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2. Resources Chapter Presentation Visual Concepts Transparencies Standardized Test Prep

3. Plant Responses Chapter 31 Table of Contents Section 1 Plant Hormones Section 2 Plant Movements Section 3 Seasonal Responses

4. Section 1 Plant Hormones Chapter 31 Objectives • Listthe actions of the five major types of plant hormones. • Describeagricultural or gardening applications for each of the five major types of plant hormones. • Discusshow growth retardants are used commercially.

5. Section 1 Plant Hormones Chapter 31 Groups of Hormones • Plant hormones are formed in many plant parts and regulate many aspects of growth and development. Hormonal responses often have adaptive advantages. • There are five major groups of plant hormones: auxins, gibberellins, ethylene, cytokinins, and abscisic acid.

6. Section 1 Plant Hormones Chapter 31 Types of Plant Hormones

7. Section 1 Plant Hormones Chapter 31 Auxins • Auxinsare hormones involved in plant-cell elongation, shoot and bud growth, and rooting. • A well-known natural auxin isindoleacetic acid, or IAA.

8. Section 1 Plant Hormones Chapter 31 Auxins

9. Section 1 Plant Hormones Chapter 31 Auxins, continued Synthetic Auxins • Synthetic auxins are used for killing weeds, stimulating root formation, and stimulating or preventing fruit drop. • Naphthalene acetic acid, or NAA, is used to promote root formation on stem and leaf cuttings. NAA can also be applied to a cut shoot tip of the stem to mimic apical dominance (inhibition of lateral bud growth due to presence of a shoot tip).

10. Section 1 Plant Hormones Chapter 31 Apical Dominance

11. Section 1 Plant Hormones Chapter 31 Gibberellins • Gibberellinsare used to increase the size of fruit, to stimulate seed germination, and to brew beer.

12. Section 1 Plant Hormones Chapter 31 Ethylene • Ethyleneis used to ripen fruit and promote abscission, the detachment of leaves, flowers, or fruits.

13. Section 1 Plant Hormones Chapter 31 Ethylene

14. Section 1 Plant Hormones Chapter 31 Cytokinins • Cytokininsare used to culture plant tissues in the lab and to promote lateral bud growth of flower crops.

15. Section 1 Plant Hormones Chapter 31 Cytokinins

16. Section 1 Plant Hormones Chapter 31 Abscisic Acid • Abscisic acidpromotes dormancy in plant buds, maintains dormancy in seeds, and causes stomata to close.

17. Section 1 Plant Hormones Chapter 31 Other Growth Regulators • Growth retardantsare widely used to reduce plant height.

18. Section 2 Plant Movements Chapter 31 Objectives • Listthe environmental stimuli to which plants respond for each type of tropism. • Explainthe current hypotheses regarding auxins and their function in phototropism and gravitropism. • Describetwo types of nastic movements, and explain how they help a plant survive.

19. Section 2 Plant Movements Chapter 31 Tropisms • Tropisms and nastic movements are plant responses to environmental stimuli. • Tropisms occur slowly; nastic movements happen more quickly. • Atropismis a response in which a plant grows either toward or away from an environmental stimulus.

20. Section 2 Plant Movements Chapter 31 Tropism

21. Section 2 Plant Movements Chapter 31 Tropisms, continued Phototropism • Phototropismis thought to occur in some plants when auxin moves to the shaded side of a plant and causes cells there to elongate more than the cells on the lighted side. • Solar tracking,also calledheliotropism, is the motion of leaves or flowers as they follow the sun’s movement across the sky.

22. Section 2 Plant Movements Chapter 31 Tropisms, continued Thigmotropism • Thigmotropismis a plant’s growth response to touching a solid object. • For example, tendrils and stems of vines, such as morning glories, coil when they touch an object.

23. Section 2 Plant Movements Chapter 31 Tropisms, continued Gravitropism • Gravitropismis a plant’s response to gravity. • Itis thought to occur when auxin accumulates on the lower sides of a horizontal root and stem. • This accumulation causes cell elongation on the lower side of the stem and inhibits cell elongation on the lower side of the root.

24. Section 2 Plant Movements Chapter 31 Gravitropism in Plants

25. Section 2 Plant Movements Chapter 31 Tropisms, continued Chemotropism • Plant growth that occurs in response to a chemical is calledchemotropism. • An example of chemotropism is the growth of a pollen tube after a flower is pollinated.

26. Section 2 Plant Movements Chapter 31 Nastic Movements • Nastic movementsare responses to environmental stimuli but are independent of the direction of the stimuli.

27. Section 2 Plant Movements Chapter 31 Nastic Movements, continued Thigmonastic movements • Thigmonastic movementsoccur in response to touch, such as the closing of the leaf trap of a Venus’ flytrap around an insect.

