Question 1

A long-day plant will flower if

Accepted Answer

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

Question 2

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

Accepted Answer

Watering every third day to soak the soil to 2.0 inches encourages deeper root growth, making the lawn more drought-resistant and better able to stay green during hot, dry conditions.

Question 3

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

Accepted Answer

Plants that have their flowering inhibited by being exposed to bright lights at night are short-day plants.

Question 4

Regarding positive gravitropism exhibited by plant roots,

Accepted Answer

All of the above choices are correct. Positive gravitropism in plant roots is mediated by auxin, which causes more rapid elongation of cells on the upper side of the root, leading to downward curvature towards gravity. Gravity also causes auxin to accumulate on the lower side of roots, further promoting differential cell elongation. Additionally, the phenomenon of positive gravitropism depends upon the inhibition of cell elongation in certain cells by auxins.

Question 5

Plant cells begin synthesizing large quantities of heat-shock proteins

Accepted Answer

Heat-shock proteins are synthesized by plant cells in response to high temperatures, typically above 40°C, to help protect and repair proteins that may become denatured due to heat stress.

Question 6

All of the following are responses of plants to cold stress except

Accepted Answer

Conversion of the fluid mosaic cell membrane to a solid mosaic one is not a response of plants to cold stress. It is an adaptive response of mesophilic enzymes to high temperatures, allowing the maintenance of the enzyme structure and function in a more rigid membrane.

Question 7

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

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 8

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

Accepted Answer

In extremely cold regions, woody species may survive freezing temperatures by increasing cytoplasmic levels of specific solute concentrations, such as sugars. This increases the solute concentration within the cell, preventing the water from freezing and thus protecting the cell from damage caused by ice crystals.

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 is an immediate short-term response of plants to heat stress?

Accepted Answer

The immediate short-term response of plants to heat stress is the production of heat-shock proteins like those of other organisms. These proteins help in stabilizing the protein structures against heat denaturation. The production of heat-shock carbohydrates is a long-term response, and the opening of stomata and evolution into more xerophytic plants are not immediate responses to heat stress.

Question 10

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

Accepted Answer

Short-day plants require a night that is longer than a certain length (usually around 12-13 hours) to trigger flowering. This is because the production of a flowering hormone called florigen is stimulated during long periods of darkness.

Question 11

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 guard cell hormone under water-deficit conditions. Most likely the hormone is

Accepted Answer

ABA (abscisic acid) is a hormone that is known to play a role in regulating plant responses to water stress. When plants are under water-deficit conditions, they produce ABA, which helps to close stomata and reduce water loss through transpiration. Therefore, it is most likely that the plant discovered by the research team produces ABA as a guard cell hormone under water-deficit conditions.

Question 12

In nature, poinsettias bloom in early March. Research has shown that the flowering process is triggered three months before blooming occurs. In order to make poinsettias bloom in December, florists change the length of the light-dark cycle in September. Given the information and clues above, which of the following is a False statement about poinsettias?

Accepted Answer

Interrupting the dark period affects flowering in short-day plants like poinsettias, so statement D is false.

Question 13

If the range of a species of plants expands to a higher latitude, which of the following processes is the most likely to be modified by natural selection?

Accepted Answer

Photoperiodic response is the sensitivity of an organism to changes in day length and is critical for determining the timing of seasonal events such as reproduction. If the range of a plant species expands to a higher latitude, the duration of daylight hours will change, and natural selection is likely to favor plants that can adjust their timing of flowering or other reproductive events in response to the new photoperiodic conditions.

Question 14

A botanist exposed two groups of the same plant 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?

Accepted Answer

The plants flowered with longer daylight, suggesting they are long-day plants, which typically flower in spring or early summer.

Question 15

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

Accepted Answer

Research on gravitropic responses of roots and stems has shown that the effect of a plant hormone, such as auxin, can depend on the tissue. For example, auxin causes bending towards gravity in stems but inhibits growth in roots. This indicates that different tissues can have different responses to the same hormone.

Question 16

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

Accepted Answer

The answer of Vines in tropical rain forests must grow...

Question 17

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

Accepted Answer

Recent evidence using Arabidopsis has shown that florigen is a protein that is synthesized in leaves and travels to the shoot apical meristem where it initiates flowering. This mechanism involves the activation of a gene called FT (Flowering Locus T) in leaves by a transcription factor called FD, which allows the production of the florigen protein. The florigen protein then moves through the phloem to the shoot apical meristem where it interacts with a receptor called FLOWERING LOCUS T1 (FT1) to promote flowering.

Question 18

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?

Accepted Answer

Abscisic acid is a plant hormone that is known to play a role in regulating water balance in plants. It is involved in the closure of stomata, reducing water loss and increasing the plant's ability to survive drought conditions. Therefore, increasing the amount of abscisic acid in a plant may help it become more resistant to drought.

Question 19

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

Accepted Answer

The answer of If a short-day plant has a critical...

Question 20

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?

Accepted Answer

The cypress, which grows in swamps, likely has larger intercellular spaces in its roots to facilitate gas exchange in waterlogged conditions, unlike the pine that grows in sandy soil.

Quiz 39: Plant Responses to Internal and External Signals