9780073532264: Biological Investigations Lab Manual.

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Sub-disciplines of biology are defined by the scale at which life is studied, the kinds of organisms studied, and the methods used to study them: biochemistry examines the rudimentary chemistry of life; molecular biology studies the complex interactions among biological molecules ; cellular biology examines the basic building-block of all life, the cell ; physiology examines the physical and chemical functions of tissues , organs , and organ systems ; ecology examines how organisms interact in their environment ; and evolutionary biology examines the processes that produced the diversity of life. [3]

Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-Dīnawarī (828–896), who wrote on botany, [10] and Rhazes (865–925) who wrote on anatomy and physiology . Medicine was especially well studied by Islamic scholars working in Greek philosopher traditions, while natural history drew heavily on Aristotelian thought, especially in upholding a fixed hierarchy of life.

Biology began to quickly develop and grow with Anton van Leeuwenhoek 's dramatic improvement of the microscope . It was then that scholars discovered spermatozoa , bacteria , infusoria and the diversity of microscopic life. Investigations by Jan Swammerdam led to new interest in entomology and helped to develop the basic techniques of microscopic dissection and staining . [11]

Advances in microscopy also had a profound impact on biological thinking. In the early 19th century, a number of biologists pointed to the central importance of the cell . Then, in 1838, Schleiden and Schwann began promoting the now universal ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life , although they opposed the idea that (3) all cells come from the division of other cells. Thanks to the work of Robert Remak and Rudolf Virchow , however, by the 1860s most biologists accepted all three tenets of what came to be known as cell theory . [12] [13]

Meanwhile, taxonomy and classification became the focus of natural historians. Carl Linnaeus published a basic taxonomy for the natural world in 1735 (variations of which have been in use ever since), and in the 1750s introduced scientific names for all his species. [14] Georges-Louis Leclerc, Comte de Buffon , treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent . Though he was opposed to evolution, Buffon is a key figure in the history of evolutionary thought ; his work influenced the evolutionary theories of both Lamarck and Darwin . [15]

A central organizing concept in biology is that life changes and develops through evolution, and that all life-forms known have a common origin . The theory of evolution postulates that all organisms on the Earth , both living and extinct, have descended from a common ancestor or an ancestral gene pool . This universal common ancestor of all organisms is believed to have appeared about 3.5 billion years ago . [22] Biologists regard the ubiquity of the genetic code as definitive evidence in favor of the theory of universal common descent for all bacteria , archaea , and eukaryotes (see: origin of life ). [23]