Ch.28 External Factors and Plant Growth Verified Test Bank

Chapter 28: External Factors and Plant Growth

Multiple-Choice Questions

Which of the following is NOT a finding from experiments on the role of auxin in phototropism of coleoptile tips?

a. Light does not affect the total amount of auxin.

b. Light does not destroy auxin.

c. Auxin migrates from the lighted side to the shaded side.

d. More auxin can be isolated from the shaded side of an intact tip than from the lighted side.

e. If the tip is split and the two halves separated by a barrier, more auxin can be isolated from the shaded side than from the lighted side.

______ light is the most effective in producing a phototropic response.

a. Green

b. Yellow

c. Orange

d. Blue

e. Red

According to the original hypothesis on negative gravitropism of shoots, auxin is redistributed to the ______ side where it ______ cell expansion.

a. lower; stimulates

b. lower; inhibits

c. upper; stimulates

d. upper; inhibits

e. upper; first inhibits then stimulates

In roots and shoots, the statoliths are:

a. chloroplasts.

b. amyloplasts.

c. plasma membranes.

d. cell walls.

e. lignified cells.

In roots, statoliths are localized in the:

a. endodermis.

b. vascular tissues.

c. starch sheath.

d. epidermis of the root cap.

e. root cap columella.

When a growing root is oriented horizontally, the amyloplasts in the central column of the rootcap:

a. slide downward.

b. float upward.

c. attach to the nuclear envelope.

d. attach to the mitochondria.

e. do not move.

In the current model of root gravitropism, elongation is _____ in the upper side of the distal elongation zone and ______ along the lower side.

a. stimulated; stimulated

b. stimulated; suppressed

c. suppressed; stimulated

d. suppressed; is neither stimulated nor suppressed

e. is neither stimulated nor suppressed; suppressed

Which of the following statements concerning hydrotropism is FALSE?

a. It is the directed growth of roots in response to moisture.

b. Decapped roots do not curve hydrotropically.

c. Under normal gravity, hydrotropism is suppressed by gravitropism.

d. Auxin apparently is required for hydrotropism.

e. Inhibitors of auxin influx and efflux also inhibit hydrotropism.

Which of the following statements about thigmotropism is FALSE?

a. It enables roots to navigate around rocks.

b. It is a response to contact with a solid object.

c. An example is the climbing of tendrils.

d. Cells touching the support lengthen more than cells on the other side.

e. The stems of peas can store the memory of tactile stimulation.

Which of the following statements about circadian clocks is FALSE?

a. Input pathways and output pathways are the parts of the clock that do not interact.

b. Conceptually they consist of three parts.

c. They cause the regular oscillation of 30-40 percent of Arabidopsis genes.

d. The central oscillator is the part of the clock that generates rhythmic behavior.

e. Input pathways are the part of the clock that carries information to the oscillator.

In terms of the circadian clock, gating refers to the observation that stimuli of _____ strength employed at different times of the day can result in ______ intensity of response.

a. different; a smaller

b. different; the same

c. different; different

d. equal; the same

e. equal; a different

Long-day plants flower:

a. in the summer.

b. in early spring or fall.

c. when exposed to eight hours of daylight.

d. when the light period is shorter than a critical length.

e. without respect to day length.

Which of the following statements concerning photoperiodism is FALSE?

a. Short-day plants in the early spring or fall.

b. Spinach and lettuce are examples of long-day plants.

c. Day-neutral plants flower without respect to photoperiod.

d. Photoperiodic behavior remains constant over a wide range of temperatures.

e. In some plants, only a single exposure to the critical day-length will produce a response.

Experiments on cocklebur have shown that the ______ perceives the photoperiod.

a. apical meristem

b. columella

c. leaf blade

d. petiole

e. stem

If a short-day plant receives a one-minute exposure to light in the middle of the dark period rather than continuous darkness, it will:

a. produce more flowers.

b. produce smaller flowers.

c. produce larger flowers.

d. flower at a lower temperature.

e. not flower.

Light with a wavelength of about ______ nanometers is the most effective for interrupting the dark period of both short-day and long-day plants.

a. 220

b. 340

c. 440

d. 660

e. 730

Suppose lettuce seeds are exposed to a series of alternating flashes of red light (abbreviated R) and far-red light (abbreviated FR). (E.g., a flash of red light followed by a flash of far-red light is denoted as R→RF.) Which of the following series of flashes would result in the germination of those seeds?

a. FR only

b. R→FR

c. R→FR →R→FR

d. R →FR→R→FR→R

e. R→FR→R→FR→R→FR

Which of the following statements about P_r and P_fr is FALSE?

a. They are photoreceptors.

b. They participate in photoconversion reactions.

c. P_r is the biologically active form.

d. P_r absorbs 660-nanometer light.

e. P_fr absorbs 730-nanometer light.

