KKH56 INQ2SE CH01 p001 041 final.indd · Page 1 · 12/11/06...

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KH56_INQ2SE_CH01_p001_041_final.indd · Page 1 · 12/11/06 · 4:26:06 PMKH56_INQ2SE_CH01_p001_041_final.indd · Page 1 · 12/11/06 · 4:26:06 PM

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Think of science as a way to explore and understand the natural world. The concepts in physical, life, and earth science connect in many

ways. Making these connections helps you understand the world around you.

During this school year, you and your classmates will have opportunities to explore many ideas that span the sciences. You will explore these ideas as scientists do, through the process of scientific inquiry. Your year will be filled with activities, projects, labs, and interactive readings. Each learning experience is designed to help you better understand science content, as well as to see science as a way of knowing and understanding that content.

As you work through these activities, you will discover that your study of science is actually a study of systems. Look at the opening art for this chapter. How does each picture represent a system? You are familiar with body systems as an example of systems in life science. But, have you ever thought of a population as a

system? Systems exist all around you. In physical science, there are mechanical systems and systems that include chemical reactions. The health of our planet depends on the proper functioning of systems that recycle matter. The water and the carbon cycles are examples of two such systems. As you study science and recognize these systems, you will use models, mathematics, and inquiry to study the world. You will see that the world has many aspects that are changing and many aspects that remain

constant. Keep these ideas in mind as you work through the units this year and become a scientist in your own school investigating the world around you.

Investigations by Design


3Chapter 1 Investigations by Design

In chapter 1, Investigations by Design, you will explore the process of science. In particular, you will review some of what you already know about science. Then you will deepen your understanding of the design of scientific investigations and the characteristics that make the design a credible one. Scientists do this process every day, whether they are exploring the universe or developing new medicines. In past science classes, you learned that many questions can be answered using science. You also explored how scientists use evidence and inference to develop explanations. In this chapter, you will build on these understandings and apply rigorous criteria to scientific design.

Goals for the Chapter By the end of chapter 1, you will be able to answer these questions:

• What characterizes a scientifically testable question?

• How do I design and conduct a scientific investigation?

• By what measures do I evaluate the design of others?

• How do I communicate the results of a scientific investigation to others?

We will introduce you to some important tools and techniques in this chapter that will continue to help you in science class every year. These tools and techniques include the following:

1. Your science book. This book includes many tools to help you learn science. Most important, you will find clearly drawn connections that help you understand what you are learning, how you got there, and where you are going. These connections are in the form of chapter organizers, chapter introductions, and narrative.

2. The BSCS 5E instructional model. You may notice that this student book is different from traditional textbooks. As you learn science this year, you will be immersed in doing science. You will learn through inquiry and connect science to the real world. The BSCS 5Es will guide you through your learning journey in each chapter, allowing you to build your own understanding. The 5Es are engage, explore, explain, elaborate, and evaluate. By using this model, BSCS puts into practice what we know about how students learn best.

3. Chapter organizers. These organizers are included in each chapter. They are a tool to help you see where you are, where you have been, and where you are headed in your learning.

4. Learning strategies. These strategies will help as you are developing your understanding of science. You will use these strategies as you read, organize data, reveal what you have learned, and work in groups. These learning strategies will work not only in your science class but in other classes as well. They will help you develop skills that you can also use outside of school.


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5. Toolbox activities. These activities provide extra practice for some of the skills you will develop this year. Your teacher will share these activities with you as needed.

6. Your science notebook. It is critical that you keep track of your results and your growing understanding in a notebook designated for science. That way both you and your teacher will have a record of your learning.

7. Your teammates. When you work in a team, you will make the most of multiple minds. Learning good teamwork skills will prepare you for the work world. Many great discoveries and decisions are made as teams, not as individuals.

8. Investigations. When you do science, you will model the process of inquiry that scientists use. At the same time, you will learn how to ask and answer questions you have about the natural world.

Term

How term relates dissociation and acid-base

strength

Hydronium ion

Dissociation

Equilibrium position

Soluble

Double arrow

Cation

Anion

Force of attraction

Will my design answer the question?

Have I considered all of the variables?

How will I record and organize my data?

Name _____________________ Date ______________


5Chapter 1 Investigations by Design

9. Questions. When you ask questions of yourself and your classmates, you will contribute to your own understanding. When you answer questions posed in your book, you will demonstrate your understanding.

10. Readings. When you read about the work of other scientists, you will learn about their explorations of science. When you add their knowledge to the understandings about science that you are creating, your understandings will deepen.

11. Scoring rubrics. The scoring rubrics you will use this year outline the expectations your teacher has for the work you will do at the end of each chapter.

To learn about scientific inquiry and to use the tools and techniques of this chapter, you will participate in the following activities:

A Clean Design

Small Problem?

Why and How Do We Inquire?

Valid or Deceptive?

Killing Germs? Digging Deeper


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Linking Question

How does my design reflect the process of

scientific inquiry?

