Deck 9: Biological Clocks

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.

Answer 1

continue in the absence of environmental cues such as light-dark and temperature cycles.

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

Answer 2

circalunidian

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.

Answer 3

resetting it to synchronize with a particular environmental 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.

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.

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.

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.

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.

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.

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.

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

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

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

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.

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.

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.

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.

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.

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.

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.

Question 21

When the SCN was isolated from neural input by a knife cut that created an island of hypothalamic tissue, the neural activity in the hypothalamic island

A) remained continuous in constant darkness, failing to support the idea that the SCN is the master clock.
B) remained continuous in constant darkness, providing support for the idea that the SCN is the master clock.
C) remained rhythmic in constant darkness, failing to support the idea that the SCN is the master clock.
D) remained rhythmic in constant darkness, providing support for the idea that the SCN is the master clock.

Question 22

The genetic basis for the circadian cycle involves a loop of gene activity: the Clock/Bmal1 complex turns on the activity of both per and cry genes; products from these bind with a protein product of the tau gene; the per/cry/tau complex suppresses the action of the Clock/Bmal1 complex, etc. This cycle takes about _____ hour(s) to complete.

A) 1
B) 4
C) 12
D) 24

Question 23

Silver and colleagues (1996) conducted transplant experiments in which hamster donor SCN tissue was enclosed within a capsule before being transplanted into a host hamster whose clocks ran at different rates.

A) The capsule allowed neural processes to grow, but did not allow nutrients and diffusible molecules to flow between the host and graft tissue.
B) The destruction of the SCN in the host animal prior to transplant made it highly rhythmic.
C) The encapsulated grafts restored the activity rhythm in the host, with the period length characteristic of the donor SCN.
D) The study demonstrated that the animals' activity rhythms are caused by the SCN sending signals over neural pathways.

Question 24

In mammals, the rhythmic production of two hormones, _______, are thought to be important in entraining peripheral oscillators.

A) cortisol and testosterone
B) estrogen and testosterone
C) melatonin and cortisol
D) melatonin and estrogen

Question 25

Humans can travel across time zones faster than our biological clock can reset to the new local time. This causes problems because

A) one's body time may be out of phase with local time, and different body rhythms may be peaking at inappropriate times relative to one another.
B) people traveling west are affected by jet lag, but those traveling east usually are not, creating difficulties in social interactions within the newly formed group.
C) physiological processes may be severely disrupted, interfering with mental process that otherwise typically remain unaffected.
D) the resetting to a new day-night cycle may require several hours to complete.

Question 26

If you have asthma, you are most likely to suffer an attack

A) at unpredictable times, because your SCN is malfunctioning.
B) between 6 a.m. and noon.
C) between noon and 6 p.m.
D) during the night.