Question 1

A defining characteristic of biological clock-controlled rhythms is that cycles
A) continue in the absence of environmental cues such as light-dark and temperature cycles.
B) operate on at least a circannual rhythm rather than simply a circadian rhythm.
C) operate on a single period within a particular species, such as circalunidian rhythm.
D) require the presence of environmental cues such as light-dark and temperature cycles.

Accepted Answer

Biological clock-controlled rhythms, such as circadian rhythms, are endogenous and can continue even in the absence of external cues like light-dark and temperature cycles, demonstrating the internal mechanism's control over these rhythms.

Question 2

The period of a cycle in a laboratory setting is usually more consistent than that in nature; this difference is described with the prefix circa. Thus, a cycle that would coincide approximately with a lunar day would be described as being
A) circadian
B) circalunidian
C) circamonthly
D) circannual

Accepted Answer

Circalunidian refers to cycles that approximate the lunar day, aligning with the context of the question. Circadian relates to a roughly 24-hour cycle, circamonthly is not a standard term for describing biological rhythms, and circannual refers to yearly cycles.

Question 3

Entraining a biological clock means
A) forcing it to run according to an environmental cycle such as seasonal differences, that is different from its usual one, such as daily light-dark cycles.
B) removing all environmental cues and allowing the clock to free-run.
C) resetting it to synchronize with a particular environmental cycle.
D) all of the above.

Accepted Answer

Entraining a biological clock involves resetting it to synchronize with a specific environmental cycle, such as the light-dark cycle.

Question 4

If a nocturnal laboratory subject that is being maintained under conditions of constant darkness experiences a brief light pulse early during its circadian night, it will
A) be largely unaffected.
B) become active earlier than expected the next day.
C) become active later than expected the next day.
D) become completely disoriented.

Accepted Answer

The answer of If a nocturnal laboratory subject that is...

Question 5

Entrainment of the biological clock is especially important for animals living
A) in the oceans.
B) in the temperate zone.
C) in the tropics.
D) near the magnetic poles.

Accepted Answer

Entrainment of the biological clock is crucial for animals living in the temperate zone because they experience significant seasonal changes in day length and weather conditions, requiring adaptation to varying environmental cues for survival and reproduction.

Question 6

The biological clock remains accurate in spite of large changes in environmental temperature.
A) If the clock were as sensitive as most other chemical reactions are to temperature changes, it would function as a thermometer rather than a clock.
B) If the clock were sensitive to temperature, the biological clocks of some animals would run at different rates at different times of day.
C) This is surprising if one assumes that the timing mechanism is rooted in the cells' biochemistry.
D) All of the above.

Accepted Answer

All the statements support the idea that the biological clock's accuracy despite temperature changes is notable and contrasts with typical biochemical reactions' temperature sensitivity, highlighting the uniqueness of biological clocks.

Question 7

An animal that is active primarily at dawn and dusk would be described as
A) clock-shifted.
B) crepuscular.
C) diurnal.
D) nocturnal.

Accepted Answer

Crepuscular animals are those that are active primarily during twilight, which includes dawn and dusk. This term specifically describes their activity patterns, differentiating them from diurnal (active during the day) and nocturnal (active at night) animals.

Question 8

The fiddler crab (Uca pugnax) alternates periods of activity with periods of quiescence every 12.4 hours. This pattern is typical of an animal whose activity cycles are synchronized with
A) days shortening and the temperature dropping.
B) neap tides.
C) the full moon.
D) tidal changes.

Accepted Answer

The fiddler crab's activity cycle of 12.4 hours aligns with the tidal changes, as this duration is close to the average time between two high tides or two low tides in most coastal areas, indicating its activities are synchronized with the ebb and flow of tides rather than lunar phases, temperature changes, or the length of days.

Question 9

Some birds experience significant changes in body mass and size of testes. These are changes that typically occur according to a(n)
A) annual rhythm.
B) daily rhythm.
C) lunar day rhythm.
D) monthly rhythm.

Accepted Answer

These changes in birds are typically associated with an annual rhythm, often in response to the changing seasons which affect breeding behaviors and physiological preparations for those periods.

Question 10

Welsh and colleagues (1995) removed neurons from the suprachiasmatic nuclei (SCN) of a newborn rat and grew them in a tissue culture. They then added tetrodotoxin, a chemical that prevents action potentials that require sodium ions. When the tetrodotoxin was washed out of the cells,
A) the firing rhythm reappeared, but the phase was disrupted by the 2.5 day application of tetrodotoxin.
B) the firing rhythm reappeared, with a phase predicted by the initial cycles.
C) the neurons failed to resume their original spontaneous rhythm in the rate of their firing.
D) the researchers found that the cells had died.

