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Biological Science

By | September 2011
Page 1 of 2
1.1 The Cell Theory (pages 1-4) 
A fundamental goal of biological science is to discover traits and processes that unify the diversity of living organisms. In the mid-1800s, the development of the cell theory and the theory of evolution identified some of these key unifying features and launched biology as a modern science. The cell theory states that all living organisms are made of cells and that all cells arise from preexisting cells. The theory of evolution states that all organisms are related by common ancestry and that the characteristics of populations change through time. Evolution is caused by natural selection, which occurs when certain heritable traits cause some individuals to leave more offspring than others. 1.2 The Theory of Evolution by Natural Selection (pages 4-5)  The cell theory and theory of evolution predict that all organisms are part of a genealogy of species, and that all species trace their ancestry back to a single common ancestor. To reconstruct this phylogeny, biologists have analyzed the sequence of ribonucleotides in a molecule called SSU RNA that is found in all cells. A tree of life, based on similarities and differences in these sequences, has recently been constructed and is currently the focus of intense research. According to the information contained in SSU RNA, the tree of life’s shape defines three major lineages among organisms: the Bacteria, Archaea, and Eukarya. Analyses of other molecules and traits have largely supported the conclusions made from SSU RNA data.

1.3 The Tree of Life (pages 5-9) 
The cell theory and theory of evolution predict that all organisms are part of a genealogy of species, and that all species trace their ancestry back to a single common ancestor. To reconstruct this phylogeny, biologists have analyzed the sequence of ribonucleotides in a molecule called SSU RNA that is found in all cells. A tree of life, based on similarities and differences in these sequences, has recently been...

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