by Miller & Levine

[complete Table of Contents]

Use the pull-down menu to jump to any of the Book's 40 Chapters:

Additional Resources:

All about Plant Hormones
A web site from the UK

Plant Hormones
from Ohio State University



Chapter 25
Plant Responses and Adaptation

In this chapter, students will read about the effects of the four major types of plant hormones (auxins, cytokinins, gibberellins, and ethylene); plant responses such as tropisms, photoperiodism, and responses to seasonal changes; and mechanisms of adaptation to extreme environments and attacks by insect predators. The links below lead to additional resources to help you with this chapter. These include Hot Links to Web sites related to the topics in this chapter, the Take It to the Net activities referred to in your textbook, a Self-Test you can use to test your knowledge of this chapter, and Teaching Links that instructors may find useful for their students.

Hot Links

Chapter Self-Test

Take it to the Net Teaching Links

What are Web Codes?

Web Codes for Chapter 25:
Miller & Levine: Issue: Are Herbal Drugs Safe?
SciLinks: Plant Hormones

Section 25-1: Hormones and Plant Growth
Plant hormones are chemical substances that control a plant's patterns of growth and development and the plant's responses to environmental conditions.
Auxins are produced in the apical meristem and are transported downward into the rest of the plant. They stimulate cell elongation.
Cytokinins are produced in growing roots and in developing fruits and seeds. They stimulate cell division and the growth of lateral buds, and cause dormant seeds to sprout.
Gibberellins produce dramatic increases in size, particularly in stems and fruit.
In response to auxins, fruit tissues release small amounts of the hormone ethylene. Ethylene then stimulates fruits to ripen.

Section 25-2: Plant Responses
Plant tropisms include gravitropism, phototropism, and thigmotropism. Each of these responses demonstrates the ability of plants to respond effectively to conditions in which they live.
Photoperiodism in plants is responsible for the timing of seasonal activities such as flowering and growth.
As cold weather approaches, deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant.

Section 25-3: Plant Adaptations
To take in sufficient oxygen, many aquatic plants have tissues with large air-filled spaces through which oxygen can diffuse.
Plant adaptations to a desert climate include extensive roots, reduced leaves, and thick stems that can store water.
Plants that have specialized features for obtaining nutrients include carnivorous plants and parasites.
Many plants defend themselves against insect attack by manufacturing compounds that have powerful effects on animals.





Click Here for Science News articles on Plants

(Complete Index of Articles)

Return to BIOLOGY Home Page