Difficulty: Mixed
How long is a typical circadian cycle?
A About 24 hours
B About 12 hours
C Exactly one week
D About 90 minutes
Answer: A. About 24 hours Circadian rhythms are daily cycles that usually repeat about every 24 hours.
Which environmental cue most strongly resets the body clock?
A Room color
B Light and darkness
C Meal size alone
D Shoe pressure
Answer: B. Light and darkness The light-dark cycle is the strongest external cue for circadian timing.
Where is the human master clock located?
A Cerebellum
B Pituitary gland
C Suprachiasmatic nucleus
D Spinal cord
Answer: C. Suprachiasmatic nucleus The suprachiasmatic nucleus, or SCN, coordinates the central circadian clock.
Which sense carries daytime light cues to the clock?
A Taste
B Smell alone
C Touch alone
D Vision through the eyes
Answer: D. Vision through the eyes Light information received through the eyes helps align the clock with day and night.
What does melatonin mainly signal in the evening?
A Begin digestion
B Prepare for sleep
C Raise alertness
D Build muscle
Answer: B. Prepare for sleep Melatonin rises in darkness and signals that the body should prepare for sleep.
Which hormone naturally helps prepare the body to wake?
A Cortisol
B Insulin
C Melatonin
D Growth hormone
Answer: A. Cortisol Cortisol follows a daily rhythm and naturally helps prepare the body to wake.
Why can bright evening light delay sleepiness?
A It stops digestion
B It lowers body temperature instantly
C It ends REM sleep
D It can suppress melatonin
Answer: D. It can suppress melatonin Bright artificial light late in the evening can disrupt melatonin release.
What is an example of a circadian rhythm?
A A knee reflex
B A single sneeze
C Daily sleep-wake timing
D A broken bone
Answer: C. Daily sleep-wake timing Sleep-wake timing is one of the body’s daily circadian rhythms.
Besides sleep, which process follows circadian timing?
A Hormone release
B Hair length each minute
C Bone shape overnight
D A single cough
Answer: A. Hormone release Circadian rhythms influence hormone release as well as sleep, appetite, and temperature.
Which phrase best describes a chronotype?
A A sleep-stage count
B Natural timing preference
C A meal nutrient
D A breathing rate
Answer: B. Natural timing preference Chronotype describes a person’s tendency toward earlier or later daily timing.
Someone who naturally prefers earlier bedtimes may be called what?
A A late chronotype
B A sleep stage
C An early chronotype
D A light sensor
Answer: C. An early chronotype Early chronotypes tend to feel ready for sleep and wake earlier.
What may shift the body clock later in the evening?
A A dark quiet room
B Morning daylight
C A regular wake time
D Bright artificial light
Answer: D. Bright artificial light Late bright light can delay circadian signals that support sleep.
Which daily habit can support stable circadian timing?
A Changing bedtime hourly
B Skipping daylight
C Consistent wake time
D Sleeping at random times
Answer: C. Consistent wake time Keeping a regular sleep and wake schedule gives the body clock predictable cues.
How can morning daylight help the sleep-wake rhythm?
A It removes sleep need
B It reinforces daytime timing
C It stops melatonin forever
D It replaces nighttime sleep
Answer: B. It reinforces daytime timing Daytime light helps synchronize the internal clock with the local day.
What can happen when local time changes after a long flight?
A Temporary circadian misalignment
B Instant clock reset
C Permanent loss of REM
D No body response
Answer: A. Temporary circadian misalignment Travel across time zones can leave the body clock temporarily out of sync with local time.
Which experience commonly follows rapid travel across time zones?
A Sleep apnea
B Night terror
C Sleepwalking
D Jet lag
Answer: D. Jet lag Jet lag is a temporary mismatch between internal timing and the destination’s day-night schedule.
Why may night-shift work challenge circadian timing?
A Work conflicts with night biology
B It removes all sleep stages
C It changes eye color
D It prevents all hormone release
Answer: A. Work conflicts with night biology Working at night can conflict with the body’s usual day-active, night-sleep timing.
