Hickory Dickory
Dock: The Biological Clock
Lesson Plan
Overview
Animals
use a number of different cues to determine when it is time to migrate. In this lesson, students will investigate
the effect of day length, or photoperiod, on animal migrations, and make
additional connections between their own biological cues (e.g. feeling hungry) and
migration cues of animals.
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Suggested Lesson
Sequence |
Please see Migrations del Mundo and Seasonal Changes module descriptions. |
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Lesson Level |
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Science
Connections |
· Students will investigate how the day length (photoperiod) changes seasonally, and that this change can trigger biological actions in animals. ·
Students
will discriminate between natural and human-made cues that trigger
their own movements. · Students will make the connection between their own cues for movement and those cues used by animals to start their own movements and migrations. |
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Mathematics
Connections |
·
Students
will calculate the amount of time that elapses between sunrise and sunset
using manual and computer methods. ·
In working
to subtract and add time, students will become more familiar with working in
alternate base numerical systems (i.e. 60 minutes equal one hour). |
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Technology
Connections |
·
Students
will use the Internet to find the photoperiod of their home town and
determine the sunrise and sunset times for days in each of the four seasons. |
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Lesson Assessment Tools |
Assessment
and Standards Table (Word) |
Materials
This lesson requires Powerpoint Reader (Windows / Mac), and Quicktime Player.
Photoperiod Activity Sheet—one copy per student
Computer with
Internet connection
Weather section of
the local newspaper
Hickory Dickory Dock movie (Quicktime), starring Pixel the Satellite
Biological
Clock Interactive Slideshow (Powerpoint)
Biological
Clock Assessment Slideshow (Powerpoint)
About
the slideshows: These slideshows are not meant for students
to read through on their own. They are intended to be viewed together, to
outline and illustrate a discussion of the lesson's themes, led by the
teacher. You might have a different student read each slide's text.
Vocabulary
Biological
clock: A
function inside the body of any living thing which controls biological rhythms
(patterns) such as sleep, migration, reproduction, and other changes.
Photoperiod: The amount
of time that some amount of light occurs over the course of a day.
Vocabulary
Note: students will likely be unfamiliar with
other vocabulary presented in this lesson.
This is done intentionally, to spur additional conversations and
discussion about these words and their meanings. Encourage your students to ask about words they may be unfamiliar
with.
I.
Assessing Prior Knowledge
In the Nomad Land lesson,
students recorded their migrations for one day. Ask the students to review their list of migrations and ponder
the question, “how did you know when to begin your migrations?” Possible answers include the sounding of a
bell, a teacher’s instruction, and the time on the clock. If students also recorded their migrations
at home, such as on a weekend, you may want to discuss the migrational cues
they follow at home, such as getting up out of bed when the sun is shining in
their eyes. Note: if you have not yet done the
Nomad Land lesson, you may just compile a simple
list with your students of the places that they go over the course of a day and
the reasons their bodies need to go to these places (e.g. to eat, get a drink
of water, play, use the restroom, etc.).
After students
have brainstormed possible reasons for their “migrations,” ask them to think
about the world of an animal. Animals
do not have bells or classroom teachers telling them when to migrate. So then
how do animals know when to migrate?
Students should think about their own migrations outside of school and
their observations of animals to brainstorm answers to this question. The responses may be recorded on the
chalkboard or overhead for later review.
II.
Contextual Preparation
Ask the students
to imagine that they no longer have clocks, bells, or teachers telling them
when to migrate. Looking at their list
of migrations, which activities might have biological or environmental cues
that could help them decide when to move?
Which do not? What are some of
these biological or environmental cues?
(Examples of this could be that it is time to go to recess when they are
feeling jittery or tired, going to lunch when they are hungry, and falling
asleep when it is dark or they are tired.
In contrast, they may say that going to periods for math or music has no
such cues, except that they have simply come to expect that it is time for
these activities.)
To further set the
stage for this lesson, view the Biological Clock
animated movie narrated by Pixel the Satellite. The transcript for this animation is provided below, for you and
your students’ use:
(Pixel
is listening to a clock ticking in outer space) 1. “Time is so
interesting! ‘Time for dinner! Time for bed!’ You probably know these times very well. People tell time by using watches, clocks,
and calendars. Animals need to know
when to eat and sleep, too. But how
does an animal tell time without having a watch, clock, or calendar to
read? There are many secrets of nature
that animals use to tell time using what is called the “Biological Clock”. And you know what? People have biological clocks too. What is a biological clock used for? And, how can you learn to read your own biological clock? You’ll learn all about this with your
teacher in the next lesson. In the mean
time, I’m late for a meteor shower! See
you soo-oon!”
