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Ch 31 Biology Notes Essay

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CH 31 Notes

31.1

Plant hormones help coordinate growth, development, and responses to stimuli.

- hormone - signaling molecule that binds to receptor and triggers responses

- plant growth regulator - are like plant hormones to help control/regulate plant physiological processes

     - prduced in very low concentrations 

Discovery of Plant Hormones

- growth response that results in plant organs curving away or toward a stimuli = tropism

     - phototropism = toward or away from light

          - shoots - positive phototropism

          - roots - negative phototropism

- phototropism only occurs when tip is exposed to light    

     - only works when chemicals can pass thru to the tip and coleoptile

- asymmetric distribution of certain substances that may act as growth inhibitors which are more concentrated in lighted side of a stem not shaded side

Survey of Plant Hormones

- major classes of plant hormones - auxin, cytokinins, gibberellins, brassinosteroids, abscisic acid, and ethylene

Auxin

- any chemical substance that promotes elongation of coleoptiles.  

- produced in shoot tips and transports from tip to base.

- effects = stimulate cell elongation and regulating plant architecture

Role of Auxin in Cell Elongation

- moves from shoot tip down to region of cell elongation --> binds to receptor in plasma membrane

- acid growth hypothesis - proton pumps play major role in growth response of cells to auxin by stimulating H+ pumps (increases voltage and lowers pH of cell wall which activates expansins that break cross links between microfibrils and loosens the cell wall & increases membrane potential allows more ions into the cell --> more water intake and +turgor)

- rapidly alters gene expression so that new cells of cell elongation to make new proteins quickly

Auxin's Role in Plant Development

- polar transport region of auxin = central element controlling spatial organization (pattern...

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