chp25.organismal.fall2017.pdf - BIOLOGY PowerPoint Image...

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10/24/2017 1 BIOLOGY Chapter 25 SEEDLESS PLANTS PowerPoint Image Slideshow CHAPTER 25: SEEDLESS PLANTS Main Sections: 25.1 – early plant life 25.2 – green algae: precursors of land plants 25.3 Bryophytes 25.4 Seedless Vascular Plants 25.1 EARLY PLANT LIFE Main Points: Discuss the challenges to plant life on land Describe the adaptations that allowed plants to colonize the land Describe the timeline of plant evolution and the impact of land plants on other living things 25.1 EARLY PLANT LIFE > 300,000 species of plants known, of them majority are seed plants (260,000 – next chapter) Plants include all land plants (next slide). Sometimes algae included in plant kingdom No matter what Green algae is closest relative to land plants Eukaryote supergroup method with 6 supergroups has algae all as protists in different groups. Archaeplastida – super group with green & red algae and land plants FIGURE 25.6 This table shows the major divisions of green plants. 500 mya (Ordivician period)– first land plants ~400 mya (Devonian period)- first vascular plants evolve (xylem, phloem) Eventually seed plants form (gymnosperms – naked seeds usually in cones) Nonvascular and Vascular plants all have modern day descendants that have speciated and have overall diversified (extinctions occur too) over geological time 25.1 EARLY PLANT LIFE: CHALLENGES ON LAND Transition from green algae in water to land plant was challenging…. Why? Easier to dry out Many solutions – advanced adaptations in “higher” vascular plants Air isn’t as dense: structural support Major solution - vascularization More UV exposure Major solution – develop flavonoids (more later) Dispersal more difficult (gametes or adults have to fly instead of float) Major solutions – alternation of generations opens doors to many reproductive strategies following same basic pattern
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10/24/2017 2 25.1 EARLY PLANT LIFE: ADAPTATIONS FOR LAND Adapting to drier conditions, several strategies: Tolerance (can dry out to be brown and then rehydrate to full green and soft body that was relatively undamaged) Live in damp, cool, humid places (early nonvascular plants in particular – mosses- but also early vascular plants like ferns) Later: develop dessication resistant adaptations Vascularization ( more to come…) In extremely dry conditions – more advanced adaptations for water conservation (cacti) Major adaptations in all land plants (not in green algae): 1. Alternation of generations 2. Apical meristem in roots and shoots Alternation of generations Life cycle where there are haploid and diploid multicellular stages Compare to humans: diplotonic – dominant diploid life stage with single celled haploid gametes that exist for a very short time Haplodiplodontic plants (plants that alternate generations ) Seedless nonvascular plants: gametophyte is dominant (body of moss) Seeded vascular plants: often sporophyte is dominant (trees) 1. Gametophyte (haploid) multicellular 2.
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