When lettuce seeds are exposed to red light:

a. P_fr is converted to P_r.

b. P_r is converted to P_fr.

c. 660-nanometer light is converted to 730-nanometer light.

d. 730-nanometer light is converted to 660-nanometer light.

e. they will not germinate.

Which of the following statements concerning the phytochrome molecule is FALSE?

a. The phytochromes in Arabidopsis are encoded by just 2 genes.

b. Most plants have several different phytochromes.

c. The chromophore portion is similar to the phycobilins in cyanobacteria.

d. One part is a protein.

e. The chromophore portion absorbs light.

When phytochromes interact with PIF proteins, what happens next?

a. The PIF proteins bind DNA.

b. The PIF proteins enter the endoplasmic reticulum.

c. The PIF proteins enter the nucleus.

d. The PIF proteins are degraded.

e. The PIF proteins are polymerized.

An etiolated eudicot seedling:

a. has a short stem.

b. has small leaves.

c. is green.

d. lacks plastids.

e. cannot undergo further growth.

Compared with similar plants growing in full sunlight, plants growing in the shade of other vegetation:

a. receive more red light and less far-red light.

b. are usually shorter.

c. receive more wavelengths below 700 nanometers than above.

d. have a reduced red/far-red ratio.

e. receive more reflected light and less transmitted light.

If a leaf is given an inductive cycle and then removed immediately the plant _____, but if the leaf is removed several hours after photoinduction, then the plant _______.

a. won’t flower; won’t flower

b. will flower; won’t flower

c. won’t flower; will flower

d. won’t be vernalized; will be vernalized

e. will be vernalized; won’t be vernalized

In Arabidopsis, what is the correct order of action of the following flower-promoting genes?

a. FT then GI then CO

b. CO then FT then GI

c. CO then GI then FT

d. GI then CO then FT

e. FT then CO then GI

The florigen FT is produced in:

a. vessel elements.

b. companion cells.

c. tracheids.

d. sieve-tube elements.

e. guard cells.

Winter rye is usually planted in the ______, and it flowers in the ______.

a. early spring; summer

b. early spring; autumn

c. early spring; winter

d. summer; following spring

e. autumn; following summer

In the process of vernalization, early ______ is stimulated by exposing the germinating seeds to ______ temperatures.

a. dormancy; low

b. flowering; low

c. germination; low

d. dormancy; high

e. germination; high

Vernalization takes place directly in the cells of the:

a. shoot apical meristem.

b. leaf blade.

c. petiole.

d. stem.

e. hypocotyl.

Stratification is the process used by horticulturalists in which seeds are:

a. moistened and exposed to low temperature.

b. moistened and exposed to high temperature.

c. mechanically abraded.

d. soaked in alcohol.

e. dried.

Which of the following statements about bud scales is FALSE?

a. They may contain growth inhibitors.

b. They protect the bud against desiccation.

c. They restrict the movement of oxygen into the bud.

d. They insulate the bud from heat loss.

e. They have leaf primordia in their axils.

In temperate regions, the acclimation of buds is initiated primarily by decreasing ______, and it produces ______.

a. daylength; cold hardiness

b. temperature; cold hardiness

c. moisture; moisture resistance

d. levels of growth inhibitors; early flowering

e. numbers of bud scales; early flowering

The direction of a nastic movement is always ______ the direction of the stimulus.

a. away from

b. toward

c. at right angles to

d. at an oblique angle to

e. independent of

In nyctinastic movements, leaves:

a. twine around a support such as a fence post.

b. have their stomata open during the night and closed during the day.

c. are rolled during the day and unrolled at night.

d. are oriented vertically in darkness and horizontally in light.

e. are oriented horizontally in darkness and vertically in light.

Which of the following statements about a pulvinus is FALSE?

a. It is a joint-like thickening at the base of a leaf or a leaflet.

b. It is responsible for most nyctinastic leaf movements.

c. It lacks vascular tissue.

d. It contains parenchyma cells.

e. Some of its cells undergo changes in turgor.

In Mimosa pudica, movement of leaflets involves all of the following changes in cells of the pulvinus EXCEPT:

a. accumulation of sucrose unloaded from the phloem.

b. an influx of potassium ions from the apoplast.

c. a change in turgor pressure.

d. an efflux of water.

e. a decrease in water potential.

The rapid closure of leaves of the Venus flytrap is now thought to be due to:

a. changes in turgor pressure in the cells beneath the epidermis.

b. changes in turgor pressure in the upper epidermis.

c. changes in turgor pressure in cells of the pulvinus.

d. acid-induced wall loosening of motor cells.

e. unloading of sucrose from the phloem.

In contrast to thigmonastic movements, thigmomorphogenesis:

a. is a response to touch.

b. is a response to a mechanical stimulus.

c. is independent of the direction of the stimulus.

d. involves cells of the pulvinus.

e. involves an altered growth pattern.

