13-ch17-plants(1) - Chapter 17 Plants, Fungi & the...

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Unformatted text preview: Chapter 17 Plants, Fungi & the Colonization of Land The The greening of earth (by plants, 500 mya) try to imagine earth before plants land plants – “embryophyte” clade (vs. protists) are defined by their terrestrial adaptations but some have returned to aquatic environments some have returned to aquatic environments • • • • • • appx. 290,000 species extant supply Oxygen Oxygen constitute the base of the trophic pyramid (food chain) provide structural diversity (= habitats for other species) structural diversity habitats for other species) stabilize landscapes (e.g., prevent erosion) role in chemical / nutrient cycles... Terrestrial Terrestrial ecosystem was a paradise waiting to happen when plants invaded land 500 million years ago abundance of untapped resources... • sunlight unfiltered by water (or plankton competitors) unfiltered by water (or plankton competitors) • abundant CO2 • mineral nutrients nutrients • few herbivores or pathogens (yet) but consider the trade-off... tradehigher surface area to volume ratio photosynthesis gas exchange water loss surface area to volume: small or large? why? surface area to volume: small or large? why? branches and leaves on an oak tree surface area to volume: small or large? area to small or large? why? acorn from an oak tree surface area to volume: small or large? why? Key Key terrestrial adaptations • • • • • roots & shoots (with stem cells at growing tips) leaves (photosynthetic organ) vessels (transport water, food) (t seeds (protect offspring until conditions are favorable) flowers (very successful reproductive structures) (very successful reproductive structures) cuticle – waxy extracellular epidermal covering; prevents water loss from plant surfaces Nonvascular Nonvascular plants include: hornworts Nonvascular plants generally form groundgroundhugging carpets and are only a few cells thick. true mosses liverworts • no true roots, leaves or vessels • require water for the dispersal of sperm • spores are dispersed by wind peat – large deposits of un-decayed organic material formed primarily from the sphagnum moss (in bogs) decomposition is slowed by: is slowed by: - phenol in cell walls - low nutrient levels - low temperature vascular vascular plant adaptations vascular tissue – system of tubes for transport & support xylem – conducts water and minerals (up from roots) phloem – conducts sugar sugar (down from leaves) root – organ that anchors plant & absorbs water, nutrients leaf – organ that increases surface area for photosynthesis The first vascular plants The first vascular plants were were seedless. Their descendants include ferns & club mosses. successful adaptation: 93% of plant species alive today are vascular! Carboniferous forest – 300 mya, seedless vascular plants dominated the landscape (= fossil fuels) (= seed seed plant adaptations adaptations microscopic reproductive structures • ovules (contain female gametophyte) • pollen (contains male gametophyte) male gametophyte) gametophyte = multicellular haploid structure (not just one cell, like ovum or sperm) parent plant provides plant provides - nutrients - protection seeds (protected embryo) are resistant & dispersable compared to spores = huge competitive edge! huge competitive edge! Gymnosperms Gymnosperms bear “naked” seeds, typically on cones conifers – pines, firs, redwoods (most diverse) Cycad Welwitschia Ginkgo Ephedra Important Important moments in plant evolution plant 1) life on land 2) vessels 4) stay tuned for the next step: flowers! 3) seeds Angiosperm reproduction involves flowers & fruits flower – short stem w/ modified leaves & reproductive structures stem w/ modified leaves reproductive structures successful adaptation: 90% of plant species alive today are angiosperms! fruit (forms after pollination) – after pollination) mature ovary; for seed protection & dispersal diverse strategies for dispersal Adaptations Adaptations for pollination illustrate mutualism & coevolution coevolution: when two different species reciprocally influence each other’s adaptations through many generations of ecological interactions pollinator: pollinator: vision in ultraviolet spectrum genetic variation variation nutritional reward pollinatee: ultraviolet "landing strip" to attract pollinator(s) Flowers have ways of making sure they get "what they want" in exchange for their investment in nutritional rewards "nectar thieves" and pollen eaters evolutionary arms race Some flowers are very selective about their pollinators What's that smell? Another way to attract a pollinator... Coevolution Coevolution as a component of artificial selection: a plant’s eye view of the human-crop partnership human- PBS The Botany of Desire Michael Pollan (environmental journalist) Apple: Sweetness 00:04:18 – 30:50:00 http://video.pbs.org/video/1283872815 ...
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