Light and Sleep Lesson #1
Table of Contents
Light and Sleep Lesson #1 ................................................................................... 2
Lesson Goal ............................................................................................................................................... 2
Objectives ................................................................................................................................................. 2
Next Generation Science Standards Alignment ........................................................................................ 2
Time Required ........................................................................................................................................... 4
Materials Needed...................................................................................................................................... 4
Prerequisite Knowledge ............................................................................................................................ 4
Preconceptions ......................................................................................................................................... 4
Before the Lesson ..................................................................................................................................... 5
Safety ........................................................................................................................................................ 5
Procedures/Instructional Strategy ............................................................................................................ 5
Differentiated Instruction ....................................................................................................................... 14
Extension ................................................................................................................................................. 14
Student Sheet #1: Exploring Organism Rhythms ............................................... 17
Objective ................................................................................................................................................. 17
Procedure................................................................................................................................................ 17
Student Sheet #1: Exploring Organism Rhythms - KEY....................................... 25
Objective ................................................................................................................................................. 25
Procedure................................................................................................................................................ 25
Optional Maps .................................................................................................. 33
Appendix .......................................................................................................... 36
Circadian Rhythms Fact Sheet ................................................................................................................ 36
Cyclic Behavior of Animals ...................................................................................................................... 40
1
Light and Sleep Lesson #1
Grade Level:
Subject:
6-8
Earth/Life Science
Lesson Goal
Students will use data to build their conceptual understanding that the presence and/or absence of light
is important for controlling circadian and circannual rhythms.
Objectives
Students will:



Analyze the nature of circannual rhythms within organisms*
Analyze the nature of circadian rhythms within organisms*
Construct an explanation of how light affects circadian rhythms
*Note: The definition of circannual rhythms is a biological cycle or rhythm with a period length of
approximately one year. The definition of circadian rhythms is a biological cycle or rhythm with a period
length of about 24 hours.
Next Generation Science Standards Alignment
Note: This lesson does not fully meet a specific performance expectation of the Next Generation Science
Standards (NGSS) but supports student achievement of the performance expectations listed below. The
lesson is not a full unit of study; therefore, you should consider how it could be incorporated into your
own unit of study.
2
Performance Expectations:
Middle School-Life Science1-8. Gather and synthesize information that sensory receptors
respond to stimuli by sending messages to the brain for immediate behavior or storage of
memories. [Assessment Boundary: Assessment does not include mechanisms for the
transmission of this information.]
Middle School-Life Science2-1. Analyze and interpret data to provide evidence for the effects of
resource availability on organisms and populations of organisms in an ecosystem. [Clarification
Statement: Emphasis is on cause and effect relationships between resources and growth of
individual organisms and the numbers of organisms in ecosystems during periods of abundant
and scarce resources.]
Disciplinary Core Ideas:
LS1.D: Information Processing
Each sense receptor responds to different inputs (electromagnetic, mechanical, chemical),
transmitting them as signals that travel along nerve cells to the brain. The signals are then
processed in the brain, resulting in immediate behaviors or memories.
LS2.A: Interdependent Relationships in Ecosystems
Organisms, and populations of organisms, are dependent on their environmental interactions
both with other living things and with nonliving factors.
Crosscutting Concepts:
Cause and Effect: Cause and effect relationships may be used to predict phenomena in natural
systems.
Patterns: Patterns can be used to identify cause and effect relationships.
Graphs, charts, and images can be used to identify patterns in data.
Science and Engineering Practices:
Obtaining, Evaluating, and Communicating Information: Gather, read, and synthesize
information from multiple appropriate sources and assess the credibility, accuracy, and possible
3
bias of each publication and methods used, and describe how they are supported or not
supported by evidence.
Planning and Carrying Out Investigations: Conduct an investigation to produce data to serve as
the basis for evidence that meet the goals of an investigation.
Analyzing and Interpreting Data: Analyze and interpret data to provide evidence for
phenomena.
Constructing Explanations: Construct an explanation that includes qualitative or quantitative
relationships between variables that predicts and/or describes phenomena.
Time Required
Three 40-minute periods
Materials Needed



Large whiteboards for groups OR large pieces of paper
Student access to computers, tablets, or other devices that have internet capability
Student Sheet #1
Note: The Word document provided includes the lesson plan, the student sheet, and a student sheet key,
allowing you to customize the lesson and student sheet for what is best in your classroom.
