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Learning science is a process that is both individual and social. Like researchers, engineers, mathematicians, or physicians who work in teams to answer questions and to solve problems, students in science classrooms often need to interact with their peers to develop deeper knowledge of scientific concepts and ideas. The GroupWork activities were developed to foster an environment in which groups of students work cooperatively to

  • plan experiments,
  • collect and review data,
  • ask questions and offer solutions,
  • use data to explain and justify their arguments,
  • discuss ideas and negotiate conflicting interpretations,
  • summarize and present findings,
  • and explore the societal implications of the scientific enterprise.

The GroupWork environment is one in which students are “doing science” as a team. Suggestions about when to introduce these group activities are included in the Teacher Activity Notes.

Format and Organization of GroupWork Activities Each GroupWork activity includes teacher activity notes, an activity guide, an individual report, resource materials, and at times, data sheets. The activity guide contains instructions for the group's task and questions to be discussed as students plan for and work on a group product. Resource materials are varied. They might include textual information, visual resources such as photos, drawings, graphs or diagrams, video, or audiotapes. Individual reports by students are an integral part of each activity to be completed in class or as part of a homework assignment. Planning information for the teacher is found on the Teacher Activity Notes page.

Sets of GroupWork activities are organized around a central concept or a basic scientific question-a “big idea.” Ideally, as students rotate to complete these activities, they encounter this central idea, question, or concept in different scientific contexts or in different social settings. These rotations provide students with multiple opportunities to grapple with the material, explore related questions and dilemmas, look at different representations, and think of different applications. Figure 1 shows how students rotate from activity to activity around the “big idea.”

The GroupWork activities were designed to be open-ended to foster the development of higher-order thinking skills. Such open-endedness allows students to decide as a group how to go about completing the task, as well as what the final group product might be. Open-ended group activities increase the need for interaction as students serve as resources for one another, draw upon each other's expertise and knowledge, and take advantage of their different problem-solving strategies. When groups are heterogeneous and include students with many different intellectual abilities, the repertoire of strategies and previous experiences is rich and diverse. As students interact with their peers, they learn how to communicate effectively, justify their arguments when challenged, and examine scientific problems from different perspectives. Such interaction scaffolds students' knowledge of scientific concepts and principles.

These GroupWork activities then are quite different from traditional lab activities that include more step-by-step procedures and are crowded with details. In addition to reading, writing, and computing (the traditional academic abilities), students use many different intellectual abilities to complete their task. They make observations, pose questions, plan investigations; they use and create visual models, access and interpret scientific information from different sources and from different media, and convey scientific findings in diagrams, graphs, charts, or tables. The use of a wide array of resource materials provides students with additional ways to access and use information, as well as with additional opportunities to demonstrate their intellectual competence and be recognized for their contributions. We have included in the Teacher Activity Notes a partial list of some of the multiple abilities students might be observed using in these group activities.

When group activities are open-ended, rich, and intellectually demanding, a single student will not be able to complete the task in a timely fashion by himself or herself. Making students responsible as a group to interpret a challenging task and to design a common product or group presentation increases group interdependence. Teachers know, however, that it is also important to hold each student personally accountable for contributing to the group's success and for mastering the concepts or the big idea of the activity. To do so, students are required to complete individual written reports in which they respond in their own words to key discussion questions and summarize what they have learned in the group activity. These written responses can be useful for teachers in gauging and monitoring student understanding and progress.

Role of the Teacher Planning ahead and organizing the classroom for GroupWork is important for the successful implementation of group activities. We suggest that you refer to Elizabeth Cohen's book, Designing GroupWork: Strategies for Heterogeneous Classrooms, published by Teachers College Press in 1994. (See also Lotan, R.A., J.A. Bianchini, and N. C. Holthuis (1996). “Complex Instruction in the Science Classroom: The Human Biology Curriculum in Action,” in R. J. Stahl, (Ed.) Cooperative Learning in Science. A Handbook for Teachers, Addison-Wesley Publishing Company)

Many teachers have realized that when students work in groups, direct instruction is no longer practical. The teacher can't be everywhere at once, telling students exactly what to do and how to do it. Thus, teachers delegate authority to students and students take responsibility for their own behavior and their own learning. Rather than constantly turning to the teacher for help, students talk with each other to find out what they should be doing and to solve the challenging problems assigned to them. Teaching students to work collaboratively and to be responsible to one another as a group is an important prerequisite for successful GroupWork. Students also support the smooth operation of groups when they have learned to play different roles in their groups effectively. For example, the facilitator sees to it that everyone in the group knows what has to be done and gets help when necessary. The recorder keeps notes of the group's discussions and checks to see if individual reports have been completed. The materials manager sees to it that the group has all the equipment necessary and that the tables are cleared at the end of the lesson. The reporter presents the findings of the group during wrap-up time. When the activity involves hazardous materials, a safety officer might be needed. Every student must have a role to play, and roles rotate so students learn how to perform each role competently.

