Campbell Biology: Concepts and Connections, 8e (Reece et al.)
Chapter 33 Control Systems in Plants
33.1 Multiple-Choice Questions
1) Which of the following is an example of an evolutionary adaptation that decreases herbivory?
A) Plants of the milkweed family produce a toxin that Monarch butterflies can store in their
bodies.
B) Corn plants attacked by herbivores release an airborne chemical that turns on defensive genes
in nearby corn plants.
C) Caterpillars that feed on plants tend to be green.
D) Damaged, partially eaten leaves can seal off the damaged area by hardening cell walls.
2) Plants grow toward light through the action of
A) hormones.
B) nerves.
C) solar energy.
D) chloroplasts.
3) Grass shoots bend toward the light because, on the shadowed side, a(n)
A) reduction in auxin levels promotes cell elongation.
B) reduction in auxin levels prevents cell elongation.
C) increase in auxin levels promotes cell elongation.
D) increase in auxin levels promotes cell division.
4) One experiment in phototropism involved cutting off the tips of grass seedlings before
exposing them to light from one side. The decapitated seedlings did not bend toward the light. A
valid conclusion from this experiment would be that
A) plants cannot engage in photosynthesis without the tip of the plant.
B) light is perceived by the tip of grass plants.
C) a foil cover over the tip of the seedlings would cause them to bend.
D) hormones are produced in all parts of the plant.
5) Plant hormones
A) must be produced in large quantities to be effective.
B) act on all cells they encounter.
C) are chemical signals that influence growth and development.
D) are rare and produced only in response to stress.
6) Which of the following statements about plant hormones is true?
A) Plant hormones are produced in very small concentrations.
B) Plant hormones mainly affect reproductive processes.
C) Individual hormones typically have single, specific effects.
D) Plant hormones play a vital role in photosynthesis.
7) What is one main effect of auxins on plant growth?
A) They reduce growth by inhibiting cell division.
B) They increase growth by promoting cell elongation.
C) They increase growth by increasing the rate of photosynthesis.
D) Auxins have no effect on plant growth.
8) If the auxin that is produced by an apical meristem is transported in equal amounts down all
sides of a twig, the twig will probably
A) elongate evenly.
B) branch near its tip.
C) flower.
D) bend away from the apical meristem.
9) When a nursery worker pinches off the terminal buds on a young chrysanthemum plant to
make it grow bushy, which of the following plant hormones is mainly responsible for growth of
side branches?
A) an auxin
B) a gibberellin
C) a cytokinin
D) abscisic acid
10) Which class of hormones produced in the roots of plants promotes cell division and growth
and retards the aging of flowers and leaves?
A) gibberellins
B) phytochromes
C) cytokinins
D) ethylene
11) The most reliable way to stimulate branching in a plant is to
A) apply auxin to the axillary buds.
B) remove the terminal bud.
C) give short-day light treatments.
D) add extra fertilizer.
12) Shoot branching is controlled mainly by the interaction of
A) auxins and gibberellins.
B) auxins and cytokinins.
C) gibberellins and cytokinins.
D) cytokinins and abscisic acid.
13) The event that triggers fruit formation is the growth of a pollen tube through the carpel of a
flower. Which of the following is a reasonable hypothesis about the basis of this effect?
A) Pollen tubes grow in response to a cytokinin produced by the carpel.
B) Pollen tubes grow in response to abscisic acid.
C) The growing pollen tube produces ethylene.
D) The growing pollen tube produces auxins and/or gibberellins.
14) Which of the following hormones might induce seeds treated with it to break dormancy?
A) an auxin
B) a cytokinin
C) a gibberellin
D) ethylene
15) Fruit that forms on an unpollinated plant in response to a hormone will lack
A) flavor.
B) seeds.
C) rind.
D) naturally occurring hormones.
16) Bush beans grow as small bushes rather than as vines because their internodes are short and
they branch close to the apical meristem. Which of the following substances, if applied to a bush
bean, might cause it to grow as a vine?
A) a cytokinin
B) a gibberellin
C) abscisic acid
D) ethylene
17) Which of the following substances induces “bolting,” the rapid elongation of a plant stem?