Prerequisite Knowledge


Students are expected to know that from any place on Earth, the maximum height that the Sun
reaches in the sky above that place during the day gradually rises and falls during the year.
Students need a basic understanding of the seasons and day length.
Preconceptions
CLM003: The maximum height the Sun reaches in the sky on any given day is the same everywhere on
Earth (AAAS Project 2061, n.d.).
4
Students do not realize that circadian rhythms are found in single-celled organisms, plants, and animals
(including humans) (Dunlap et al., 2004).
Before the Lesson


Download any desired images from this lesson to a computer for projecting or print out copies
for students.
If you are unfamiliar with circadian rhythms and sleep, it is recommended that you visit “Sleep
Topics” at http://sleepfoundation.org/sleep-topics and read “The Time of Our Lives” at
http://learn.genetics.utah.edu/content/inheritance/clockgenes/.
Safety
There are no known safety issues with this lesson.
Procedures/Instructional Strategy
ENGAGE
1. Review the following northern hemisphere dates with students:
a. Summer Solstice (first day of summer): June 21, 2015
b. Fall Equinox (first day of fall) September: 23, 2015
c. Winter Solstice (first day of winter): December 21, 2015
d. Spring Equinox (first day of spring): March 20, 2015
2. Have students work in groups of three to four. Provide each group a large white board or large
piece of paper (18” x 24”). Have students divide the white board or paper into 4 quadrants as
shown in Figure 1 below. In the first quadrant write the word “summer.” In the second quadrant
write the word “fall.” In the third quadrant write the word “winter.” And in the fourth quadrant
write the word “spring.”
Summer
Fall
5
Winter
Spring
Figure 1. Worksheet for season quadrant group data.
3. Ask students to list natural events that signal a change in seasons. Encourage students to list
events that are specific to their geographic region.
Hint: By providing each student with a different colored marker, the teacher will be able to easily
visualize who is contributing.
Example answers could include changes in day length, changes in weather (precipitation and
temperature), bloom times, planting/harvesting times, hibernation, migration, etc.
4. Circulate the room as students work. Assist any groups with brainstorming as needed.
Differentiation strategy: This activity could be done as a whole group. For English language
learners, consider asking them to draw pictures of events that represent the seasons.
5. After 10 minutes, have each group write a claim that identifies which of the factors listed on
their board or paper would cause birds to migrate or bears to hibernate (or other behavioral
responses they listed). A claim is a statement explaining a phenomenon and is based on
evidence. Therefore, students should also justify why this factor is important from their
collected notes.
Example answer: Day length is important because it signals to birds to migrate. (CLAIM) Seeing
geese migrate south in September and migrate north in the spring supports my claim, since days
start to get shorter after the summer solstice and longer after the winter solstice.
(JUSTIFICATION/EVIDENCE)
6. Call on each group of students, asking them to explain their claim and the justification for their
claim. The following questions can help the students develop their claim:
a. What observations or inferences can you use to support your claim? An inference is an
explanation of a concept or phenomenon based on evidence. Evidence can include
observations you have made.
b. What can you use to support your justification?
c. How does your claim demonstrate an organism’s ability to adapt to its environment?
d. How do organisms respond to changes in seasons?
e. How do organisms benefit from changes in seasons?
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7. Hold a class discussion regarding the student claims. Ask the class the following questions:
a. How many claims identified a nonliving factor as the most important factor? Answers
will vary.
b. How many identified a living factor as the most important? Answers will vary.
c. How do nonliving factors impact living things? Answers will vary.
d. In what ways are humans affected by seasonal change? Answers will vary.
Note: Teachers may wish to introduce the terms abiotic factor and biotic factor at this time.
Abiotic factors are the nonliving components of the environment, such as temperature, sunlight,
and humidity. Biotic factors are the living components of the environment and include organisms
such as producers, consumers, and decomposers.
8. Tell students that they have identified year-long cycles and changes. These are called circannual
rhythms (e.g., migration, hibernation, etc). A seasonal change that is not a behavior is day
length, or the amount of daylight an area receives. Ask students to give examples of how the
amount of daylight an area receives affects plants and animals. Note: To prompt discussion, it
may be useful to give examples of local, seasonal plant growth and/or animal behaviors with
which students are familiar. Some optional images are provided showing geese migrating
(circannual) and a morning glory flower opening (responds to daylight).
Figure 2. These geese form a "V" shape when migrating south in the fall.