Accepted Answer

The firing rhythm of neurons from the suprachiasmatic nuclei (SCN) is intrinsic and can persist in isolation from the rest of the brain. When Welsh and colleagues removed these neurons and treated them with tetrodotoxin, which blocks action potentials, and then washed it out, the neurons resumed their firing rhythm. This demonstrates the resilience and autonomy of the SCN's circadian rhythm-generating mechanism, which can maintain its phase even after being temporarily halted.

Question 11

When an adult fruit file emerges from its pupal case, it does so during a short interval around dawn when the atmosphere is cool and moist, allowing the flies to expand their wings with a minimal loss of water. The procedure takes several hours to complete. The fruit fly is best exemplifying which of the following advantages of clock-controlled behavior?
A) anticipation of environmental change
B) continuous measurement of time
C) entrainment by environmental cycles
D) synchronization of behavior with an event that cannot be sensed directly

Accepted Answer

The fruit fly's emergence around dawn demonstrates anticipation of environmental change, as it takes advantage of the cool and moist conditions to expand its wings with minimal water loss.

Question 12

Honeybees fly to flowers for nectar that they have learned are open only during restricted times of the day, even though the flowers are far from the hive. The honeybees are best exemplifying which of the following advantages of clock-controlled behavior?
A) anticipation of environmental change
B) continuous measurement of time
C) entrainment by environmental cycles
D) synchronization of behavior with an event that cannot be sensed directly

Accepted Answer

The honeybees are synchronizing their behavior with the opening times of the flowers, which they cannot sense directly from the hive, indicating an internal clock mechanism.

Question 13

A worker honeybee indicates the direction to a nectar source through a dance that tells them of the proper flight bearing relative to the sun, even if the nectar source was discovered earlier in the day. The dancing bee is best exemplifying which of the following advantages of clock-controlled behavior?
A) anticipation of environmental change
B) continuous measurement of time
C) entrainment by environmental cycles
D) synchronization of behavior with an event that cannot be sensed directly

Accepted Answer

The dancing bee uses its internal clock to adjust the direction of the dance relative to the sun's position, which changes throughout the day. This demonstrates continuous measurement of time, allowing the bee to communicate the correct direction to the nectar source.

Question 14

DeCoursey and colleagues (1997) destroyed the SCN of some antelope ground squirrels (Ammospermophilus leucurus) and compared their survival rate outdoors to that of intact animals. They found that
A) a predatory cat killed 60% of the SCN-lesioned squirrels, but only 29% of the control animals.
B) both SCN-lesioned and control squirrels were active primarily during daylight.
C) the SCN-lesioned animals were more likely than control animals to be active on the ground surface at night.
D) all of the above.

Accepted Answer

DeCoursey and colleagues' study showed that SCN-lesioned squirrels had altered activity patterns, making them more vulnerable to predation at night, which is reflected in all the statements provided. The SCN (suprachiasmatic nucleus) is crucial for regulating circadian rhythms, and its destruction led to the squirrels being more active at times when they were more at risk, thus affecting their survival rates.

Question 15

DeCoursey and colleagues (2000) compared survival rates of three groups of eastern chipmunks (Tamias striatus): an SCN-lesioned group, a sham-lesioned group, and an intact, control group. They found that
A) activity levels among the three groups were surprisingly unaffected by the experimental treatments.
B) mortality rates due to predation were significantly higher in the SCN-lesioned group than in the other two.
C) the primary cause of mortality was malnutrition resulting from the SCN-lesioned group's failure to spend enough time foraging.
D) the sham-lesioned and the control groups died at higher rates than the SCN-lesioned group, demonstrating the benefit of the surgery for the SCN-lesioned group.

Accepted Answer

The SCN (suprachiasmatic nucleus) is involved in regulating circadian rhythms, which can affect an animal's behavior and its ability to avoid predators. Lesioning the SCN would disrupt these rhythms, potentially making the chipmunks more vulnerable to predation compared to those with intact or sham-lesioned SCN, leading to higher mortality rates in the SCN-lesioned group.

Question 16

Which of the following statements regarding biological clocks is FALSE?
A) A complex nervous system or endocrine system is an essential component of the biological clock.
B) The cells that make up tissues and organs often have their own independent clocks.
C) There are clocks scattered throughout an animal's body.
D) Unicellular organisms have biological clocks.

Accepted Answer

Biological clocks do not necessarily require a complex nervous system or endocrine system to function. Many organisms, including unicellular ones, have biological clocks that are based on cellular mechanisms rather than complex systems.

