal name “protists.” 1. Systematists have split protists into many kingdoms In the five-kingdom system of classification, the eukaryotes were distributed among four kingdoms: Protista, Plantae, Fungi, and Animalia. So far, the plant, fungus, and animal kingdoms are surviving the taxonomic remodeling though their boundaries have been expanded to include certain groups formerly classified as protists. However, systematists have split protists into many kingdoms. Modern systematists have crumbled the former kingdom of protists beyond repair.
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Protista was defined partly by structural level (mostly unicellular eukaryotes) and partly by exclusion from the definitions of plants, fungi, or animals. However, this created a group including single-celled microscopic members, simple multicellular forms, and even complex giants like seaweeds. The kingdom Protista formed a paraphyletic group, with some members more closely related to animals, plants, or fungi than to other protists. Systematists have split the former kingdom Protista into as many as 20 separate kingdoms. Still,“protist” is used as an informal term for this great diversity of eukaryotic kingdoms. 2. Protists are the most diverse of all eukaryotes Protists are so diverse that few general characteristics can be cited without exceptions. Most of the 60,000 known protists are unicellular, but some are colonial and others multicellular. While unicellular protists would seem to be the simplest eukaryotic organisms, at the cellular level they are the most elaborate of all cells. A single cell must perform all the basic functions performed by the collective of specialized cells in plants and animals. Protists are the most nutritionally diverse of all eukaryotes, Most protists are aerobic, with mitochondria for cellular respiration. Some protists are photoautotrophs with chloroplasts. Still others are heterotrophs that absorb organic molecules or ingest larger food particles. A few are
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This note was uploaded on 08/28/2010 for the course SCIENCE 101 taught by Professor Wong during the Spring '10 term at Rutgers.

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Ch28WordLectureOutline - CHAPTER 28 THE ORIGINS OF...

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