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Figure 3. Morning Glory flowers close at night and open again in the morning.
Possible Answers: Animal behaviors such as migration and hibernation; plant behaviors such as
flowering and losing leaves.
9. Tell students that environmental triggers may vary, but they are going to focus on one they
know exists: day length. Lead students to the realization that the amount of day length is critical
for plants and animals. Ask students to define day length.
Day length refers to the length of time there is light in the sky on a daily basis.
Note: Other factors that are important include precipitation and temperature.
EXPLORE
1. Pass out Student Sheet #1. This activity will bridge two days. Pace your students so that they
spend time on each step and can supply thoughtful answers supported by evidence from the
Journey North website (see Student Sheet #1).
Note: If you have students at different reading levels or with different needs, the Word document will
allow you to customize the student sheet for what is best in your classroom.
EXPLAIN
1. Tell students that the Journey North website shows cycles over the course of a year. Are there
any cycles humans have? Prompt students to think about if there is anything in the environment
that triggers feeling tired, hungry, energetic, sleepy, etc.
Note: Answers can be based on a daily (circadian) and/or seasonal (circannual) basis.
Answers will vary.
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2. Inform students that although people don’t respond to environmental cues exactly like plants
and animals, they still have cycles that are driven by external factors such as daylight. Ask
students for examples of 24-hour animal behavior and evidence of this behavior.
Possible answers include nocturnal animals hunting at night, diurnal birds not singing at night,
morning glory flowers blooming when the sun rises but closing up when the sun sets, etc.
3. Explain circadian rhythms in humans using the following possible sources:
a. Fact Sheet
http://www.nigms.nih.gov/education/pages/factsheet_circadianrhythms.aspx
b. Cyclic Behavior of Animals http://www.ck12.org/biology/Cyclic-Behavior-ofAnimals/lesson/Cyclic-Behavior-of-Animals/
Note: This resource is a creative commons resource and can be printed and distributed to
students. You can find these two resources in the Appendix of this document.
ELABORATE
1. Show students Figure 4 (below), the human biological circadian clock. Explain that melatonin is a
chemical produced by the pineal gland in the brain (Figure 5). The body produces more when
there is less light, which makes humans less alert and more sleepy. Exposure to light decreases
the amount of melatonin produced (For information on melatonin, visit
http://sleepfoundation.org/sleep-topics/melatonin-and-sleep.)
9
Figure 4. The human biological circadian clock. These times and designations can vary for a given individual on
different days and, of course, among individuals.
Figure 5. The pineal gland is small and located in the brain.
2. Have students work with a partner to answer the following questions:
a. How does your body get you ready for sleep?
Answer: Melatonin rise is associated with onset of sleep.
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b. What relationships exist between a person’s body functions and the light/dark cycle (24
hours)?
Answers will vary, but students should cite evidence from the image. This can include
when melatonin secretion decreases in the morning as the Sun rises, the body starts
normal processes again and will grow more alert. When melatonin secretion increases
at night after the Sun has set, the body suppresses normal functioning so the person can
fall asleep. Other possible answers include alertness, bathroom breaks, physical
coordination, body temperature, etc.
c. How does your body get you ready for waking up?
Answer: The body produces less melatonin with an increase in light, which signals the
body to wake up.
d. When is the optimal time that students should take tests?
Answer: According to the image, 10:00 a.m. is a time of “high alertness.” This may be an
optimal time to take a test.
e. When is the optimal time to play sports?
Answer: From 14:30 (2:30 p.m.) to 17:00 (5:00 p.m.) are times of best coordination,
fastest reaction time, and greatest cardiovascular efficiency and muscular strength.
Therefore, the best time to play sports would be between 2:30 and 5:00 p.m.
3. Discuss the answers with the class. You may wish to have students hypothesize about the
following:
a. Why do you think humans follow a 24-hour circadian cycle?
Scientists believe that living organisms adapted the 24-hour circadian cycle to help
adapt to the Earth’s 24-hour rotation (see
http://learn.genetics.utah.edu/content/inheritance/clockgenes/).
b. You fly in an airplane to Paris, leaving Washington, DC at 4:30 p.m. and arriving in Paris
the next day at 8:45 a.m. What effect do you think this will have on your body? Note:
Paris is six hours ahead of Washington, DC.
