by Miller & Levine
[complete Table of Contents]
the pull-down menu to jump to any of the Book's 40 Chapters:
about Plant Hormones
A web site from the UK
from Ohio State University
Plant Responses and Adaptation
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
25-1: Hormones and Plant Growth
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
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
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
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.
25-3: Plant Adaptations
To take in sufficient oxygen, many aquatic
plants have tissues with large air-filled spaces through which oxygen
Plant adaptations to a desert climate
include extensive roots, reduced leaves, and thick stems that can store
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