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Transcript
Gymnosperms: vascular seed bearing plants with a naked seed coat › No fruit around the seed Conifers: seeds develop in a female cone while male cones develop pollen Most are evergreens with needle or scale-like leaves that have thick cuticles They make up the most abundant (pines), tallest (redwoods), and oldest (bristlecone pine) trees Cycads: palm-like trees that flourished during the Mesozoic era › Only about 130 species still exist- confined to tropics and subtropics › They bear massive cone-shaped strobili that produce either pollen (transferred by air currents) or ovules Ginkgos: reduced in diversity from the Mesozoic to only one surviving species today › Unusual in being deciduous › Hardy, showing resistance to insects, disease, and air pollutants Bonsai Ginkgos Gnetophytes: most unusual gymnosperms › Live in tropical and desert areas The pine tree (sporophyte) produces two kinds of cones › Male cones produce sporangia that yield microspores that develop into pollen grains (male gametophyte) › Female cones produce ovules that yield megaspores (female gametophyte) Pollination is the arrival of a pollen grain on the female reproductive parts, after which a pollen tube grows toward the egg Fertilization, which is delayed for up to a year, results in zygote that develops into an embryo within the conifer seed Angiosperms: vascular seed plants that make flowers and fruits › After fertilization, the ovule becomes the seed and the ovary becomes the fruit Most angiosperms develop rapidly and produce seeds quicker than gymnosperms Development of the flower lead to the attraction of insects, birds, and other animals that helped reproduction occur rapidly › Lead to a great deal of coevolution in flower development and pollinators When buffeted by severe environmental challenges, the flowering plants did well › Thanks to their protective seeds and help from pollinators Flowering plants arose from 3 lineages and comprise a tremendous diversity Three major groups: 1. Magnolids: include magnolias, avocados, nutmeg and black pepper plants 2. Eudicots: include familiar shrubs, trees (except conifers), and herbaceous plants 3. Monocots: include grasses, lilies, and major food-crop grains Magnolids Eudicots Monocots The female gametophyte forms the ovary Pollen forms inside stamens Pollination leads to double fertilization: one sperm fertilizes the egg, the second sperm fertilizes a cell that becomes the endosperm Ovary tissue develops into the fruit that covers the seeds Table 23.1 Table 23.2 Page 388