Answer: You will probably suffer something called jet lag in which your regular sleep
patterns are out of sync with the actual time. That means that your body thinks it is a
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different time than the actual time. When your plane lands in Paris, your body will think
it is 2:45 a.m. instead of 8:45 a.m.
EVALUATE
Based on the Journey North maps, students should have an understanding that different organisms have
different circadian rhythms, but that the circadian rhythm is affected by light/day length.
Have students create a concept map or T-chart showing the link between organisms and both circadian
(daily) and circannual (seasonal) rhythms.
Example concept maps
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Example T-chart comparing daily and seasonal rhythms
Examples of Daily Rhythms
Waking up, sleeping, blood pressure, body
temperature
Examples of Seasonal Rhythms
Migration, bloom times, leafing out, hibernation,
reproduction, flowering
13
Have students write a response to the following question: How does light affect circadian rhythms?
Look for student understanding of the manifestations of circadian rhythms in different organisms
(concept map). Some students may answer the question with “Flowers bloom earlier.” This answer is
not complete. While it shows that the student understands flowering is a result of circadian rhythms, it
does not use evidence for justification. An acceptable response would be: “Flowers bloom earlier when
day length is longer because there is more light.” This answer shows the student is making the
connection between light and circadian rhythms. Expect students to give the evidence (and reasoning) in
their responses.
Differentiated Instruction
Provide students who have difficulty navigating the Journey North site with printed maps downloaded
from the site.
Allow students to work in groups.
Emphasizing the connections to various countries can help engage students with different cultural
backgrounds.
Extension
1. Natural light is important to more than just behavior. Show students the following images and have
them investigate the relationship between natural light and Vitamin D.
Answer: Natural light, or sunlight, is necessary to convert a chemical in the skin into Vitamin D3, which is
transported to the liver and kidneys where it is made into Vitamin D. Sunlight is more than just visible
light, it also includes infrared and ultraviolet (UV). UV light is the focus of this problem.
Rickets is a disorder caused by a deficiency of Vitamin D. It can result in stunted growth. Therefore, light
affects growth as well as behavior.
14
Figure 6. Rickets leg x-ray. Image courtesy: Dr. Michael L. Richardson, Licensed under CC BY-SA 1.0.
Figure 7. Rickets x-ray. Image courtesy: Frank Gaillard, Licensed under CC BY-SA 3.0.
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Figure 8. Illustration of legs with normal bone growth versus rickets.
References
Dunlap,J., Loros, J., DeCoursey, P. (2004). Chronobiology: Biological Timekeeping. Sinauer Associates.
16
Name: ________________________________
Date: _____________
Student Sheet #1: Exploring Organism
Rhythms
Objective
Analyze the daily and annual rhythms within organisms.
Procedure
This worksheet is divided into five parts to explore patterns in organism behavior.





Part 1: Examining Photoperiod
Part 2: Exploring Spring 2015 Data
Part 3: Exploring Archived Data Sets
Part 4: Investigating an Organism’s Relationship to Day Length
Part 5: Going Further
Part 1: Examining Photoperiod
Photoperiod refers to the amount of sunlight an area receives. Go to the Journey North 2015 Sunlight
and Seasons Information Map at http://www.learner.org/jnorth/maps/photo_spring2015.html (or scan
the QR code below), which shows the reported amount of day length across the United States.
17
Select November 1 from the top left dropdown menu (see circled location in Figure 1).
Figure 1. 2015 Sunlight and seasons information map.
What pattern do you see on November 1?
Now select May 1 from the dropdown calendar. What pattern do you see?
18
Part 2: Exploring Spring 2015 Data
Go to http://www.learner.org/jnorth/maps/galleries/2015/spring.html (see Figure 2) or scan the QR
code below. You will be exploring data collected during the spring of 2015.
Figure 2. Spring 2015 Journey North data.
Select one of the following organisms to investigate: robins, earthworms, common loons, singing frogs,
or barn swallow. Note: Selecting the word “home” that appears underneath each map will lead to more
information about the featured organism.
Select the map for your organism. What do the dates of the sightings tell you about your chosen
organism?
19
Part 3: Exploring Archived Data Sets
Go to https://www.learner.org/jnorth/maps/archives.html (see Figure 3) or scan the QR code to explore
additional data sets and interactive maps.
