The Diversity and Plants - General Biology - Lecture Slides | BIOL 1002, Study notes of Biology

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Chapter 21: The Diversity of Plants The Plant Evolutionary Tree • Certain anatomical features represent milestones in the evolution of plants – Appearance of vascular tissue and lignin – Appearance of pollen and seeds – Appearance of flowers and fruits The Evolutionary Origin of Plants • Several lines of evidence support the hypothesis that green algae gave rise to plants – DNA comparisons show green algae are plants’ closest living relatives – Both use the same type of chlorophyll and pigments in photosynthesis – Both store food as starch – Both have cell walls made of cellulose Characteristics of Plants • Multicellularity • Ability to photosynthesize • Exhibit alternation of generations (a multicellular diploid generation alternates with a multicellular haploid generation) Alternation of Generations – Diploid (2N) sporophyte plant produces haploid (N) spores through meiosis – Spores divide by mitosis and develop into haploid gametophyte plants – Haploid gametophyte plant produces haploid gametes through mitosis – Gametes fuse to form diploid zygotes, which divide by mitosis and develop into diploid sporophytes Terrestrial Adaptations • Roots or rootlike structures – Anchor plant – Absorb water and nutrients from soil • Waxy cuticle covers leaves and stems – Reduces evaporative H2O loss • Stomata (singular, stoma) – Allow gas exchange when open – Reduce evaporative H2O loss when closed Terrestrial Adaptations • Conducting vessels – Transport H2O and nutrients throughout plant • Lignin – Stiffening agent found in cell walls; supports plant body • Pollen – A reduced male gametophyte that allows wind (instead of water) to carry sperm to eggs The Bryophytes • Lack true roots, stems, or leaves • Have rhizoids, rootlike anchoring structures • Limited body size b/c no vascular tissue • Most are restricted to moist habitats – Motile sperm must swim to egg • Include liverworts and mosses Mosses Copyright © 2005 Pearson Prentice Hall, Inc. thallus (leaflike part) close-up of gemmae (spores) Liverworts gemmae cup The Seedless Vascular Plants • Gametes develop within archegonia and antheridia • Motile sperm swim to egg • Formed the first forests – Gave rise to present-day coal deposits • Include club mosses, horsetails, and ferns Seedless Vascular Plants: Club Mosses • Present-day club mosses are only a few inches tall • Leaves are small and scalelike • Lycopodium (ground pine) grows on temperate forest floors 7) o o_ ° 2. a D £ a © o® o o_ n ” ° = 2 > O Seedless Vascular Plants: Ferns • Largest and most diverse group of seedless vascular plants • Have well developed, broad leaves (called “leaflets”) • Leaves emerge from coiled “fiddleheads” Ferns: Reproduction • Sporophyte produces haploid spores within sporangia • Sperm swim to egg The Seed Plants • Produce pollen and seeds – Pollen grains contain sperm-producing cells • Dispersed by wind or pollinators • Eliminate need for sperm to swim to egg – Seeds consist of: • Embryo • Seed-coat (protects embryo) • Food supply (nourishes emerging plant) • May retain dormant for days, months, or years • Dispersed by wind, water, and animals Seed Plants: Gymnosperms • Non-flowering seed plants • First fully terrestrial plants to evolve • Includes conifers, ginkgos, and cycads Gymnosperms: Conifers • Include pines, firs, spruce, hemlocks, and cypresses • Most abundant in cold latitudes and at high elevations • Adapted to dry, cold conditions: – Retain green leaves throughout the year (evergreen) – Thin, needle-like leaves covered with waterproofing material (reduces evaporation) – Produce an “antifreeze” in sap Conifer Seeds Develop in Cones • Trees produce both male and female cones – Male cones are relatively small • Produce pollen • Pollen dispersed by wind – Female have woody scales (“pinecones”) • Produce seeds at base of each scale Gymnosperms: Ginkgos • Represented by a single species, Ginkgo biloba • Trees are either male or female – Female trees bear foul-smelling, fleshy seeds – Male trees extensively planted in U.S. cities (resistant to pollution) • Ginkgo extract supposedly improves memory Copyright © 2005 Pearson Prentice Hall, Inc. Gymnosperms: Cycads • Probably evolved from ferns • Most abundant in tropical or subtropical climates • Are either male or female • Grow slowly and live for a long time – One Australian specimen estimated to be 5000 years old Seed Plants: Angiosperms • 3 major adaptations have contributed to dominance of angiosperms – Flowers – Fruits – Broad leaves Flowers • Flowers have reproductive male and reproductive female structures on them • Believed to have evolved from gymnosperm ancestors – Animals: eat protein-rich pollen – Plants: using animals as pollinators • Most flowers are showy and attract pollinators • stamen (male) carpel (female) petal sepal ovule in an ovary Fruits Encourage Seed Dispersal • Fruits are mature ovaries that contain developing seeds • Various fruit adaptations help disperse seeds – Fleshy fruits entice animals to eat them (seeds pass through digestive tract unharmed) – Burrs cling to animal fur – Winged fruits are carried through the air Broad Leaves • Collect more sunlight for photosynthesis than narrow leaves of gymnosperms • Photosynthetic advantage is offset because broad, tender leaves are more appealing to herbivores than tough, waxy needles of conifers – Angiosperm defenses include: • Physical defenses (thorns, spines, resins) • Chemical defenses (make plant Group Vascular Plants Subgroup Ferns Conifers Flowering plants Relationship * caccne Gametophyte dominant—sporophyte lops from zygote Sporophyte dominant—develops from zygote retained on gametophyte Sporophyte dominant—microscopic gametophyte develops within sporophyte ye dominant—microscopic gametophyte develops within sporophyte Transfer of R luctive Cells Motile sperm swims to stationary egg retained on gametophyte Motile sperm swims to stationary egg retained on gameiophyte Wind-dispersed pollen carries sperm to stationary agg in cone Pollen, dispersed by wind or animals, carries sperm to stationary egg within flower Emiy Em : Coakeeus Oceurs within archegonium of gametophyte Oceurs within archegonium of gametophyte Occurs within a protective seed containing a food supply Occurs within a protective seed containing a food supply; seed encased in fruit Copyright © 2005 Pearson Prentice Hall, Inc. Dispersal Hapleid spores carried by wind Hapleid spores carried by wind Seeds containing diploid sporophyte embryo disper by wind or animals Fruit, carrying seeds, dispersed by animals, wind, or water Water and Nutrient Transport Structures. Present Present Present Present