III.
Student Activities
1. Background
information for the teacher: Some
animals make long migrations during certain periods of the year, such as the
Swainson’s hawk or green sea turtles studied in the lesson
. How exactly do these animals know when to migrate? Migrational
cues can come from a variety of sources.
One very important such cue is the length of the day. As the seasons change, the length of the
sunlit day, called the photoperiod,
also changes. In fact, scientists have
learned that day length (photoperiod) is one of the most critical factors
controlling the biological clock of animals.
2. View
the Biological Clock Interactive Slide
Show
now with your students. Students learn
about the connection between the sun, photoperiod, and animal functions in this
slide show. Take the time to point out
the recurring themes in this slide show, including points such as animal
functions, seasons, and day length. By
the end of the slide show, students should be able to recognize the importance
of day length (photoperiod) in animals’ lives.
3.
Ask the students to hypothesize about which seasons, or even which days,
have the longest photoperiods (spring and summer) and which have the shortest
(autumn and winter). How can we test our hypotheses? Is it possible to measure the photoperiod of a day? How could a student do this on her/his own? (They could measure the time from sun-up to
sun-down).
4. Using information from the weather section of that day’s local newspaper, write the times of sunrise and sunset on the board. Calculate with your students the time between sunrise and sunset using any hour/minute counting method. First, you might count the hours, then add the remaining minutes. For example, if sunrise occurs at 6:43 a.m. and sunset occurs at 5:52 p.m., you might count whole hours ending with :43 (e.g. 7:43am, 8:43am, etc. until reaching 5:43pm, and then add the extra 9 minutes to your total to arrive at the answer of 11 hours, 9 minutes). As an alternative, you might first point out that there are 17 minutes between 6:43am and 7:00am, then count whole hours until 5:00pm, then add the remaining 52 minutes. This method would reveal an answer of 10 hours, 69 minutes. Using both methods will help students to become more familiar working with a “base-60” system (60 minutes equaling one hour). At this time, you might also introduce the concept of “24-hour”, or “military” time, whereby 1:00pm is written as 13:00, etc. Students will learn that using “24-hour” time simplifies time calculations when the time period spans the noon hour.
5. Hand
out the Photoperiod Activity
Sheet. Students will repeat the manual time
calculation exercise described above on their own.
6. From
the above calculations, students will now know the photoperiod of one day, but
how does the photoperiod of your home town change over time? One way for students to calculate the way
photoperiods of their town change over time is to visit the web site: http://aa.usno.navy.mil/data/docs/RS_OneDay.html
Using
the same Photoperiod Activity
Sheet, students
will test their hypothesis about which seasons have the longest or shortest
photoperiods. Students should choose
days from within each of the four seasons.
Students may need assistance calculating the length of the photoperiod
or the time elapsed from sunrise to sunset.
Concrete manipulatives such as an actual clock could be helpful. When the photoperiods are calculated, write
them on the activity sheet. Ask
children: Would you have to wake up earlier or later to measure the start of
the photoperiod in the summer, compared to in the winter? (Earlier)
7. Referring to their data, students should
answer these questions:
What
season has the longest day? (The Spring/Summer
transition, also called the summer solstice.) What season has the shortest day? (The fall/winter transition, also called the winter solstice.) When do you think the days begin to get
longer? (Although the shortest day the
winter is Dec. 21 (winter solstice), they begin to get longer after this date. This may not be evident unless children
collect more photoperiod data over time.) When do days begin to get
shorter? (Although June 21 (summer solstice)
is the longest day, the days begin to get shorter after this date in the
Northern Hemisphere).
8.
Have students remember back to some of the reasons animals migrate
(reproduction, availability of food, temperature changes). Just as animals do not have classroom
clocks, they also do not have calendars.
How might photoperiods help animals know what time of the year it
is? Scientists believe that
photoperiods serve as a type of “early warning signal” to tell of upcoming
changes in climate or food availability.
These signals trigger long-range migratory animals to produce special
hormones in their bodies. After the
hormones are produced, the animal begins to ready itself for the upcoming
migration by eating large amounts to produce fat stores. Then, environmental cues such as food
scarcity or cold temperatures may be the final push to send the animal on its
migratory path. Importantly, these
hormonal changes do not occur in
non-migratory animals!
