Question 1

Vines in tropical rain forests must grow toward large trees before being able to grow toward the sun. To reach a large tree, the most useful kind of growth movement for a tropical vine presumably would be the opposite of
A) positive thigmotropism.
B) positive phototropism.
C) positive gravitropism.
D) sleep movements.
E) circadian rhythms.

Accepted Answer

Positive phototropism is growth towards light, so the opposite would be growth away from light, which is not useful for vines that need to reach large trees before growing towards the sun.

Question 2

In extremely cold regions, woody species may survive freezing temperatures by
A) emptying water from the vacuoles to prevent freezing.
B) decreasing the numbers of phospholipids in cell membranes.
C) decreasing the fluidity of all cellular membranes.
D) producing canavanine as a natural antifreeze.
E) increasing cytoplasmic levels of specific solute concentrations, such as sugars.

Accepted Answer

Woody species in extremely cold regions can increase cytoplasmic levels of specific solute concentrations such as sugars which reduce the amount of free water in cells, decreasing the likelihood of ice crystal formation and preventing damage to cellular structures. This process is known as cryoprotection or osmotic adjustment.

Question 3

Plants that have their flowering inhibited by being exposed to bright lights at night are
A) day-neutral plants.
B) short-night plants.
C) devoid of phytochrome.
D) short-day plants.
E) long-day plants.

Accepted Answer

Short-day plants have their flowering inhibited by exposure to bright lights at night. This is because they require a certain amount of darkness to promote flowering.

Question 4

A short-day plant exposed to nights longer than the minimum for flowering but interrupted by short flashes of light
A) never flower.
B) might flower depending upon the duration of the light flash.
C) will not be affected and will flower.
D) might flower depending upon the wavelengths of the light flashes.
E) will still flower if ethylene is administered.

Accepted Answer

Short-day plants require uninterrupted long nights to flower. Light flashes can interrupt this process, and the effect depends on the wavelength of the light, as certain wavelengths can reset the plant's internal clock.

Question 5

What do the results of research on gravitropic responses of roots and stems show?
A) Different tissues have the same response to auxin.
B) The effect of a plant hormone can depend on the tissue.
C) Some responses of plants require no hormones at all.
D) Light is required for the gravitropic response.
E) Cytokinin can only function in the presence of auxin.

Accepted Answer

The results of research on gravitropic responses of roots and stems show that the effect of a plant hormone can depend on the tissue. Different tissues can have different responses to auxin. This suggests that the hormone is involved in the response, but that other factors may also be important. Other responses of plants do not require hormones, and light is not required for the gravitropic response. Cytokinin can function independently of auxin.

Question 6

Which of the following is a likely response of plants to cold stress?
A) the production of a specific solute "plant coagulant " that reduces water loss
B) reducing the size of ice crystals
C) conversion of the fluid mosaic cell membrane to a solid mosaic one
D) an increase in sterol concentration of membrane lipids so that the membranes remain flexible
E) increasing the proportion of unsaturated fatty acids in the membranes

Accepted Answer

The answer of Which of the following is a likely...

Question 7

Which of the following best describes positive gravitropism exhibited by plant roots?
A) It is mediated by auxin similar to the phototropism responses in shoots.
B) It depends on an inhibition of elongation of some cells.
C) Gravity causes gibberellins to accumulate on the lower side of roots.
D) The phenomenon depends upon inhibition of cell elongation of certain root cells by abscisic acid.
E) All of the above are correct.

Accepted Answer

Positive gravitropism in plant roots is mediated by auxin, similar to the phototropism responses in shoots. The auxin moves from the upper side of the root to the lower side due to gravity, causing differential cell elongation and resulting in growth towards the center of the Earth. Gibberellins and abscisic acid do not play a direct role in this phenomenon.

Question 8

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
A) falling statoliths trigger gravitropism.
B) starch accumulation triggers the negative phototropic response of roots.
C) starch grains block the acid growth response in roots.
D) starch is converted to auxin, which causes the downward bending in roots.
E) starch and downward movement are necessary for thigmotropism.

Accepted Answer

The discovery that a plant can grow its roots downward without forming starch grains refutes the hypothesis that falling statoliths (which are dense, starch-containing plastids) trigger gravitropism, as it shows that root growth direction can be determined without the presence of starch grains.

