October  2012  

  1    

What  makes  me  tick…tock?  Circadian  rhythms,  genetics  and  health  

Lesson  5:  How  do  environment  and  modern  society  influence  our  rhythms?  

I.  Overview  In  this  lesson,  students  apply  what  they  have  learned  about  circadian  processes  to  issues  relevant  to  human  light  exposure,  species  biology  and  ecology.  Students  use  light  meters  to  examine  light  exposure  differences  around  their  school  to  illustrate  the  possible  influences  of  habitat/workplace  on  light  exposure.  Students  read  and  discuss  a  series  of  short  articles  that  exemplify  the  interaction  between  environment  and  circadian  rhythms.  Students  develop  a  scientific  explanation  to  answer  the  question:  Does  environment  influence  circadian  rhythms?  Through  these  activities,  students  explore  how  cues  from  the  environment  entrain  their  biological  daily  clocks.  In  addition,  they  examine  examples  of  how  endogenous  circadian  clocks  in  different  species  have  adapted  over  time  to  allow  the  species  to  survive  in  their  light  environment.  

Connections  to  the  Driving  Question  In  this  lesson,  students  investigate  how  the  environment,  particularly  exposure  to  light,  can  affect  the  circadian  rhythm.  Students  look  at  external  cues  that  can  cause  changes  to  the  circadian  rhythm,  as  opposed  to  internal  gene  and  protein  expression  studied  in  previous  lessons.  

Connections  to  the  Previous  Lesson  In  the  previous  lesson,  students  examine  how  changes  to  one’s  internal  structures,  such  as  DNA  and  protein,  lead  to  changes  in  sleep  patterns.  Now,  students  look  at  how  light  exposure  can  affect  both  humans’  and  animals’  circadian  rhythms.  This  is  an  external  cue,  or  zeitgeiber  that  has  caused  the  animals  to  evolve  in  a  particular  direction  to  be  better  suited  for  their  environment.  Thus,  the  external  environment  selected  for  particular  gene  expression,  leading  to  changes  in  the  animals’  internal  clock.  

II.  Standards/  Benchmarks  

National  Science  Education  Standards  

Content  Standard  C:  The  Behavior  of  Organisms  • Organisms  have  behavioral  responses  to  internal  changes  and  to  external  stimuli.  Responses  to  

external  stimuli  can  result  from  interactions  with  the  organism’s  own  species  and  others,  as  well  as  environmental  changes;  these  responses  either  can  be  innate  or  learned.  The  broad  patterns  of  behavior  exhibited  by  animals  have  evolved  to  ensure  reproductive  success.  Animals  often  

    October  2012  

  2    

live  in  unpredictable  environments,  and  so  their  behavior  must  be  flexible  enough  to  deal  with  uncertainty  and  change.  Plants  also  respond  to  stimuli.  (9–12  C:  6/2)  

• Behavioral  biology  has  implications  for  humans,  as  it  provides  links  to  psychology,  sociology,  and  anthropology.  (9–12  C:  6/4)  

Content  Standard  A:  Abilities  Necessary  to  Do  Scientific  Inquiry  • Identify  questions  and  concepts  that  guide  scientific  investigations.  Students  should  form  a  

testable  hypothesis  and  demonstrate  the  logical  connections  between  the  scientific  concepts  guiding  a  hypothesis  and  the  design  of  an  experiment.  They  should  demonstrate  appropriate  procedures,  a  knowledge  base,  and  conceptual  understanding  of  scientific  investigations.  (9–12  A:  1/1)  

• Design  and  conduct  scientific  investigations.  Designing  and  conducting  a  scientific  investigation  requires  introduction  to  the  major  concepts  in  the  area  being  investigated,  proper  equipment,  safety  precautions,  assistance  with  methodological  problems,  recommendations  for  use  of  technologies,  clarification  of  ideas  that  guide  the  inquiry,  and  scientific  knowledge  obtained  from  sources  other  than  the  actual  investigation.  The  investigation  may  also  require  student  clarification  of  the  question,  method,  controls,  and  variables;  student  organization  and  display  of  data;  student  revision  of  methods  and  explanations;  and  a  public  presentation  of  the  results  with  a  critical  response  from  peers.  Regardless  of  the  scientific  investigation  performed,  students  must  use  evidence,  apply  logic,  and  construct  an  argument  for  their  proposed  explanations.  (9–12  A:  1/2)  