A) a gibberellin
B) abscisic acid
C) ethylene
D) phytochrome
18) About how many gibberellins have been identified in plants?
A) one
B) five
C) over one hundred
D) thousands
19) Which type of plant hormone generally acts as a growth inhibitor?
A) auxins
B) gibberellins
C) cytokinins
D) abscisic acid
20) Under what conditions would you expect a plant to have the highest concentration of abscisic
acid?
A) in a wet tropical rain forest
B) in a cool environment after a heavy rain
C) in a houseplant growing in low light conditions
D) in a desert after a long drought
21) Which hormone prevents a seed released in the fall from germinating immediately?
A) auxins
B) abscisic acid
C) gibberellins
D) ethylene
22) What stimulates germination of desert plant seeds after a hard rain?
A) production of auxins
B) removal of abscisic acid
C) cooler temperatures
D) activation of cytokinins
23) In leaf abscission, the abscission layer forms where the
A) leaf stalk joins the stem.
B) axillary bud joins the stem.
C) root joins the stem.
D) leaf stalk joins the leaf.
24) Which of the following is a good way to ripen a green, unripe fruit?
A) putting it in a darkened area such as a drawer or box
B) placing it in a sealed plastic bag with an overripe banana
C) placing it in a microwave, on low power, for 5 minutes
D) placing it under a bright light for 24 hours
25) Which of the following is one adaptive advantage for deciduous plants that lose their leaves
during the winter?
A) It prevents water loss from leaves when soil water is unavailable due to freezing.
B) Production of new leaves each spring is more efficient than supporting old leaves all winter.
C) If leaves are damaged by frost, the tree will die.
D) A layer of leaves on the ground helps keep plant roots warm.
26) In many grocery stores, fresh fruits are sold in plastic bags dotted with holes so that they will
not overripen. The main function of the holes is to
A) permit the fruit to drain after being washed.
B) facilitate diffusion of ethylene away from the fruit.
C) prevent buildup of CO2.
D) facilitate diffusion of O2 to the fruit.
27) Which of the following lists the events leading to leaf fall in deciduous trees in the correct
order?
A) formation of abscission layer, increase in ethylene levels, decrease in auxin levels
B) shortening days, increase in ethylene production, formation of abscission layer
C) shortening days, formation of abscission layer, decrease in ethylene levels
D) decrease in ethylene levels, shortening days, formation of abscission layer
28) Synthetic auxins are used commercially
A) to promote seed germination.
B) to promote flowering in ornamental crops.
C) to promote side branching to produce bushier crops.
D) as a broadleaf weed killer.
29) There is concern over the use of 2,4-D, a synthetic plant hormone, as a weed killer because
the by-product dioxin
A) can cause irreversible mutations in crop plants.
B) causes massive fish kills when it gets into lakes and streams.
C) can cause birth defects and leukemia in mammals.
D) weakens the shells of the eggs of predatory birds, resulting in the death of their offspring.
30) Which of the following growth responses causes the shoots of a plant grown in the dark to
grow upward?
A) phototropism
B) thigmotropism
C) photoperiodism
D) gravitropism
31) The plant growth response to touch is known as
A) gravitropism.
B) geotropism.
C) bolting.
D) thigmotropism.
32) What dense storage granules in plant cells are thought to contribute to gravitropism?
A) starch
B) cellulose
C) proteins
D) chlorophyll
33) Which of the following processes underlies the thigmotropic behavior of a green bean
tendril?
A) rotation of the tendril in response to photoperiod
B) rotation of the tendril in response to a biological clock
C) extra proliferation of cells on the shaded side of the tendril
D) slower growth on the side where an object is touching the tendril
34) Mimosa plants spread their leaflets during the day and fold them at night. You decide to
design an experiment to test whether Mimosa’s leaf movements are controlled by a biological
clock. Which of the following experiments would be the best test of your hypothesis?
A) Growing the plant indoors and turning the lights on in the middle of the night. If a biological
clock is controlling leaf movement, the leaves will open.
B) Putting the plant in a dark closet in the middle of the day. If the leaves close, a biological
clock mechanism is ruled out.
