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Download Lecture 10, Angiosperms - Cal State LA
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# of families Evolution of Plant Biodiversity Seedless vascular plants Gymnosperms dominate Angiosperms First gymnosperms Mackenzie 2003 Phylum Anthophyta, Angiosperms (Flowering plants) 250,000 species named to date Key Angiosperm features “Angion” = container, “sperm” = seed Advanced transport tissues tracheids + vessels in xylem tissue, wide channels for moving water Flowers + pollination syndromes more efficient reproduction: deliver your pollen to eggs of your own species Protected seeds inside fruit provides means of dispersal for offspring, via animals that eat fruit, or wind, or water Key Angiosperm features “Angion” = container, “sperm” = seed Advanced transport tissues tracheids + vessels in xylem tissue, wide channels for moving water tracheids have an extra, outer cell wall re-inforced with lignin, a super-strong material that allows stems of plants to stand upright - there are holes in the lignin wall to allow water to flow from one to the next - cells are dead by the time they function in water transport - wood is basically just lots of tracheids pressed together Tracheids and vessel elements Gymnosperm xylem tissue contains only tracheids Angiosperm xylem contains both tracheids and vessel elements Tracheids = elongated single cells that transport water in the xylem tissue - pass water cell-to-cell Vessel elements = wider vessels Tracheids and vessel elements Understand the progressive adaptations to life on dry land that culminated in the super-successful angiosperms p. 639 Reproductive structures of seed plants Gymnosperms Angiosperms Flower Pistil/Carpel(s) Stamen Petal Sepal Tip of stamen is the anther, which contains the microsporangia produce microspores grow into pollen grains, housing male gametophyte (only 2 cells big!) Anther releasing pollen grains (after meiosis) Base of carpel = ovary, protective structure that contains ovules the megaspore inside each ovule grows into the female gametophyte 1 egg nucleus 2 polar nuclei, which will become the endosperm Double Fertilization Pollen grain has 2 cells 1 grows into pollen tube, penetrates ovary other 1 forms 2 sperm: sperm #1 fertilizes egg sperm #2 fuses with both polar nuclei to form the endosperm (3N, triploid) Endosperm becomes food for the growing embryo Double Fertilization Each ovule is initially surrounded by two integuments After fertilization, these become the hardened seed coat The whole ovary wall then thickens into the pericarp, the thick outer wall of the fruit Ovule becomes seed, ovary becomes fruit Campbell & Reece 2002 Angiosperm seeds aren’t exposed like naked gymnosperm seeds Instead, they are protected by a ripened ovary wall (pericarp), sometimes with additional “accessory” parts like the outer tissue of this apple Stern 1991 Pollination syndromes Co-evolution between angiosperms and their animal pollinators - animal gets a reward of sugary nectar (energy-rich) - plant attaches or dusts animal with pollen, which will then be transferred to the next flower Termed co-evolution because changes in one partner trigger compensating changes in the other - for example: This flower has a mechanism causing stamens to arch over and dust the back of a honeybee with pollen Plants pollinated by nocturnal animals (moths, bats) have flowers that bloom at night Many flowers are distinctively shaped so only a co-evolved pollinator has the right length appendage to reach in, get the nectar reward Hummingbird pollinated flowers are usually red with long tubes Some flowers have patterns in ultraviolet part of light spectrum - invisible to us but clear to insect eyes; can form landing strips Seed dispersal wind-dispersed seeds are fluffy or have “wings” to increase drag Fruit dispersal burrs = dry fruit with hooks to stick to animals Fruit dispersal Most plants invest lots of energy in their fruit for one reason: This disperses the offspring of the plant, as the animal eventually poops out the undigested seeds somewhere else The seeds of many plants cannot develop until they have passed through an animal’s digestive system! p. 648 of Freeman 3rd ed. vascular plants Gymnosperms Carnivorous plants A source of nitrogen is essential for cells to make proteins - usually nitrate, the water-soluble compound NO3-2 Plants that live in nutrient-poor, swampy conditions may be unable to get nitrogen from the soil through their roots Some therefore capture and digest insects as a source of nitrogen Venus flytrap swings closed when 2 of 3 trigger hairs are bent by an insect Other plants drown insects in contained water or catch them on sticky leaves Parasitic angiosperms Cuscuta sp. (dodder) Monotropa sp. Non-photosynthetic; parasitize other plants to obtain nutrition Plant Chemistry Because plants can’t move, many produce toxic chemicals to protect themselves from herbivorous animals and competitors - many plants leach chemicals out into the surrounding soil to inhibit growth of competitors (termed allelopathy) - others produce toxins such as caffeine & nicotine, to deter herbivorous animals from eating their leaves Humans use plant chemicals as medicinal or recreational drugs - 25% of modern medicines involve the plant products - co-evolved insect herbivores can tolerate chemical defenses of their particular “host” plant, leading to host specialization Plant Revenge Plants can tell when a caterpillar is eating them, by recognizing its spit Plants may release airborne chemicals that attract wasps, which come and sting the caterpillar The wasps paralyze the caterpillar and lay their eggs inside it wasp larvae eat the living but paralyzed caterpillar from the inside Plant-insect Coevolution = Biodiversity Most species on earth, by the numbers, are herbivorous insects - more than 135,000 species of beetles feed on flowering plants Studies suggest that when angiosperms started speciating, beetles that fed on them also divided into specialist populations, which each evolved into new beetle species Coevolution can promote species formation - when one plant evolves into two different species, so do its parasites, predators and pollinators! Plant-insect Coevolution = Biodiversity Consider what happens when an ancestral plant undergoes speciation and evolves into two distinct plant species... mountains Plant-insect Coevolution = Biodiversity Consider what happens when an ancestral plant undergoes speciation and evolves into two distinct plant species... Rain forest species Desert species Plant-insect Coevolution = Biodiversity But what happens to the pollinators (say, butterflies) and herbivores (beetles) that were symbionts of that ancestral plant...? pollinator (butterfly) herbivore (beetle) Plant-insect Coevolution = Biodiversity But what happens to the pollinators (say, butterflies) and herbivores (beetles) that were symbionts of that ancestral plant...? Rain forest species Desert species Pollinators and herbivores also form new species when their host plant speciates coevolution promotes formation of many new species Human Dependency on Angiosperms Crucial to the global carbon cycle Critical habitat for animals (including us) Our economy is dependent upon angiosperms (ecosystem functions) Sources of everyday products (e.g. hardwoods, medicines) Source of our food (directly or indirectly) – over 80% of our food comes from only six species: rice, soy, wheat, corn, sorghum, and millet