• Use  technology  and  mathematics  to  improve  investigations  and  communications.  A  variety  of  technologies,  such  as  hand  tools,  measuring  instruments,  and  calculators,  should  be  an  integral  component  of  scientific  investigations.  The  use  of  computers  for  the  collection,  analysis,  and  display  of  data  is  also  a  part  of  this  standard.  Mathematics  plays  an  essential  role  in  all  aspects  of  an  inquiry.  For  example,  measurement  is  used  for  posing  questions,  formulas  are  used  for  developing  explanations,  and  charts  and  graphs  are  used  for  communicating  results.  (9–12  A:  1/3)  

Content  Standard  A:  Understanding  about  Scientific  Inquiry  • Scientists  rely  on  technology  to  enhance  the  gathering  and  manipulation  of  data.  New  

techniques  and  tools  provide  new  evidence  to  guide  inquiry  and  new  methods  to  gather  data,  thereby  contributing  to  the  advance  of  science.  The  accuracy  and  precision  of  the  data,  and  therefore  the  quality  of  the  exploration,  depends  on  the  technology  used.  (9–12  A:  2/3)  

• Scientific  explanation  must  adhere  to  criteria  such  as:  a  proposed  explanation  must  be  logically  consistent;  it  must  abide  by  the  rules  of  evidence;  it  must  be  open  to  questions  and  possible  modification;  and  it  must  be  based  on  historical  and  current  scientific  knowledge.  (9–12  A:2/5)  

• Results  of  scientific  inquiry  —  new  knowledge  and  methods  —  emerge  from  different  types  of  investigations  and  public  communication  among  scientists.  In  communicating  and  defending  the  results  of  scientific  inquiry,  arguments  must  be  logical  and  demonstrate  connections  between  natural  phenomena,  investigations,  and  the  historical  body  of  scientific  knowledge.  In  addition,  

    October  2012  

  3    

the  methods  and  procedures  that  scientists  used  to  obtain  evidence  must  be  clearly  reported  to  enhance  opportunities  for  further  investigation.  (9–12  A:  2/6)  

III.  Learning  Objectives    

Learning  Objectives   Assessment  Criteria   Location  in  Lesson  Explain  how  circadian  processes  are  vital  to  all  forms  of  life  (Why  do  we  have  circadian  rhythms?)  

Circadian  rhythms  are  necessary  for  survival  to  signal  when  it  is  time  to  eat,  the  availability  of  food,  when  to  sleep,  the  presence  of  predators,  and  the  need  to  release  waste.  

Opening  of  Lesson  

Describe  the  impact  that  modern  society  (light  exposure)  has  on  endogenous  timekeeping  

Because  light  exposure  is  pervasive  in  modern  society,  that  is,  it  is  rarely  completely  dark  when  it  is  night  time,  some  humans  experience  disruptions  in  their  sleep  patterns.  The  internal  cues  that  signal  when  it  is  time  to  eat,  sleep,  etc.  rely  on  external  exposure  to  light.  So,  when  the  external  cues  change,  the  internal  clock  can  also  change.    

Activities  1  and  2  

Use  a  light  intensity  meter  to  measure  luminance  at  different  locations    

Students  place  the  light  meter  probe  at  an  area  they  want  to  measure.  They  then  record  the  amount  of  light  in  lux  in  a  data  table  that  they  have  created  prior  to  collecting  the  data.    

