Download The correct answer is b

1. If you exposed seeds to a series of red light versus far-red light treatments, which
of the following exposure treatments would result in seed germination?
a. Red; far-red
b. Far-red; red
c. Red; far-red; red; far-red; red; far-red; red; far-red
d. None of the above
The correct answer is b—
A. Answer a is incorrect. The last exposure was far-red, thus converting
phytochrome to the Pr state, the biologically inactive state.
The correct answer is b—Far-red; red
B. Answer b is correct. Exposure to the red light will produce Pfr, the biologically
active state.
The correct answer is b—
C. Answer c is incorrect. See the reason in answer a.
The correct answer is b—
D. Answer d is incorrect. Answer b is correct.
2. Which of the following statements provides a true example of both
photomorphogenesis and phototropism?
a. Phototropism is growth toward blue light, and photomorphogenesis is
growth toward red light.
b. Phototropism is growth toward blue light, and photomorphogenesis is
germination triggered by red light.
c. Phototropism is growth toward red light, and photomorphogenesis is
germination triggered by blue light.
d. Phototropism is movement toward blue light that does not involve growth;
photomorphogenesis is movement toward red light that does involve
growth.
The correct answer is b—
A. Answer a is incorrect. Photomorphogenesis is not growth toward red light, but
rather is the establishment of form (that is, germination) triggered by red light.
The correct answer is b—Phototropism is growth toward blue light, and
photomorphogenesis is germination triggered by red light.
B. Answer b is correct. Phototropism is growth triggered by blue light receptors and
photomorphogenesis is germination triggered by red light.
The correct answer is b—
C. Answer c is incorrect. Phototropism is growth toward blue light and
photomorphogenesis is germination triggered by red light, not blue light.
The correct answer is b—
D. Answer d is incorrect. Phototropism is a growth response and
photomorphogenesis is a germination response. Photomorphogenesis is not a
directional response to light.
3. If you were to plant a de-etiolated (det2) mutant Arabidopsis seed and keep it in a
dark box, what would you expect to happen?
a. The seed would germinate normally, but the plant would not become tall
and spindly while it sought a light source.
b. The seed would fail to germinate because it would not have light.
c. The seed would germinate, and the plant would become tall and spindly
while it sought a light source.
d. The seed would germinate, and the plant would immediately die because it
could not make sugar in the dark.
The correct answer is a—The seed would germinate normally, but the plant would not
become tall and spindly while it sought a light source.
A. Answer a is correct. The det2 gene encodes an enzyme involved in the etiolation
response. Without this gene, plants will not undergo the etiolation response (that
is, they will not grow tall and spindly in a light-seeking response).
The correct answer is a—
B. Answer b is incorrect. The det2 gene does not influence seed germination.
The correct answer is a—
C. Answer c is incorrect. This is the normal etiolation response and requires a wildtype copy of the det2 gene.
The correct answer is a—
D. Answer d is incorrect. Seedlings store some nutrient reserves in the coleoptiles so
that they do not have to begin photosynthesis immediately after germination.
4. Which of the following statements is NOT true of phytochrome?
a. Pr is converted to Pfr when exposed to red light.
b. Pfr is the biologically active form of phytochrome.
c. Phytochrome triggers many light responses by regulating gene expression.
d. Phytochrome controls most seed germination in plants.
The correct answer is d—
A. Answer a is a true. Thus, it is incorrect.
The correct answer is d—
B. Answer b is a true. Thus, it is incorrect.
The correct answer is d—
C. Answer c is a true. Thus, it is incorrect. Phytochrome does trigger many
responses for gene expression.
The correct answer is d—Phytochrome controls most seed germination in plants.
D. Answer d is the correct. It is a false statement. Some, but not all plants rely on a
phytochrome-mediated response for germination.
5. We often have the misconception that plants are unable to move in their
environment. Many plants, however, display daily movements to maximize their
capacity to absorb light energy (such as, bean leaves). These daily changes in
shape are caused by—
a. changes in turgor in specific cells
b. growth of specific cells
c. muscle contraction in the leaves
d. temperature changes in the environment
The correct answer is a—changes in turgor in specific cells
A. Answer a is correct. When cells in the pulvini region lose turgor the leaves will
fall, and when these cells regain turgor the leaves rise in the horizontal plane.
The correct answer is a—
B. Answer b is incorrect. Daily shape changes are reversible and growth is defined as
an irreversible change in shape.
