What makes me tick tock?

Transcription

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 1

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, 2

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 3

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 4

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 5

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: The National Park Service has information about the habitat impact of artificial light focuspartner1.htm 6

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. 7

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, 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. 8

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 ( 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 9

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. 10

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. 11

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? 12

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. ( 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 13

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. 14