Activity  1  

Illustrate  the  impact  that  animal  habitat  has  on  circadian  rhythms    

In  the  readings,  all  of  the  animals’  circadian  rhythms  were  influenced  by  their  natural  habitats.  Due  to  the  ever-­‐changing  light  exposure  for  the  reindeer  in  their  natural  habitat,  they  do  not  have  suprachiasmatic  nuclei  to  help  them  keep  an  internal  clock.  The  mosquitoes’  subjective  day  length  directly  correlated  to  the  length  of  day  in  their  natural  habitat.  The  Collembolans  insect  is  not  exposed  to  any  light  so  its  cycle  of  molting  and  reproducing  is  dependent  on  the  end  of  one  action  to  trigger  the  start  of  the  next  action.  Finally,  the  sled  dogs’  melatonin  levels  varied  depending  on  which  latitude  

Activity  2  

    October  2012  

  4    

they  naturally  live  as  well  as  their  amount  of  exercise.  Melatonin  production  increases  at  dusk  and  is  inhibited  by  light,  signaling  the  time  to  rest.  The  dogs  that  live  further  north,  and  thus  have  more  varied  light  exposure,  have  lower  melatonin  levels.  This  reduces  their  sensitivity  to  light,  making  it  easier  to  rest  when  there  are  long  daylight  hours.  When  dogs  are  training,  their  melatonin  levels  are  also  reduced.    

 

IV.  Adaptations/  Accommodations  This  lesson  can  be  adapted  to  emphasize  the  impact  of  light  exposure  on  human  health  (Activity  1)  and  biological  function.  The  interaction  between  human  light  exposure  and  behavior  (sleep-­‐wake  cycle)  is  an  accessible  example  of  environmental  impact  on  human  behavior.  Further,  this  activity  addresses  how  this  paradigm  has  changed  over  time  with  exposure  to  artificial  light  at  night  and  the  impacts  on  human  health.  However,  this  lesson  further  describes  how  circadian  processes  of  all  species  are  affected  by  their  natural  habitat  and  can  therefore  be  adapted  for  ecology  or  environmental  science  classes.  The  fundamental  objective  is  to  reconcile  circadian  patterns  in  different  species  with  their  habitat  to  understand  how  environment  and  behavior  interact.  

This  activity  can  be  adapted  so  that  it  can  be  done  within  the  classroom.  These  ideas  could  be  particularly  useful  if  there  are  a  limited  number  of  light  intensity  meters  available.  The  class  can  measure  the  light  intensity  within  the  classroom  at  different  times  of  the  day.  This  can  also  be  carried  on  throughout  the  school  year  to  determine  if  there  are  differences  in  light  intensity  depending  on  the  season.  The  class  could  also  measure  the  light  in  different  parts  of  the  room,  such  as  near  the  window  and  by  the  door.  Again,  the  goal  is  to  demonstrate  that  light  intensity  does  change  with  the  environment.    

One  possible  extension  of  this  activity  is  to  have  some  students  take  the  light  sensors  to  various  places  in  the  community.  They  can  test  the  light  inside  certain  locations  and  outside  others.  These  students  will  keep  record  of  their  data  and  will  present  their  findings  to  the  rest  of  this  class.  Based  on  these  results,  new  discussions  about  light  and  the  environment  may  emerge.    

Activity  2  can  be  adapted  to  include  alternate  readings  or  be  presented  in  a  different  form.  Readings  may  be  assigned  as  homework  or  as  stations  in  the  classroom,  as  time  permits.  

V.  Timeframe  for  activity  

    October  2012  

  5    

Opening  of  Lesson  • Introduction  to  Modern  Society/Environment  and  Circadian  Rhythms  –  10  minutes  

Main  Part  of  Lesson  • Activity  1:  Light  Intensity  Data  Collection  –  40  minutes  • Activity  2:  Do  circadian  rhythms  depend  on  habitat?  –  40  minutes  

Conclusion  of  Lesson  • Wrap-­‐Up  Discussion  –  10  minutes  

VI.  Advanced  Preparation  and  Materials  

Activity  1:  Light  Intensity  Data  Collection  

Materials:  • Light  meters  and  accompanying  electronics  (1/group  of  3-­‐4  students)  • Copies  of  the  Epworth  Sleepiness  Scale  questions  (if  students  interview  school  personnel)  

Preparation:    • Locate  necessary  materials  and  determine  how  to  use  them  properly  so  that  a  thorough  

explanation  can  be  given  to  students.    • Speak  with  other  staff  members  to  determine  those  that  would  be  willing  and  available  to  be  

“interviewed”  by  the  students.    

