CHAPTER 31 PLANT RESPONSES TO INTERNAL AND EXTERNAL SIGNALS
Scientific Skills Exercise
Teaching objective: This exercise is designed to give students practice in interpreting a bar
graph and in understanding experimental design and interpretation.
Teaching tips: A version of this Scientific Skills Exercise can be assigned in MasteringBiology.
Many students are surprised by the extent of chemical communication between plants. You may
Answers:
1. The stomatal openings in plants 6-8 are smaller than those of the other plants; the stomatal
2. Pea plants apparently do signal their drought-stressed condition to their neighbors, as
Suggested Answers for End-of-Chapter Essay Questions
See the general information on grading short-answer essays and the suggested rubric at the
beginning of this document.
8. Scientific Inquiry
The biologist could employ a fan to see how the direction of the wind affects the unpalatability
9. Focus on Evolution
A small seed has few food reserves to feed the germinating seedling. Thus, small seeds have to
10. Focus on Interactions
Sample key points:
Phytochromes are photoreversible pigments that switch between a red-absorbing form (Pr)
and far-red-absorbing form (Pfr), depending on light quality.
Phytochromes are major determinants of shoot architecture. Shaded conditions lower the
Sample top-scoring answer:
Because plants are photoautotrophs, their growth and survival depend on their shoots,
particularly their leaves, being exposed to optimal sunlight. Phytochromes are photoreversible
pigments that play a major role in altering plant development in response to light. Phytochrome
11. Synthesize Your Knowledge
biomass and its ability to harvest resources from its environment. Wounding of the plant will