Investigations by Design

Linking Question

How can I design a scientific investigation of my own?

EXPLORE

EXPLAIN

Small Problem?

Key Ideas:• All questions are not testable

with science.• Careful design and

implementation of a scientific investigation lead to valid results.

• Communicating scientific results is important to scientific inquiry.

��

�ENGAGE

A Clean Design

Key Ideas:• Careful design of scientific investigations is essential to ensure

that the investigation has a good chance to provide answers.• Scientific investigations include attention to the control of

variables.

��

sterile swab

��

��

�


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Linking Question

How can I demonstrate what I have learned about the

process of scientific inquiry?

Linking Question

How can the process of scientific inquiry help

me to evaluate scientific claims in the media?

CHAPTER

1 Major Concepts

� Scientific investigations include• A testable question• A design that leads to valid and reliable

results• Observations and measurement• An appropriate way of communicating and

defending a scientific argument

� Scientific inquiry is a systematic, nonlinear process that increases our chances of solving certain types of problems.

��

�

EXPLAIN

Why and How Do We Inquire?

Key Idea:Scientific Inquiry is a systematic, nonlinear process.

EVALUATE

Killing Germs? Digging Deeper

Key Ideas:• Scientific investigations include

• a testable question• a design that leads to valid and reliable results• an appropriate way of communicating and defending a scientific argument.

ELABORATE

Valid or Deceptive?

Key Ideas:• All “science” that is reported in

the media is not valid.• Researchers and scientists

must be able to defend their arguments and reproduce their results.

��


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A Clean Design A successful restaurant system depends on many parts working together successfully. From the production of french fries to the cleanliness of the work area and workers, everyone and every part works together to make the restaurant successful. Have you ever worked in a restaurant? If so, you know that all employees are required to wash their hands frequently (figure 1.1). If you spread disease by not washing your hands properly, then the system breaks down and the success of the restaurant suffers.

� Figure 1.1 Hand washing. Why is it so important to wash your hands regularly?

When you were younger, your parents may have reminded you to wash your hands before dinner. An important safety practice in science class and in any science laboratory is to wash your hands before leaving the lab. It should be clear to you why washing your hands in both of these situations is so important. In A Clean Design, you will work with a partner to investigate hand washing. You will use the simple act of hand washing as a way to think about the criteria of a good scientific investigation.


Chapter 1 Investigations by Design 9

MaterialsFor each team of 2 students

access to germ simulator

access to an ultraviolet light source

access to hand soap and a sink

! Cautions

Always use caution when using any chemical in the laboratory. Only apply the germ simulator to your hands—do not ingest it. Do not look directly into the ultraviolet light source. Looking at ultraviolet light directly can damage the corneas, lenses, and retinas of your eyes.

Process and Procedure Germ simulator is a substance that glows when exposed to ultraviolet (UV) light (see figure 1.2). In this activity, the germ simulator represents germs (the substance is not manufactured to contain germs). This simulator is used for many applications, such as determining how well restaurant employees wash their hands.

1. Experiment with the germ simulator and make some observations by completing Steps 1a–f.

a. Apply a small amount of germ simulator to your hands and rub it in like lotion.

b. When your teacher darkens the room, take turns placing your hands under the UV light. Discuss your observations with your partner.

c. Record your observations with words and detailed drawings in your science notebook.

d. Wash and dry your hands as you normally do. e. When your teacher darkens the room, place your hands

under the UV light again. What do you see? Discuss your observations with your partner.

f. Record your results in your science notebook with words and drawings.

2. Imagine that students in another high school science class observed the same phenomenon that you just witnessed. They wondered if the length of time that people spent washing their hands made a significant difference in how clean their hands got. Three lab groups, A, B, and C, designed investigations to answer the question, “Does the length of time you spend washing your hands affect the amount of germs that remain?” Use this focus question as you complete Steps 2a–c.

� Figure 1.2 Germ simulator. Does simple hand washing remove all the bacteria on your hands?


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a. Review all the investigations and look for differences. b. Think of a way to organize the differences in each investi-

gation so that you can easily compare the 3 investigations. Consider using a table or a chart. Record this information in your science notebook as you read the investigations.

c. Read the investigations designed by each lab group: investigation A, investigation B, and investigation C.

Remember, germ simulator is used to represent germs; it is not manufactured to contain germs.

3. Discuss with your partner which investigation (A, B, or C) is most likely to give you meaningful results and answers the question, “Does the length of time you spend washing your hands affect the amount of germs that remain?”

a. Record the investigation you chose and the reasons why you chose it in your science notebook.

b. Record the reasons you did not choose the other 2 investigations.

4. Discuss the investigations and your answers as a class.

Procedure

1. Ask for 3 student volunteers. 2. Apply exactly 1 milliliter (mL) of germ

simulator to the hands of each volunteer. Spread the germ simulator very evenly, covering both the top and bottom of their hands. Make sure that they do not touch anything.

3. Shine the ultraviolet (UV) light on the hands of each student. Identify where the germ simulator is present. Take a photograph of both the top and the bottom of their hands.

