CHAPTER 39
PLANT RESPONSES TO
INTERNAL AND EXTERNAL SIGNALS
Learning objectives
Read pages 821-849 of “Biology” Campbell 9th edition to make your Cornell notes and
understand the following learning objectives below. Supplementary reading can be from
the photocopied supplements from “Biology Study Guide” Campbell & Reece and Cliff
Notes AP Biology. Remember the following are NOT questions but guidelines for your
note taking. Reading for comprehension and identifying key ideas and concepts is a skill
required for AP Biology. NO COPIED NOTES ALLOWED!
Signal Transduction and Plant Responses
 Compare the growth of a plant in darkness (etiolation) to the characteristics of
greening (de-etiolation).
 Describe the signal pathways associated with de-etiolation.
 Describe the two main mechanisms by which a signaling pathway can activate an
enzyme.
Plant Responses to Hormones
 Why is the term “plant growth regulator” used to describe plant hormones?
 List six classes of plant hormones, describe their major functions, and note where
they are produced in the plant.
Plant Responses to Light
 Define circadian rhythm and explain what happens when an organism is artificially
maintained in a constant environment.
 Define photoperiodism.
 Distinguish between short-day, long-day, and day-neutral plants. Explain why
these names are misleading.
Plant Responses to Other Environmental Stimuli
 Describe how plants apparently tell up from down. Explain why roots display
positive gravitropism and shoots exhibit negative gravitropism.
 Distinguish between thigmotropism and thigmomorphogenesis.
 Provide a plausible explanation for how a stimulus causing rapid leaf movement
can be transmitted through the plant.
Plant Defenses against Herbivores and Pathogens
 Explain how plants deter herbivores with physical and chemical defenses.
 Describe how plants may recruit parasitoids to attack herbivorous caterpillars.
 Describe how the hypersensitive response helps a plant limit the damage from
pathogen attack.
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