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plant_diversityI_web

plant_diversityI_web - Evolution of Plants Appeared on land...

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Structural, chemical, and reproductive adaptations enabled plants to colonize land* Appeared on land ~ 475 mya Evolutionary history: increasing adaptation to terrestrial environment. Colonization of land by plants transformed biosphere new adaptive zones Evolution of Plants *(Adaptations to shallow water may have pre-adapted plants)
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Specializations: facilitate extraction of resources needed for photosynthesis (water, minerals, carbon dioxide, light) from above and below ground Also help plant survive & reproduce in non- aquatic environment
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Roots - anchor plant in place & absorb water (& dissolved minerals) Vascular tissue – transports water; also minerals and food through plant Problems & Solutions to Life on Land 1. Obtaining Water:
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a.Evolution of cuticle - a waxy layer covering the surface of all plant parts exposed to air b. * Evolution of multi-cellular gametangia (sex organs) - helped protect the delicate gametes from drying out c.Evolution of a resistant coat on spores that prevents drying out - sporopollenin* 2. Preventing excessive water loss: *this polymer also found in charophyceans * derived key trait present in nearly all land plants
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Early land plants & modern seedless plants: gametes develop in moist chambers of parent Gametangia of a Moss male female developing sperm developing egg - prevents gametes from drying out see Fig. 29.9 of liverwort
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3. Getting enough energy -requires evolution of support cells such as fibers - * growth in length facilitated by apical meristems (localized zones of cell division at shoots & roots tips) Grow tall (above other plants) Tolerate lower light levels
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4. Gas Exchange Pores ( stomata ) allow exchange of gases for photosynthesis – but also allow escape of water
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5. Reproduction Sperm not aquatic in most plants (exceptions: mosses, liverworts, hornworts + all seedless vascular plants have flagellated sperm) * Embryophyte condition * Toughened spores * Alternation of generations ( multicellular haploid & diploid forms; also occurs in some algae)
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Zygote develops into an embryo that is nourished within a jacket of protective maternal cells Embryophyte Condition Embryo of a flowering plant maternal tissue - prevents desiccation see Fig. 29.5, p 577
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Figure 29.5
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