Activity  2:  Do  circadian  rhythms  depend  on  habitat?  

Materials:  • Copies  of  the  readings  and  guided  reading  questions  

o Rhythms  without  Light,  U3_L5_Reading_RhythmsWithoutLight.docx  o Lessons  from  Mosquitos,  U3_L5_Reading_LessonsFromMosquitos.docx  o Sled  Dogs  and  Exercise,  U3_L5_Reading_SledDogsAndExercise.docx  o How  do  Reindeer  Tell  Time,  U3_L5_Reading_HowDoReindeerTellTime.docx  

Preparation:  • Each  student  will  receive  one  copy  of  the  article  with  guided  reading  questions  assigned  to  their  

“expert”  group  to  work  on  before  moving  in  to  their  “jigsaw”  group.    

Homework  and  Assessments  • Readings  on  different  habitats  with  accompanying  Guided  Reading  Questions  

o U3_L5_Reading_RhythmsWithoutLight.docx  o U3_L5_Reading_LessonsFromMosquitos.docx  o U3_L5_Reading_SledDogsAndExercise.docx  

    October  2012  

  6    

o U3_L5_Reading_HowDoReindeerTellTime.docx  • Homework  reading  on  night  shifts  and  their  effects  on  health,  

U3_L5_Homework_AreNightShiftsBadForYou.docx  

VII.  Resources  and  References  • Maps  of  artificial  night-­‐sky  brightness:  http://www.lightpollution.it/worldatlas/pages/fig1.htm  • The  National  Park  Service  has  information  about  the  habitat  impact  of  artificial  light  

http://www.nps.gov/grsm/naturescience/dff509-­‐focuspartner1.htm    

   

    October  2012  

  7    

VIII.  Lesson  Implementation  

Opening  of  lesson:  Open  the  lesson  with  a  discussion  abut  why  measuring  light  intensity  is  of  interest  in  circadian  biology  and  ecology.  Ask  students  to  recall  from  previous  lessons  what  factors  influence  circadian  rhythms.  

• Why  do  you  wake  up  in  the  morning?  o Students  may  mention:  light,  alarm  clocks,  parents,  school  or  work  schedules,  their  

genes,  feeling  hungry  or  needing  to  go  to  the  bathroom,  social  activities.  Separate  this  list  into  two  categories:  internal  cues  and  external  cues.  

• What  factors  determine  animal  circadian  rhythms?  o These  are  the  same  factors  as  mentioned  above;  in  addition,  students  can  include  the  

availability  of  food,  the  presence  of  predators.  By  now,  students  should  understand  that  both  internal  factors:  such  as  genetics,  and  external  factors,  such  as  light,  influence  both  human  and  animals’  rhythms.  

 

Teacher  Content  Knowledge  At  this  stage  in  the  unit  students  should  have  a  working  definition  of  Circadian  Rhythms  as  they  relate  to  their  own  lives  and  to  the  models  they  have  worked  with  in  the  unit.  For  review,  the  criteria  for  Circadian  Rhythms  includes:  

1.  Persist  in  the  absence  of  periodic  cues  or  external  influence.  Consider  as  an  example,  the  sleep  wake  rhythm  of  a  person  living  in  a  cave.  There  are  no  longer  external  light  cues,  yet  approximate  24-­‐hour  rhythms  remain.  

2.  Retain  nearly  24-­‐hour  period  even  when  the  environment  oscillates  to  a  different  period.  To  a  certain  extent,  this  is  what  is  happening  in  the  winter  when  length  of  day-­‐light  decreases,  yet  duration  of  human  daily  activity  remains  approximately  constant.  In  animal  models,  in  a  very  short  light-­‐dark  cycle  (4  hours  on,  4  hours  off,  for  example)  mice  will  maintain  activity-­‐rest  patterns  with  about  24  hour  rhythms.  

3.  Change  phase  slowly  after  an  abrupt  change  in  the  environment  to  a  new  phase.  A  human  example  of  this  is  jet-­‐lag.  The  external  environment  has  changed,  and  it  takes  a  couple  days  for  people  to  adjust  their  own  rhythms.  

