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Chapter 11
Growth Responses and Regulation of Growth
CHAPTER OUTLINE
Genetic, hormonal, and environmental controls of growth and development
Growth movements: tropisms
Plant hormones
Auxin promotes cell elongation
Gibberellins promote stem elongation
Cytokinins promote cell division
Plants and the Environment: Phytochrome and Shade Avoidance
CHAPTER OBJECTIVES
1. Discuss genetic and environmental factors that affect plant growth and development.
2. Describe phototropism, gravitropism, and thigmotropism.
3. List several ways in which each of the following hormones affects plant growth and
LECTURE OUTLINE
I. What factors control plant growth and development?
A. What role does genetics play?
B. What are hormones?
C. What environmental (external) factors are involved?
II. What are tropisms?
A. What is phototropism?
1. How is it a useful adaptation?
C. What is thigmotropism? What plants display this adaptation?
III. What are hormones? Why is the study of plant hormones so complex?
A. What are auxins?
1. What experiments did the Darwins’ do and what conclusions did they draw?
2. What did Went contribute to our understanding of auxin?
7. Of what use are synthetic auxins? Describe two.
B. What are gibberellins?
1. How were the gibberellins discovered?
2. How does gibberellin affect the growth of dwarf plants? By what means?
3. How is gibberellin involved in bolting?
4. In what other ways does gibberellin affect flowering?
5. How is gibberellin involved in seed germination?
C. What are cytokinins?
1. How were the cytokinins discovered?
2. Why are cytokinins required for tissue culture?
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F. What other signaling molecules affect growth and development?
1. What effects do brassinosteroids have?
G. What is florigen?
1. Is there any evidence for the existence of florigen?
2. Is florigen the only signaling molecule involved in flowering?
H. What does signal transduction refer to? Describe a specific example.
IV. What does photoperiodism mean?
A. Do changes in length of light and dark periods affect the initiation of flowering?
1. What are the photoperiod requirements of short-day plants?
B. What is the main photoreceptor for photoperiodism?
1. What are the two forms of phytochrome?
2. What wavelengths of light are absorbed by each form?
3. Which form of phytochrome triggers or inhibits responses?
4. How does the relative abundance of each phytochrome form change from day
to night?
KEY TERMS
abscisic acid, p. 230
abscission, p. 230
amyloplasts, p. 223
gravitropism, p. 223
hormone, p. 225
intermediate-day plant,
salicylic acid, p. 231
senescence, p. 229
short-day/long-night plant,
TEACHING TIPS
1. Bring in potted examples of different plants to illustrate lecture discussion. With a little
planning, you can bring in normal and etiolated bean plants (gibberellin), sensitive plants
2. Place a coleus plant in a clear bag or Wardian case with a ripe apple. Set up another
3. Soak lima bean seeds overnight, then pin to a cork sheet or wood block in all different