4. Label the photographs “before washing.” 5. Ask all 3 students to wash their hands.

• The first student should wash for 1 minute under warm water using exactly 2 mL of hand soap.

• The second student should wash for 1 minute under cold water using exactly 2 mL of the same hand soap.

• The third student should wash for 1 minute under hot water using exactly 2 mL of the same hand soap.

6. Do not let the students touch anything. Allow their hands to dry in the air completely.

7. Shine the UV light on the hands of each student. Identify where the germ simulator is present. Take a photograph of both the top and the bottom of their hands.

8. Compare the before and after photographs, looking carefully for places that glow.

9. Count the number of spots that still glow in the after photographs.

10. Compare the number of spots present on each student’s hands. The hands with the fewest number of spots that glow are the cleanest.

Investigation A



Procedure

1. Ask for 1 student volunteer. 2. Set the water temperature of the sink at

30° Celsius (C). 3. Have the volunteer apply 1 mL of germ

simulator to his or her hands and spread it evenly.

4. Shine the UV light on the hands of the volunteer. Take photographs of both the top and the bottom of the volunteer’s hands. Label the photographs “before washing.”

5. Have the volunteer wash his or her hands with water for 10 seconds using 2 mL of hand soap.

6. Let the volunteer’s hands air-dry. 7. Shine the UV light on the hands of

the volunteer. Identify where the germ simulator is present. Take a photograph of both the top and the bottom of the hands. Label the photographs “after washing.”

8. Compare the photographs and record the results.

9. Have the student remove all the germ simulator by washing his or her hands.

10. Have the student repeat Steps 2–9, but increase the washing time to 15 seconds.

11. Repeat Steps 2–9 again, increasing the washing to 30 seconds.

12. Compare all the before and after photographs. The set of photographs that shows the least amount of germ simulator after washing indicates the amount of time you need to wash your hands in order to get rid of most germs.

Procedure

1. Ask for 3 student volunteers. 2. Ask all the volunteers to apply 1 mL of

germ simulator to their hands and spread it evenly on both the top and the bottom of their hands.

3. Shine the UV light on the hands of each student. Identify where the germ simulator is present. Take a picture of both the top and the bottom of their hands. Label these photographs “before washing.”

4. Have one of the students wash his or her hands in 27°C water for 15 seconds using 3 mL of hand soap.

5. Have a second student wash his or her hands in 27°C water for 30 seconds using 2 mL of the same hand soap.

6. Have the third student wash his or her hands in 27°C water for 45 seconds using 1 mL of the same hand soap.

7. Shine the UV light on each student’s hands. Take photographs and label each “after washing.”

8. Compare all the photographs. The set of photographs that shows the least amount of germ simulator after washing indicates the amount of time you need to wash your hands in order to get rid of most germs.

Investigation B Investigation C


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Reflect and Connect Discuss the following questions with your class. Record your own answers in your science notebook.

1. What information did you and your partner use about each investigation (A, B, and C) to determine which one gave valid results? Use the terms variable, control, and constant in your answer.

2. Were the results from your experience with germ simulator qualitative or quantitative? Give examples to support your answer.

Results from investigations are quantitative if the data represent measurements or specific numbers or amounts. Results are qualitative if the data describe features, characteristics, observations, or relative comparisons.

3. Consider your experience with the germ simulator and the investigation procedures you examined (A, B, and C). What criteria do you think are important for designing a scientific investigation that will give valid results? Explain your criteria.

Small Problem? In A Clean Design, the germ simulator represented common bacteria or other microorganisms that might have been on your hands. Bacteria are virtually everywhere. Figure 1.3 shows a number of bacteria on the point of a pin. These tiny organisms might or might not cause disease. If the microorganisms do cause disease, they are called pathogenic. If they do not cause disease, they are nonpathogenic. Many types of bacteria are even helpful. For example, a certain type of Escherichia coli (E. coli) resides in our intestines to aid the process of digestion.

Through years of study, scientists have learned a lot about bacteria. They have answered many questions by conducting scientific investigations. They carefully design the investigations so that they can collect the best possible data. Scientists then use the data as evidence to support explanations. In Small Problem?, you will work in a team to ask a scientifically testable question and design and conduct a scientific investigation to explore the world of bacteria through inquiry.

� Figure 1.3 SEM image of bacteria. This image taken with a scanning electron microscope (SEM) magnifies the structures 290 times. It shows the small size and large numbers of bacteria that are present on the point of a pin.



Part I: Developing a Question

Materialsnone

Process and Procedure When you think about what scientists do, what thoughts come to mind? If “scientists ask questions” popped into your head, then you’re right. Asking questions is part of the process of scientific inquiry. But scientists are not the only people who ask questions. On a daily basis, you probably ask a few questions as well. Does that make you a scientist? Of course it does. But can you always answer your questions using science? In other words, are your questions scientifically testable? In Part I of this activity, you will work individually and with a partner to develop a scientifically testable question about bacteria.

