Chapter 39 Plants

Biology, 7th Edition (Book & CD-ROM)

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Chapter 39 Plant Responses to Internal and External Signals I. II. Plant Hormones A. Tropism- any growth response that results in curvatures of whole plant organs towards or away from stimuli 1. Growth of a shoot toward light = positive phototropism 2. Growth of a shoot away from light = negative phototropism 3. Coleptopile is what controls direction of growth a. The tip of it is what is important 4. It is a chemical signal passed down from the coleptopile to a little bit underneath it B. General Information 1. Hormones control plant growth and development a. Affect division, elongation, and differentiation of cells 2. Each hormone has multiple effects 3. Hormones produced in very small concentrations, but the smallest amount can have a big effect on its growth
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Unformatted text preview: C. Survey of Plant Hormones III. IV. V. Platns respond to Stimuli A. Gravity 1. Gravitropism 2. Shoot always bends upward (positive) and root curves downward (negative) 3. Statoliths- plastsids containing dense starch grains a. Plants detect gravity by them b. Statoliths aggretgate to the root cap c. There’s more… B. Mechanical Stimuli 1. Thismomorphogenesis- changes in from mechanical stress a. Trees that are in more windy areas have shorter thicker stems than the same species somewhere else b. Rubbing the stems of a young plant changes its growth c. Vines grow straight until they touch something d. Mimosa pudica has closing leafs when it is touched 2. Thigmotropism- directional growth in response to touch 3....
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