The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
The tendency of plants to alter their growth in response to the direction of light shining on them is called phototropism. Generally the above ground shoot portion of plants tends to grow toward the light, exhibiting positive phototropism. This response increases the likelihood that the shoot will reach areas where it can maximize its ability to absorb light and carry out photosynthesis. As a result, the plant can grow more rapidly, and compete more successfully with its neighbors. Under some conditions a plant or a part of the plant such as a root may exhibit negative phototropism by growing away from the light. Phototropism is mediated by a yellow flavin pigment and responds to blue light.
A plant hormone called auxin stimulates the differential growth pattern that results in phototropism. Auxins are produced by cells in the growing tip or apical meristem of the plant and diffuse down through the lower tissues. When light strikes the stem from one side it causes the auxin to concentrate on the opposite side, away from the light. Auxin stimulates these cells to elongate. As a result, the tip bends toward the light. The bending reaction occurs in the zone of elongation, just below the rapidly dividing cells of the apical meristem
Some mobile lower forms of life in algae, protozoa and bacteria may respond to light by actually moving toward or away from it. This phenomenon is called phototaxis.