rav65819_ch26_503-522

rav65819_ch26_503-522 - ; part V diversity of life on earth...

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;;;;;;;;; part V diversity of life on earth 26 IN PRECEDING CHAPTERS, you’ve seen that many common features are found in living things. To name a few, they are composed of one or more cells, they carry out metabolism and transfer energy with ATP, and they encode hereditary information in DNA. Yet there is also a tremendous diversity of life, ranging from bacteria and amoebas to blue whales and sequoia trees. Coral reefs, such as the one pictured here, are microcosms of diversity, comprising many life forms and sheltering an enormous array of life. For generations, biologists have tried to group
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organisms based on shared characteristics. The most meaningful groupings are based on the study of evolutionary relationships among organisms. These phylogenetic approaches and a sea of molecular sequence data are leading to new evolutionary hypotheses to explain life’s diversification. In this chapter and those that follow in this unit, we explore the diversity of the living world. chapter The Tree of Life introduction 26.4 Making Sense of the Protists 26.5 Origin of Plants Bacteria are more numerous than any other organism Archaea may live in extreme environments Eukaryotes have compartmentalized cells Viruses are a special case concept outline 26.1 Origins of Life
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All organisms share fundamental properties of life Life may have had extraterrestrial origins Life may have originated on early Earth Cells evolved from the functional assembly of organic molecules 26.2 Classifcation oF Organisms Taxonomy is a quest for identity and relationships Linnaeus instituted the use of binomial names Taxonomic hierarchies have limitations 26.3 Grouping Organisms The six kingdoms are not necessarily monophyletic The three domains probably are monophyletic Molecular phylogenetics has identiFed the closest living relative of land plants Horizontal gene transfer occurred in land plants 26.6 Sorting Out the Animals The origins of segmentation are puzzling Insects and crustaceans are sister groups The mammalian family tree is emerging 503 rav65819_ch26_503-522.indd 503 rav65819_ch26_503-522.indd 503 12/8/06 1:15:13 PM 12/8/06 1:15:13 PM 26.1 Origins oF LiFe The cell is the basic unit oF liFe and today all cells come From preexisting cells. But, how can we explain the origins oF the tremendous diversity oF liFe on Earth today? The Earth Formed as a hot mass oF molten rock about 4.5 billion years ago (BYA). As the Earth cooled, much oF the water vapor present in its atmosphere condensed into liquid water that accumulated on the surFace in chemically rich oceans. One scenario For the origin oF liFe is that it originated in this dilute, hot, smelly soup oF ammonia, Formaldehyde, Formic acid, cyanide, methane, hydrogen sulFide, and organic hydrocarbons. Whether at the oceans’ edges, in hydrothermal deep-sea vents, or elsewhere, the consensus among researchers is that liFe arose spontaneously From these early waters. Although the way in which this happened remains a puzzle, we cannot escape a certain curiosity about the
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This note was uploaded on 10/15/2010 for the course BIO BIO1 taught by Professor Lipke during the Fall '09 term at CUNY Brooklyn.

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rav65819_ch26_503-522 - ; part V diversity of life on earth...

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