In Arabidopsis thaliana, touch induces the expression of genes that encode proteins related to ______, suggesting a role for ______ in thigmomorphogenesis.

a. an endogenous inhibitor; the biological clock

b. amylase; starch

c. the cytoskeleton; microtubules

d. calmodulin; calcium

e. chlorophyll; magnesium

Which of the following statements about heliotropism is FALSE?

a. It is a diurnal movement involving pulvini.

b. It is a process involving an orientation to the sun.

c. It involves the leaves and flowers of many plants.

d. It is also called solar tracking.

e. It involves a mechanism similar to that of stem phototropism.

True-False Questions

In tropisms, a response toward the stimulus is said to be negative.

Experiments using ¹⁴C-labeled auxin indicate that light causes the destruction of auxin in coleoptiles.

In shoot gravitropism, auxin is distributed to the lower side where it stimulates cell expansion.

In the shoot, the gravity-sensing cells are called statoliths.

In roots, statocytes are located in the root cap.

The ageotropum mutant of pea plants lacks both a hydrotropic response and a gravitropic response.

An example of thigmotropism is the twisting growth of tendrils.

Circadian rhythms persist even when all environmental conditions are kept constant.

Photoperiodism pertains to events that are influenced by the relative lengths of light and dark.

In order to flower, short-day plants must have a light period shorter than a critical length, and long-day plants must have a light period longer than a critical length.

With respect to effect on flowering, the middle of the dark period is the part most sensitive to interruption by a flash of light.

The wavelength of light most effective in causing germination of lettuce seeds is 730 nanometers.

If lettuce seeds are exposed first to red light followed immediately by exposure to far-red light the seeds will germinate.

Phytochrome-interacting factors (PIFs) are located in the nucleus.

The floral stimulus can move across a graft as well as through agar.

In Arabidopsis, the floral stimulus is produced in companion cells of leaves.

In Arabidopsis, the FT gene encodes the FT protein, which is the florigen.

Vernalization is the exposure of flower buds to low temperatures to promote early flowering.

Seed dormancy can usually be overcome by placing the seeds in a warm, moist environment.

In the process of scarification, seeds are treated with solvents that dissolve the waxes in the seed coat.

Cold hardiness refers to the process of preparing the plant for winter.

The bulbs of tulips and hyacinths can be “forced” by bringing them indoors before the temperature drops.

The sleep movements of plants are an example of nastic movements.

The seismonastic movements of Mimosa pudica involve changes in the pulvini.

Regular rubbing or bending of a stem stimulates its elongation.

The mechanism underlying heliotropism involves pulvini at the base of leaves and leaflets.

Essay Questions

1. The Tropisms; pp. 660–662; moderate

Describe the mechanism by which coleoptiles bend toward the light. Support your answer with experimental evidence.

2. The Tropisms; pp. 662–664; moderate

Compare and contrast the starch-statolith and the hydrostatic pressure hypotheses of gravity sensing.

3. The Tropisms; pp. 664–665; moderate

What is hydrotropism? What evidence supports the hypothesis that hydrotropism is not simply a form of gravitropism?

4. Circadian Rhythms; pp. 665–666; moderate

What is the difference between a free-running and an entrained circadian rhythm? In nature, how is entrainment achieved?

5. Circadian Rhythms; pp. 665–667; easy

In what ways is the circadian clock useful to plants? How is the effect of temperature an important aspect of this usefulness?

6. Photoperiodism; pp. 668–669; moderate

Define photoperiodism. Distinguish between short-day, long-day, and day-neutral plants. In what ways are the first two names misnomers?

7. Photoperiodism; pp. 670–672; difficult

Describe the photoconversion reactions of phytochrome. Use these reactions to explain why a lettuce seed exposed first to red light and then to far-red light will not germinate.

8. Photoperiodism; pp. 671–672; moderate

Describe the two parts of the phytochrome molecule. What is known about the mechanism of action of phytochrome?

9. The Floral Stimulus; p. 674; difficult

What type of molecule is florigen? Where in the plant is it synthesized, how is it transported, and how does it exert its effects?

10. Vernalization: Cold and the Flowering Response; p. 674; moderate

Describe the procedure of vernalization. In what ways is it economically important?

11. Dormancy; pp. 674–676; moderate

How is dormancy adaptive in an evolutionary sense? Describe some mechanisms that have evolved to break seed dormancy.

12. Nastic Movements and Solar Tracking; p. 678; easy

How is a nastic movement different from a tropism?

13. Nastic Movements and Solar Tracking; p. 678; moderate

What is a pulvinus? How do pulvini function in nastic movements? Give some examples.

14. Nastic Movements and Solar Tracking; p. 680; easy

What is thigmomorphogenesis, and in what ways is it adaptive?