1. Read the following fictitious story.Health Inspector!

You and your friends are having lunch when there is an announcement over the intercom. The principal informs you that a health inspector will be at the school next week. The health inspector’s job is to make sure the school is clean not only on the surface, but also beneath the surface in areas that we cannot see. While your principal says that everyone has done a very good job keeping the school clean, it is important to know where the health inspector might find problems. The principal asks for your help as scientists. After talking with your friends and your science teacher, you decide that there might be microorganisms like bacteria that general cleaning missed. You decide that this might be something your science class could investigate.

� Figure 1.4 Can you and your classmates investigate the presence of microorganisms in your school?


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2. Make a table similar to figure 1.5 in your science notebook. This will help you organize the information you already have.

� Figure 1.5 Organization table. Make a table like this in your science notebook to organize your information.

3. Fill in your table by completing these steps. a. Think about what you know about the situation in Health

Inspector! Record your ideas in the “what I know” column. b. Think about what you already know about bacteria. Record

your ideas in the “knowledge I have” column. c. Think about any questions that come to mind that you could

investigate. Record your questions in the “what I wonder” column.

4. Meet with a partner and share and revise your table using Steps 4a–d as a guide.

a. Share your table with your partner and discuss your responses in each column. Read these responses aloud to your partner.

b. Ask for advice on how to make your table more complete. c. Revise your table if you think your partner’s advice is better

than yours.

What I Know

What are the facts

from the reading?

Knowledge I Have

What do I know

about bacteria or

other microorganisms?

What I Wonder

What questions

come to mind?



d. Switch roles and listen carefully to your partner.

This process of first thinking (Step 3), sharing (Step 4a), advising (Step 4b), and revising (Step 4c) is called the think-share-advise-revise (TSAR) strategy. You will use this throughout the year in every science subject area.

5. As a class, determine which questions in the “what I wonder” column are scientifically testable in your science class. Agree on which question your class will investigate.

A scientifically testable question is a question addressed and likely answered by designing and conducting a scientific investigation. Evidence gathered in the investigation supports a scientific explanation.

PART I

Answer the following questions with your class. Make notes of the class discussion of each answer in your science notebook.

1 Deciding on a scientifically testable question is the first step in designing a good investigation. Answer Questions 1a–b about these questions.

a. How did you determine which questions were scientifically testable?b. Give an example of a question that is testable and one that is not.

Explain your choices.

2 Describe how you think research scientists determine scientifically testable questions they will pursue. In your description, consider how this task by a research scientist is similar to or different from your task of choosing a testable question.


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Part II: Design Time

Materialsnone

Process and Procedure In Part I of this investigation, you read about a fictional situation at your school and the possible presence of microorganisms. You developed a scientifically testable question based on the situation. In Part II, you will focus on designing a scientific investigation to answer your question. As you design your investigation, you will continue to engage in the process of scientific inquiry. What are the criteria for designing a good investigation? What evidence do you need to collect to answer the question your class is asking? Think about the three investigations you examined in A Clean Design. Remember that the design of the investigation leads you to either valid or invalid results (figure 1.6). You and two other students will make up one team of scientists for this activity.

� Figure 1.6 Planning an investigation. What are the criteria for a good scientific investigation? You will consider these criteria as you and your team plan a scientific investigation.



1. As a class, review what you think are the important criteria of a good scientific investigation. Take notes on your class discussion and record these ideas in your science notebook.

2. Read the protocol Culturing Bacteria to find out how scientists investigate bacteria. Then look at the materials that are available in your classroom.

3. With your team of scientists, design an investigation that will answer the class question from Part I. To make sure your investigation answers your question with valid results, use the following in your design.

a. What is your rationale? How will this investigation test your question?

b. How can you keep the investigation fair? In other words, how will you try to keep all factors or variables constant except for the one you are testing?

A well-controlled investigation only tests one factor at a time and keeps all other factors the same. Factors that are kept the same in each group are called constants. The one factor that changes is called the variable.

c. How will you set up a control?

In an investigation, the control receives no treatment. All other groups are compared against the control.

d. What type of data will you collect to answer the question? e. What tools will you use and what materials will you need? f. What safety precautions will you take? g. How will you organize your data? Will your data be

qualitative or quantitative? h. How will you analyze your data? How will you develop an

explanation and how will you support this explanation? i. How will you validate your investigation? 4. Write a step-by-step procedure for your investigation. Include

labeled diagrams, charts, or tables. 5. Present your team’s design and procedure to the class. 6. As a class, choose 1 procedure that all teams will follow.

Record this procedure in your science notebook.

ProtocolProtocol


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ProtocolCulturing Bacteria

Culturing bacteria or other microorganisms involves growing them on a prepared medium, such as an agar plate. Bacteria can be transferred to agar plates using different tools such as toothpicks, fingers, or pipets. The technique for these tools is described here. No matter which technique you use, bacteria are grown on plates following the same method. This method is described at the end of the protocol.