28. Section 2 Plant Movements Chapter 31 Nastic Movements, continued Nyctinastic movements • Nyctinastic movements occur in response to the daily cycle of light and dark, such as the cyclical vertical and horizontal positioning of leaves in prayer plants.

29. Section 2 Plant Movements Chapter 31 Types of Plants

30. Section 3 Seasonal Responses Chapter 31 Objectives • Definephotoperiodism. • Describethe role of critical night length in flowering. • Explainthe process of vernalization. • Explainchanging fall colors in leaves.

31. Section 3 Seasonal Responses Chapter 31 Photoperiodism • Photoperiodismis a plant’s response to changes in the length of days and nights.

32. Section 3 Seasonal Responses Chapter 31 Photoperiodism, continued Day Length and Night Length • Plants fit in one of three photoperiodic classes for flowering: day-neutral plants (DNPs), short-day plants (SDPs), and long-day plants (LDPs). • Short-day and long-day plantshave a specific requirement for darkness, called the critical night length. Day neutral plants are not affected by day length.

33. Section 3 Seasonal Responses Chapter 31 Photoperiodism, continued Adjusting the Flowering Cycles of Plants • Flower growers who want to obtain winter flowering of LDPs simply expose them to a low level of incandescent light in the middle of the night. • Summer flowering of SDPs is obtained by covering the plants in the late afternoon with an opaque cloth so that the SDPs receive enough darkness.

34. Section 3 Seasonal Responses Chapter 31 Photoperiodism, continued Regulation by Phytochrome • Plants monitor changes in day length with a bluish, light-sensitive pigment calledphytochrome.

35. Section 3 Seasonal Responses Chapter 31 Flowering and Photoperiodism

36. Section 3 Seasonal Responses Chapter 31 Photoperiodism

37. Section 3 Seasonal Responses Chapter 31 Vernalization • Vernalizationis the promotion of flowering by cold temperatures. • Farmers often plant wheat seeds in the fall so that the seedlings can be exposed to winter temperatures and will flower before summer droughts begin.

38. Section 3 Seasonal Responses Chapter 31 Fall Colors • Changing fall colors in tree leaves are due to chlorophyll degradation, which reveals other pigments already present.

39. Section 3 Seasonal Responses Chapter 31 Dormancy

40. Chapter 31 Standardized Test Prep Multiple Choice 1. Which of the following is the name for the process in which flowering is stimulated by exposure of plants to cold? A. dormancy B. vernalization C. thigmotropism D. photoperiodism

41. Chapter 31 Standardized Test Prep Multiple Choice, continued 1. Which of the following is the name for the process in which flowering is stimulated by exposure of plants to cold? A. dormancy B. vernalization C. thigmotropism D. photoperiodism

42. Chapter 31 Standardized Test Prep Multiple Choice, continued 2. Which of the following is a result of abscission? F. Leaves fall off stems. G. Cuttings are produced. H. Plants sense night length. J. Abscisic acid is produced.

43. Chapter 31 Standardized Test Prep Multiple Choice, continued 2. Which of the following is a result of abscission? F. Leaves fall off stems. G. Cuttings are produced. H. Plants sense night length. J. Abscisic acid is produced.

44. Chapter 31 Standardized Test Prep Multiple Choice, continued 3. Which of the following describes the relationship between nastic movements and a stimulus? A. Nastic movements occur without a stimulus. B. Nastic movements occur toward a stimulus. C. Nastic movements occur away from a stimulus. D. Nastic movements occur independently of the direction of a stimulus.

45. Chapter 31 Standardized Test Prep Multiple Choice, continued 3. Which of the following describes the relationship between nastic movements and a stimulus? A. Nastic movements occur without a stimulus. B. Nastic movements occur toward a stimulus. C. Nastic movements occur away from a stimulus. D. Nastic movements occur independently of the direction of a stimulus.

46. Chapter 31 Standardized Test Prep Multiple Choice, continued 4. What is the response of a plant to the length of days and nights called? F. gravitropism G. phototropism H. photoperiodism J. thigmotropism

47. Chapter 31 Standardized Test Prep Multiple Choice, continued 4. What is the response of a plant to the length of days and nights called? F. gravitropism G. phototropism H. photoperiodism J. thigmotropism

48. Chapter 31 Standardized Test Prep Multiple Choice, continued The illustration below shows a growing seedling. Use the illustration to answer the question that follows.

49. Chapter 31 Standardized Test Prep Multiple Choice, continued 5. Which of the following statements about this seedling is true? A. The seedling is exhibiting abscission. B. The shoot is exhibiting positive phototropism. C. The roots are exhibiting negative gravitropism. D. The seedling is exhibiting negative thigmotropism.

50. Chapter 31 Standardized Test Prep Multiple Choice, continued 5. Which of the following statements about this seedling is true? A. The seedling is exhibiting abscission. B. The shoot is exhibiting positive phototropism. C. The roots are exhibiting negative gravitropism. D. The seedling is exhibiting negative thigmotropism.