Question 1

In the autumn, the leaves of some trees change colour. This happens because chlorophyll breaks down and the accessory pigments become visible. What hormone is responsible for this?
A) phototropin
B) abscisic acid
C) cytokinin
D) ethylene

Accepted Answer

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

Question 2

Which of the colours of visible light induces curvature in coleoptile most effectively?
A) red
B) blue
C) violet
D) orange

Accepted Answer

Blue light induces curvature in coleoptile most effectively. This has been demonstrated in numerous experiments and is believed to be due to the activation of phototropin proteins, which are sensitive to blue light. Red light, on the other hand, is known to inhibit coleoptile growth and often induces a straightening response. Therefore, B) blue is the best choice for the colour of visible light that induces curvature in coleoptile most effectively.

Question 3

Phytochrome plays a critical role in seed germination. Which of the colours maximises the seed germination?
A) red
B) blue
C) violet
D) orange

Accepted Answer

Phytochrome absorbs red light most effectively, triggering the process of germination in seeds. A study showed that the exposure of red light for a few seconds can increase the germination rate of lettuce, radish, and carrot seeds by 30-40%. Blue, violet, and orange light have comparatively lower effectiveness in enhancing seed germination.

Question 4

Mammalian eyes sense light because the photoreceptor cells have molecules called "opsins", which change structure when exposed to light. Which of the following plant molecules would be analogous to mammalian opsins in their light-sensing ability?
A) auxin and phytochrome
B) auxin and Pfr
C) Pfr and phytochrome
D) cytokinins and phototropins

Accepted Answer

Pfr (far-red light absorbing form of the phytochrome protein) and phytochrome are the plant molecules analogous to mammalian opsins in their light-sensing ability. They change structure when exposed to light and are involved in regulating plant growth and development in response to light conditions. Auxin and cytokinins are plant hormones involved in growth and development, and phototropins are plant proteins involved in responding to directional light cues.

Question 5

________ prevents seeds from germinating until conditions are favourable for the growth of the plant.
A) Ethylene
B) Zeaxanthin
C) Gibberellin
D) Abscisic acid

Accepted Answer

Abscisic acid is known as the "stress hormone" in plants and is responsible for inhibiting seed germination until environmental conditions such as sufficient water and light are present for the plant to grow.

Question 6

The biological clock controlling circadian rhythms must ultimately ________.
A) depend on environmental cues
B) affect gene transcription
C) stabilise on a 24-hour cycle
D) speed up or slow down with increasing or decreasing temperature

Accepted Answer

The biological clock controlling circadian rhythms is located in the suprachiasmatic nucleus (SCN) of the hypothalamus, which contains genes that regulate the production of proteins involved in circadian rhythms. This involves gene transcription, indicating that choice B is correct. The clock is able to stabilise on a 24-hour cycle due to feedback loops created by the protein products of these genes. The clock can be influenced by environmental cues such as light exposure, but ultimately it is the gene expression that controls the circadian rhythm. Temperature does not have a direct effect on the biological clock, so choice D is incorrect.

Question 7

Upon exposure to blue light, plants not only begin to grow toward the light, but move their chloroplasts to the sunny side of each cell. The adaptive advantage of moving chloroplasts to the sunny side of each cell ________.
A) maximises light absorption by the chloroplasts for photosynthesis
B) increases production of phototropic hormones
C) maximises heat absorption by the chloroplasts for cellular respiration
D) increases adenosine triphosphate (ATP) production during the light-independent reactions

Accepted Answer

When chloroplasts are moved to the sunny side of each cell, they can maximise light absorption, which is used for photosynthesis. This adaptive advantage allows the plant to produce more food, which can aid in growth and reproduction.

Question 8

Suppose a plant had a photosynthetic pigment that absorbed far-red wavelengths of light. In which of the following environments could that plant thrive?
A) on the surface of a lake
B) on the forest floor, beneath a canopy of taller plants
C) on the ocean floor, in very deep waters
D) on mountaintops, closer to the sun

Accepted Answer

The far-red wavelengths of light are the lowest energy wavelengths of visible light. Therefore, they penetrate into deeper areas of vegetation. As a result, a plant with a photosynthetic pigment that absorbs far-red light could thrive beneath another plant canopy, where other pigments might not be able to absorb enough light.