Question 9

Most scientists agree that global warming is underway; thus, it is important to know how plants respond to heat stress. Which of the following would be a useful line of inquiry to try and improve plant response and survival to heat stress?
A) the production of heat-stable carbohydrates
B) increased production of heat-shock proteins
C) the opening of stomata to increase evaporational heat loss
D) protoplast fusion experiments with xerophytic plants
E) all of the above

Accepted Answer

Increased production of heat-shock proteins allows plants to better withstand high temperatures by protecting their proteins from heat-induced damage. The other options may also have some potential to improve plant response to heat stress, but there is more evidence supporting the effectiveness of heat-shock proteins.

Question 10

Which of the following watering regimens will be most effective at keeping a lawn green during the hot, dry summer months?
A) daily sprinkling to soak the soil to 0.5 inch
B) sprinkling every other day to soak the soil to 1.0 inch
C) sprinkling every third day to soak the soil to 2.0 inches
D) daily sprinkling to soak the soil to 0.5 inch or sprinkling every other day to soak the soil to 1.0 inch
E) sprinkling every other day to soak the soil to 1.0 inch or sprinkling every third day to soak the soil to 2.0 inches

Accepted Answer

Deep watering every third day allows roots to grow deeper, making the lawn more drought-resistant and efficient in water usage.

Question 11

Bald cypress and loblolly pine are both gymnosperm trees native to the southern United States. The cypress grows in swamps; the pine grows in sandy soil. How do you think their anatomies differ?
A) There are larger intercellular spaces in the roots of the cypress than in the roots of the pine.
B) Water-conducting cells are larger in the stems of the cypress than in the stems of the pine.
C) The springwood and summerwood are more distinct in the cypress.
D) There is less parenchyma in the roots of the cypress than in the pine roots.
E) There are no major anatomical differences between these species because they're both gymnosperms.

Accepted Answer

The cypress, which grows in swamps, likely has larger intercellular spaces in its roots to facilitate gas exchange in waterlogged conditions.

Question 12

If you wanted to genetically engineer a plant to be more resistant to drought, increasing amounts of which of the following hormones might be a good first attempt?
A) abscisic acid
B) brassinosteroids
C) gibberellins
D) cytokinins
E) auxin

Accepted Answer

Abscisic acid is known to play a key role in plant response to drought stress by regulating stomatal closure, reducing water loss and increasing water-use efficiency. Therefore, increasing amounts of abscisic acid may increase the plant's ability to withstand drought conditions.

Question 13

The initial response of the root cells of a tomato plant watered with seawater would be to
A) rapidly produce organic solutes in the cytoplasm.
B) rapidly expand until the cells burst.
C) begin to plasmolyze as water is lost.
D) actively transport water from the cytoplasm into the vacuole.
E) actively absorb salts from the seawater.

Accepted Answer

When plant cells are watered with seawater, they will experience plasmolysis, which is the loss of water from the cytoplasm due to the high salt concentration of seawater. The root cells will start to shrink and lose their turgor pressure, causing them to detach from the root and ultimately lead to cell death. Therefore, the initial response of the root cells would be to start plasmolyzing as they lose water.

Question 14

Plant cells begin synthesizing large quantities of heat-shock proteins
A) after the induction of chaperone proteins.
B) in response to the lack of CO₂ following the closing of stomata by ethylene.
C) when desert plants are quickly removed from high temperatures.
D) when they are subjected to moist heat (steam) followed by electric shock.
E) whenever the external temperature exceeds the threshold where photosynthesis is negatively impacted.

Accepted Answer

Heat-shock proteins are produced in response to stress conditions, including high temperatures that negatively impact cellular processes such as photosynthesis. These proteins help protect cells by preventing the aggregation of denatured proteins and assisting in their refolding.

Question 15

If a short-day plant has a critical night length of 15 hours, then which of the following 24-hour cycles will prevent flowering?
A) 8 hours light/16 hours dark
B) 4 hours light/20 hours dark
C) 6 hours light/2 hours dark/light flash/16 hours dark
D) 8 hours light/8 hours dark/light flash/8 hours dark
E) 2 hours light/20 hours dark/2 hours light

Accepted Answer

A short-day plant requires uninterrupted darkness longer than its critical night length to flower. A light flash during the dark period, as in option D, interrupts the dark period, preventing flowering.

Question 16

What does a short-day plant require in order to flower?
A) a burst of red light in the middle of the night
B) a burst of far-red light in the middle of the night
C) a day that is longer than a certain length
D) a night that is longer than a certain length
E) a higher ratio of Pr to Pfr

Accepted Answer

Short-day plants require a night that is longer than a certain length in order to flower.

