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Unformatted text preview: PLANT EVOLUTION PLANT CHAPTER 23 Setting the Stage for Plants Setting Earth’s atmosphere was originally Earth’s oxygen free oxygen Ultraviolet radiation bombarded the Ultraviolet surface surface Photosynthetic cells produced oxygen Photosynthetic and allowed formation of a protective ozone layer ozone Invading the Land Invading Cyanobacteria were probably the first to spread into Cyanobacteria and up freshwater streams and Later, green algae and fungi made the journey together Every plant is descended from Every species of green algae species Chlorophyta) Chlorophyta) (The The Plant Kingdom The Nearly all are multicelled Nearly All are photoautotrophs All Energy from sun Carbon dioxide from air Minerals dissolved in Minerals water water Fig. 23-2, p.372 Evolutionary Trend mitosis zygote (2n) multicelled sporophyte (2n) fertilization Diploid Haploid meiosis gametes (1n) mitosis multicelled gametophytes (1n) spores (1n) mitosis Fig. 23-6a, p.374 zygote only, no sporophyte op h gam yte’ s im etop p hyte ’s im ortanc e por tanc e spo r green algae bryophytes ferns gymnosperms angiosperms Fig. 23-6b, p.374 EVOLUTIONARY TRENDS OF PLANTAE: ADAPTATIONS TO LIFE ON LAND ADAPTATIONS Non vascular Vascular (rhizoidstrue roots) (True true stems and leaves with vessels to transport water and photosynthetic products). photosynthetic Waxy cuticle to hold in moisture HomosporousHeterosporous (one type of sporophyll Heterosporous two types of sporophylls where the production of two megaspores and microspores develop into separate male and female gametophytes (pollen and ovule): eliminates the necessity of water for fertilization eliminates Seedless seed producing flowering,fruiting,seed producing producing Nonvascular Plants Nonvascular Bryophytes Fewer than 19,000 Fewer species species Three groups Liverworts Hornworts Hornworts Mosses BRYOPHYTES: moss BRYOPHYTES: Small, nonvascular, nonwooody Small, Gametophyte dominates life cycle; has leaflike, Gametophyte stemlike, and rootlike parts stemlike, Usually live in wet habitats Flagellated sperm require water to reach eggs Considered a “dead end” in evolution since the Considered haploid gametophyte stage is dominant AND because they lack vascular tissue because mature sporophyte (sporeproducing structure and stalk), still dependent on gametophyte Zygote grows, develops into a sporophyte while still attached to gametophyte. zygote fertilization Diploid Stage Haploid Stage Spores form by way of meiosis and are released. Sperm reach eggs by moving through raindrops or film of water on the plant surface. Spores germinate. Some grow and develop into male gametophytes. meiosis rhizoids spermproducing structure at shoot tip of male gametophyte: Anthridia egg-producing structure at shoot tip of female gametophyte: Archegonia Other germinating spores grow and develop into female gametophytes. MOSS LIFE CYCLE Fig. 23-8b, p.376 Seedless Vascular Plants Seedless Like bryophytes Live in wet, humid places Require water for fertilization Unlike bryophytes Sporophyte is free-living and Sporophyte has vascular tissues has INCLUDE: Fern (Pterophyta), Horsetails Fern (ancient and primative), Wiskferns Wiskferns Ferns (Pterophyta) Ferns 12,000 species, mostly tropical Sporophyte structure most common Sporophyte Perennial underground stem (rhizome) Roots and fronds arise from rhizome Young fronds are coiled “fiddleheads” Mature fronds divided into leaflets Spores form on lower surface of some Spores fronds fronds Fern Life Cycle Fern Sporophyte still attached to gametophyte sorus zygote fertilization egg sperm Fig. 23-12 p. 391 rhizome Diploid Stage meiosis Haploid Stage Spores develop Spores are released mature gametophyte Spore germinates Rise of Seed-Bearing Plants Rise TRAITS Seeds appeared Seeds about 360 million years ago Seed ferns and Seed gymnosperms were dominant at first dominant Angiosperms arose Angiosperms later later Microspores that give rise to pollen Microspores grains (the male gametophyte) grains Megaspores give rise to ovules (the Megaspores female gametophyte) female More water-conserving than seedless More vascular plants vascular Fertilized ovules become seeds Seeds can remain dormant until conditions are good for plant to germinate and grow germinate Pollen Pollen and Ovules Ovules are haploid female Ovules reproductive structures that become seeds become Consist of: Female gametophyte (Ovule) Female which produces egg cell (Ova) which Nutrient-rich tissue, endosperm Nutrient-rich or cotyledon, will feed the developing embryo developing Jacket of cell layers forms a Jacket protective seed coat around the seed seed Pollen grains are spermbearing haploid male bearing gametophytes that develop from microspores microspores Allows transfer of sperm Allows to egg without water to Can drift on air currents Can or be carried by pollinators pollinators Traits of Seed-Bearing Plants Seed-Bearing Pollen grains Arise from megaspores Develop into male gametophytes Can be transported without water Seeds develop from ovules Embryo sporophyte inside nutritive tissues Embryo and a protective coat and Can withstand hostile conditions GYMNOSPERMS: THE NAKED SEED PLANTS IE: Conifers GYMNOSPERMS GYMNOSPERMS Plants with “naked seeds” Seeds don’t form inside an Seeds ovary, No fruits or flowers ovary, CONIFERS Widest known, largest Widest number of living species number Woody trees or shrubs Woody Most are evergreen Bear seeds on exposed cone Bear scales scales CONES Woody scales of a “pine Woody cone” are the parts where megaspores formed and developed into female gametophytes :Ovule gametophytes Male cones, where Male microspores and pollen are produced, are not woody produced, Pine Life Cycle section through one ovule (the red “cut” in the diagram to the left): surface view of a female cone scale (houses two ovules) ovule section through a pollen sac (red cut) mature sporophyte seed coat embryo nutritive tissue surface view of a scale of a male strobilus (houses two pollen sacs) zygote fertilization seedling seed formation Diploid Stage Haploid Stage meiosis meiosis spermproducing cell pollen tube (view inside an ovule) eggs pollination (wind deposits pollen grain near ovule) Microspores Megaspores form, develop form; one into pollen develops into grains. the female gametophyte. Germinating pollen grain (the male gametophyte). Sperm nuclei form as the pollen tube grows toward the egg. female gametophyte Fig. 23-16, p.383 Angiosperms Angiosperms Flowering plants Dominant land plants Dominant (260,000 species) (260,000 Ovules and (after Ovules fertilization) seeds are enclosed in an ovary ovary Produce Flowers and Produce Fruits Fruits petal stamen (microspores form here) sepal carpel (megaspores form here) ovule in an ovary Fig. 23-18, p.384 sporophyte Flowering Plant Life Cycle Cycle Diploid Double fertilization Haploid Meiosis Meiosis mitosis without cytoplasmic division pollination microspores two sperm enter ovule female gametophyte Fig. 23-20, p. 399 People and Plants People Plant domestication Plant began about 11,000 years ago years About 3,000 species About have been used as food food Now about 200 Now plants are major crops crops OTHER USES Lumber, paper, and fuel Lumber, Furniture Furniture Rope Rope Thatched roofing Thatched Natural insecticides Drugs Drugs ...
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