What does entrainment mean for a body clock?
A A sleep stage
B Synchronization with time cues
C A type of dream
D A meal plan
Answer: B. Synchronization with time cues Entrainment is the alignment of biological rhythms with environmental time cues.
Which cue can influence circadian rhythms besides light?
A Hair color
B Handedness
C Meal timing
D Foot size
Answer: C. Meal timing Food intake, activity, stress, and social cues can also affect circadian rhythms.
What is the SCN’s broader role?
A Digest proteins
B Filter blood
C Control bones
D Coordinate body clocks
Answer: D. Coordinate body clocks The SCN helps synchronize circadian rhythms across organs and tissues.
Which pattern may be natural for many teenagers?
A No circadian rhythm
B Permanent daytime sleep
C No need for sleep
D Later sleep timing
Answer: D. Later sleep timing Many teens naturally prefer later bedtimes and later morning sleep than adults.
What can irregular sleep timing do to daily rhythms?
A Guarantee deeper sleep
B Prevent all awakenings
C Make timing less consistent
D Erase body clocks
Answer: C. Make timing less consistent Irregular schedules can make it harder to keep sleep timing aligned with daily cues.
Which phrase describes being out of sync with local day and night?
A Sleep inertia
B Circadian misalignment
C Dream recall
D Muscle fatigue
Answer: B. Circadian misalignment Circadian misalignment means internal timing does not match the surrounding environment.
What does the body clock help regulate?
A Sleep and wake timing
B Only breathing
C Only digestion
D Only vision
Answer: A. Sleep and wake timing The central clock helps determine when the body feels awake or ready for sleep.
Why are regular daytime activities useful as time cues?
A They stop aging
B They reinforce daily patterns
C They cancel darkness
D They prevent all stress
Answer: B. They reinforce daily patterns Regular routines provide predictable cues that can support circadian alignment.
What does the body do with daylight information?
A Creates the sun
B Stops all hormones
C Ends sleep pressure
D Aligns internal timing
Answer: D. Aligns internal timing Light information helps the brain align internal timing with the external day.
Can every person’s internal clock have identical timing?
A Yes, exactly alike
B Only in summer
C No, natural timing varies
D Only during sleep
Answer: C. No, natural timing varies People differ in natural timing and chronotype.
Which behavior may make evening sleep harder?
A Late bright screen exposure
B Morning outdoor light
C Regular daytime activity
D A quiet bedtime routine
Answer: A. Late bright screen exposure Bright screen light late in the evening can interfere with circadian preparation for sleep.
What may happen to melatonin as darkness begins?
A Its release can increase
B It disappears permanently
C It becomes cortisol
D It blocks all dreams
Answer: A. Its release can increase The dark phase supports the evening rise in melatonin.
Why is the circadian system called an internal clock?
A It displays the time
B It counts sleep stages only
C It organizes daily timing
D It measures room temperature
Answer: C. It organizes daily timing Circadian clocks coordinate recurring daily patterns in body functions.
Which part of the day generally provides a strong light cue?
A Midnight darkness
B A closed drawer
C A dim closet
D Morning daylight
Answer: D. Morning daylight Daylight, especially during daytime, helps keep the internal clock aligned.
What can late-night light signal to the brain?
A That a meal is finished
B That it is still daytime
C That deep sleep began
D That the body is dehydrated
Answer: B. That it is still daytime Bright artificial light can act as a false daytime cue.
Which factor may affect a person’s natural sleep timing?
A Shoe size
B Eye color
C Age
D Handwriting
Answer: C. Age Circadian timing can vary with age, and many teens naturally prefer later timing.
How do body clocks across organs work together?
A They never interact
B The master clock coordinates them
C The lungs control all clocks
D They follow meal size only
Answer: B. The master clock coordinates them The SCN serves as a master clock coordinating rhythms in other tissues.
Which schedule gives circadian cues more predictability?