 

This  lesson  will  focus  on  one  of  the  most  powerful  of  these  external  factors:  Light.  This  lesson  explores  the  effects  of  light  exposure  on  human  health  and  on  animal  behavior.    

    October  2012  

  8    

Show  students  the  image  of  the  world  at  night  (Figure  1).  And  ask  students  to  compare  this  image  to  what  the  world  would  have  looked  like  before  the  widespread  use  of  electrical  lighting.  Ask  the  students:  

• What  might  have  caused  these  differences?    • What  are  the  implications  of  this  change?  

 

 

Figure  1:  Image  of  the  earth  at  night:  light  from  unnatural  sources.  Source:  Astronomy  picture  of  the  day,  http://antwrp.gsfc.nasa.gov/apod/ap001127.html  

 

Teacher  Content  Knowledge  In  1800,  there  would  have  been  very  little  “light  at  night”  because  there  was  no  electricity.  Human  daily  patterns  would  have  followed  the  pattern  of  their  environment:  working  while  it  was  light,  and  resting  when  it  was  dark.  Modern  society  is  very  different;  people  work  late  into  the  night,  or  only  at  night.  In  the  United  States,  many  factories  have  night  shifts  and  stores  may  be  open  24  hours  a  day.  

The  availability  of  light  at  night  has  changed  the  patterns  of  human  behavior:  people  are  not  limited  to  a  daily  cycle  that  relies  on  natural  light  from  the  sun.  In  addition  to  the  changing  patterns  of  sleep-­‐wake  activity,  the  exposure  to  light  has  changed  over  time.  Especially  near  large  cities,  it  is  almost  never  completely  dark.  Streetlights  and  shop  signs  are  on  all  night.    

Some  epidemiologists  believe  that  this  light  exposure  is  impacting  human  circadian  rhythms  and  may  lead  to  some  health  problems,  like  increased  risk  for  some  cancers.  

    October  2012  

  9    

Recently,  Denmark  recognized  shift  work  as  a  probable  carcinogen.  Shift  workers,  people  who  work  during  the  night,  are  exposed  to  light  at  night.  Corresponding  to  this  exposure  is  a  decrease  in  the  hormone,  melatonin,  which  is  the  body’s  cue  to  get  sleepy.  In  this  situation,  the  internal  circadian  clock  is  at  odds  with  the  environmental  cues.  Clinicians  and  scientists  are  beginning  to  understand  more  about  the  biological  mechanisms  of  the  impacts  on  health,  mood,  and  behavior  in  these  paradigms.  The  impacts  of  circadian  disruption  on  human  health  will  be  discussed  in  Lesson  6.  

“Light  Pollution”  may  also  impact  the  environment:  migration  and  predator/prey  relationships  can  be  altered  by  light  exposure.  The  National  Park  Service  has  more  information  about  the  habitat  impact  of  artificial  light  (http://www.nps.gov/grsm/naturescience/dff509-­‐focuspartner1.htm).    

 

Share  with  students  that  today  they  will  conduct  an  experiment  where  they  measure  the  amount  of  light  in  their  own  environment,  including  common  places  around  the  school.  With  this,  they  will  observe  how  the  absence  or  presence  of  light  affects  their  sleepiness  throughout  the  day.  

Main  Part  of  Lesson:  

Activity  1:  Light  Intensity  Data  Collection  To  introduce  the  activity,  ask  students  the  following  questions  to  engage  in  a  discussion  about  how  people  can  measure  light  exposure:  

• How  does  light  exposure  differ  in  different  environments?    • How  does  our  exposure  to  light  change  throughout  the  day?    • How  does  our  exposure  change  throughout  the  year?  • Why  does  light  exposure  matter?  • How  can  we  measure  exposure  to  light?  

In  the  discussion,  light  exposure  can  be  discussed  at  a  global  level,  but  the  discussion  should  be  directed  towards  students’  lives  and  locations  they  encounter  on  a  typical  school  day.  For  example,  does  the  exposure  of  light  differ  for  people  in  classrooms  with  windows,  compared  to  people  in  the  gym  or  cafeteria,  where  there  are  often  no  windows?    