Figure 3. Past seasons data from Journey North.
a. Under the box that says “Spring 2014 Sightings,” select the link to “Spring 2014 Maps.” You will
go to a page that features 22 maps, some static and others interactive. The maps represent
observable events related to plants, animals, and weather. Each of the selections contains a
map, a list of reported sightings, and a background page about the species.
b. Select an organism whose behavior you would like to explore further. Note: Do NOT select
symbolic monarchs, whooping cranes, signs of the seasons, or habitat projects. Select the map
for your organism. For some organisms, such as the Monarch butterfly, you can filter the results
by selecting various dates.
20
c. Examine three years of sightings for your organism. Describe any similarities and/or differences
between the maps. Things to consider:
 Is the activity level of your species (e.g., migration) similar each year? If yes, what
factors would trigger an organism to react in the same way each year?

Is there a specific week or month of maximum sightings?
21
Part 4: Investigating an Organism’s Relationship to Day Length
Using either the current season or past seasons, develop a question to explore related to an organism’s
activity and day length. For example, Is there a relationship between day length and the first frog heard
singing? You will then use the maps to answer your question. The maps will provide evidence for your
answer.
Figure 4 is an example of how to answer the question Is there a relationship between day length and the
first frog heard singing. It shows that as day length increases, more frogs could be heard singing. In
addition, frogs in more northern regions begin singing later in the spring. This is due to colder
temperatures.
Figure 4. Map showing data collected of frogs first heard singing.
22
Using an organism of your choice, develop a question to investigate to determine how day length
impacts the organism. Use the maps from the Journey North website to answer your question.
a. Your question:
b. What patterns do you notice?
c. What do you think is happening and why?
d. What is your hypothesis?
e. What did you find out when you investigated your question?
f.
What other explanations could be plausible (i.e., an alternative hypothesis)?
23
Part 5: Going Further
What other types of behaviors do you think are linked to day length or the amount of light organisms
receive? Use the Journey North site to support your ideas. Below are some questions to consider:
a. When did your chosen organism begin to migrate? Note: Not all species migrate.
b. Was there a peak week during which your selected organism was spotted?
c. Is the activity of your organism linked to the availability of food and/or habitat? For example,
what is the relationship between: Monarch butterflies and milkweed? Between robins and
earthworms? Between leaf out and orioles?
Extend
The study of seasonal changes shown by plants and animals is called phenology. As the climate gets
warmer, organisms are moving farther north. Many plants are now blooming earlier than they used to in
the past. What effect will this have on types of birds that depend on plants for seeds and fruit?
Optional Project: Keep a journal in which you document temperature, length of day, and sightings of a
specific organism.
24
Name: ____________KEY_________________
Date: _____________
Student Sheet #1: Exploring Organism
Rhythms - KEY
Objective
Analyze the daily and annual rhythms within organisms.
Procedure
This worksheet is divided into five parts to explore patterns in organism behavior.





Part 1: Examining Photoperiod
Part 2: Exploring Spring 2015 Data
Part 3: Exploring Archived Data Sets
Part 4: Investigating an Organism’s Relationship to Day Length
Part 5: Going Further
Part 1: Examining Photoperiod
Photoperiod refers to the amount of sunlight an area receives. Go to the Journey North 2015 Sunlight
and Seasons Information Map at http://www.learner.org/jnorth/maps/photo_spring2015.html (or scan
the QR code below), which shows the reported amount of day length across the United States.
25
Select November 1 from the top left dropdown menu (see circled location in Figure 1).
Figure 1. 2015 Sunlight and seasons information map.
What pattern do you see on November 1?
The photoperiod or day length decreases with increasing latitude.
Now select May 1 from the dropdown calendar. What pattern do you see?
The photoperiod or day length increases with increasing latitude.
26
Part 2: Exploring Spring 2015 Data
Go to http://www.learner.org/jnorth/maps/galleries/2015/spring.html (see Figure 2) or scan the QR
code below. You will be exploring data collected during the spring of 2015.
Figure 2. Spring 2015 Journey North data.
Select one of the following organisms to investigate: robins, earthworms, common loons, singing frogs,
or barn swallow. Note: Selecting the word “home” that appears underneath each map will lead to more
information about the featured organism.
Select the map for your organism. What do the dates of the sightings tell you about your chosen
organism?
Answer: the season progresses the organism is spotted in more northerly locations.
27
Part 3: Exploring Archived Data Sets
Go to https://www.learner.org/jnorth/maps/archives.html (see Figure 3) or scan the QR code to explore
additional data sets and interactive maps.