Sterile Swab or Toothpick 1. Scrape the source of the bacteria with a sterile swab or toothpick. 2. Gently (be careful not to gouge the agar) streak the bacteria from

the sterile swab or toothpick in a zigzag pattern onto one side of an agar plate (see figure).

3. Draw bacteria from the first zigzag and make a new streak onto the adjacent side of the agar plate.

4. Repeat the process on a third side of the plate.

sterile swab

Use a cotton swab or toothpick to make zigzag patterns as shown here.



Finger Gently (be careful not to gouge the agar) streak your finger in a zigzag pattern onto the agar plate (see figure). Note: this method is only used when culturing microorganisms found on your fingers. You must never touch samples of microorganisms already on the agar.

petri dish

agar

Use this method only if you are culturing microorganisms found on your fingers.

Pipet Using a transfer pipet, gently drop the source bacteria (for example, pond water or bacteria culture) onto the agar plate (see figure). Use a sterile swab to streak the sample across the agar.

Growing Bacteria After the bacteria are transferred to the agar plate, tape the plate shut. Place the agar plate upside down in the incubator (or at room temperature) to grow.

transfer pipetUse this method if you are using pond water or a liquid source of bacteria.

Turn your plates upside down in the incubator so condensation will not drip on the agar.


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Part III: Conducting an Investigation

MaterialsFor the entire class

37°C incubator or source of warmth for growing bacteria

30% bleach solution

biohazard disposal bags

For each team of 3 students3 pairs of safety goggles

3 pairs of gloves

2 petri dishes containing nutrient agar

2 sterile swabs

1 permanent marker

PART II

Answer the following questions with your team of scientists. Make notes of your discussion of each answer in your science notebook.

1 Consider your investigation design and the variables involved to answer Questions 1a–e.

a. What variables are held constant in your investigation?b. What is the variable in your investigation?c. Why is it important to test only 1 variable at a time?d. What is your control?e. Why do you need to have a control?

2 Think back to the 3 investigations presented in the activity A Clean Design. Did all of these represent sound scientific investigations? Would each investigation guide scientists to collect evidence? Would that evidence support an explanation for the question asked?

3 Describe why it is important for scientists to design scientifically sound investigations.



tape

other materials as needed

2 index cards

3 Scientific Investigation Report handouts

! Cautions

Wear safety goggles and gloves while conducting the investigation. Do not open petri dishes until you are ready to use them. Tape the petri dishes shut after you collect your sample. Soak the contaminated petri dishes in a 30% bleach solution after you are finished making your observations. Properly wipe down work areas in your classroom and discard disposable items as directed by your teacher. Be sure to wash your hands before you leave your science class.

Process and ProcedureMost of the time, scientists work collaboratively

to gather as much information and data as possible. Your class will now work together to conduct an investigation to answer the question you asked in Part I. The time you spent designing a scientific investigation will help you conduct a valid investigation with reliable, and interesting results. Like the student scientists in figure 1.7, it is time to put your plan to work.

Day 1

1. Before you begin your investigation, reread the question your class is attempting to answer. Based on what you already know, what do you think the results of your investigation will show? Record your prediction as a hypothesis in your science notebook.

Remember, a hypothesis is a statement that suggests an explanation for an observation or an answer to a scientific problem. Your hypothesis suggests a causal relationship or an if/then relationship. You base your hypothesis on your prior knowledge.

2. Review the investigation agreed upon by your class. Verify your understanding of the procedures with your team.

3. Obtain the materials your team needs. Remember to take safety precautions.

� Figure 1.7 Students at work. These students have planned their investigation well and have gotten their teacher’s approval. Now they are following their plan. What do you think they will find on this doorknob?

Wear safety goggles and gloves while conducting

the investigation.


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4. Carry out the investigation carefully; obey all safety precautions. To complete your team’s part, do Steps 4a–e.

a. Obtain a sample from the location that your team is testing. Prepare a petri dish with the sample by following the class procedure.

Remember, the investigation needs to be as controlled as possible.

b. Properly dispose of all materials as directed by your teacher. c. Tape the petri dish shut and do not open the dish again. You

can make all your observations through the lid. d. Label your dish with the location, date, and team name.

Write on the bottom of the petri dish (the bottom contains the agar).

e. Store your petri dish upside down in the incubator at 37°C or as your teacher directs.

Day 2

1. On an index card, write a brief description of your team’s assigned test location. Retrieve your petri dish and place it next to your index card on display (figure 1.8).

� Figure 1.8 Day 2. Your bacteria have grown in the incubator. Now it’s time to share your results with the rest of the class. Mark your test location on an index card.



2. Make a data table according to the class design for recording your results in the investigation. Record the table in your science notebook.

3. Examine all the petri dishes from the other teams in your class. Record your observations and results in your data table as well as those of the other teams of scientists.

4. Listen as your teacher leads a class discussion of these investigations. Make notes in your science notebook of all explanations given for the different results.

Reflect and Connect Work first with your team and then individually to complete the following tasks.