Question 9

Which of the following environmental factors can be sensed by plants?
I. gravity
II. pathogens
III. wind
IV. light
A) only I and III
B) only I, II, and IV
C) only II, III, and IV
D) I, II, III, and IV

Accepted Answer

Plants have the ability to sense a variety of environmental factors including gravity (which influences their direction of growth), pathogens (triggering immune responses), wind (affecting growth patterns and physical strength), and light (guiding photosynthesis and growth direction).

Question 10

If you were shipping green bananas to a supermarket thousands of miles away, which of the following chemicals would you want to eliminate from the plants' environment?
A) carbon dioxide
B) cytokinins
C) ethylene
D) auxin

Accepted Answer

Ethylene is a plant hormone that promotes ripening and senescence in fruits. Therefore, eliminating ethylene from the environment of green bananas during shipping would help to delay the ripening process and keep the bananas fresh for longer. Carbon dioxide, cytokinins, and auxin do not directly impact fruit ripening and would not have a significant effect on the shelf life of the bananas.

Question 11

Plants often use changes in day length (photoperiod) to trigger events such as dormancy and flowering. It is logical that plants have evolved this mechanism because photoperiod changes ________.
A) are more predictable than air temperature changes
B) predict moisture availability
C) are modified by soil temperature changes
D) can reset the biological clock

Accepted Answer

Photoperiod changes are more predictable than air temperature changes, making them a reliable trigger for plants to regulate important developmental events such as dormancy and flowering. Moisture availability and soil temperature changes can also be important environmental cues for plants, but photoperiod changes are generally more reliable in signaling seasonal changes. Additionally, photoperiod changes can also reset the biological clock in plants, helping them synchronize their physiological processes with the changing seasons.

Question 12

Which type of mutant would be most likely to produce a bushier phenotype?
A) auxin overproducer
B) strigolactone overproducer
C) cytokinin underproducer
D) strigolactone underproducer

Accepted Answer

The answer of Which type of mutant would be most...

Question 13

As cytokinins are primarily produced in roots, what route would they travel to influence lateral shoot formation in a recently topped tree?
A) symplastic
B) tracheids/vessels
C) phloem
D) apoplastic

Accepted Answer

The answer of As cytokinins are primarily produced in roots,...

Question 14

A population of plants experiences several years of severe drought. Much of the population dies due to lack of water, but a few individuals survive. You set out to discover the physiological basis for their adaptation to such an extreme environmental change. You hypothesise that the survivors have the ability to synthesise higher levels of ________ than their siblings do.
A) auxin
B) gibberellin
C) cytokinin
D) abscisic acid

Accepted Answer

Abscisic acid (ABA) is a plant hormone that plays a critical role in regulating water balance and stress responses. During drought conditions, plants increase their synthesis of ABA, which helps to close stomata (pores on leaves) to reduce water loss through transpiration. This allows the plant to conserve water and survive in conditions of limited water availability. Therefore, the survivors of the severe drought are likely to have the ability to synthesise higher levels of ABA than their siblings do, which would have helped them to survive by conserving water. The other hormones (auxin, gibberellin, cytokinin) are not directly involved in regulating water balance and are not likely to have been the basis for the survival of the drought-affected plants.

Question 15

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 ________.
A) negative thigmotropism
B) negative phototropism
C) negative gravitropism
D) the opposite of circadian rhythms

Accepted Answer

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

Question 16

A gardener in Canada wants to surprise his mother on her birthday and make her favourite hibiscus bush flower in May instead of at the end of June. The bush is growing in the greenhouse. Which of the following might make the hibiscus bush flower early?
A) grafting leaves of a hibiscus that was exposed to long nights
B) grafting leaves of a hibiscus that was exposed to short nights
C) exposing flower buds of the hibiscus bush to long nights
D) exposing flower buds of the hibiscus bush to short nights

Accepted Answer

The answer of A gardener in Canada wants to surprise...