Internal
changes in animals are often triggered by changes in the photoperiod. These internal (physiological) changes can
arise due to changes in hormones or other internal concentrations. The rhythmic internal changes that do take
place within animals regularly on a recurring basis (whether season to season,
such as with long-range migrations, or day-to-day, such as with nomadic
migrations and other behaviors) constitute what is called an animal’s biological clock.
Questions for Class Discussion:
1.
Do humans have a biological clock?
Does this biological clock tell humans to sleep in the daytime or in the
nighttime? Does this biological clock
tell humans to migrate long distances every year, like the hawk or hummingbird?
Humans do have internal
biological clocks. Examples are
feelings of hunger or waking up without alarm clocks. Some nomadic humans migrate and follow migrating animals/food
sources during seasonal changes, but it is not known as to whether these human
migrations are linked to the human biological clock.
2. When is the photoperiod longest? When is it the shortest?
Photoperiod is longer in the
summer (because the Northern Hemisphere is tilted toward the sun and thus
receives more light). In the winter
photoperiod is shorter (because the Northern Hemisphere earth is titled away
from the sun).
3. Why is photoperiod important to migratory
animals?
Photoperiod is a migrational
cue for animals to begin migrations. (see explanation in Activity step #8)
4. How is the photoperiod different from an
animal’s biological clock?
Photoperiod is an external
cue that triggers internal physiological changes in an animal, such hormonal
changes. These internal changes that
occur regularly constitute an animal’s biological clock.
5.
Which cues for a student’s movements over the course of a day are
natural, and which are human-made? How
do these cues relate to the migrational cues of an animal?
Cues such as getting out of
bed when the sun is out is a natural cue.
Cues such as bells or alarm clocks are human-made. The photoperiod is a natural cue that
affects the migration and some other functions of animals.
Display the Biological Clock Assessment Slide Show to your
students, allowing them to answer the questions posed on the slide show in
writing, perhaps on the back of their activity sheets. This slide show, along with students’
answers to the above discussion questions, will provide a good representation
of students’ knowledge gained through this lesson.
Students should understand the concept of photoperiod as a migration cue for animals. Children should be able to calculate the photoperiod given a particular sunrise/sunset time. They should also be able to link surface color changes with seasonal changes. Finally, children should also be able to compare their own cues for movement with migrational cues for animals.
Answers to the questions on the Assessment Slide Show are as follows:
Slide 2:
Photo 1 (winter: snow) most closely corresponds to the photoperiod seen in Day "C."
Photo 2 (fall: harvest) most closely corresponds to the photoperiod seen in Day "A."
Photo 3 (summer: green grass) most closely corresponds to the photoperiod seen in Day "B."
Slide 3:
1. A bird would prepare to fly south in the fall. This day would have a photoperiod like Day "A." This photoperiod would indicate to the bird that soon the weather would be changing colder.
2. Chickens would want to lay the most eggs during the late spring and early summer, so that if the eggs hatch their babies will have warm weather to help them survive their early weeks of life. Such a day would have a photoperiod such as that seen in Day "B." Note that some students may recognize that Day "A" can also represent a springtime photoperiod, which would also be an acceptable answer. Hens usually begin laying eggs in the spring after they begin experiencing about 14 hours of daylight. In fact, some chicken farmers use indoor lighting to change the photoperiod such that it "tricks" hens into laying eggs year-round!
Lesson Extensions for Authentic Assessment
1. Have students plot the photoperiod of their
town over the course of the year on a graph, and discuss the trends seen in the
photoperiod.
2. Have students choose another site in the
world (for example, the wintering site of the Swainson’s Hawk as discussed the
Hawk in Flight lesson) and calculate the
changing photoperiod there over the course of the year. How does the photoperiod of this other site
compare with that in the students’ home town?
3. Using a globe and a flashlight, show in a
darkened room how as the earth changes its tilt, the length of the photoperiod
of a location on the rotating globe will change. Which way does the earth tilt in the summer (Northern hemisphere
towards sun)? Which way does it tilt in
the winter (opposite way)? What are the
changes in photoperiod as seen by the changes in the amount of time the globe
is lit by the flashlight? Are there any
parts of the world that could have a photoperiod of 24 hours, or zero hours
(polar latitudes)?