Delegating authority doesn't mean that the teacher Withdraws from the class or completely stays out of the action. Instead of being the focal point of the classroom, the teacher carefully observes the students as they work in the groups, stimulates and extends their thinking, and provides specific feedback.

Equalizing Participation among Members of the Group Making sure that all members of the group have access to the materials and that one group member doesn't take over or dominate the group while another withdraws are among the principal challenges of GroupWork. Teachers can increase participation of students by explaining how the different intellectual abilities are relevant to the successful completion of the task. The teacher states that while no one group member has all the abilities, everyone in the group has some of the intellectual abilities necessary to complete the task successfully. Furthermore, after careful observation of the students' work in groups, the teacher can publicly acknowledge those students who have made relevant contributions and explain specifically how these contributions made the group move forward and become more successful. It is important that the teacher be able to notice the intellectual contributions of students who have low academic or peer status, and who are frequently left out of group interactions. These strategies are particularly relevant in untracked classrooms, where students have a wide range of previous academic achievement (mainly in reading) or where significant proportions of students are English-language learners. Teachers, classmates, and the low-status students themselves need to understand that when many different intellectual abilities are necessary to complete a task successfully, everybody's contribution becomes critical to the success of the group. As more previously low-achieving students feel and are expected to be competent, their participation in the group increases, and subsequently their learning achievements increase as well.

Rachel A Lotan, Ph.D.

School of Education

Stanford University

Figure 1 Activity Rotation in GroupWork

GroupWork Contents

Activity Duration Materials Activity Summary

1. GroupWork 1

Orientation Activity: What's in the Box?

50 minutes Sealed box with assorted items inside This introductory demonstration requires students to consider the way in which people seek to learn about objects or events. The teacher must apply this to the cell-how to scientists know about the cell?

2. GroupWork 2

Comparing the Light Microscrope and the Electron Microscope

40 minutes Microscope, microscope slides, cover slips, cheek (squamous epithelial) cells or prepared slides, methylene blue, and art supplies Students use a light microscope to examine cheek cells. They compare the light microscope and the electron microscope by designing advertisement.

3. GroupWork 3

Experimenting with Bacteria Cells

50 minutes 2 petri dishes with agar and bacteria, and any of the following: antibiotic discs, refrigerator, ultraviolet light source, salt, sugar, vinegar Students design an experiment to determine the effects of various factors on bacterial cell growth and reproduction. They develop procedures for conducting the experiment and methods for data collection.

4. GroupWork 4

Eggstraordinary Cell Membranes

50 minutes 4 eggs with dissolved shells (one in air, one in colored water, one in corn syrup, one in vegetable oil), art supplies Students examine two eggs without shells to learn about the structure and function of cell membranes. They are asked to create a model of a cell membrane.

5. GroupWork 5

Cancer: A Disease of the Cell

40 minutes None Students examine resource materials on cancer. They are asked to refute of defend a legal case that relates the incidence of cancer to one or more risk factors.

6. GroupWork 6

Culminating Activity: Analyzing Results of a Bacteria Experiment

40 minutes 2 petri dishes with agar and bacteria from GroupWork Activity 3, art supplies (such as markers, poster paper, cardboard), costumes, and props Students observe bacteria, analyze the results of bacterial cell growth, and present their findings on the factors affecting their growth.

GroupWork 1: Teacher Activity Notes - Orientation Activity: What's in the Box?

Big Idea: How Do Scientists Know about the Cell?

PLAN

Summary

Students participate in a demonstration that requires them to consider the ways in which people seek to understand objects or events. Students are then asked to apply this to the cell: how do scientists know about the cell? NOTE: There is no student activity card for this activity.

Group Size 4 to 5 students

Objectives

Students:

  • identify an unknown object using indirect evidence and observations.
  • predict how scientists study objects like cells without seeing them with the naked eye.

Multiple Abilities

  • Observing carefully, recording data correctly and clearly (ability to be precise)
  • Explaining clearly and fully, using words precisely (communication skills)

Student Materials

  • A closed wooden or cardboard box that contains one or two somewhat familiar but not necessarily commonplace objects (e.g., an egg beater, a computer diskette, or part of a machine)

Estimated Time 50 minutes

Suggested Use

  • This set of activities works well near the end of the unit.

