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Chapter 39 Notes (Plant's Response to External and Internal Signals)

Chapter 39 Notes (Plant's Response to External and Internal Signals)

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Chapter 39 Notes (Plant's Response to External and Internal Signals) AP Biology & Honors Human Anatomy 1. Basic Mechanism of Plant Response – Signal Transduction Pathway (KNOW GENERAL CONCEPT FOR SALDAMANDO’S CLASS!!) a. The step(s) between a plant's perception of a change in the environment and the plant's response to that change b. Three main steps: Reception, Transduction, and Response i. Reception: Signals, whether internal or external are first detected by receptors Receptors are proteins that change shape in response to a specific stimulus Example- Phytochrome is a light absorbing receptor ( present in the cytoplasm) for de-etilation(greening) These receptors are sensitive to very weak environmental and chemical signals, thus they need to be amplified. ii. Transduction: Second messengers transfer and amplify signals from receptors – process of transduction Weak signals are amplified by second messengers- small internally produced chemicals that transfer and amplify the signal from the receptors to proteins that cause the specific response. Example- Light causes phytochrome to undergo a conformation change that leads to increase levels of the second messengers cyclic GMP and Ca 2+ Increase cyclic GMP and calcium may in turn activate specific protein kinases iii. Response Ultimately a signal transduction pathway leads to regulation of one or more cellular activities. These are responses to stimulation involve the increased activity of certain enzymes. 2. General Information on the Plant Response a. Plants adjust their growth and development in response to environmental cues. b. Plants can actually move by responding to the stimuli (Tropism). i. Growth movements up or down in response to gravity --- gravitropism. ii. Growth movements toward or away from light ---phototropism. iii. Changes in plant growth form in response to wind or touch --- Thigmotropism. iv. Rapid responses using action potentials (similar to human’s nervous system). c. Tropism can be either classified into positive or negative. i. Positive – follow the stimuli
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Chapter 39 Notes (Plant's Response to External and Internal Signals) ii. Negative – Go against the stimuli d. Phototropism – Plants growing in a partially dark environment will grow toward light.
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