The correct answer is a—
C. Answer c is incorrect. Leaves have no muscles.
The correct answer is a—
D. Answer d is incorrect. Although temperature can influence plant growth, it is not
responsible for the daily changes in shape that bean plants demonstrate.
6. When Charles and Francis Darwin investigated phototropisms in plants, they
discovered that—
a. auxin was responsible for light-dependent growth
b. light was detected at the shoot tip of a plant
c. light was detected below the shoot tip of a plant
d. only red light stimulated phototropism
The correct answer is b—
A. Answer a is incorrect. It was Went who discovered that the phototropic response
involved a chemical that he named auxin.
The correct answer is b—light was detected at the shoot tip of a plant
B. Answer b is correct. The Darwin experiments determined that the tip of a plant
was responsible for the phototropic response.
The correct answer is b—
C. Answer c is incorrect. When the Darwins blocked light from reaching the stem
below the tip of a plant, the phototropic response was normal.
The correct answer is b—
D. Answer d is incorrect. Phototropisms can be mediated by blue light receptors.
7. Auxin promotes a plant to grow toward a light source by—
a. increasing the rate of cell division on the shaded side of the stem
b. shortening the cells on the light side of the stem
c. causing cells on the shaded side of the stem to elongate
d. decreasing the rate of cell division on the light side of the stem
The correct answer is c—
A. Answer a is incorrect. Auxin does not promote growth toward a light source by
increasing the rate of cell division.
The correct answer is c—
B. Answer b is incorrect. Auxin does not promote growth toward a light source by
shortening cells on the light side of the stem.
The correct answer is c—causing cells on the shaded side of the stem to elongate
C. Answer c is correct. Auxin causes cells to elongate on the shaded side of the stem,
thus causing the stem to bend toward the light.
The correct answer is c—
D. Answer d is incorrect. Auxin does not decrease the rate of cell division on the
light site of the stem.
8. Which of the following statements is NOT true of auxin?
a. It usually travels downward in a plant.
b. We do not know how auxin is involved in cell signaling.
c. It likely initiates cell wall acidification.
d. Indoleacetic acid is its most common form.
The correct answer is b—
A. Answer a is true. It is an incorrect response.
The correct answer is b—We do not know how auxin is involved in cell signaling.
B. Answer b is false. It is the correct response. The auxin receptor and its role in
signaling are known.
The correct answer is b—
C. Answer c is true. It is an incorrect response.
The correct answer is b—
D. Answer d is true. It is an incorrect response.
9. You have come up with a brilliant idea to stretch your grocery budget by buying
green fruit in bulk and then storing it in a bag that you have blown up like a
balloon. As you need fruit, you would take it out of the bag, and it would
miraculously ripen. How would this work?
a. The bag would block light from reaching the fruit, so it would not ripen.
b. The bag would keep the fruit cool, so it would not ripen.
c. The high CO2 levels in the bag would prevent ripening.
d. The high O2 levels in the bag would prevent ripening.
The correct answer is c—
A. Answer a is incorrect. Fruit will ripen in the absence of light.
The correct answer is c—
B. Answer b is incorrect. The bag is not necessarily cold. Furthermore, although
cool temperatures may slow the ripening process, they cannot stop it.
The correct answer is c—The high CO2 levels in he bag would prevent ripening.
C. Answer c is correct. CO2 is more concentrated in exhaled air and inhibits
production of ethylene, which in turn is required for ripening in fruit. If ethylene
synthesis is inhibited, ripening will be prevented.
The correct answer is c—
D. Answer d is incorrect. O2 stimulates production of ethylene, which in turn
stimulates fruit ripening. Furthermore, O2 concentrations are low in exhaled air.
10. If you were to accidentally plant a mutant strain of barley that could not
synthesize the plant hormone abscisic acid (ABA), what would you expect to
happen?
a. The shoots would elongate too much and fall over because they could not
support themselves.
b. The shoots would not elongate normally, and you would get short plants.
c. The seeds would germinate prematurely.
d. The leaves would fall off the plant.
The correct answer is c—
A. Answer a is incorrect. ABA does not influence cell elongation in plants.
The correct answer is c—
B. Answer b is incorrect. ABA does not influence cell elongation in plants.
The correct answer is c—The seeds would germinate prematurely.
C. Answer c is correct. ABA promotes dormancy in seeds; in the absence of ABA,
seeds will not remain dormant.