IMPLEMENT

1. Tell students that you have found this box in your attic, and you want to find out what is in it. However, you can't get it open! Divide students into groups and brainstorm ways to find out what is in the box.

2. Have students select a reporter in each group. Allow students to discuss methods for finding out for 3 to 5 minutes. Have reporter from each group share the group's responses. As they come up with ideas, write them on the chalkboard, grouping them by method. Add any other ideas that students didn't think of themselves such as the following:

  • Shake it and make some assumptions based on the noise.
  • Use technology, such as an X-ray or stethoscope.
  • Conduct a controlled experiment. For example, if I think it's a particular object, I could create a similar apparatus with known objects and then compare such characteristics as weight, movement, and sound.

3. After each group reporter reports the group ideas, explain that scientists often can't use a textbook that has all the answers in it when they are studying something. Rather, they have to analyze different pieces of evidence carefully and then make conclusions. Emphasize that science is not simply a collection of facts or beliefs, but of interpretations of evidence. Compare the methods a scientist might use to study cells (observations, technology, and empiricism) with the suggestions given by students to determine the contents of the box.

Background Information

None required

Extend This Activity

Ask students to design an experiment or new technology that would help them determine what is in the box, as scientists have done to study the cell in greater detail. Compare this to the exchange of ideas between science and technology in the study of cells.

Extension Questions

How does the analogy of a cell as a box that cannot be opened accurately represent how scientists study cells? How is it not a good comparison?

ASSESS

Use the group presentation, individual report, and group discussion to assess if students can

  • observe carefully and use indirect evidence to identify an unknown object.
  • explain their predictions based on concrete observations or indirect evidence.
  • predict, using the analogy of the unknown object in a box, how scientists often use various kinds of evidence to study cells.

GroupWork 1 Individual Report: Orientation Activity: What's in the Box? (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

1. Describe at least three methods one could use to determine what is in the box.

2. a. What evidence will these methods provide?

b. What questions will you still have after using these methods?

GroupWork 2: Teacher Activity Notes - Comparing the Light Microscope and the Electron Microscope

Big Idea: How Do Scientists Know about the Cell?

PLAN

Summary

Students use a light microscope to examine cells and then analyze information about the electron microscope. They compare the uses and advantages of each type of microscope by designing catalog advertisements for a scientific supply company.

Group Size 4 to 5 students

Objectives

Students:

  • identify cells and nuclei using a light microscope.
  • explain reasons for using both light microscopes and electron microscopes to study cells.

Multiple Abilities

  • Observing carefully, recording data correctly and clearly (ability to be precise)
  • Making detailed and lifelike drawings (artistic ability)
  • Creating an engaging and influential presentation (creative ability)
  • Explaining clearly and fully, using words precisely (communication skills)

Student Materials

  • Microscope, microscope slides, cover slips, cheek (squamous epithelial) cells or prepared slides, methylene blue, poster paper, colored pens or pencils

Estimated Time 50 minutes

Suggested Use

  • This set of activities works well near the end of the unit.

IMPLEMENT

  1. Before beginning this activity, remind students of the proper handling and use of the light microscope. Remind students that they should not point the mirror directly at the sun. Make sure that they know how to prepare a wet-mount slide by placing their sample onto the slide, adding a drop of methylene blue, mixing it with the toothpick, and covering it with the slip cover. They need to focus the microscope on low power first, then medium and high powers.
  2. If you do not wish students to prepare slides of their own cheek cells, have prepared slides on hand for them to use. Examples of prepared slides include erythrocytes, lymphocytes, sperm, eggs, cardiac muscle, and neural retina.
  3. It is important for students to see that the field of view changes as the magnification changes, allowing us to see either the “big picture” with little detail at the lowest power or much greater detail with a smaller field of view at the highest power. At low power, many small clumps of cells may be visible because of the large field of view. At medium power, cells will appear larger, and there will be fewer of them due to the reduced field of view. Nuclei within each cell may appear as darker spots. At high power, probably only one or two clumps of cells will be visible, with the dark nuclei clear within each cell. The double-layered cell membrane may also be visible.

