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19 20.1 Origins of Plant Life KEY CONCEPT Plant life began in the water and became adapted to land. (Charophytes are the ancestors of plants) 19 20.1 Origins of Plant Life Kingdom Plantae • Characteristics of all plants –Multicellular –Autotrophic –Eukaryotic 19 20.1 Origins of Plant Life • Plants faced difficulties to maintain life on land –Obtaining resources- from air and soil- special organs –Staying upright- support tissues-lignin-c. wall –Maintaining moisture-waxy cuticle, stoma-pores on leaf –Reproducing- protective jacket for gametes, eggs remain in female parent where they are fertilized 19 20.1 Origins of Plant Life • Important plant characteristics likely originated in charophytes. – multicellular body allowing for specialization of cells and tissues – cell division that allows for chemical communication between cells – reproduction involving sperm swimming to egg 19 20.1 Origins of Plant Life • True plants evolved through natural selection. – Ancestral charophytes lived in areas of shallow water. – Those that could survive longer dry periods were favored. – First true plants probably grew at edges of water. – True plants have embryos that develop while attached to female parent. 20.1 Origins of Plant Life Evidence: Charophytes are ancestors of green plants • • • • Cell walls- 20-60% cellulose Similar chloroplasts Similar mitosis and cytokinesis Similar genes and rRNA sequences 19 20.1 Origins of Plant Life • True plants evolved through natural selection. 19 20.1 Origins of Plant Life Plants have adaptations that allow them to live on land. • Challenges of living on land have selected for certain plant adaptations. Maintaining moisture • A cuticle allows plants to retain moisture. – waxy, waterproof layer – holds moisture in 19 20.1 Origins of Plant Life • Stomata are tiny holes in the cuticle. stoma – can open and close – allow air to move in and out (CO2 and O2) – Closing holds in moisture 19 20.1 Origins of Plant Life • A vascular system allows resources to move to different parts of the plant. – collection of specialized tissues – brings water and mineral nutrients up from roots – disperses sugars from the leaves – allows plants to grow higher off the ground (lignin) xylem phloem water and mineral nutrients sugars 19 20.1 Origins of Plant Life • Lignin allows plants to grow upright. lignin plant cells – hardens cell walls of some vascular tissues – provides stiffness to stems 19 20.1 Origins of Plant Life • Pollen grains allow for reproduction without free-standing water. – pollen grains contain a cell that divides to form sperm – pollen can be carried by wind or animals to female structures 19 20.1 Origins of Plant Life • A seed is a storage device for a plant embryo. – seed coats protect embryos from drying wind and sunlight – embryo develops inside the ovary of a female plant 19 20.1 Origins of Plant Life Alternations of Generations- Taking turns A plant's life cycle alternates between the gametophyte and sporophyte generations. Gametophytes produce gametes Sporophytes produce spores Four major Groups of plants: bryophytes, pteridophytes, gymnosperms, and angiosperms. 20.1 Origins of Plant Life Spores differ from gametes 1. Spores can develop into a new organism with fusing or mating. 1. Gametes must fuse- zygote 2. Spores have tough, protective coats to resist harsh conditions 1. Gametes are affected by harsh conditions-cold, heat, drying. 20.1 Origins of Plant Life 4 Main plant Groups 1. Bryophytes- mosses- oldest – No seeds, no lignin-hardened vascular tissue 2. Pteridophytes- ferns - No seeds, have lignin-hardened vascular tissue 3. Gymnosperms- cone-bearing plants - First to have seeds-”naked seeds”- no chamber - Specialized leaves Seeds- embryo with a food store Plants can spread via seeds without drying out. 4. Flowering plants- angiosperms - Seeds in ovaries- protection, dispersal 19 20.1 Origins of Plant Life • Plants have adaptations that prevent animals from eating them. – spines and thorns – defensive chemicals