BIO51_PLANTS_PART_A

BIO51_PLANTS_PART_A - Plants The Greening of Earth Looking...

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Plants The Greening of Earth Looking at a lush landscape It is difficult to imagine the land without any plants or other organisms Figure 29.1
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For more than the first 3 billion years of Earth’s history The terrestrial surface was lifeless Since colonizing land Plants have diversified into roughly 290,000 living species
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Land plants evolved from green algae Researchers have identified green algae called charophyceans as the closest relatives of land plants
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Morphological and Biochemical Evidence Many characteristics of land plants Also appear in a variety of algal clades
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There are four key traits that land plants share only with charophyceans Rose-shaped complexes for cellulose synthesis 30 nm Figure 29.2
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Peroxisome enzymes Structure of flagellated sperm Formation of a phragmoplast
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Genetic Evidence Comparisons of both nuclear and chloroplast genes Point to charophyceans as the closest living relatives of land plants Chara , a pond organism (a) 10 mm Coleochaete orbicularis , a disk- shaped charophycean (LM) (b) 40 µm Figure 29.3a, b
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Adaptations Enabling the Move to Land In charophyceans A layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out The accumulation of traits that facilitated survival on land May have opened the way to its colonization by plants
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Land plants possess a set of derived terrestrial adaptations Many adaptations Emerged after land plants diverged from their charophycean relatives
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Defining the Plant Kingdom Systematists Are currently debating the boundaries of the plant kingdom Plantae Streptophyta Viridiplantae Red algae Chlorophytes Charophyceans Embryophytes Ancestral alga Figure 29.4
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Some biologists think that the plant kingdom Should be expanded to include some or all green algae Until this debate is resolved The textbook retains the embryophyte definition of kingdom Plantae
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Derived Traits of Plants Five key traits appear in nearly all land plants but are absent in the charophyceans Apical meristems Alternation of generations Walled spores produced in sporangia Multicellular gametangia Multicellular dependent embryos
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APICAL MERISTEMS Apical meristem of shoot Developing leaves 100 µm Apical meristems of plant shoots and roots . The light micrographs are longitudinal sections at the tips of a shoot and root. Apical meristem of root Root 100 µm Shoot Figure 29.5 Apical meristems and alternation of generations Haploid multicellular organism (gametophyte) Mitosis Mitosis Gametes Zygote Diploid multicellular organism (sporophyte) Alternation of generations: a generalized scheme MEIOSIS FERTILIZATION 2 n 2 n n n n n n Spores Mitosis ALTERNATION OF GENERATIONS
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Walled spores; multicellular gametangia; and multicellular, dependent embryos WALLED SPORES PRODUCED IN SPORANGIA MULTICELLULAR GAMETANGIA MULTICELLULAR, DEPENDENT EMBRYOS Spores Sporangium
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This note was uploaded on 04/17/2008 for the course BIO 051 taught by Professor Land during the Fall '07 term at Pacific.

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BIO51_PLANTS_PART_A - Plants The Greening of Earth Looking...

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