Chapter Objectives

1. Describe the hypothesis, experiments, and conclusions about mechanisms of phototropism proposed by
   1. Charles Darwin
   2. Francis Darwin
   3. Peter Boysen Jensen
   4. F. W. Watt
2. List 5 classes of plant hormones, describe their major functions, and recall where they are produced in the plant
3. Explain how a hormone may cause its effect on plant growth and development
4. Describe a possible mechanism for polar transport of auxin
5. According to the acid-growth hypothesis, explain how auxin can initiate cell elongation
6. Explain wy 2,4-D is widely used as a weed killer
7. Explain how the ratio of cytokinin to auxin affects cell division and cell differentiation
8. Define apical dominance and describe th check-and-balance control fo lateral branching by suxins and cytokinins
9. List several factors besides auxin from the terminal bud that may control apical dominance
10. Describe how stem elongation and fruit growth depend on a synrgism between auxin and gibberillins
11. Explain how the probable mechanism by which gibberellins trigger seed germination
12. Describe how abscisic acid (ABA) helps prepare a plant for winter
13. Explain the antagonistic relationship between ABA and gibberillins and how it is possible for growing buds to have a higher concentration of ABA than dormant buds
14. Give an example of how ABA can act as a stress hormone
15. Describe the role of ethylene in plant senescence, fruit ripening, and leaf abscission
16. Discuss how the study of mutant varieities of plants has heightened our understanding of plant hormones
17. Describe the components of a signal-transduction pathway
18. List 2 environmental stimuli for leaf abscission
19. Define tropism and lit 3 stimuli that induce tropisms and a consequent change of body shape
20. Explain how light causes a phototropic response
21. Describe how plants apparently tell up from down and explain why roots display positive gravitropism and shoots exhibit negative gravitropism
22. Distingush between thigmotropism and thigmomorphogenesis
23. Describe how motor orans within pulvni can cause rpaid leaf movement and sleep movements
24. Provide a plausible explanation for how a stimulus that causes rapid leaf movement can be transmitted through the plant
25. Define circadian rhythm and explain what happens when an organism is artiicially maintained in a constant environment
26. List some common factors that entrain biological clocks
27. Define photoperiodism
28. Distinguish among short-day plants, long-day plants, and day-neutral plants; give common examples of each and explain how they depend on critical night length
29. Provide evidene for the existence of a florigen
30. Explain how the interconversion of phytochrome can act as a switching mechanism to help plants detect sunlight and trigger many plant responses to light
31. Using photoperiodism as an example, explain how an integrated control system can regulate a plant process such as flowering
32. Explain the molecular basis of resistance to nonvirulent pathogens
33. Describe the local and systemic response to virulent pathogens

Chapter Terms:

Chapter Outline Framework

1. Plant Hormones
   1. Research on how plants grow toward light led to the discovery of plant hormones
   2. Plant hormones help coordinate growth, development, and responses to environmental stimuli
   3. Analysis of mutant plants is enhancing plant research
   4. Signal-transduction pathways link cellular responses to hormone signals and environmental stimuli
2. Plant Movements as Models for Studying Control Systmes
   1. Tropisms orient the growth of plant organs
   2. Turgor movements are relatively rapid, reversible plant responses
3. Control of Daily and Seasonal Responses
1. Biological clocks cotrol circadian rhythms
2. Photoperiodism synchronizes may plant responses to changes of season
4. Phytochromes
1. Phytochromes function as photoreceptors in many plant responses to light and photoperiod
2. Phytochromes may help entrain the biological clock
5. Plant Responses to Environmental Stress
   1. Plants cope with environmental stress throught a combination of developmental and physiological responses
6. Defense Against Pathogens
   1. Resistance to disease depends on a gene-for-gene recognition between plant and pathogen
   2. The hypersensitive response (HR) contains an infection
   3. Systemic acquired resistance (SAR) extends protection against pathogens to the whole plant

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