The correct answer is c—
D. Answer d is incorrect. Despite its name, ABA is not involved in abscission.
11. Just as auxin and cytokinin counterbalance each other in many respects,
gibberellins are countered by which plant hormone?
a. Ethylene
b. Brassinosteroids
c. Abscisic acid
d. Oligosaccharins
The correct answer is c—
A. Answer a is incorrect. Ethylene and gibberellins do not have a truly specific
“antagonistic” relationship.
The correct answer is c—
B. Answer b is incorrect. See the same reason as a.
The correct answer is c—Abscisic acid
C. Answer c is correct. Gibberellins and abscisic acid counterbalance each other
quite often, such as in the control of dormancy and senescence.
The correct answer is c—
D. Answer d is incorrect. See the same reason as a.
12. Gibberellins are used to increase productivity in grapes because they—
a. cause fruits to be larger by promoting cell division within the fruit
b. increase the internode length so the fruits have more room to grow
c. increase the number of flowers produced, thus increasing the number of
fruits
d. all of the above
The correct answer is b—
A. Answer a is incorrect. Gibberellins do not increase cell division in the fruit, at
least directly.
The correct answer is b—increase the internode length so the fruits have more room to
grow
B. Answer be is correct. Gibberellins do increase internode lengths in the bunch to
give the grapes more room to grow.
The correct answer is b—
C. Answer c is incorrect. Gibberellins do not control the number of flowers
produced.
The correct answer is b—
D. Answer d is incorrect. Answers a and c are incorrect.
13. Which of the following might NOT be observed in a plant that is grown on the
Space Shuttle in space?
a. Phototropism
b. Photomorphogenesis
c. Circadian rhythms
d. Gravitropism
The correct answer is d—
A. Answer a is incorrect. Light still exists in space and could thus cause
phototropisms.
The correct answer is d—
B. Answer b is incorrect. See the same reason as a.
The correct answer is d—
C. Answer c is incorrect. Plants would still go through internally controlled circadian
rhythms, and light would still be present to entrain the cycle.
The correct answer is d—Gravitropism
D. Answer d is correct. Gravity would be absent on the Space Shuttle, so
gravitropisms would not occur.
Challenge Questions
1. Discuss the similarities and differences between thigmotropism and turgor
movement.
Answer—A thigmotropism is a directional growth movement in response to touch. Cells
on one side of a stem may grow faster than cells on the other side, allowing the plant to
bend toward or away from the source of the touch. Turgor movements can also occur in
response to touch. But unlike thigmotropisms, they are not growth responses. For
example, the leaflets on a Mimosa plant fold almost instantly when touched. This
happens because water leaves cells on one side of the pulvinus (stemlike region at base of
the leaflet), but not the other side. Water later returns to the cells that have lost turgor
pressure, but no growth has occurred.
2. Compare the mechanisms that animals and plants use to survive harsh
environments by thinking of an equivalent animal response for each of the
following—
a. dormancy
b. thigmomorphogenesis
c. abscission
d. phototropism
Answer—a. Dormancy in an animal is somewhat like hibernation, but a hibernating
animal maintains a higher water content than a dormant seed. Also, hibernation cannot be
extended for as long as dormancy is extended in some seeds.
b. Thigmomorphogenesis is growth in response to touch. Animals respond to
touch in a variety of ways, including moving away when they sense danger from touch. A
possible example of a thigmomorphogenesis analogy in humans would be wearing a
brace for scoliosis (a condition that causes abnormal spine development). The pressure
(extended touch) from the brace allows the spine to develop in a more normal pattern. In
plants, growth responses can occur in response to a much briefer touch with less pressure.
c. Abscission is analogous to a male deer naturally losing its antlers (its rack). In
both cases, cells die at the point of attachment and the body part is discarded.
d. Phototropism is a growth movement toward light. Since most animals move,
there is a greater tendency for an animal to move toward or away from light rather than
grow toward or away from light. Tanning would not be a good example of a
phototropism equivalent in plants, because it does not involve a directional growth
response.
3. Tree burls, often caused by tumor growths on the trunk and branches of trees, are
highly prized and very valuable to woodworkers because of their beautiful grain
pattern. If you wanted to start a “tree burl farm,” how would you go about doing
so?
Answer—Developing a commercial tree burl farm would require trees, obviously, but
you would need to initiate the growth of a tumor on the tree. One way you could do this
would be to infect the trees with Agrobacterium tumefaciens, which inserts DNA into the
plant cell DNA. This DNA specifically codes for enzymes necessary for cytokine and
auxin production. Increasing the levels of these plant hormones can cause massive cell
division, which develops a tumor, or burl. If you were successful in doing this, you could
harvest the tree burls and sell them at top dollar.