Question 17

Who might be interested in using cytokinins?
A) grocers, to spray on fruit to enhance ripening in the store
B) consumers, to spray on fruit before eating to enhance taste
C) florists, to dip stems in to keep leaves green longer
D) farmers, to spray on fruit after picking to stall ripening

Accepted Answer

The answer of Who might be interested in using cytokinins?
A)...

Question 18

Many plants flower in response to day-length cues. Which of the following statements best summarises this phenomenon?
A) As a rule, short-day plants flower in the summer.
B) As a rule, long-day plants flower in the spring or autumn.
C) Long-day plants flower in response to long days, not short nights.
D) Flowering in short-day and long-day plants is controlled by phytochrome.

Accepted Answer

Flowering in both short-day and long-day plants is controlled by the phytochrome system, which detects changes in light duration and quality, influencing flowering based on day-length cues.

Question 19

If a farmer wanted more loosely packed bunches of grapes, he would most likely spray the immature bunches with ________.
A) auxin
B) gibberellins
C) cytokinins
D) abscisic acid

Accepted Answer

Gibberellins are known to promote the elongation of fruits, including grapes, which could result in more loosely packed bunches. Spraying immature grape bunches with gibberellins may encourage the grapes to grow longer and more spaced out on the bunch. This would result in a looser bunch of grapes. Auxin, cytokinins, and abscisic acid are less likely to have this effect on grape bunches.

Question 20

Seed packets give a recommended planting depth for the enclosed seeds. The most likely reason some seeds are to be covered with only ½ centimetre of soil is that the ________.
A) seedlings do not have an etiolation response
B) seeds require light to germinate
C) seeds require a higher temperature to germinate
D) seeds are very sensitive to waterlogging

Accepted Answer

Seeds that require light to germinate should not be planted deeply as they need exposure to sunlight to sprout. Planting them too deep could prevent them from germinating, as they may not receive the necessary amount of light. Therefore, covering these seeds with only ½ centimetre of soil would ensure they receive enough light to properly germinate.

Quiz 39: Plant Responses to Internal and External Signals

In the autumn, the leaves of some trees change colour. This happens because chlorophyll breaks down and the accessory pigments become visible. What hormone is responsible for this?

Which of the colours of visible light induces curvature in coleoptile most effectively?

Phytochrome plays a critical role in seed germination. Which of the colours maximises the seed germination?

Mammalian eyes sense light because the photoreceptor cells have molecules called "opsins", which change structure when exposed to light. Which of the following plant molecules would be analogous to mammalian opsins in their light-sensing ability?

________ prevents seeds from germinating until conditions are favourable for the growth of the plant.

The biological clock controlling circadian rhythms must ultimately ________.

Upon exposure to blue light, plants not only begin to grow toward the light, but move their chloroplasts to the sunny side of each cell. The adaptive advantage of moving chloroplasts to the sunny side of each cell ________.

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

Which of the following environmental factors can be sensed by plants? I. gravity II. pathogens III. wind IV. light

If you were shipping green bananas to a supermarket thousands of miles away, which of the following chemicals would you want to eliminate from the plants' environment?

Plants often use changes in day length (photoperiod) to trigger events such as dormancy and flowering. It is logical that plants have evolved this mechanism because photoperiod changes ________.

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

As cytokinins are primarily produced in roots, what route would they travel to influence lateral shoot formation in a recently topped tree?

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 ________.

A gardener in Canada wants to surprise his mother on her birthday and make her favourite hibiscus bush flower in May instead of at the end of June. The bush is growing in the greenhouse. Which of the following might make the hibiscus bush flower early?

Who might be interested in using cytokinins?

Many plants flower in response to day-length cues. Which of the following statements best summarises this phenomenon?

If a farmer wanted more loosely packed bunches of grapes, he would most likely spray the immature bunches with ________.

Seed packets give a recommended planting depth for the enclosed seeds. The most likely reason some seeds are to be covered with only ½ centimetre of soil is that the ________.