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Chapter 8

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Biology 1001A

Biology Independent Study Reading- Lecture 4 Chapter 8 1. Approximate times by which the first cells, and the first eukaryotic cells had appeared/ - Prokaryotic cells existed 3.5-3.8 billion years ago and 1.5 billion years ago, some diver- sified into Eukaryotic cells - Prokaryots contain no nuclear membrane, cytoskeleton or complex organelles, and di- vide by binary fission - The three kingdoms of organisms (eukaryotes, Eubacteria and Archaea) are thought ot have originated from a single common ancestor LUCA - All organisms on The Tree of Life are bound together by four essential facts - They share a common inheritance - Their past has been long enough for inherited changes to accumulate - The discoverable relationships among organisms are the result of evolution - Discoverable biological processes explain how organisms arose and how they were modified through time by the process of evolution 2. Eukaryotes Prokaryotes Has internal membranous networks does not have internal membranous organelles networks (nuclear membrane) cytoskeleton (most of the time) no organelles mitotic cell division no cytoskeleton compartments in the form of organelles allow binary fission eukaryotes to isolate enzymes for reactions, the lack of internal membranous networks confine the translation and transcription of means no organelles which means the do DNA not have the compartments that allow the the evolution of compartmentalization was a synthesis of protein major step in the diversification of eukaryotes The Different kingdoms for classifying living things - Two-Kingdom - classified into Plantae and Animalia at first based on structure, function, move- ment and metabolism but by the middle of the 20th century, divided into prokaryotes (single celled organisms) and eukaryotes (multi-celled organisms Biology Independent Study Reading- Lecture 4 Chapter 8 - However, there are still many similarities between prokaryotes and eukaryotes which show that a deep structural homology underlies life as do deep genetic and molecular homologies - Five-Kingdom - It was realized that neither the prokaryotic nor the eukaryotic life were mono- phyletic branches of the tree of life ( they did not come from one origin) they were polyphyletic (groups that have multiple independent origins) - Because of this fact, not all unicellular organisms are closely related to each other, so the classification began to change in 1959 with Whittaker who said the prokaryotes and eukaryotes were represented by five kingdoms: prokaryotes, protists, fungim plants and animals - Three-Kingdom - 1980 Woese found that rRNA formed sequences from an archaebacterium were different from other prokaryotes - with further molecular testing, it was found that the prokaryote and eukaryote kingdoms were artificial and so was born the three-kingdoms : eubacteria, (major forms of bacteria) archaea (unicells with different cell walls than bacteria and life in harsher conditions) , and eukarya (contains some unicellular organ- isms and fungi plants and animals) - o
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