Background Information

The naked, human eye cannot see most eukaryotic cells. They are too small-between 10 and 30 micrometers in diameter. Why can't we see such small objects? The answer lies in the physiology of the eye. If two objects are farther apart than 100 micrometers, the light beams that are reflected from the objects into the eye fall on different detector cells (rods or cones) in the retina. Thus, the eye is able to resolve the two objects-to tell that there are two objects instead of one. However, if the two objects are closer together than 100 micrometers, the light beams fall on the same detector. We then see only one object.

In order to distinguish individual cells, to say nothing of their structures, humans must use instruments that provide greater resolution. Resolution is defined as the minimum distance that two points can be separated and still be seen as two points. One way to increase resolution is to increase magnification-to use microscopes. Indeed, most of our current knowledge about cell structure has been gained through use of microscopes.

Three centuries ago, Robert Hooke and Antonie von Leeuwenhoek used simple, light microscopes to magnify the size of cells so that the cells appeared larger than 100 micrometers. These simple microscopes magnified images of cells by bending light through a single glass lens. Leeuwenhoek's microscope, for example, consists of (1) a plate with a single lens, (2) a mounting pin that holds the specimen to be observed, (3) a focusing screw that moves the specimen nearer to or farther from the eye, and (4) a specimen-centering screw. Although simple in construction, this type of microscope provides a magnification of 266 times, as good as many modern microscopes. It makes visible structures that are less than 1 micrometer (100 nanometers) in thickness.

To learn how a simple microscope works, examine the figures below. The size of the image that falls on the retina depends on how close the object is to the eye-the closer the object, the bigger the picture. The eye, however, is not able to focus comfortably on an object closer than about 25 centimeters; it is limited by the size and thickness of its lens. A glass lens interposed between the object and eye, as in a simple microscope, provides additional focusing power. Because the object is closer, the image on the back of the eye is bigger than it would have been had the object been 25 centimeters away from the eye. As a result, we perceive the object as magnified.

Extension Questions

  • How did the invention of the light microscope influence scientific knowledge and practice?
  • Define science and technology. What is the relationship between the two? What evidence can you provide for this relationship?

ASSESS

Use the group presentation, individual report, and group discussion to assess if students can

  • identify cells and nuclei using the light microscope.
  • observe and explain structural differences in various cells.
  • explain the benefits of the advanced technology of the electron microscope.
  • describe the use of each kind of microscope.
  • explain why and how scientists might use one or the other kind of microscope to study cells.

GroupWork 2 Activity Guide: Comparing the Light Microscope and the Electron Microscope (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Introduction

One of the first important sources of information about cells came from the light microscope. As technology improved, the electron microscope was developed to study cells in a different way. In this activity you consider the relative usefulness of these two tools.

Materials

  • Microscope
  • Microscope slides
  • Cover slips
  • Cheek (squamous epithelial) cells or prepared slides
  • Methylene blue
  • Art supplies such as poster paper, colored pens, or pencils

Procedure

Step 1 Working in pairs, use the microscope to examine a sample of epithelial cells (from the inside of a person's cheek). First, prepare the slide and add a drop of methylene blue to the slide. On your Data Sheet, make a diagram of your observations when using the microscope on low, medium, and high powers.

Step 2 As a group, discuss the following question. What are the differences in the field of view when using the microscope at low, medium, and high powers?

Step 3 Compare and contrast the diagrams of the cells under a light microscope on Resource 1 with the diagrams you created.

Step 4 Examine the information about the electron microscope on Resource 2. In your opinion, why and how do scientists use both kinds of microscopes (light and electron)?

Step 5 Your group is the advertising team for a scientific supply company, and you need to develop an advertisement for both the light microscope and the electron microscope. Make sure to include the following in your advertisement.

  • A description of the use of each kind of microscope.
  • Why and how scientists might use one or the other kind of microscope to study cells.
  • An explanation of the benefits of the advanced technology of the electron microscope.

GroupWork 2 Data Sheet: Comparing the Light Microscope and the Electron Microscope (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

1. Diagram of cells at Low Power

2. Diagram of cells at Medium Power

3. Diagram of cells at High Power

GroupWork 2 Resource 1: Comparing the Light Microscope and the Electron Microscope (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

GroupWork 2 Resource 2: Comparing the Light Microscope and the Electron Microscope (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Brief Discussion of Electron Microscopes

There are two kinds of electron microscopes. The first kind is called the transmission electron microscope. Transmission electron microscopes use electrons transmitted through the material being observed to visualize the specimen. The specimen is prepared as a very thin section. Areas of the specimen that permit the transmission of many electrons, called electron-transparent regions, show up bright. Areas that scatter electrons away from the image, called electron-opaque regions, appear dark. Transmission electron microscopes are capable of resolving objects only 0.2 nanometers apart, or five times the diameter of a hydrogen atom!