Tell  students  that  they  will  travel  around  the  school  measuring  the  light  intensity  in  different  areas.  They  will  also  interview  people  in  each  area  to  learn  more  about  their  daily  patterns  of  activity.  With  this  data,  they  will  begin  to  draw  conclusions  about  light  exposure  and  its  correlation  to  circadian  rhythms.    

Show  students  what  a  light  meter  looks  like  and  demonstrate  how  it  is  to  be  

    October  2012  

  10    

used.  It  is  important  that  the  students  determine  what  settings  should  be  used  and  how  many  decimal  places  the  values  should  have.  

Discuss  as  a  class  what  areas  student  will  go  to  test  light  intensity:  

• Where  is  a  good  place  to  go  that  does  not  have  much  light?  • Where  is  a  place  that  has  a  lot  of  light?  • What  about  the  differences  between  natural  light  and  artificial  light?  

A  variety  of  areas  with  different  amounts  of  light  and  numbers  of  windows  should  be  identified.  Before  going  and  collecting  data,  students  need  to  make  predictions  and  develop  hypotheses  about  what  they  think  they  will  find:  

• Which  areas  will  have  the  greatest  light  intensity  measurement?  The  lowest?  • Will  this  have  an  effect  on  the  people  working  in  these  areas?  • If  so,  what  kind  of  effect  will  it  have?  

Using  the  questions  and  areas  discussed,  create  a  data  table  that  students  will  use  to  record  their  observations  and  data.  Have  students  identify  categories  that  should  be  included  in  the  tables.  They  will  then  record  the  light  intensity  in  lux,  the  SI  unit  for  luminous  flux,  or  the  intensity  of  light  over  a  given  area.  Below  is  an  example  of  the  data  table:  

Location   Source  of  Light  (either  natural  or  artificial)  

Light  Intensity  (lux)   Observations  

Window  of  classroom        School  cafeteria        Classroom  with  lights  off        School  gym        Bathroom          

If  there  are  people  in  any  of  the  areas  that  are  willing  and  available  to  participate  in  an  interview,  have  students  interview  them  about  their  “sleepiness”  scale.  The  “comments”  section  will  be  used  to  record  Epworth  Sleepiness  Scale  scores  from  the  individuals  in  those  areas.    

After  the  table  has  been  created,  place  students  in  groups  and  allow  them  to  travel  around  the  school  using  the  light  meters  to  collect  data.  As  a  group,  they  need  to  decide  upon  5  or  more  locations  that  they  would  like  to  test.    

If  other  staff  members  are  not  available  or  willing  to  be  interviewed,  the  class  can  discuss  whether  or  not  they  think  that  people  in  different  areas  would  have  different  daily  patterns  of  activity.  

    October  2012  

  11    

Following  data  collection,  generate  a  class  data  table  on  the  board  to  help  connect  all  of  the  students’  data  and  discoveries.  Using  this  data,  students  will  identify  which  areas  have  the  highest  light  intensity  and  which  areas  have  the  lowest.    

Allow  students  to  compare  these  results  with  their  initial  predictions  to  determine  if  their  hypothesis  was  accurate.    

If  staff  members  were  available  to  be  interviewed,  then  the  class  will  try  to  determine  if  there  is  any  relationship  between  light  intensity  and  sleepiness.    

• Did  anyone  you  talked  to  report  very  high  or  very  low  sleepiness?    • If  so,  where  did  they  spend  most  of  their  day?    • What  was  the  light  intensity  in  that  room?  • How  do  these  results  compare  to  the  predictions  that  were  made  earlier?  

 

Teacher  Pedagogical  Content  Knowledge  The  goal  of  this  activity  is  to  introduce  students  to  thinking  about  light  intensity  and  the  fact  that  it  changes  with  environment.  If  the  results  of  the  Epworth  Sleepiness  Scale  do  not  show  any  correlations  between  light  intensity  and  sleepiness,  then  discuss  potential  reasons  with  the  students.  Because  staff  often  move  from  room  to  room  or  travel  outdoors,  there  may  not  be  a  noticeable  difference  between  people  in  various  areas  of  the  school.  

