1. Plant Responses to Internal and External Signals
Chapter 39
Plant Responses to Internal and External Signals

2. A flash of far-red light during a critical-length dark period
will induce flowering in a long-day plant.
will induce flowering in a short-day plant.
will not influence flowering.
will increase the Pfr level suddenly.
will be negated by a flash of red light.
Answer: c
Source: Taylor - Student Study Guide for Biology, Sixth Edition, Test Your Knowledge Question #9.

3. The heavy line in this figure illustrates the relationship between auxin concentration and cell growth in stem tissues. If the same range of concentrations was applied to lateral buds, what curve would probably be produced? *
I only
II only
III only
II and III
either I or III
Answer: a
Source: Barstow - Test Bank for Biology, Sixth Edition, Question #29.
Discussion Notes for the Instructor
While this question provides for a good discussion of the function of auxin in plants it is even more useful as a reminder of the different impacts of a single hormone on different tissues This also leads to a broader discussion of signal transduction pathways and receptors.

4. A botanist exposed two groups of plants (of the same species) to two photoperiods, one with 14 hours of light and 10 hours of dark and the other with 10 hours of light and 14 hours of dark. Under the first set of conditions, the plants flowered, but they failed to flower under the second set of conditions. Which of the following conclusions would be consistent with these results?
The critical night length is 14 hours.
The plants are short-day plants.
The critical day length is 10 hours.
The plants can convert phytochrome to florigen.
The plants flower in the spring.
Answer: e
Source: Barstow - Test Bank for Biology, Sixth Edition, Question #52.

5. A botanist discovers a plant that lacks the ability to form starch grains in root cells, yet the roots still grow downward. This evidence refutes the long-standing hypothesis that
falling statoliths trigger gravitropism.
starch accumulation triggers the negative phototropic response of roots.
starch grains block the acid growth response in roots.
starch is converted to auxin, which causes the downward bending in roots.
starch and downward movement are necessary for thigmotropism.
Answer: a
Source: Barstow - Test Bank for Biology, Sixth Edition, Question #61.