A second kind of electron microscope, the scanning electron microscope, produces striking three-dimensional (3-D) images. A beam of electrons works like a fine probe to focus on the surface of the specimen, which passes back and forth rapidly. The electrons that are reflected back from the surface of the specimen, together with other electrons that the specimen itself emits, are amplified and transmitted to a television screen. There, the image can be viewed and photographed. In images made with a scanning electron microscope, depressed areas and cracks in the specimen appear dark, while elevated areas such as ridges appear light. Although scanning electron microscopes have a resolution of only 10 nanometers, they have proven to be very useful in observing and learning about many biological and physical phenomena.

There are two major drawbacks of the electron microscope. First, cells are killed in the process of preparing them for examination. Thus, the movements and reactions that occur in living cells remain largely invisible. Second, the preparation of cells for the electron microscope often damages cell structure. In other words, what is seen may differ from what is actually present in a living cell.

GroupWork 2 Individual Report: Comparing the Light Microscope and the Electron Microscope (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

1. How did you go about examining cheek cells under the light microscope? What did you learn from this process?

2. What are the differences in using a light microscope versus an electron microscope to study cells?

3. What does the use of electron microscopes in scientific research say about the relationship between science and technology?

GroupWork 3: Teacher Activity Notes - Experimenting with Bacteria Cells

Big Idea: How Do Scientists Know about the Cell?

PLAN

Summary

Students design and implement scientific experiment to determine the effects of various factors on bacterial cell growth and reproduction.

Group Size 4 to 5 students

Objectives

Students:

  • design an experiment to determine the effects of various factors on bacterial cell growth and reproduction.
  • develop procedures for conducting the experiment and methods for data collection.

Multiple Abilities

  • Logically analyzing the problem, making connections between ideas/concepts, solving a problem experimentally, making a hypothesis (reasoning ability)
  • Explaining clearly and fully, using words precisely (communication skills)

Student Materials

  • Resource
  • Individual Report
  • 2 petri dishes with agar and bacteria, and any of the following: antibiotic discs, refrigerator, ultraviolet light source, salt, sugar, vinegar, magnifying glass or microscope

Estimated Time 50 minutes

Suggested Use

  • This set of activities works well near the end of the unit.

IMPLEMENT

  1. To prepare for this activity, pour the agar plates or purchase petri dishes with the nutrient agar already inside. For instructions on preparing and pouring agar, see the manufacturer's suggestions. You need 12 petri dishes, each with 25 ml of agar so each group can have its own control and variable specimens.
  2. Before students begin this rotation of activities, you may want to brainstorm as a class how students could gather data for this experiment and how they would quantify their data. They could make a grid on the petri dish and count how many colonies (spots) they see in each grid, or they could estimate the percentage of the dish that is covered with bacteria colonies.
  3. Students will be designing and setting up their experiment during this activity. Make sure they give you an opportunity to review and approve their experimental design before they implement it. Due to the duration of bacteria growth, they will be analyzing their results during the Culminating Activity. Since groups will have started the experiment on different days, you can use the various amounts of growth as a point of discussion and analysis during the final activity.
  4. When students are choosing the variable with which to experiment, make sure mat each group chooses a different variable (sun versus darkness, warm versus cold, dry versus humid) so that you can have rich discussions about many factors that affect bacteria growth.
  5. Remind students that they must keep their petri dishes closed at all times during the experiment, as any contamination from bacteria in the air will affect their results.

Background Information

None required

ASSESS

Use the group presentation, individual report, and group discussion to assess if students can

  • state the research question.
  • predict the experimental results and give reasons for their predictions.
  • describe and justify me experimental procedures.
  • identify a “control” for their specific experiment.
  • explain the methods for data collection and recording.

GroupWork 3 Activity Guide: Experimenting with Bacteria Cells (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Introduction

Scientists have gained knowledge of the structure and function of cells in a number of different ways. Sometimes, they might simply observe a live cell under a light microscope or a prepared cell under an electron microscope. Other times, they design experiments by changing the cell or its environment and studying the effects. In this activity you are the Research Team for a biotechnology company interested in using bacteria to develop a new drug. You need to know what the best conditions for cell growth are in order to manufacture the drug.

Materials

  • Resource
  • Individual Report
  • 2 petri dishes with agar and bacteria
  • Magnifying glass or microscope
  • Other materials will vary based on experimental designs.