C) Subjecting the plant to a flash of red light in the middle of the night. If the leaves open at the
usual time the next morning, a biological clock mechanism is ruled out.
D) Putting the plant in a dark closet at nightfall. Check on the plant in the morning about 10
hours later, while the plant is still in the closet. If the leaves are open, a biological clock is
indicated.
35) Which of the following statements concerning biological clocks is false?
A) Innate circadian rhythms generally differ slightly from a 24-hour period.
B) Circadian rhythms occur with or without external stimuli.
C) Biological clocks are strongly influenced by external temperatures.
D) Movement of plants long distances very quickly induces a kind of plant “jet lag.”
36) Which of the following plant responses is affected by photoperiod?
A) gravitropism
B) apical dominance
C) onset of dormancy
D) cell division
37) What term refers to seasonal changes in the relative lengths of night and day?
A) photoperiod
B) circadian rhythm
C) gravitropism
D) phototaxis
38) A plant will only flower if the night length is longer than 14 hours. This plant is a
A) long-day plant.
B) short-night plant.
C) short-day plant.
D) day-neutral plant.
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39) A biologist interested in determining which plant organs (stems, buds, leaves, etc.) are
responsible for sensing photoperiod might perform which of the following experiments?
A) Remove the apical meristems from different parts of the plant.
B) Measure auxin levels in different parts of the plant before and after exposure to light.
C) Cover different plant organs with a foil covering to prevent light exposure.
D) Expose the plants to different wavelengths of light.
40) Which of the following is the factor that initiates flowering in long-day plants?
A) nights shorter than a critical length
B) nights longer than a critical length
C) days longer than the intervening nights
D) days shorter than a critical length
41) Christmas cactus is a short-day plant that usually blooms in the winter. Which of the
following strategies might induce it to bloom for the 4th of July?
A) putting it in a cool, well-lighted place from time to time during June
B) leaving it in a dark closet all night and part of each morning during June
C) putting it in a dark closet for a short time every afternoon during June
D) exposing it to light several times during each night in June
42) Iris is a long-day plant that normally flowers in the spring. Which of the following regimens
would be the most effective in making an iris bloom in late fall?
A) interrupting the plant’s nights at 2:00 AM with a flash of far-red light
B) interrupting the plant’s nights at 2:00 AM with a flash of red light followed by a flash of far-
red light
C) interrupting the plant’s nights at 2:00 AM with a red flash, then a far-red flash, then a red flash
D) interrupting the plant’s days at 2:00 PM by putting it in the dark
43) How does phytochrome control flowering?
A) by determining whether day length exceeds a critical minimum
B) by determining whether day length is shorter than a critical maximum
C) by sensing sunrise and sunset
D) by inducing differentiation of cells in the apical meristem
44) A plant’s first line of defense against infection is
A) Avr genes.
B) its epidermis.
C) R genes.
D) salicylic acid.
45) Which of the following is a way that plants use animals as a defense against herbivores?
A) production of an amino acid that harms herbivores
B) attraction of wasps that kill herbivorous caterpillars
C) release of microbe-killing chemicals in response to infection
D) coevolution between plants and predators
46) Fall is coming, with the prospect of frost, so you decide to pick the last tomatoes on the vine
even though they are still green. If you wanted to ripen these tomatoes, which method would be
most effective?
A) Put all the green tomatoes in a closed paper bag.
B) Put the green tomatoes in a dark closet, but with a flash of light about every 4 hours.
C) Put the green tomatoes in a plastic bag with an overripe apple.
D) Store each green tomato in a separate plastic bag and put them in the dark.
47) Citrus fruit has always been distributed from areas where the fruit is grown to other parts of
the country, often by train. In the early 1900s train cars were heated with coal, and it was
believed that this heat helped ripen the fruit. Imagine the surprise of growers and suppliers when
fruit that arrived in new boxcars heated by steam arrived unripe. Why did the fruit no longer
ripen?
A) The length of time needed to ripen the fruit was met by slow-moving older trains; newer
steam-powered locomotives arrived before the fruit ripened.
B) Ethylene, a by-product of coal burning, ripened the fruit in the cars with the coal stove but
was absent from the steam-powered trains.
