BB lecture 2-20-09, Plants II

BB lecture 2-20-09, Plants II - Chapter 29(pp.600-615...

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Chapter 29 (pp.600-615) – Initial land colonization by plants (continued) Learning objectives: Describe the main characteristics of bryophytes Be aware that ‘ bryophytes ’ is a general term for non-vascular plants: Liverworts, hornworts, and mosses; Bryophyta is a phylum consisting only of the mosses Diagram the general life cycle of a bryophyte Describe the ecological and economic significance of bryophytes Describe the main characteristics of pterophytes
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REVIEW: Derived Traits (homologies) of Plants Five key traits appear in nearly all land plants but are absent in the charophyceans 1. Apical meristems [regions of active cell division at tips of shoots/roots] 2. Alternation of generations [multicellular gametophytes/sporophytes] 3. Walled spores produced in sporangia [w/ sporopollenin – resists dessication] 4. Multicellular gametangia [gametes produced w/in multicellular organs] 5. Multicellular dependent embryos [nutrients derived from parental tissues]
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Figure 29.5 Alternation of generations: a generalized scheme A key point: Both the sporophyte (2n) and the gametophyte (n) generations are represented by multicellular bodies .
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On haploid versus diploid – remember: HAPLOID Any product of meiosis is haploid Any spore is haploid (in plants) Any mitotic product of a spore is haploid All gametes are haploid DIPLOID Any product of fertilization is diploid Any zygote is diploid Any mitotic product of a zygote (like a sporophyte) is diploid
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A hypothesis for the origin of sporophytes is a mutation delayed meiosis until one or more mitotic divisions of the zygote had occurred. This multicellular, diploid sporophyte would have more cells available for meiosis.
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