Plant Diversity - Plant Diversity 1 From water to land a...

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Plant Diversity 1) From water to land a) Land plants evolved from green algae b) Most plants are terrestrial c) “land plants”= all plants in contrast to algae, which are photosynthetic protists d) 290,000 described species of land plants e) Plants supply O2 f) Plants supply food! (most are autotrophs) g) Charophyceans (a group of green algae) are the closest relatives of land plants h) Land plants = embryophytes (still being debated) i) Chara and coleochaete are closest living relatives of land plants, based on morphological, biochemical, and genetic evidence. Most likely what land plant looked like when the first derived from water plants. Slide 5 j) When they changed from water plant to land plant they needed a harder cell wall for structure, find a way to hold water, change how they dealt with sunlight, change their seeds (had to make them robust to desiccation), a new way to take in oxygen k) Theory: 400-500mya there was occasional drying at edge of pond, species that were wat the edges of ponds had to adapt to drying out. Critical to protect zygote from drying out. Plants may have started out only living at the edges of water. l) Whats good about living on land? i) Direct sunlight, unfiltered by water or plankton ii) Lots of CO2 iii) Soil filled with nutrients iv) Relatively few herbivores and pathogens( at least early in land evolution). . . didn’t have to put energy into defending themselves on land
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2) Terrestrial adaptations of plants a) Apical meristem= localized regions of cell division tips of roots and shoots. Elongation and branching of shoots and roots to maximize exposure to environmental resources. i) Apical meristem allows for continued growth throughout plants life. EX: grasses have apical meristem very close to soil surface: adaptation to grazing b) Alternation of generations= multicellular haploid and multicellular diploid stages in the life cycle i) Gamethophyte= haploid phase; produces haploid gametes that fuse to form diploid zygote ii) Sporophyte= diploid phase; produces haploid spores that form into gametophytes c) Walled spores (with sporopollenin) produced in sporangia i)
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