1. Work with your team to analyze your investigation using the handout Scientific Investigation Report. Look at the requirements for your report and discuss with your team how you will answer each section from your investigation.

2. Write a lab report on your own of your investigation. Refer to the Scientific Investigation Report handout to guide you.

3. Write a cover letter to your principal that provides an overview of your investigation. This cover letter will go with your lab report. In the letter, tell your principal about your class investigation. Include the following components in the letter:

a. An introduction about yourself and your science class b. Why you are doing this investigation c. An abstract of your investigation

An abstract is a brief summary of your investigation. It should include the problem you are trying to solve, observations, explanations, and conclusions based on evidence.

d. Recommendations based on evidence from your results e. What new questions you have

Topic: common bacteriaGo to: www.scilinks.orgCode: 2Inquiry23


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Why and How Do We Inquire?You have just been immersed

in the process of scientific inquiry (figure 1.9). In Small Problem?, you developed a scientifically testable question based on a given situation. You then designed an investigation to answer that question, and you conducted that investigation. Did your investigation go smoothly? Were you able to answer your question? Do you have more questions because of the results you got from your investigation? These are all part of the process called scientific inquiry. In Why and How Do We Inquire?,

you will identify the process you experienced as a scientist in your own school. You will work in teams for this activity.

Part I: The Process of Inquiry


1 sheet of chart paper

1 set of markers

3 Process of Inquiry handouts

Process and Procedure 1. Get together with the same team of scientists you were working

with in Small Problem? Using markers, create a flowchart or diagram on chart paper that describes the general process of scientific inquiry your team went through in Parts I, II, and III of Small Problem?

Do not repeat the steps in your procedure. Instead, describe in general terms what you did. For example, the first thing you might have done is make an observation or ask a question.

2. When your team has completed its flowchart or diagram, copy it into your science notebook. Then post it in your classroom.

3. Compare your chart with those of your classmates by following Steps 3a–d.

a. Explain each step in your diagram to another team.

� Figure 1.9 Conducting an investigation. You have been acting as a scientist as you conducted your investigation. Now you will compare your investigation with the process of inquiry.



b. Listen as the other team explains its diagram. c. Discuss the similarities and differences in your diagrams. d. You all followed the same procedure. Are your charts

similar? List at least 2 similarities and 2 differences. 4. With your team, study the handout Process of Inquiry.

Compare your chart with the handout. Identify the stages on the handout that you experienced. Place an X along the paths on the handout that you experienced in your inquiry.

5. Based on information presented in the Process of Inquiry handout and your classmates’ charts, make any additions to your chart that you feel are necessary. Make the same adjustments to the diagram in your science notebook, too.

Your diagram should depict the investigation you did in Small Problem? Not all scientific inquiries proceed down the same path.

6. Read It’s about Inquiry to learn more about the process of scientific inquiry.

It’s about Inquiry

Asking a question and seeking answers is an obvious path to take when inquiring about the natural world. In Small Problem?, you developed a question and then set out to answer your question by carefully designing an investigation. You then conducted your investigation and recorded and analyzed your results. Your results might have helped you answer your question and might have presented you with new questions. You gained some knowledge and understanding of the world of bacteria and possibly identified locations in your school where bacteria were widespread. Was your scientific investigation sound? Did you collect adequate evidence? Were your results valid? Based on your experience, you can see why the design of an investigation is so important.

Scientists propose explanations based on the evidence they collect during their research. This dynamic practice of wondering and asking

questions, of making detailed observations, and of developing explanations based on those observations and evidence is the process of scientific inquiry. It is not a linear process. Look at figure 1.10 to see the different paths scientific inquiry can take. This is how scientists study the natural world.

The ProcessIn your investigation of bacteria, or

microorganisms, in your school, you used the fundamental process of scientific inquiry. This process is composed of the following methods:

• Make observations and ask questions that can be answered by scientific inquiry.

• Check your current knowledge and the knowledge of other scientists.

• Make a prediction or propose an answer that you can test (hypothesis).


26

• Test your prediction by conducting your investigation and gathering evidence through observation.

• Propose explanations based on evidence.

• Consider alternative explanations.

• Test explanations by gathering more evidence or seeing if new predictions are supported based on that explanation.

• Report (or communicate) your findings and proposed explanation.

It is important to realize that inquiry is not a prescribed, sequential process. When scientists do science, they do not just march through the steps in this order. For example, while a scientist is designing an investigation, she might come across new information that causes her to go back to her original question and change it slightly. This might lead her to make changes in the design. Or a scientist collecting data while conducting an investigation might discover a flaw in the design. This might lead him to change the design before he continues. A scientist might not only discover a flaw but might make a new discovery that also generates new questions.

In your investigation, you probably answered, or partially answered, your original question. It is likely that you also came up with new questions. If you had time, you might revise and test your explanations to be satisfied

that you answered your question completely. In this way, you are “doing” science.

� Figure 1.10 Process of inquiry. Inquiry is a dynamic practice used to study the world around you. How did you use this process to conduct your investigation?