Procedure

Step 1 Discuss with your group the following questions and record your responses.

  • What environmental factors could you change in the lab in order to test their effect on bacteria cell growth?
  • In making observations of bacteria in petri dishes, how would you know whether the cell growth was affected? What changes would you look for? How would you display your data?

Step 2 Based on the materials provided by your teacher, design an experiment to test the effects of one of the factors on your list. Write your final experimental design on the Resource. Make sure you list the Materials, the Procedure, and any questions you want to answer. Get your teacher's approval of your experimental design, then use the materials to set up the experiment in the area designated by your teacher. You will have to wait for one or more days for your cells to grow, then you can analyze the results of your experiment during the Culminating Activity.

Your product for this activity is a proposal and presentation to the president of the company that describes your experiment and includes

  • an explanation of your research question.
  • what you predict this experiment will prove.
  • the procedure you used to set up the experiment and why you did it that way.
  • how you will collect your data.

GroupWork 3 Resource: Experimenting with Bacteria Cells (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Use this sheet for your final experimental design to test the effects of your selected factors on bacterial cells. Remember to get your teacher's approval of your experimental design before you implement it.

GroupWork 3 Individual Report: Experimenting with Bacteria Cells (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

1. How did your group decide what environmental factor from your list you would test on bacteria cell growth?

2. What do you think your experiment will demonstrate about cell growth?

3. Why are you using nutrient agar in the petri dishes to grow your bacteria cells? What does this tell you about the requirement for living cells?

GroupWork 4: Teacher Activity Notes - Eggstraordinary Cell Membranes

Big Idea: How Do Scientists Know about the Cell?

PLAN

Summary

Students observe eggs without shells in various substances to determine what molecules can pass through a cell membrane. They design and construct a model of the cell membrane structure.

Group Size 4 to 5 students

Objectives

Students:

  • identify ways that molecules move into or out of the cell.
  • describe the movement of molecules through the cell membrane.
  • explain why the selective permeability of the membrane is important for the functioning of the cell.

Multiple Abilities

  • Logically analyzing the problem, making connections between ideas/concepts, hypothesizing (reasoning ability)
  • Observing carefully and accurately, recording observations correctly and clearly (ability to be precise)
  • Drawing an idea, creating a model (spatial/visual ability and creative/artistic ability)

Estimated Time 50 minutes

Suggested Use

  • This set of activities works well near the end of the unit.

Student Materials

  • Data Sheet
  • Individual Report
  • Lives of Cells Section 3, Cell Activities
  • 4 eggs with shells dissolved soaked in each of the following: vegetable oil, corn syrup, tap water with food coloring, dry in a closed container; coffee filters; strainer/colander; various small objects such as beans, sand, gravel; water; paper and colored pens or pencils

IMPLEMENT

  1. Preparing the eggs: Begin preparing the eggs about 3 days before you plan to implement the activity. To dissolve the shell of the eggs, place them in about 2 cups of vinegar for approximately 48 hours. At the end of 48 hours, rinse the eggs with water. Then place half of them in colored water for 24 hours. Place the other half in an empty or water-filled container and cover it. We suggest making some extras, as a few are bound to break.
  2. To transport the eggs safely to school, you may want to carry them in a zip-lock bag filled with water or vinegar. (The fluid will help cushion any blows the eggs may sustain in the course of the trip.) Place the bag or bags in another sealed, plastic or glass container.
  3. You may provide students with an inexpensive, hollow rubber ball commonly found in supermarkets and drugstores. These balls can be used by students to help model a cell membrane.

Background Information

Cell membranes are freely permeable to water. Water molecules can pass through pores in the sheet of lipid molecules. They do so through the process of diffusion-water molecules move from an area of higher concentration to an area of lower concentration. This form of diffusion, involving net water movement across a membrane, is called osmosis.

Cell membranes, however, are not permeable to all molecules. Rather, they are selectively permeable. Selective permeability allows the passage across a membrane of some molecules but not others. It is the result of specific protein channels extending across the membrane. A selectively permeable membrane is important in that it allows the cell to act as an isolated compartment. Thus, a cell can concentrate and/or bring together these molecules it needs to survive.

There are two ways that channels in cell membranes move molecules into and out of the cell. They are facilitated diffusion and active transport. Facilitated diffusion is the transport of molecules across a membrane by specific channels toward the direction of lowest concentration. Active transport is the transport of a molecule across a membrane, independent of the concentration, by the expenditure of chemical energy.

