Chapter 39
1. For each of the following scientists, describe their hypothesis, experiments, and conclusions about the mechanism of phototropism: a. Charles Darwin b. Francis Darwin c. Peter Boysen Jensen d. F.W. Went
2. List five 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 why 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 the check-and-balance control of lateral branching by auxins 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 upon a synergism between auxin and gibberellins.
11. Explain 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 gibberellins, 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 varieties of plants has heightened our understanding of plant hormones
17. Describe the components of a signal-transduction pathway.
18. List two environmental stimuli for leaf abscission.
19. Define tropism and list three 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. Distinguish between thigmotropism and thigmomorphogenesis.
23. Describe how motor organs within pulvini can cause rapid leaf movements 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 artificially 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 upon critical night length.
29. Provide evidence 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.