Figure 3. Past seasons data from Journey North.
d. Under the box that says “Spring 2014 Sightings,” select the link to “Spring 2014 Maps.” You will
go to a page that features 22 maps, some static and others interactive. The maps represent
observable events related to plants, animals, and weather. Each of the selections contains a
map, a list of reported sightings, and a background page about the species.
e. Select an organism whose behavior you would like to explore further. Note: Do NOT select
symbolic monarchs, whooping cranes, signs of the seasons, or habitat projects. Select the map
for your organism. For some organisms, such as the Monarch butterfly, you can filter the results
by selecting various dates.
28
f.
Examine three years of sightings for your organism. Describe any similarities and/or differences
between the maps. Things to consider:
 Is the activity level of your species (e.g., migration) similar each year? If yes, what
factors would trigger an organism to react in the same way each year?
Answers will vary.

Is there a specific week or month of maximum sightings?
Answers will vary.
29
Part 4: Investigating an Organism’s Relationship to Day Length
Using either the current season or past seasons, develop a question to explore related to an organism’s
activity and day length. For example, Is there a relationship between day length and the first frog heard
singing? You will then use the maps to answer your question. The maps will provide evidence for your
answer.
Figure 4 is an example of how to answer the question Is there a relationship between day length and the
first frog heard singing. It shows that as day length increases, more frogs could be heard singing. In
addition, frogs in more northern regions begin singing later in the spring. This is due to colder
temperatures.
Figure 4. Map showing data collected of frogs first heard singing.
30
Using an organism of your choice, develop a question to investigate to determine how day length
impacts the organism. Use the maps from the Journey North website to answer your question.
g. Your question:
Answers will vary.
h. What patterns do you notice?
Answers will vary.
i.
What do you think is happening and why?
Answers will vary.
j.
What is your hypothesis?
Answers will vary.
k. What did you find out when you investigated your question?
Answers will vary.
l.
What other explanations could be plausible (i.e., an alternative hypothesis)?
Answers will vary.
31
Part 5: Going Further
What other types of behaviors do you think are linked to day length or the amount of light organisms
receive? Use the Journey North site to support your ideas. Below are some questions to consider:
d. When did your chosen organism begin to migrate? Note: Not all species migrate.
e. Was there a peak week during which your selected organism was spotted?
f.
Is the activity of your organism linked to the availability of food and/or habitat? For example,
what is the relationship between: Monarch butterflies and milkweed? Between robins and
earthworms? Between leaf out and orioles?
Possible answers include migration and bloom times. Journey North has data related to migration of
insects, gray whales, and bird species. Data related to milkweed blooming times and leaf-out of
deciduous trees can also be examined.
Extend
The study of seasonal changes shown by plants and animals is called phenology. As the climate gets
warmer, organisms are moving farther north. Many plants are now blooming earlier than they used to in
the past. What effect will this have on types of birds that depend on plants for seeds and fruit?
The birds are out of sync with their food supply. This may impact their ability to successfully raise their
young.
Optional Project: Keep a journal in which you document temperature, length of day, and sightings of a
specific organism.
32
Optional Maps
33
34
35
Appendix
Circadian Rhythms Fact Sheet
What are circadian rhythms?
Circadian rhythms are physical, mental and behavioral changes that follow a roughly 24- hour cycle,
responding primarily to light and darkness in an organism's environment. They are found in most living
things, including animals, plants and many tiny microbes. The study of circadian rhythms is called
chronobiology.
Figure 1. Illustration of the human brain with the suprachiasmatic nucleus labelled.
Are circadian rhythms the same thing as biological clocks?
No, but they are related. Our biological clocks drive our circadian rhythms.
What are biological clocks?
The biological clocks that control circadian rhythms are groupings of interacting molecules in cells
throughout the body. A "master clock" in the brain coordinates all the body clocks so that they are in
synch.
36
What is the master clock?
The "master clock" that controls circadian rhythms consists of a group of nerve cells in the brain called
the suprachiasmatic nucleus, or SCN. The SCN contains about 20,000 nerve cells and is located in the
hypothalamus, an area of the brain just above where the optic nerves from the eyes cross.
Do circadian rhythms have a genetic component?
Yes. Researchers have already identified genes that direct circadian rhythms in people, fruit flies, mice,
fungi and several other model organisms used for studying genetics.
Does the body make and keep its own circadian rhythms?