Extend This Activity

Ask students to brainstorm other substances they could put the shell-less egg into to find out what molecules will cross the cell membrane, then have them try it at home or in class.

Extension Questions

  • What other ways can molecules move into and out of the cell?
  • What purpose does a selectively permeable membrane serve?
  • Why is it important for scientists to learn how cell membranes work? Provide a real-life example.

ASSESS

Use the group presentation, individual report, and group discussion to assess if students can

  • identify ways for molecules to move into or out of the cell (diffusion and active transport).
  • describe how some molecules pass through the membrane, while others are excluded from either the inside or outside of the cell.
  • explain why the selective permeability of the membrane is important for the functioning of the cell.

GroupWork 4 Activity Guide: Eggstraordinary Cell Membranes (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Introduction

Scientists often try to learn how cells work by studying the structure and function of their parts. To do so, they often conduct experiments to see how different conditions affect a cell. In this activity, you observe a single cell that's easy to see without a microscope: a chicken egg!

Materials

  • Data Sheet
  • Individual Report
  • Lives of Cells Section 3, Cell Activities
  • 4 eggs with shells dissolved soaked in each of the following: vegetable oil, corn syrup, tap water with food coloring, dry in a closed container Coffee filters
  • Strainer/colander
  • Various small objects such as beans, sand, gravel
  • Water
  • Paper and colored pens or pencils

Procedure

Step 1 On your Data Sheet, record your observations of the eggs and the substances in which they are soaking. How are they different? How are they similar?

Step 2 In your group, discuss the following questions.

  • Based on your observations, which substances or molecules do you think can cross the cell membrane? How do you know? Consider the molecules that are inside and outside of the egg.
  • How does an experiment like this help scientists learn about the structure of cells and cell membranes?

Step 3 Design and build a model to represent the cell membrane you have observed. Use your model to answer the following questions.

  • How do some molecules pass through the membrane, while others are excluded from either the inside or the outside of the cell?
  • What is the importance of the selective permeability of the cell membrane for the cell to function effectively?

GroupWork 4 Data Sheet: Eggstraordinary Cell Membranes (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Diagram and describe your observations about the differences and similarities between the eggs.

GroupWork 4 Individual Report: Eggstraordinary Cell Membranes (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

1. What was the purpose of having a shell-less egg that wasn't in any substance but air?

2. Draw a picture of your model of a cell membrane.

3. How does an experiment like this help scientists understand cells?

GroupWork 5: Teacher Activity Notes - Cancer: A Disease of the Cell

Big Idea: How Do Scientists Know about the Cell?

PLAN

Summary

Students examine resource materials that deal with cancer and several environmental factors. They use these materials to defend or refute a legal case that relates the incidence of cancer to one or more of these factors.

Group Size 4 to 5 students

Objectives

Students:

  • identify factors that cause cancer.
  • describe how cancer cells move and change in the body.
  • interpret graphs correlating incidence of cancer in various populations to environmental factors.
  • analyze data to determine whether or not it proves causation for cancer.
  • critique information to form arguments on a legal case.

Multiple Abilities

  • Logically analyzing an issue, hypothesizing, making connections between ideas and concepts (reasoning ability)
  • Analyzing and interpreting graphs (spatial/mathematical ability)

Student Materials

  • Activity Guide
  • Resources 1 and 2
  • Individual Report

Estimated Time 40 minutes

Suggested Use

  • This set of activities works well near the end of the unit.

IMPLEMENT

  1. Discuss what students may already know about cancer. Have students use the text as a resource for explaining how cancer cells develop and move throughout the body.
  2. The resources are a series of graphs showing strong correlations between various types of cancers and their risk factors. However, this is a good opportunity for students to learn the distinction between correlation and causation. In developing their product, a legal case, they may decide that more evidence is needed that shows the actual mechanism for the risk factor affecting cells, making them cancerous. On the other hand, students may decide that they already know enough about how cells work and the environmental factors in question to make a statement about causation.
  3. Encourage each group to focus on a different risk factor or kind of cancer so that a variety of evidence is presented to the class.

Extension Questions

  • How can knowing how cells are able to function help scientists develop treatments and/or cures for cancer?
  • What are other examples of diseases caused by abnormal cells?
  • What are ways to reduce your risk of cancer?

ASSESS

Use the group discussion, individual reports, and group product to assess if students can

  • identify factors that cause cancer.
  • describe how cancer cells move and change in the body.
  • interpret graphs correlating incidence of cancer in various populations to environmental factors.
  • distinguish between a correlation and a causation.
  • analyze data to determine whether or not it proves causation for cancer.
  • suggest what information is missing that could strengthen the argument or enhance the evidence.
  • explain evidence for the risk factor that causes a specific type of cancer.

