Topic 1.1

Topic 1.1 - Summary of Chapters TAIZ

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Plant Physiology Online: The Plant Kingdom A Companion to Plant Physiology, Fourth Edition by Lincoln Taiz and Eduardo Zeiger Topics Essays Study Questions Readings Help Select Chapter: Search HOME :: CHAPTER 1 :: Topic 1.1 PREVIOUS :: NEXT Topic 1.1 The Plant Kingdom Since the time of Aristotle (384–322 B.C.E.), biologists have sought to classify organisms. At first the purpose was ease of identification ("artificial" classification schemes). Carolus Linnaeus (1707–1778), arguably the greatest of the pre-modern Naturalists, sought to classify plants and other organisms according to affinity groups that reflected the mind of the Creator. Later, after Darwin, the goal of classification was to show evolutionary relationships ("natural" classification schemes). For the past 150 years, biologists have emphasized natural systems of classification and have attempted to define morphological criteria that reveal evolutionary relationships. We now know that morphology, the form and structure of organisms, is the end product of the actions of genes. Virtually all of the information needed to form a complete organism is encoded in its DNA sequences, both nuclear and cytoplasmic (mitochondria and chloroplasts). DNA sequence analysis has thus provided evolutionary biologists with a powerful new tool for arriving at a truly natural classification system On the basis of phylogenetic analyses of highly conserved DNA sequences, living organisms have been divided into three major domains: Bacteria, Archaea, and Eucarya (Woese et al. 1990) (Web Figure 1.1.A). Web Figure 1.1.A Natural classification scheme and phylogeny of living organisms, including endosymbiotic events. 1. The common ancestor of all the organisms first gave rise to the Bacteria and the common ancestor of the Archaea and the Eucarya. 2. The Archaea branch off from the Eucarya lineage. 3. The Eucarya common ancestor acquires mitochondrial endosymbiont (an alpha- proteobacterium-like cell). 4. A heterogeneous group of eukaryotes called protists branch off the lineage leading to plants, fungi, and animals. 5. The common ancestor of fungi and animals form a branch, followed by a divergence into the fungal and animal lineages. 6. The common ancestor of plants, green algae, red algae, and glaucophytes acquires
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Topic 1.1 - Summary of Chapters TAIZ

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