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Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter Presentation TransparenciesStandardized Test Prep Visual Concepts Resources

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Plant Responses Chapter 31 Table of Contents Section 1 Plant Hormones Section 2 Plant Movements Section 3 Seasonal Responses

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Plant Hormones Chapter 31 Objectives List the actions of the five major types of plant hormones. Describe agricultural or gardening applications for each of the five major types of plant hormones. Discuss how growth retardants are used commercially.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Types of Plant Hormones Section 1 Plant Hormones

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Plant Hormones Chapter 31 Auxins Auxins are hormones involved in plant-cell elongation, shoot and bud growth, and rooting. A well-known natural auxin is indoleacetic acid, or IAA.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Auxins Section 1 Plant Hormones

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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).

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Apical Dominance Section 1 Plant Hormones

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Plant Hormones Chapter 31 Gibberellins Gibberellins are used to increase the size of fruit, to stimulate seed germination, and to brew beer.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Plant Hormones Chapter 31 Ethylene Ethylene is used to ripen fruit and promote abscission, the detachment of leaves, flowers, or fruits.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Ethylene Section 1 Plant Hormones

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Plant Hormones Chapter 31 Cytokinins Cytokinins are used to culture plant tissues in the lab and to promote lateral bud growth of flower crops.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Cytokinins Section 1 Plant Hormones

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Plant Hormones Chapter 31 Abscisic Acid Abscisic acid promotes dormancy in plant buds, maintains dormancy in seeds, and causes stomata to close.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Plant Hormones Chapter 31 Other Growth Regulators Growth retardants are widely used to reduce plant height.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Plant Movements Chapter 31 Objectives List the environmental stimuli to which plants respond for each type of tropism. Explain the current hypotheses regarding auxins and their function in phototropism and gravitropism. Describe two types of nastic movements, and explain how they help a plant survive.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. A tropism is a response in which a plant grows either toward or away from an environmental stimulus.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Tropism Section 2 Plant Movements

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Plant Movements Chapter 31 Tropisms, continued Phototropism –Phototropism is 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 called heliotropism, is the motion of leaves or flowers as they follow the sun’s movement across the sky.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Plant Movements Chapter 31 Tropisms, continued Thigmotropism –Thigmotropism is 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Plant Movements Chapter 31 Tropisms, continued Gravitropism –Gravitropism is a plant’s response to gravity. –It is 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Gravitropism in Plants Section 2 Plant Movements

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Plant Movements Chapter 31 Tropisms, continued Chemotropism –Plant growth that occurs in response to a chemical is called chemotropism. –An example of chemotropism is the growth of a pollen tube after a flower is pollinated.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Plant Movements Chapter 31 Nastic Movements Nastic movements are responses to environmental stimuli but are independent of the direction of the stimuli.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Plant Movements Chapter 31 Nastic Movements, continued Thigmonastic movements –Thigmonastic movements occur in response to touch, such as the closing of the leaf trap of a Venus’ flytrap around an insect.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Types of Plants Section 2 Plant Movements

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Seasonal Responses Chapter 31 Objectives Define photoperiodism. Describe the role of critical night length in flowering. Explain the process of vernalization. Explain changing fall colors in leaves.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Seasonal Responses Chapter 31 Photoperiodism Photoperiodism is a plant’s response to changes in the length of days and nights.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 plants have a specific requirement for darkness, called the critical night length. Day neutral plants are not affected by day length.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Seasonal Responses Chapter 31 Photoperiodism, continued Regulation by Phytochrome –Plants monitor changes in day length with a bluish, light-sensitive pigment called phytochrome.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Flowering and Photoperiodism Section 3 Seasonal Responses

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Photoperiodism Section 3 Seasonal Responses

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Seasonal Responses Chapter 31 Vernalization Vernalization is 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 31 Dormancy Section 3 Seasonal Responses

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued The illustration below shows a growing seedling. Use the illustration to answer the question that follows. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 6. cell elongation : gibberellins :: cell division : F. auxins G. ethylene H. cytokinins J. abscisic acid Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 6. cell elongation : gibberellins :: cell division : F. auxins G. ethylene H. cytokinins J. abscisic acid Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued The diagrams below represent three different growing conditions. Use the diagrams to answer the question that follows. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 7. In which of the conditions will a long-day plant with a critical night length of 8 hours flower? A. 1 B. 2 C. 1 and 3 D. 2 and 3 Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 7. In which of the conditions will a long-day plant with a critical night length of 8 hours flower? A. 1 B. 2 C. 1 and 3 D. 2 and 3 Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Short Response The Venus’ flytrap obtains nutrients by closing its leaves around insects and then digesting the insects. Explain why a thigmonastic movement is a more useful plant response than a thigmotropic response would be in this situation. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Short Response, continued The Venus’ flytrap obtains nutrients by closing its leaves around insects and then digesting the insects. Explain why a thigmonastic movement is a more useful plant response than a thigmotropic response would be in this situation. Answer: A thigmonastic response is more appropriate in this instance because it is very rapid. A thigmotropic response would be slow, because it would involve plant growth. An insect would have moved away from the plant before a thigmotropic response could have occurred. Standardized Test Prep Chapter 31

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Prep Chapter 31 Extended Response Base your answers to parts A & B on the information below. Reproduction is essential for survival of flowering plant species. Part A Identify two plant hormones that have roles in flowering, fruiting, and/or seed or fruit dispersal, and describe these roles. Part B Identify the important environmental signals for flowering, and describe how these signals affect flowering.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Prep Chapter 31 Extended Response, continued Answer: Part A Auxins increase the setting of fruits, stimulate fruit maturation, and prevent fruit drop. Gibberellins increase fruit size, release seed dormancy, and substitute for long-day requirements for flowering. Ethylene promotes flowering in some species, fruit ripening, and fruit drop (which aids fruit and seed dispersal). Abscisic acid promotes seed dormancy. Part B: The most important environmental signals for flowering are the length of the night and temperature. Short-day plants have a minimum length of night required for flower induction, and long-day plants have a maximum length of night required for flower induction. Many plants also have a requirement for exposure to cold temperature that induces flowering.