GroupWork 5 Activity Guide: Cancer: A Disease of the Cell (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Introduction

Scientists often perform experiments on or conduct studies of cells. For example, scientists explore how cancer cells grow, reproduce, and spread to learn more about cancer. They also attempt to determine what factors cause cancer. In this activity you discover a practical reason scientists study cells.

Procedure

Step 1 Examine Resource 1. In your group, discuss the following questions.

  • What is the relationship between smoking and lung cancer for men and women in the United States over time?
  • Using your text as a resource, what might be an explanation for this relationship?

Step 2 Examine Resource 2. In your group, discuss the following questions.

  • What is the relationship between certain food consumption and cancer in countries around the world?
  • What is the relationship between locations in the United States and the incidence of cancers? What aught be an explanation for this relationship?

Step 3 Currently, cigarette companies are required to put warning labels that smoking is related to lung cancer on all packaging and advertisements. Should other factors related to cancers have warning policies as well? Your team must create a Public Information Campaign FOR or AGAINST a law that would require warning labels on any product that is shown to have a strong causal relationship with cancer. Be sure your presentation includes

  • a description of how cancer cells move and change in the body,
  • an explanation of your evidence for the risk factor you believe causes a particular kind of cancer, and
  • a description of further studies you think could be done to prove more conclusively that this factor causes cancer.

GroupWork 5 Resource 1: Cancer: A Disease of the Cell (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell

GroupWork 5 Resource 2: Cancer: A Disease of the Cell (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

GroupWork 5 Individual Report: Cancer: A Disease of the Cell (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

1. How does cancer seem to operate in the body?

2. How can we identify factors that cause cancer?

3. How does this activity help answer the question: How do scientists know about the cell?

4. Briefly describe your team's case or explanation of the connection between the evidence presented and your client's cancer.

GroupWork 6: Teacher Activity Notes - Culminating Activity: Analyzing the Results of a Bacteria Experiment

Big Idea: How Do Scientists Know about the Cell?

PLAN

Summary

Students observe bacteria, analyze the results of bacterial cell growth, and present their findings regarding their experiment with factors affecting the growth of bacteria.

Group Size 4 to 5 students

Objectives

Students:

  • conduct an experiment to determine which factors affect the growth of bacteria.
  • collect data and graphically represent the results of their experiment.

Multiple Abilities

  • Clearly and logically explaining to others how and why scientists study cells (communication skills).
  • Making connections between ideas/concepts, logically analyzing the problem, solving a problem experimentally, making a hypothesis (reasoning ability).
  • Recording data correctly and clearly, measuring accurately, explaining clearly and fully, observing carefully and accurately (ability to be precise).

Student Materials

  • Data Sheet
  • Individual Report
  • 2 petri dishes with agar and bacteria from GroupWork Activity 3
  • Art supplies, such as markers, poster paper, and cardboard; Costumes and props

Estimated Time 40 minutes

Suggested Use

  • This set of activities works well near the end of the unit.

IMPLEMENT

Students have experimented with different variables over a period of time. Therefore, be sure to discuss the differences between student results with respect to both the time that has elapsed since they set up the experiment and the different variables they tested.

Extension Questions

  • Since the 1960s, most biological research has focused on molecular and cellular phenomena. Why do you think this is the case?
  • How can knowledge about cells be used to learn how the human body works?

ASSESS

Use the group discussion, individual reports, and group product to assess if students can:

  • make accurate observations.
  • collect data and graphically represent the results of their experiment.
  • explain the differences and similarities between the two petri dishes.
  • recommend methods the Drug Development Team should use in growing bacteria in the lab, and/or methods they should not use.

GroupWork 6 Activity Guide: Culminating Activity: Analyzing the Results of a Bacteria Experiment (Student Reproducible)

Big Idea: How Do Scientists Know about the Cell?

Introduction

When experimenting with cells, scientists must make careful observations and analyze the results in order to make conclusive statements about cell growth. Your team designed and set up an experiment to study how a particular environmental factor affects the growth of bacteria. What conclusive statements can you make about cells based on what you observe in your own experimental results?

Materials

  • Data Sheet
  • <

Image Attributions

Description

Authors:

Grades:

6 , 7 , 8

Date Created:

Feb 23, 2012

Last Modified:

Apr 29, 2014
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