Question 17

A long-day plant will flower
A) in the late fall.
B) when the night is shorter than a critical value.
C) only under artificial light in the summer.
D) during short days with proper fertilization.
E) regardless of the photoperiod imposed.

Accepted Answer

Long-day plants require a minimum critical period of darkness to flower, and any night length below that threshold will induce flowering. Therefore, option B is the correct choice. Option A is incorrect because long-day plants typically flower in the late spring or summer, not in the late fall. Option C is incorrect because long-day plants require natural light to flower, not artificial light. Option D is incorrect because long-day plants require long nights, not short nights, to flower. Option E is incorrect because long-day plants are photoperiodic, meaning their flowering is influenced by day-length.

Question 18

You are part of a desert plant research team trying to discover crops that will be productive in arid climates. You discover a plant that produces a hormone under water-deficit conditions that triggers a suite of drought responses. Most likely the hormone is
A) ABA.
B) GA.
C) IAA.
D) 2, 4-D.
E) salicylic acid.

Accepted Answer

ABA (abscisic acid) is known for triggering a suite of responses to drought conditions in plants. This hormone signals the closure of stomata to prevent water loss, as well as the activation of genes that promote the synthesis of osmoprotectants and antioxidants, which help the plant survive under conditions of water scarcity. Therefore, it is likely that the plant in question produces ABA under water-deficit conditions to enhance its drought tolerance.

Question 19

Classic experiments suggested that a floral stimulus, florigen, could move across a graft from an induced plant to a noninduced plant and trigger flowering. Recent evidence using Arabidopsis has recently shown that florigen is probably
A) a phytochrome molecule that is activated by red light.
B) a protein that is synthesized in leaves, travels to the shoot apical meristems, and initiates flowering.
C) a membrane signal that travels through the symplast from leaves to buds.
D) a second messenger that induces Ca⁺⁺ ions to change membrane potential.
E) a transcription factor that controls the activation of florigen-specific genes.

Accepted Answer

Recent evidence using Arabidopsis has shown that florigen is a protein that is synthesized in leaves, travels to the shoot apical meristems, and initiates flowering. This supports choice B.

Question 20

A long-day plant will flower if
A) the duration of continuous light exceeds a critical length.
B) the duration of continuous light is less than a critical length.
C) the duration of continuous darkness exceeds a critical length.
D) the duration of continuous darkness is less than a critical length.
E) it is kept in continuous far-red light.

Accepted Answer

The answer of A long-day plant will flower if
A) the...

Quiz 39: Plant Responses to Internal and External Signals

Vines in tropical rain forests must grow toward large trees before being able to grow toward the sun. To reach a large tree, the most useful kind of growth movement for a tropical vine presumably would be the opposite of

In extremely cold regions, woody species may survive freezing temperatures by

Plants that have their flowering inhibited by being exposed to bright lights at night are

A short-day plant exposed to nights longer than the minimum for flowering but interrupted by short flashes of light

What do the results of research on gravitropic responses of roots and stems show?

Which of the following is a likely response of plants to cold stress?

Which of the following best describes positive gravitropism exhibited by plant roots?

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

Most scientists agree that global warming is underway; thus, it is important to know how plants respond to heat stress. Which of the following would be a useful line of inquiry to try and improve plant response and survival to heat stress?

Which of the following watering regimens will be most effective at keeping a lawn green during the hot, dry summer months?

Bald cypress and loblolly pine are both gymnosperm trees native to the southern United States. The cypress grows in swamps; the pine grows in sandy soil. How do you think their anatomies differ?

If you wanted to genetically engineer a plant to be more resistant to drought, increasing amounts of which of the following hormones might be a good first attempt?

The initial response of the root cells of a tomato plant watered with seawater would be to

Plant cells begin synthesizing large quantities of heat-shock proteins

If a short-day plant has a critical night length of 15 hours, then which of the following 24-hour cycles will prevent flowering?

What does a short-day plant require in order to flower?

A long-day plant will flower

You are part of a desert plant research team trying to discover crops that will be productive in arid climates. You discover a plant that produces a hormone under water-deficit conditions that triggers a suite of drought responses. Most likely the hormone is

Classic experiments suggested that a floral stimulus, florigen, could move across a graft from an induced plant to a noninduced plant and trigger flowering. Recent evidence using Arabidopsis has recently shown that florigen is probably

A long-day plant will flower if