Circadian rhythms are produced by natural factors within the body, but they are also affected by signals
from the environment. Light is the main cue influencing circadian rhythms, turning on or turning off
genes that control an organism's internal clocks.
How do circadian rhythms affect body function and health?
Circadian rhythms can influence sleep-wake cycles, hormone release, body temperature and other
important bodily functions. They have been linked to various sleep disorders, such as insomnia.
Abnormal circadian rhythms have also been associated with obesity, diabetes, depression, bipolar
disorder and seasonal affective disorder.
How are circadian rhythms related to sleep?
Circadian rhythms are important in determining human sleep patterns. The body's master clock, or SCN,
controls the production of melatonin, a hormone that makes you sleepy. Since it is located just above
the optic nerves, which relay information from the eyes to the brain, the SCN receives information about
incoming light. When there is less light—like at night—the SCN tells the brain to make more melatonin
so you get drowsy.
37
How are circadian rhythms related to jet lag?
Jet lag occurs when travelers suffer from disrupted circadian rhythms. When you pass through different
time zones, your body’s clock will be different from your wristwatch. For example, if you fly in an
airplane from California to New York, you "lose" 3 hours of time. So when you wake up at 7:00 a.m.,
your body still thinks it’s 4:00 a.m., making you feel groggy and disoriented. Your body’s clock will
eventually reset itself, but this often takes a few days.
Figure 2. Sleeping fruit flies.
How do researchers study circadian rhythms?
Scientists can learn about circadian rhythms by studying humans or by using model organisms that have
similar "clock" genes. Basic researchers doing these experiments can control the subject's environment
by altering light and dark periods and then look for changes in gene activity or other molecular signals.
How does circadian rhythm research contribute to human health?
Understanding what makes biological clocks tick may lead researchers to treatments for sleep disorders,
jet lag and other health problems. Learning more about the genes responsible for circadian rhythms will
also enhance our understanding of biological systems and the human body.
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Learn more:
Resetting Our Clocks: New Details about How the Body Tells Time[2]
Tick Tock: New Clues About Biological Clocks and Health[3]
A Light on Life's Rhythms: Profile of Cara Altimus[4]
NIGMS is a part of the National Institutes of Health that supports basic research to increase our
understanding of biological processes and lay the foundation for advances in disease diagnosis,
treatment and prevention. For more information on the Institute's research and training programs, see
http://www.nigms.nih.gov[5].
(Content reviewed November 2012)
Links
1.
2.
3.
4.
5.
http://www.nigms.nih.gov/education/Pages/los-ritmos-circadianos.aspx
http://publications.nigms.nih.gov/insidelifescience/resetting-our-clocks.html
http://publications.nigms.nih.gov/insidelifescience/biological-clocks.html
http://publications.nigms.nih.gov/findings/sept11/lightliferhythms.asp
http://www.nigms.nih.gov/
Writer
Patty McGinnis
39
Cyclic Behavior of Animals
Jessica Harwood
Douglas Wilkin, Ph.D.
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Printed: January 30, 2015
AUTHORS
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Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
CONTRIBUTORS
Doris Kraus, Ph.D.
Niamh Gray-Wilson
Jean Brainard, Ph.D.
Sarah Johnson
Jane Willan
Corliss Karasov
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C HAPTER
Chapter 1. Cyclic Behavior of Animals
1
Cyclic Behavior of Animals
• Identify animal behaviors that occur in cycles.
• Explain hibernation and migration.
• Define circadian rhythms and biological clock.
What are these butterflies doing?
Monarch butterflies gather in large groups as they migrate 2,500 miles south each fall. They return to the north in the
spring. This migration is a cycle that repeats every year.
Cycles of Behavior
Many animal behaviors change in a regular way. They go through cycles. Some cycles of behavior repeat each year. Other
cycles of behavior repeat every day.
Yearly Cycles
An example of a behavior with a yearly cycle is hibernation. Hibernation is a state in which an animal’s body processes
are slower than usual, and its body temperature falls. An animal uses less energy than usual during hibernation. This
helps the animal survive during a time of year when food is scarce. Hibernation may last for weeks or months. Animals
that hibernate include species of bats, squirrels, and snakes.
Most people think that bears hibernate. In fact, bears do not go into true hibernation. In the winter, they go into a deep
sleep. However, their body processes do not slow down very much. Their body temperature also remains about the same as
usual. Bears can be awakened easily from their winter sleep.