It’s about Inquiry, continued



The DesignWhen scientists focus on the design of an

investigation, they have to make sure that the design itself guides them to the answer to their question and controls for error (figure 1.11). If the design is poor, the results are not valid. Proper design of an investigation includes the following considerations:

• Design an investigation that answers the question in the most appropriate and direct manner.

• Control as many variables as possible. The scientist changes only the variable being tested.

• Set up a control group. Sometimes one group is not exposed to the tested variable. This group serves as a comparison group to determine that the results were due to the tested variable and not to some other factor. For example, if scientists are studying the effectiveness of a new arthritis medicine, one group does not take the medicine. Scientists compare this group with the group taking the medicine.

• Use mathematics and technology tools appropriately to collect and analyze data.

• Collect and organize data appropriately.• Include numerous trials, samples, or subjects

in each investigation.

Will my design answer the question?

Have I considered all of the variables?

How will I record and organize my data?

Name _____________________ Date ______________

� Figure 1.11 Investigation design. What should you think about first when designing an investigation?

Answer the following questions in your science notebook.

1 What makes the design of an investigation useful and valid?

2 Now that you’ve learned more about the process of scientific inquiry and about designing scientific investigations, think back to your investigation in Small Problem? as you answer Questions 2a–b.

a. Suggest additional adjustments to the design of your investigation in Small Problem? Describe why you feel these adjustments are necessary.

b. How would these adjustments make the design of your investigation more valid?


28

Part II: Observations Leading to Discoveries

MaterialsFor each student

1 Process of Inquiry handout from Part I

Process and Procedure 1. Read Observations Leading to Discoveries. Use the turn-and-

talk literacy strategy to help you understand the reading by following Steps 1a–h.

a. Choose a partner to work with during this reading. b. Read the first paragraph of the reading silently. c. When both you and your partner finish the paragraph,

decide which one of you will go first to complete Step 1d. d. Turn to your partner and summarize what you read. Relay

your summary aloud as your partner listens. e. Listen as your partner gives you feedback on your summary.

Discuss anything that is confusing to you. f. Each of you will read the next paragraph silently. g. Switch roles; this time your partner will summarize verbally

and you will offer feedback. h. Continue this process. Read each paragraph silently and

alternate roles as you summarize and offer feedback aloud.

This strategy is the turn-and-talk strategy. You will use this literacy strategy throughout the year to help you understand what you are reading.



Observations Leading to Discoveries

In your scientific investigation, you made discoveries about bacteria around your school by beginning with a question. Scientists learn and make discoveries by observing and asking “Why” or “What if” questions. In this reading, you will learn about a man who, when faced with a problem, helped change our way of life. He did this by making observations, asking questions, and engaging in scientific inquiry.

It was the 1840s—a time before scientists had discovered disease-causing organisms. A young Hungarian doctor, Ignaz Semmelweis (figure 1.12), worked in a hospital in Vienna, Austria. As part of his studies, he dissected cadavers (performed autopsies) in one part of the hospital. He also worked in the same hospital delivering babies in the division I ward.

Results of Semmelweis’s studies revealed that 13 percent of the women giving birth in the division I ward were dying of a disease called “childbed fever” (known scientifically as puerperal fever). Only about 2 percent of the women in the other division of the hospital were dying of childbed fever. The divisions were right next to each other, and pregnant women were cared for similarly in all ways except one: in division I, physicians and their students delivered the babies; in the other division, midwives and their students delivered the babies.

Semmelweis began to investigate. He noticed that when the hospital experienced

a violent epidemic of childbed fever, no such epidemic was seen elsewhere in the city of Vienna. He observed that the death rate in home deliveries was much lower than at the hospital in which he worked. He noticed that even homeless mothers too poor to go to the hospital did not contract the fever even after delivering babies themselves in back alleys.

Semmelweis continued his inquiry. Two major correlations came to the surface. First, if the birth was especially traumatic, the mother had a greater chance of contracting childbed fever. Second, closing down division I always stopped the deaths caused by childbed fever.

� Figure 1.12 Ignaz Semmelweis (1818–1865). Semmelweis used the process of inquiry to solve a lethal problem in a Vienna hospital.

“One’s mind, once stretched by a new idea, never regains its original dimensions.”

—Oliver Wendell Holmes


30

Semmelweis continued to seek the cause of the high death rates from childbed fever. One day, Semmelweis’s former professor of forensic pathology, a man he admired greatly, sliced his finger with a scalpel as he performed an autopsy in division I of the hospital. A few days later, the man was dead. He had become severely ill of sepsis (blood poisoning) and showed symptoms that were very similar to those seen in women with childbed fever. Devastated by his former professor’s death, Semmelweis resolved to work harder to understand and prevent childbed fever.

Semmelweis hypothesized that the cause of his professor’s sepsis was the same as that of childbed fever. He proposed that the source was “cadaver particles.” Semmelweis thought that the attending physicians in division I transmitted these particles from cadavers to mothers during childbirth.