C) The light from the coal-burning stoves caused the fruits to experience short nights, so they
ripened.
D) The steam prevented the buildup of abscisic acid, which is needed to ripen fruit.
48) In plant research labs, plants are often grown in light-proof chambers where the hours of
light and dark are carefully controlled. A new researcher goes into a chamber and accidentally
turns on the light during the “dark” period. What is likely to happen?
A) If the plants are short day plants, there will be no impact.
B) If the researcher can quickly produce a flash of far-red light and close the door, there will be
no impact.
C) If the plants are not yet flowering, there will be no impact.
D) If the light is only red light and not far-red light, there will be no impact.
49) A student wanted to plant an avocado seed to try to grow an avocado plant, but she could not
tell which end of the seed was the bottom and which was the top. She asked her friends what she
should do. Which one has the best response?
A) One friend said it doesn’t matter in which direction the seed is planted as long as there is a
strong light on the soil, since the shoots will seek the light and turn the seed right side up.
B) One friend said to put the seed in in any direction, because as the seed is watered, it will be
able to detect the direction the water is coming from and point the shoots that way.
C) One friend suggested a compromise: Put the seed sideways, since gravity will ensure that the
shoots grow up and the roots grow down.
D) One friend said just to put the seed in one direction or the other, because it will only sprout if
it is in the right direction, and there’s a 50/50 chance that it will be in the right orientation.
50) Plant cells treated with auxin would not be able to enlarge under which of the following
conditions?
A) lack of light for growing
B) presence of other hormones in the plant
C) absence of lysosomes in the plant cells
D) inability of the cell to take up water
51) Application of herbicides may have unintended consequences because
A) different types of plants respond differently to the same herbicide.
B) plants may increase or decrease the production of hormones in order to avoid the effect of
herbicides.
C) plants may concentrate the herbicides in their fruits so that they can be released from the
plant.
D) plants create new mutations to avoid herbicides, and those new mutations may have
unintended consequences.
33.2 Art Questions
1) Which plant in Went’s experiment shows auxin stimulating elongation in the left side of the
plant only?
A) plant A
B) plant B
C) plant C
D) plant D
2) In addition to demonstrating that auxin stimulates elongation, this diagram also shows that
A) application of additional auxin causes greater bending.
B) the application of auxin causes growth.
C) removing shoot tips also removes auxin receptors.
D) the lower parts of the hoot are able to detect light.
3) In the figure, the shoot emerged through the soil toward the light rather than growing down in
the direction of the roots due to
A) thigmotropism.
B) phototropism.
C) gravitropism.
D) circadian rhythm.
4) Which of the following statements is supported by this figure?
A) The greater the concentration of auxin, the more promotion of root elongation occurs.
B) Auxin concentrations below 10-8 g/L promote both root and stem elongation.
C) Auxin concentrations around 10-4 g/L promote stem elongation but inhibit root elongation.
D) Auxin concentrations above 0.9 g/L are best for promoting stem elongation.
5) If you cut off the top of a carrot and place it in water to see if you can get it to grow new roots,
you should add
A) more than 10-2 g/L of auxin.
B) approximately 10-8 g/L of auxin.
C) at least 10-6 g/L of auxin.
D) equal amounts of auxin and cytokinin.
33.3 Scenario Questions
After reading the paragraphs below, answer the questions that follow.
A student taking a plant physiology class is interested in investigating what will happen if the
apical bud is removed from a growing plant and supplementary hormones are introduced.
He set up his experiment with two groups of plants of the same species. In groups A and B, the
apical buds were removed and the cut apical ends were wrapped with hormone-impregnated
cotton. The plants were observed over a five-week period for growth and development. In group
A, many axillary buds and leaves appeared along the sides of the stem, but the plants had
minimal root growth. In group B, minimal growth occurred in the shoot and roots, and no
axillary buds formed.
1) What hormone was in the cotton used to wrap the apical ends of the group A plants?
A) cytokinin
B) giberellin
C) ethylene
D) auxin
2) What hormone was in the cotton used to wrap the apical ends of the group B plants?
A) cytokinin
B) giberellin
C) abscisic acid
D) auxin