OBJECTIVES
CHAPTER 35
After
reading this chapter and attending lecture, the student should be able to:
1. For
each of the following scientists, describe their hypothesis, experiments and
conclusions about the mechanism of phototropism:
a. Charles Darwin c. Peter Boysen Jensen
b. Francis Darwin d. F.W. Went
2. List
five classes of plant hormones, describe their major functions and recall where
they are produced in the plant.
3. Explain
how a hormone may cause its effect on plant growth and development.
4. Describe
a possible mechanism for polar transport of auxtn.
5. According
to the acid-growth hypothesis, explain how auxin can initiate cell elongation.
6. Explain
why 2,4-D is widely used as a weed killer.
7. Explain
how the ratio of cytokinin to auxin affects cell division and cell
differentiation.
8. Define
apical dominance and describe the check-and-balance control of lateral
branching by auxins and cytokinins.
9. List
several factors besides auxin from the terminal bud that may control apical
dominance.
10. Describe
how stem elongation and fruit growth depend upon a synergism between auxin and
gibberellins.
11. Explain
the probable mechanism by which gibberellins trigger seed germination.
12. Describe
how abscisic acid (ABA) helps prepare a plant for winter.
13. Explain
the antagonistic relationship between ABA and gibberellins, and how it is
possible for growing buds to have a higher concentration of ABA than dormant
buds.
14. Give
an example of how ABA can act as a “stress hormone”.
15. Describe
the role of ethylene in plant senescence, fruit ripening and leaf abscission.
16. List
two environmental stimuli for leaf abscission.
17. Define
tropism and list three stimuli that induce tropisms and a consequent change of
body shape.
18. Explain
how light causes a phototropic response.
19. Describe
how plants apparently tell up from down, and explain why roots display positive
gravitropism and shoots exhibit negative gravitropism.
20. Distinguish
between thigmotropism and thigmomorphogenesis.
21. Describe
how motor organs within pulvini can cause rapid leaf movements and sleep
movements.
22. Provide
a plausible explanation for how a stimulus that causes rapid leaf movement can
be transmitted through the plant.
23. Define
circadian rhythm and explain what happens when an organism is artificially
maintained in a constant environment.
24. List
some common factors that entrain biological clocks.
25. Define
photoperiodism.
26. Distinguish
among short-day plants, long-day plants and day-neutral plants; give common
examples of each and explain how they depend upon critical night length.
27. Provide
evidence for the existence of a florigen.
28. Explain how the interconversion of
phytochrome can act as a switching mechanism to help plants detect sunlight and
trigger many plant responses to light.
29. Using photoperiodism as an example, explain
how an integrated control system can regulate a plant process such as
flowering.
30. Describe
the components of a signal-transduction pathway.