Activity  2:  Do  circadian  rhythms  depend  on  habitat?  In  this  activity,  students  (in  groups)  are  given  readings/articles  on  organisms  in  various  environments  and  geographical  locations.  As  a  class,  they  decide  whether  or  not  habitat  has  a  direct  impact  on  circadian  rhythms.  Ask  the  students:  

• What  kinds  of  environmental  cues  influence  daily  activity  patterns?  o We  know  that  cues  from  the  environment  influence  our  daily  rhythms.  These  cues  can  

be  light,  temperature,  food  availibility*,  and  social  cues.    

Explain  to  the  students  that  light  is  a  powerful  external  cue.  The  movement  of  the  earth  around  the  sun  causes  the  daily  pattern  of  light  and  darkness.  Because  we  live  in  these  daily  oscillating  conditions,  we  have  adapted  to  this  environment  by  evolving  our  own  intrinsic  (or  endogenous)  circadian  clocks.  While  

                                                                                                                         

*  In  laboratory  experiments,  rats  and  mice  with  restricted  feeding  schedules  re-­‐set  their  clocks  to  the  times  of  day  when  food  was  available,  preferentially  over  when  the  lights  were  on  or  off.  Even  if  food  was  available  only  during  lights-­‐on  (a  time  when  nocturnal  animals  are  normally  resting)  animals  would  wake  up  for  the  food.  

    October  2012  

  12    

these  rhythms  persist  in  constant  conditions,  they  are  fine-­‐tuned  daily—or  even  reset—by  our  external  environment.  In  this  activity  we  will  explore  how  closely  united  circadian  clocks  are  to  the  environment.    

It  makes  sense  that  animals  living,  as  humans  do,  in  an  approximate  24-­‐hour  light-­‐dark  cycle  would  have  clocks  of  about  24  hours.  Ask  students  to  think  about  exceptions  to  this  situation:  

• What  would  the  daily  rhythms  look  like  in  animals  living  in  conditions  where  there  is  no  sun  exposure?    

• What  about  animals  living  in  geographical  regions  where  the  length  of  daylight  changes  dramatically  over  the  course  of  the  year?  

Have  students  small  groups  read  the  same  article  about  the  circadian  rhythms  and  habitats  of  different  species.  They  should  answer  the  provided  discussion  questions  about  these  articles  together.  After  they  have  completed  this  activity,  assign  students  to  new  groups  of  3–5  students,  in  which  each  student  has  read  a  different  article.  In  these  new  groups,  they  will  take  turns  summarizing  their  article  to  the  group,  acting  as  the  expert  in  their  particular  topic,  and  then  together  form  conclusions  about  the  interaction  between  circadian  rhythms  and  the  environment.    

Literature  provided  with  this  lesson  includes  prepared  readings  based  on  primary  research  articles  and  corresponding  guided  reading  and  discussion  questions.    

After  students  have  worked  through  the  readings  and  discussed  them  in  the  two  different  groups,  have  students  come  back  together  for  a  whole  class  discussion.  Here  in  this  discussion,  have  students  defend  the  statement:  “Environment  influences  the  circadian  rhythm  of  the  species  native  to  that  habitat”  citing  evidence  from  their  readings.  The  following  questions  can  be  used  as  guiding  discussion  questions  to  help  students  develop  their  position:  

• Why  do  animals  have  endogenous  (intrinsic)  rhythms?    o Students  should  discuss  the  impact  of  environment  on  species  circadian  rhythm.  That  is,  

because  we  live  in  an  environment  with  daily  light-­‐dark  rhythms,  it  makes  sense  that  we  would  be  active  at  times  that  allow  us  to  make  use  of  the  environment.  

o In  the  case  of  reindeer,  may  a  rigid  circadian  clock  actually  be  a  disadvantage  for  living  in  an  ever-­‐changing  light  environment?    

