Chapter 39: Plant Responses to Internal and External Signals

Transcription

1 AP Biology Reading Guide Name Chapter 39: Plant Responses to Internal and External Signals Concept 39.1 Signal transduction pathways link signal reception to response This concept brings together the general ideas on cell communication from Chapter 11 with specific examples of signal transduction in plants. As with animals, plants have receptors that trigger signal transduction pathways when activated. Let s begin with a review of three steps in signal transduction. Step 1: Reception. Cell signals are detected by receptors that undergo changes in shape in response to a specific stimulus. Step 2: Transduction. Transduction is a multistep pathway that amplifies the signal. This effect allows a small number of signal molecules to produce a large cellular response. Step 3: Response. Cellular response is primarily accomplished by two mechanisms: a. increasing or decreasing mrna production b. activating existing enzyme molecules 1. Have you ever seen a shriveled potato sending out skinny, pale sprouts? The sprouts are skinny and pale as a result of growing in darkness. What is this process collectively called? 2. If you move the potato into the light, the sprout will respond by forming short, sturdy stems and broad, green leaves. What is this response to light called? 1

2 3. The figure below gives a specific example of a signal transduction in plants for the greening or de-etiolation response described above. a. In the table below, summarize what occurs along each step of the signal transduction pathway. b. Number the picture to match your steps. c. What are the two second messengers in the pathway? Reception Transduction Response Concept 39.2 Plant hormones help coordinate growth, development, and responses to stimuli 4. a. Both plants and animals have hormones. What is the original definition of hormone? b. Identify three reasons why do modern plant biologists argue that the definition is too narrow? (1) (2) (3) 2

3 5. What is a tropism? 6. The diagram below describes early experiments on phototropism conducted by Charles and Francis Darwin. What can be concluded from these experiments? CONCLUSION There are many plant hormones and you are not required to memorize all of them and there functions. However, understanding some of the major functions of 3 particular plant hormones is valuable. Let s narrow your focus to the auxins, gibberellins, and ethylene. 7. On pages , read the sections titled auxin and The role of Auxin in Cell Elongation. Summarize the role of auxin in the bending of the coleoptile during phototropism. 8. Skip to pages and read the sections titled Gibberellins, Stem Elongation, and Fruit Growth. a. Summarize how gibberellin works with auxin to promote stem elongation. b. Summarize how the application of gibberellins is used in the agriculture industry. 3

4 9. Skip to pages and read all the sections beginning with Ethylene through Fruit Ripening. a. Summarize the role of ethylene in a plant s triple response to mechanical stress. b. Summarize the role of ethylene in senescence and leaf abscission. c. Why do deciduous trees lose their leaves? d. Summarize the role of ethylene in fruit ripening. e. How are scientists using our knowledge of ethylene and fruit ripening for commercial applications? Concept 39.3 Responses to light are critical for plant success 10. Researchers have determined that plants have two major classes of light receptors. List each class. (1) (2) 11. What are three different responses initiated by blue light? (1) (2) (3) 4

5 12. Read carefully the discussion of phytochromes and how they work. Pay attention to the two types of red light. What is the wavelength of red light? Of far-red light? 13. To make sense of all this, you will want to read carefully the Phytochromes and Shade Avoidance section. Which type of red light is more common in a shaded area? Why? 14. a. What is a circadian rhythm? b. Give one plant example and one human example. 15. What is the photoperiod? 16. Plants detect photoperiod, and in many species it affects their time of flowering. Explain each of the following, and give an example of a plant that is in the group. Plant Type Explanation Example Short-day plant Long-day plant Day-neutral plant 5

6 17. The plant in the sketch below is a short-day plant. For each numbered line, explain why flowering occurs or does not occur with respect to R, FR, and the critical dark period. Line 1 Explanation Concept 39.4 Plants respond to a wide variety of stimuli other than light 18. What is gravitropism? How may a plant detect gravity? 19. What is thigmotropism? How is it adaptive? 20. List six different ways in which a plant responds to water deficit. (1) (2) (3) (4) (5) 6

7 21. Select any other stress situation besides water deficit, and explain plant mechanisms for dealing with this. Concept 39.5 Plants respond to attacks by herbivores and pathogens 22. Identify the defenses that plants have evolved to combat excess heribory and provide an example of each. Type of Defense Example 23. Describe two examples of a plant producing chemicals to deal with herbivory. Example 1 Example Identify the two lines of defense against pathogens. (1) (2) 7

8 25. What the difference between a virulent pathogen and an avirulent pathogen? 26. Gene-for-gene recognition is a form of plant disease resistance that involves recognition of pathogen-derived molecules. (This system works similarly to our own immune systems where antigens are recognized by antigen receptors.) Plants produce R proteins using a set of resistance genes (R genes). These R proteins will recognize pathogen-derived molecules called elicitors. Elicitors are the equivalent of what we call antigens, and the proteins produced by plants are the equivalent of what we call antigen receptors. Plants have hundreds of R genes, each producing a R protein that is specific for a particular pathogen-derived molecule. The recognition of an elicitor by an R protein triggers a signal transduction pathway leading to an arsenal of defense responses such as a hypersensitive response and a systemic acquired resistance. Summarize each defense mechanism below. Defense Mechanism Specific or Nonspecific? Description Hypersensitive response (local signaling) Systemic acquired resistance (long distance signaling) 8