HW #39 - AP Biology Period 4 #22 Liem Nguyen 3/4/10...

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AP Biology Period – 4 #22 Liem Nguyen 3/4/10 Homework #39 ( 090313 ): Chapter 39 (due Friday 090313 ) Total points: 40 for Attempt on all questions Concept Map: 10 Points Chapter 39: Plant Responses to Internal and External Signals Objectives Signal Transduction and Plant Responses 1. Compare the growth of a plant in darkness (etiolation) to the characteristics of greening (de-etiolation). Plants in darkness grow long, lack elongated roots Large leaves get ripped moving through the dirt Chlorophyll is useless underground Plant must concentrate all resources on finding light Etiolation is the morphological adaptations for growing in darkness. The most effective in plants that encounter continuous darkness when sprouting underground (potato). The de- etiolation are the changes of a plant shoot undergoes in response to sunlight. It slows elongation of stems, leaves expand, roots elongate, and the shoot produces chlorophyll. 2. Describe the signal pathways associated with de-etiolation. Phytochromes detect light, send a signal to second messengers Second messengers amplify the signal Activates proteins that cause stems to slow growth Production of chlorophyll and the elongation of roots The phytochromes detect light, and then send a signal to second messengers. In the signal pathway associated with de-etiolation a plant cell’s reception of a signal, then is transduced into a response. The signal binding to a specific receptor stimulates the cell to produce relay molecules, such as second messengers. These relay molecules trigger the cell’s various responses to the original signal. 3. Describe the role of second messengers in the process of de-etiolation. Second messengers amplify the effects of the activated photoreceptors Allows very small amounts of light to initiate change in a plant Transfer and amplify the signal from the receptor to other proteins The second messengers are small, internally produced chemicals that transfer and amplify the signal from the receptor to other proteins that cause the response. In de-etiolation, each activated phytochrome molecule gives rise to hundreds of molecules of a second messenger, possibly leading to the activation of hundreds of molecules of a specific enzyme.
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4. Describe the two main mechanisms by which a signaling pathway can activate an enzyme. 2 main mechanisms by which a signaling pathway can activate an enzyme Transcriptional regulation and post translational modification Transcription factors on the DNA control transcription Produce enzymes to carry out a function Post translational modification of proteins Proteins already exist, but they are modified so that they carry out the task There are two main mechanisms, each mechanism by which a signal promotes a new developmental course may depend on the activation of positive transcription factors or negative transcription factors or both. These mutants have defects in a negative transcription factor that inhibits the expression of other genes normally activated by light.
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HW #39 - AP Biology Period 4 #22 Liem Nguyen 3/4/10...

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