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Download 1d. Plantstaxonomy,reprod,response
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Plant hormones auxins gibberellins abscisic acid ethylene cytokinins brassicosteroids AP Biology 2005-2006 Response to light: Phototropism Growth towards light Hormone: Auxin asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side AP Biology 2005-2006 Apical dominance Controls cell division & differentiation axillary buds do no grow while apical bud exerts control shoot root AP Biology 2005-2006 Gibberellins Family of hormones over 100 different gibberellins identified Effects stem elongation fruit growth seed germination AP Biology plump grapes in grocery stores have been treated with gibberellin hormones while on the vine 2005-2006 Abscisic acid (ABA) Effects slows growth seed dormancy high concentrations of Abscisic acid germination only after ABA is inactivated down or leeched out survival value: seed will germinate only under optimal conditions light, temperature, moisture AP Biology drought tolerance rapid stomate closing 2005-2006 Ethylene Ethylene is a hormone gas released by plant cells Multiple effects response to mechanical stress triple response slow stem elongation thickening of stem curvature to stem growth leaf drop (like in Fall) apoptosis AP Biology fruit ripening 2005-2006 Apoptosis & Leaf drop Ethylene & auxin many events in plants involve apoptosis (pre-programmed cell death) death of annual plant after flowering differentiation of xylem vessels What is the evolutionary advantage of loss of leaves in autumn? loss of cytosol shedding of autumn leaves AP Biology 2005-2006 Fruit ripening Adaptation hard, tart fruit protects developing seed from herbivores ripe, sweet, soft fruit attracts animals to disperse seed Ethylene triggers ripening process breakdown of cell wall softening conversion of starch to sugar sweetening positive feedback system ethylene triggers ripening ripening stimulates more ethylene production AP Biology 2005-2006 Applications Truth in folk wisdom! one bad apple spoils the whole bunch ripening apple releases ethylene to speed ripening of fruit nearby Ripen green bananas by bagging them with an apple Climate control storage of apples AP Biology high CO2 storage = reduces ethylene production 2005-2006 Flowering Response Triggered by photoperiod relative lengths of day & night night length—“critical period”— is trigger Plant is sensitive to red light exposure What is the evolutionary advantage of photoperiodism? AP Biology Short-day plants Long-day plants Synchronizes plant responses to 2005-2006 season Circadian rhythms Internal (endogenous) 24-hour cycles 4 O’clock Noon Midnight Morning glory AP Biology 2005-2006 Response to gravity How does a sprouting shoot “know” to grow towards the surface from underground? environmental cues? roots = positive gravitropism shoots = negative gravitropism settling of statoliths (dense starch grains) may detect gravity AP Biology 2005-2006 Response to touch Thigmotropism Mimosa (Sensitive plant) closes leaves in response to touch AP Biology Caused by changes in osmotic pressure = rapid loss of K+ = rapid loss of H2O = loss of turgor in cells 2005-2006 Plant defenses Defenses against herbivores AP Biology 2005-2006 Plant defenses Defenses against herbivores coevolution Parasitoid wasp larvae emerging from a caterpillar AP Biology 2005-2006