 |  Biology, 6/e Author Dr. George B. Johnson,
Washington University
Author Dr. Peter H. Raven,
Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer,
Carleton College
Contributor Dr. Jonathan Losos,
Washington University
How Plants Grow in Response to the Environment
Answers to Review Questions|
Chapter 41 (p. 836)
1. The stems are positively phototropic and grow toward the light. This allows the leaves to capture a greater amount of light energy.
2. Auxin increases the plasticity of the plant cell wall, allowing greater stretching during active cell growth.
3. Cytokinins are produced by roots and developing fruit and are derived from the biomolecule adenine.
4. Gibberellins are usually lacking in genetically dwarfed plants.
5. There are several ways of inducing flowering. One could change day length, use far-red or blue light, or apply gibberellin. If all of these fail, wait. The plant may flower autonomously.
6. The day length is probably the problem. The variation of day length is greater in Canada than in Mexico. The plants may need longer or shorter exposure to light. For some plants it is the length of darkness that is important.
7. Cells cause the movement to occur based on unequal turgor pressure on either side of the leaf. The sensitive plant further reacts with altered permeability to specific ions that allows the plant to respond very quickly to tactile stimulus.
8. Plants may initiate a hyperactive response (HR) and seal off the invaders by surrounding them with "suicide cells" that die rapidly around the invader. Plants may also have a chemical response, producing phytoalexins that are antimicrobial agents. Plants incapable of HR may make changes in local cell walls, attempting to block further penetration. Plants may also make systemic responses. There are wound responses with similar but slower components to HR.
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2002 McGraw-Hill Higher Education