Question 17

Researchers from the laboratory headed by Hall and Kay have determined that fruit flies (Drosophila) have a multitude of independent biological clocks located throughout their bodies. They accomplished this by
A) being able to tell when the period (per) gene was turned on.
B) genetically engineering fruit flies to contain the firefly luciferase gene.
C) observing the molecular activity of important clock genes in a single, living, intact fly.
D) all of the above.

Accepted Answer

The correct answer is D because the researchers were able to determine the presence of multiple biological clocks in fruit flies by employing a combination of techniques: identifying when the period (per) gene was activated, genetically modifying fruit flies to contain the firefly luciferase gene, and observing the molecular activity of crucial clock genes in a single, living, intact fly. These approaches together allowed them to make their discovery.

Question 18

The experiments with glowing fruit flies demonstrated that
A) cultures of isolated fruit fly body parts, such as the head or thorax, did not glow rhythmically.
B) rhythmic per gene activity will synchronize with light-dark cycles, but cannot, by itself, maintain a free-running period length.
C) the glow rhythms continued in constant darkness with a free-running period length.
D) the thorax was the only body part in which the clocks remained synchronized in the prolonged absence of light.

Accepted Answer

The experiments showed that the glow rhythms, which are indicative of the per gene activity, continued even in constant darkness, demonstrating the ability of the internal clock to maintain a free-running period length without external cues.

Question 19

An individual animal may have many biological clocks scattered throughout its body.
A) Peripheral clocks, having the most direct contact with the surrounding environment, control the synchronization process with the master clock.
B) The clocks are placed so that information about the environment reaches each clock directly.
C) The many clocks must be synchronized so that all the rhythmic processes occur at the appropriate time relative to one another and the environment's cycles.
D) There is one master clock that must be entrained by the light-dark cycle, but the others are entrained by other cycles and typically run independently of one another.

Accepted Answer

The many clocks within an animal's body must be synchronized to ensure that all biological rhythms align properly with each other and with environmental cycles. This synchronization is crucial for the organism's overall functioning and adaptation to its surroundings.

Question 20

The photoreceptors for light entrainment in mammals are located in
A) a different part of the retina than the ones involved in vision.
B) cells that contain the photopigment melanopsin.
C) ganglion cells.
D) all of the above.

Accepted Answer

The photoreceptors for light entrainment in mammals are indeed located in a different part of the retina than those involved in vision, contain the photopigment melanopsin, and are found in ganglion cells. These specialized cells are crucial for regulating circadian rhythms in response to light.

Quiz 9: Biological Clocks

A defining characteristic of biological clock-controlled rhythms is that cycles

The period of a cycle in a laboratory setting is usually more consistent than that in nature; this difference is described with the prefix circa. Thus, a cycle that would coincide approximately with a lunar day would be described as being

Entraining a biological clock means

If a nocturnal laboratory subject that is being maintained under conditions of constant darkness experiences a brief light pulse early during its circadian night, it will

Entrainment of the biological clock is especially important for animals living

The biological clock remains accurate in spite of large changes in environmental temperature.

An animal that is active primarily at dawn and dusk would be described as

The fiddler crab (Uca pugnax) alternates periods of activity with periods of quiescence every 12.4 hours. This pattern is typical of an animal whose activity cycles are synchronized with

Some birds experience significant changes in body mass and size of testes. These are changes that typically occur according to a(n)

Welsh and colleagues (1995) removed neurons from the suprachiasmatic nuclei (SCN) of a newborn rat and grew them in a tissue culture. They then added tetrodotoxin, a chemical that prevents action potentials that require sodium ions. When the tetrodotoxin was washed out of the cells,

Honeybees fly to flowers for nectar that they have learned are open only during restricted times of the day, even though the flowers are far from the hive. The honeybees are best exemplifying which of the following advantages of clock-controlled behavior?

DeCoursey and colleagues (1997) destroyed the SCN of some antelope ground squirrels (Ammospermophilus leucurus) and compared their survival rate outdoors to that of intact animals. They found that

DeCoursey and colleagues (2000) compared survival rates of three groups of eastern chipmunks (Tamias striatus) : an SCN-lesioned group, a sham-lesioned group, and an intact, control group. They found that

Which of the following statements regarding biological clocks is FALSE?

Researchers from the laboratory headed by Hall and Kay have determined that fruit flies (Drosophila) have a multitude of independent biological clocks located throughout their bodies. They accomplished this by

The experiments with glowing fruit flies demonstrated that

An individual animal may have many biological clocks scattered throughout its body.

The photoreceptors for light entrainment in mammals are located in