A Changing sleep times daily
B Bright light at midnight
C Random meal timing
D Similar daily sleep times
Answer: D. Similar daily sleep times Regular sleep and wake times provide consistent timing cues.
Why may light at night affect sleep timing?
A It changes clock signals
B It measures sleep stages
C It guarantees alertness tomorrow
D It eliminates sleep pressure
Answer: A. It changes clock signals Light is a potent environmental signal and nighttime exposure can disrupt circadian timing.
Which statement about circadian rhythms is accurate?
A They involve only the eyes
B They occur across body systems
C They stop during sleep
D They last one minute
Answer: B. They occur across body systems Nearly every tissue and organ has daily rhythms coordinated with the day-night cycle.
What is one possible effect of circadian disruption?
A Difficulty sleeping at usual times
B Permanent blindness
C Instant memory loss
D No effect on alertness
Answer: A. Difficulty sleeping at usual times Misaligned rhythms may cause difficulty sleeping and reduced daytime alertness.
Should someone self-prescribe bright-light treatment for a disorder?
A Use any lamp at night
B Avoid all daylight
C Change schedules hourly
D Discuss treatment with a clinician
Answer: D. Discuss treatment with a clinician Light therapy timing depends on the condition; a healthcare professional can guide its use.
When can bright artificial light be especially disruptive?
A During a bright morning
B At midday outdoors
C Late in the evening
D After waking at dawn
Answer: C. Late in the evening Late-evening bright light can delay melatonin release and sleep preparation.
What is the relationship between darkness and sleep signaling?
A Darkness creates adenosine instantly
B Darkness stops all hormones
C Darkness causes jet lag
D Darkness supports melatonin release
Answer: D. Darkness supports melatonin release Dark conditions support the evening rise of melatonin.
Which statement describes biological rhythms broadly?
A Recurring changes in body activity
B One-time reflexes
C Random events only
D Permanent body traits
Answer: A. Recurring changes in body activity Biological rhythms are recurring patterns in physical, mental, or behavioral activity.
How can a steady meal schedule help some shift workers?
A It cures every disorder
B It adds a regular cue
C It replaces sleep
D It blocks light
Answer: B. It adds a regular cue Regular meal timing is one routine cue that may support circadian management.
What does internal circadian timing respond to?
A Only spoken language
B Only exercise intensity
C Environmental time cues
D Only room furniture
Answer: C. Environmental time cues Light, darkness, food, activity, and other cues help synchronize internal clocks.
Which statement about circadian rhythms and digestion is correct?
A Digestion has daily timing
B Digestion stops at night
C Only sleep has rhythms
D Meals erase rhythms
Answer: A. Digestion has daily timing Circadian timing can influence appetite and digestion as well as sleep.
Why can weekend schedule shifts cause difficulty Monday?
A They add extra sleep stages
B They stop body clocks
C They remove morning light
D Timing may shift from weekdays
Answer: D. Timing may shift from weekdays Large changes between weekday and weekend schedules can shift sleep timing and make readjustment harder.
What is a sensible first step for a steadier sleep-wake rhythm?
A Use bright light at midnight
B Skip all outdoor light
C Keep a regular daily schedule
D Vary wake time widely
Answer: C. Keep a regular daily schedule A consistent daily routine, including sleep and wake times, can support circadian alignment.
Which source is the strongest natural daytime time cue?
A A phone alarm
B Sunlight
C A room fragrance
D A quiet pillow
Answer: B. Sunlight Sunlight is a strong environmental cue that helps synchronize daily rhythms.
Can circadian timing affect alertness during the day?
A No, alertness never varies
B Yes, alertness follows daily rhythms
C Only during dreams
D Only after meals
Answer: B. Yes, alertness follows daily rhythms Circadian rhythms affect sleepiness and alertness across the day.
What is a key takeaway about the body clock?
A It controls only dreams
B It follows no daily cycle
C Light and routines shape timing
D It is a wristwatch
Answer: C. Light and routines shape timing Light and regular daily cues help synchronize the body’s internal timing.