• Where  else  on  the  planet  might  you  expect  to  see  a  similar  situation?  • Without  light  cues,  are  there  daily  rhythms  in  activity?  • Why  would  an  animal  in  a  constant  environment  need  an  internal  clock?  

Conclusion  of  Lesson:  The  closing  discussion  ties  together  themes  from  the  light  exposure  activity  and  the  rhythms  and  habitat  jigsaw  reading  activity.  Have  students  discuss  how  environment—for  an  individual  or  for  a  species—impacts  internal  rhythms  and  behavior.  Ask  students:  

• How  can  we  determine  an  individual’s  light  exposure?    

    October  2012  

  13    

• Does  this  change  depending  on  environment?    o Students  should  recall  earlier  in  the  lesson  how  they  collected  and  analyzed  data  from  

around  the  school.  They  should  talk  about  what  results  they  found  in  this  activity  and  whether  findings  were  expected  (did  they  confirm  their  predictions?).  

• Are  there  any  new  questions  that  they  can  think  of  that  came  from  their  results?  o Remind  students  that  a  good  experiment  is  not  always  about  finding  all  the  answers,  but  

about  generating  new  questions.  • How  is  light  exposure  different  for  humans  and  animals?    

o Ask  students  to  think  about  how  light  exposure  is  different  for  humans  and  animals.  • What  are  some  differences  in  circadian  rhythms  among  species?    

o Students  can  talk  about  their  readings  and  small  group  discussions.  They  may  mention  the  response  of  Megan  Mahoney  in  the  Ask  the  Scientist  segments  they  watched.  

• Does  environment  influence  circadian  rhythms?    o Students  should  be  able  to  support  their  answers  with  evidence  from  their  readings,  and  

from  their  discussions  about  the  light  intensity  measurements  they  collected.  

To  start  thinking  about  Lesson  6  and  human  health,  ask  students:    

• How  might  modern  society  be  changing  the  exposure  to  light  for  humans?  • What  consequences  might  this  have?  

Provide  students  with  the  Homework  Reading  and  questions  about  the  health  consequences  of  shift-­‐work,  “Are  night  shifts  bad  for  you?”  

Additional  Discussion  Topics  and  Activities:  1. Ecology  and  Circ-­‐annual  Rhythms:  (based  on  the  research  of  Richard  Primack  at  Boston  

University).  Organisms  have  circadian  (daily)  rhythms,  and  circ-­‐annual  (yearly)  rhythms.  Circannual  rhythms  include  migration,  mating  behavior,  hibernation,  and  even  growth.  This  example  joins  conversations  about  circadian  biology  and  ecology.  There  are  annual  rhythms  in  many  species:  migration  for  birds,  life  cycles  for  insects,  flowering  times  for  trees.  These  rhythms  are  cued  by  the  environment  and  by  endogenous  rhythms;  and  are  susceptible  to  changes  in  the  environment.  Currently,  research  on  climate  change  has  included  observations  about  differences  in  timing  of  bird  migration  and  changes  in  the  time  of  spring  flowering.  The  interaction  of  these  changes  may  determine  the  survival  of  species.  (http://people.bu.edu/primack/climate_change.html)  

2. Habitat  and  Adaptation  Extension:  Students  are  presented  with  a  hypothetical  scenario  (e.g.,  a  volcanic  eruption  blocks  out  the  sun  for  several  weeks,  global  temperatures  rise  by  5°F)  and  have  to  write  a  story  based  on  the  knowledge  they  have  amassed  throughout  the  unit  on  how  a  population’s  circadian  rhythms  would  be  affected.  

Assessment  

    October  2012  

  14    

For  the  light  intensity  measurement  activity  (Activity  1),  teachers  will  assess  student  data  tables.  These  can  be  assessed  based  on  neatness/organization,  thorough  completion,  etc.  Class  discussion  following  the  guided  reading  questions  of  Activity  2  should  indicate  a  student  understands  the  influence  of  environment  on  circadian  rhythms.  Additionally,  students  can  write  a  CER  response  to  support  the  statement  “Environment  influences  the  circadian  rhythm  of  the  species  native  to  that  habitat.”