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Chapter 1. Cyclic Behavior of Animals
Another example of a behavior with a yearly cycle is migration. Migration is the movement of animals from one place to
another. Migration is an innate behavior that is triggered by changes in the environment. For example, animals may
migrate when the days get shorter in the fall. Migration is most common in birds, fish, and insects. In the Northern
Hemisphere, many species of birds, including robins and geese, travel south for the winter. They migrate to areas where it
is warmer and where there is more food. They return north in the spring. A flock of migrating geese is pictured below (
Figure 1.1).
FIGURE 1.1
These geese are flying south for the win- ter.
Flocks
of
geese
migrate
in
V-shaped
formations.
Some animals migrate very long distances. The map shown below shows the migration route of a species of hawk called
Swainson’s hawk ( Figure 1.2). About how many miles do the hawks travel from start to finish? Are you surprised that
birds migrate that far? Some species of birds migrate even farther. Whales also are known to migrate thousands of miles
each year to take advantage of warmer waters in the winter months. The great migration of millions of zebra, wildebeest
and other antelope in East Africa also occurs yearly. Each year around 1.5 million wildebeest and 300,000 zebra (along
with other antelope) go in search of food and water, traveling a distance of around 1800 miles.
Birds and other migrating animals follow the same routes each year. How do they know where to go? It depends on the
species. Some animals follow landmarks, such as rivers or coastlines. Other animals are guided by the position of the sun, the
usual direction of the wind, or other clues in the environment.
Daily Cycles
Many animal behaviors change at certain times of day, day after day. For example, most animals go to sleep when the sun sets
and wake up when the sun rises. Animals that are active during the daytime are called diurnal. Some animals do the opposite.
They sleep all day and are active during the night. These animals are called nocturnal. Examples of nocturnal animals include
bats, foxes, possums, skunks and coyotes. Many mammals (including humans), insects, reptiles and birds are diurnal.
Animals may eat and drink at certain times of day as well. Humans have daily cycles of behavior, too. Most people start to
get sleepy after dark and have a hard time sleeping when it is light outside. Daily cycles of behavior are called circadian
rhythms.
In many species, including humans, circadian rhythms are controlled by a tiny structure called the biological clock. This
structure is located in a gland at the base of the brain. The biological clock sends signals to the body. The signals cause
regular changes in behavior and body processes. The amount of light entering the eyes helps control the biological clock.
The clock causes changes that repeat every 24 hours.
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Chapter 1. Cyclic Behavior of Animals
FIGURE 1.2
The migration route of Swainson’s hawk
starts in North America and ends in South
America.
Scientists learned their mi-
gration route by attaching tiny tracking
devices to the birds.
The birds were then
tracked by satellite.
On the migration
south, the hawks travel almost 5,000 miles
from start to finish.
Summary
• Yearly cycles of behavior include hibernation and migration.
• Daily cycles of behavior, including sleeping a waking, are called circadian rhythms.
Explore More
Use the resources below to answer the questions that follow.
Explore More I
• Red Knot Migration - Port Royal Sound at http://www.youtube.com/watch?v=P21xTCFrJbU (2:07)
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Chapter 1. Cyclic Behavior of Animals
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57412
• Thousands of Red Knots migrate through New Jersey at http://www.youtube.com/watch?v=TE5EHoBWd
AA (2:55)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57413
1.
2.
3.
4.
How far do Red Knots (Calidris canutus) migrate each year?
Are Red Knots the only species of bird to use horseshoe crab (Limulus polyphemus) eggs as a resource?
What information do scientists collect from the red Knots? How do they use this information?
Why do scientists think Red Knot populations are declining? How is this connected to their extremely long
migration?
Explore More II
• Ocean Life - Vertical Migration Aggregation at http://www.youtube.com/watch?v=zVQd9pn8j6E (7:16)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57414
1. What is the largest migration of animals on the planet? When does this occur?
2. Why do animals undergo this migration? What types of organisms undergo this migration?
3. How does the timing of this migration vary throughout the year?
Review
1.
2.
3.
4.
What are two examples of yearly cycles of behavior?
What is the difference between a nocturnal and a diurnal animal?
What is a circadian rhythm?
What controls circadian rhythms in humans? Explain how this process works.
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Chapter 1. Cyclic Behavior of Animals
References
1. Chris Burke. These geese fly in a V-shaped formation while migrating south for the winter . CC BY 2.0
2. U.S. Geological Survey. The route of migration for Swainson’s hawk . Public Domain
5