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Download Plants & The Colonization of Land
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Plant Diversity General Characteristics of Plants All plants are: Eukaryotic Autotrophic Multicellular Cell Walls with cellulose Chloroplasts w/ chlorophyll a, b, and carotenoids May have waxy cuticle to prevent water loss. Stomata allow gas exchange. Plants probably evolved from green algae (charophytes) Chloroplast similarity Biochemical similarities Cell Wall similarities Charophytes No alternation of generations No cuticle needed Jacketed gametes No protection of embryos v. Plants Alternation of generations Cuticle (prevents water loss/dessication) Jacketed gametes (protects from dessication) Protected embryo (protects from dessication) Alternation of Generations Sporophyte (2N) Mitosis Meiosis Zygote (2N) Spores (N) fertilization Gametes (egg & sperm Gametophyte (N) Evolutionary Trend Figure 23.2 Page 386 zygote GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM Classifying Plants Plants can be divided into 2 major categories based on their characteristics: Nonvascular Plants Do NOT have specialized tissues to transport water and nutrients Instead, these plants transport water from cell-to-cell by osmosis Vascular Plants Have specialized tissues to transport water and nutrients in plants Xylem – carries water upward from roots Phloem – carries nutrients and carbohydrates produced by photosynthesis Nonvascular Plants (Bryophytes) Again, these plants do not have specialized tissues to transport water and nutrients and instead rely on osmosis Thus, these plants must be small Why? Major types of bryophytes (nonvascular plants): Mosses Liverworts Hornworts Nonvascular Plants/ Bryophytes Mosses Have rhizoids that anchor them to the ground (instead of roots) Depend on water for fertilization The sperm must swim to the egg Therefore, nonvascular plants must live in MOIST environments Gametophyte is the dominant phase of the life cycle Moss/ Bryophyte Life Cycle zygote Zygote grows, develops into a sporophyte while still attached to gametophyte. mature sporophyte Diploid Stage Fertilization Haploid Stage Meiosis Spores germinate. spermproducing structure Figure 23.5 Page 388 eggproducing structure male gametophyte female gametophyte Vascular Plants/Tracheophytes Reminder: Vascular plants have specialized tissues to transport water and nutrients in plants Xylem & phloem Vascular plants (tracheophytes) can be divided into 2 categories: Seedless vascular plants Seed (vascular) plants Seedless Vascular Plants Have true roots, leaves, and stems Consist of ferns, club mosses, and horsetails Seedless Vascular Plants Ferns – A Close Up Diploid sporophyte is the dominant stage Have rhizomes, which are underground stems Fronds: large “leaves” where spores develop Develop spores in sporangia on underside of fronds Reproduce using spores A sorus (plural: sori) is a cluster of sporangia Fern Life Cycle Sporophyte still attached to gametophyte sorus zygote fertilization egg rhizome Diploid Stage meiosis Haploid Stage Spores develop Spores are released sperm Figure 23.9 Page 391 mature gametophyte Spore germinates Seed (Vascular) Plants Have true roots, leaves, and stems Have the ability to form seeds, which are used for reproduction Seed plants are the most dominant group of photosynthetic organisms on land There are 2 types of seed (vascular) plants: 1. gymnosperms 2. angiosperms Seed (Vascular) Plants Gymnosperms = “cone bearers” “naked seeds” – not enclosed in ovaries Bear seeds directly on the surfaces of cones Cones = sporophyte structures that produce gametophytes (seeds) Coniferous trees are the major example Pines, junipers, spruces, etc. section through one ovule surface view of one cone scale (houses two ovules) Pine Life Cycle ovule surface view of one cone scale (houses a pollen-producing sac) mature sporophyte seed coat section through a pollen-producing sac zygote seeding pollen tube spermproducing cell Diploid embryo seed fertilization meiosis Haploid microspores eggs form megaspores pollination form female gametophyte Figure 23.17 Page 396 Seed (Vascular) Plants Angiosperms = flowering plants Seeds are enclosed by an ovary Flowers are reproductive organs Flowering plants contain ovaries Evolutionary advantage attract pollinators Ovaries surround and protect seeds Ovary develops into a fruit after pollination & helps with seed dispersal when eaten Examples: Maple trees, tulips, grass sporophyte Flowering Plant Life Cycle Diploid Double fertilization Haploid pollination two sperm enter ovule Meiosis microspores female gametophyte Meiosis mitosis without cytoplasmic division Figure 23.20 Page 399 Evolutionary Tree for Plants Nested monophyletic groups green zygophytes, charophytes bryophytes lycophytes algae related groups horsetails ferns cycads ginkgos conifers gnetophytes flowering plants seed plants euphyllophytes embryophytes (land plants) vascular plants (closely related groups)