Question 1

Which of the following illustrates a commercial application of cytokinins?

Accepted Answer

Cytokinins are used in floristry to delay the aging of leaves and flowers, keeping them fresh longer, which is a commercial application.

Question 2

Mammalian eyes sense light because the photoreceptor cells have molecules called opsins that change structure when exposed to light. Which of the following plant molecules is most analogous to mammalian opsins in their light-sensing ability?

Accepted Answer

Phytochromes are the plant molecules most analogous to mammalian opsins in terms of their light-sensing ability. Like opsins, phytochromes change their structure in response to light, allowing plants to detect light and respond to it, such as by initiating germination or flowering.

Question 3

Vines in tropical rain forests must grow toward large trees before being able to climb toward the sun. Which of the following responses would promote vine growth towards a tree?

Accepted Answer

Negative phototropism means that the plant grows away from light, which would encourage it to grow towards the darker area under the canopy where trees are located, thus promoting growth towards a tree.

Question 4

Cytokinins, produced primarily in roots, travel by which of the following structures to influence branching in a recently topped tree (tree whose upper branches have been trimmed off)?

Accepted Answer

Cytokinins are transported from the roots to other parts of the plant primarily through the xylem.

Question 5

Charles Darwin and his son Francis did a series of experiments to test their hypothesis that the tips of grass coleoptiles sense the direction of light. In the first experiment, coleoptiles with their tips cut off did not bend toward light, but intact coleoptiles did. Why was it necessary to follow this experiment with another experiment where only the tips of treated coleoptiles were covered with opaque foil?

Accepted Answer

The follow-up experiment with the tips covered was necessary to rule out the possibility that the lack of bending in the first experiment was due to injury from cutting the tips, rather than the absence of light perception at the tips.

Question 6

Phytochrome plays a critical role in germination of some seeds. Which of these colors of light maximizes germination in these seeds?

Accepted Answer

Phytochrome is a photoreceptor in plants that is most sensitive to red light. It plays a crucial role in various plant developmental processes, including seed germination. Exposure to red light activates the phytochrome, promoting germination in many seeds.

Question 7

Plants often use changes in day length (photoperioD) to trigger events such as dormancy and flowering. Which of the following best explains why day-neutral plants are more common in the tropics than in temperate zones?

Accepted Answer

Day-neutral plants do not rely on photoperiodic changes to trigger key life events. In the tropics, where there is little variation in day length throughout the year, these plants thrive because their growth and reproductive cycles are not limited by significant changes in photoperiod.

Question 8

Upon exposure to blue light, plants not only begin to grow toward the light, but redistribute the chloroplasts to the sunny side of each cell. Which of the following best explains the adaptive advantage of moving chloroplasts to the sunny side of each cell?

Accepted Answer

Moving chloroplasts to the sunny side of each cell maximizes light absorption by the chloroplasts, which is crucial for photosynthesis. This adaptation allows plants to efficiently convert light energy into chemical energy, enhancing their growth and survival.

Question 9

In the fall, the leaves of some trees change color. This happens because chlorophyll breaks down and the accessory pigments become visible. What hormone triggers this response in plants?

Accepted Answer

The answer of In the fall, the leaves of some...

Question 10

Suppose a plant had a photosynthetic pigment that absorbed far-red wavelengths of light. In which of the following environments is the plant most likely to thrive?

Accepted Answer

Plants with pigments that absorb far-red wavelengths of light are adapted to environments with filtered sunlight, where longer wavelengths prevail due to the filtering effect of the canopy leaves above. The forest floor beneath a canopy of taller plants is such an environment, where the available light is mostly in the far-red spectrum due to the absorption of the shorter wavelengths by the leaves in the canopy.

Question 11

If a farmer wanted less tightly packed clusters of grapes, he would most likely spray the immature bunches with which of the following hormones?

Accepted Answer

Gibberellins are known to cause elongation of cells and can be used to increase the space between grapes in a cluster, leading to less tightly packed clusters. This hormone promotes growth and can influence various developmental processes in plants, including fruit enlargement and the breaking of dormancy.

Question 12

Which of the following mechanisms is most directly responsible for controlling circadian rhythms in plants?

Accepted Answer

Circadian rhythms in plants are most directly controlled by periodic oscillations of gene transcription. This involves the cyclical activation and repression of specific genes that regulate various physiological processes in accordance with a roughly 24-hour cycle, independent of external cues like light and temperature.

Question 13

Which type of mutant is most likely to produce a bushier phenotype?

Accepted Answer

Strigolactones inhibit shoot branching, so a strigolactone underproducer would likely have a bushier phenotype due to reduced inhibition of shoot branching.

Question 14

A population of plants experienced several years of severe drought. Most of the plants died due to lack of water, but a few individuals survived. The surviving plants probably produced higher levels of which of the following hormones?

Accepted Answer

Abscisic acid is known as the stress hormone in plants, playing a crucial role in enabling plants to withstand drought conditions. It helps in closing the stomata to reduce water loss through transpiration, thereby increasing the plant's ability to survive during periods of water scarcity.

Question 15

If you were shipping green bananas to a supermarket thousands of miles away, removing which of the following chemicals from the plants' environment will best prevent premature fruit ripening?

Accepted Answer

Ethylene is a plant hormone responsible for ripening in fruits, including bananas. Removing ethylene from the environment of green bananas can slow down their ripening process, making it ideal for shipping them long distances without them becoming overripe.

Question 16

Which of the following colors of visible light induces phototrophic curvature in coleoptiles most effectively?

Accepted Answer

Blue light is most effective in inducing phototropic curvature in coleoptiles, as it activates phototropins, which are blue light receptors involved in plant phototropism.

Question 17

Which hormone prevents seeds from germinating until conditions are favorable for the growth of the plant?

Accepted Answer

Abscisic acid is the hormone responsible for inhibiting seed germination until conditions are favorable, ensuring that the seed only begins to grow when it has the best chance of survival.

Question 18

Seed packets give a recommended planting depth for the enclosed seeds. Which of the following is the most likely reason some seeds are to be covered with only a thin layer of soil after planting?

Accepted Answer

Light is required for the germination of some seeds, and covering them with only a thin layer of soil ensures they receive sufficient light to trigger germination.

Question 19

An individual plant was discovered that could not grow towards light. After some research, it was determined that the reason was a defective gene that did not allow for the level of cell elongation necessary for a phototropic response. This mutation greatly reduces the fitness of the individual plant. Which of the following best explains the reduction in fitness in the mutant plant?

Accepted Answer

The ability to grow towards light (phototropism) is crucial for maximizing photosynthesis, which in turn provides the energy necessary for various plant activities, including reproduction. A plant that cannot adjust its growth direction to optimize light exposure would have reduced photosynthetic activity, leading to less energy available for reproduction, thereby reducing its fitness.

Question 20

Many plants flower in response to day-length cues. Which of the following statements correctly describes the relationship between day length and flowering?

Accepted Answer

The answer of Many plants flower in response to day-length...

Quiz 39: Plant Signals and Behavior