People could not see cadaver particles, but they could smell them. Semmelweis thought

that when the invisible particles from a cadaver came in contact with an exposed surface on a patient, such as a wound, the particles were transmitted and caused the disease.

Semmelweis instituted a strict hand-washing policy (figure 1.13) for those physicians and medical students who worked in division I. Before attending patients, all medical personnel were required to wash their hands with chlorinated limewater until their skin was slippery and the smell of the cadaver was gone. Some found this practice a great inconvenience. In the first year of this policy, however, death rates dropped from about 18 percent to about 1 percent in division I. Moreover, not a single woman died from childbed fever between March and August 1848 in Semmelweis’s division. Semmelweis felt he had evidence to support his idea that cadaver particles were responsible for the deaths in division I.

The connection Semmelweis made, that medical personnel were passing infection from their hands to mothers, was an incredible discovery. He made an observation, asked questions, and discovered a pattern. Observing patterns and asking questions are the guiding elements of much of science, historically and today.

Semmelweis lectured publicly in 1850 about his results and wrote a book about his discoveries in 1861. However, the medical community did not accept Semmelweis’s discoveries. In fact, people criticized him both personally and professionally. It was not until 1865 that Joseph Lister (the namesake for Listerine) continued in the vein of Semmelweis’s work and introduced

� Figure 1.13 Semmelweis’s hospital. Semmelweis instituted a strict hand-washing policy to stop the spread of “cadaver particles.” How did Semmelweis use the process of inquiry to solve a problem?

Observations Leading to Discoveries, continued



2. Consider what you have learned about the process of science as inquiry. Follow Steps 2a–b to explain to members of the scientific community in the 1840s what was happening in division I of the hospital.

a. Summarize the reading as part of your explanation. b. Use the handout Process of Inquiry in your explanation.

Describe the steps that Semmelweis used to solve his problem. You may use diagrams in your explanations.

Reflect and Connect Answer the following questions on your own in your science notebook.

1. Initially, the medical community did not accept Semmelweis’s discovery. Think about this as you answer Questions 1a–c.

a. Propose an improvement to Semmelweis’s process of inquiry that might have made his discoveries more readily accepted.

Use the Process of Inquiry handout as your guide.

b. Assume that Semmelweis followed the process of inquiry. Why do you think the medical profession was so reluctant to accept his ideas?

c. Think of other examples in science where a new discovery was made and the scientific community did not immediately accept the new information. Or think of a discovery that took time to prove and demonstrate that the suggestion was correct. Record at least 1 example in your science notebook.

2. Describe why the process of scientific inquiry is not linear.

the use of antiseptics to kill germs and reduce infection and disease. Lister said, “Without Semmelweis, my achievements would be nothing.” It is now well known that hand washing is important as a way to reduce the transmission of disease. It is so important, in fact, that the Centers for Disease Control have released this statement: “Hand-washing is the single most important means of preventing the spread of infection.”

Today, hand washing is part of American culture. You probably have seen signs posted in restaurant and retail restrooms stating,

“Employees must wash their hands before returning to work.” Schools also have programs that teach students about hand washing. There are even monitors above sinks in hospital intensive-care units to promote hand washing. The convenience of indoor plumbing, energy to heat water, special soaps, and health awareness makes hand washing part of our everyday regime. Semmelweis’s work left a legacy of health and hygiene that has improved our way of life today.

Topic: antisepticsGo to: www.scilinks.orgCode: 2Inquiry31


32

Valid or Deceptive?In the last several activities, you thought carefully about how to

design investigations that will answer the scientific questions you have posed. Your understanding of the important criteria for scientific

design is expanding. In Valid or Deceptive?, you will have an opportunity to extend your understanding by evaluating some claims made by scientists.

Have you ever read a headline that makes claims that sound too absurd to be true, like those shown in figure 1.14? You might wonder if these claims are real. Often, the writer of these articles or whoever is being interviewed makes the claim based on “scientific evidence.” But how did the researcher gather evidence? Did the researcher conduct his investigation in a scientifically sound manner? Are the results of the investigation valid? You will work individually as you complete this activity, so think carefully.

MaterialsFor each student1 copy of Process of Inquiry handout

Process and Procedure There are many decisions you’ll make throughout life, as a consumer and as a part of society. Things you learn, information to which you have access, and the community that surrounds you inform your decisions. If you understand the process of scientific inquiry, you can use it to help interpret information you get from many different sources. Read the sidebar Public Health Careers to learn more about how a good background in science is important to reporting scientific issues.

1. Read the following headlines:• “Skin Patch Cuts Cravings for Sweets”• “Sweeteners Cause Memory Loss”• “Pizza Protects against Sunburn and Skin Cancer”• “Aspirin Cuts Risk of Ovarian Cancer”• “Showering Daily Increases Life Span”

� Figure 1.14 Headlines in the news. Did the researcher making these claims design an investigation that gives valid results?



2. Imagine you are a reporter assigned to interview the researcher who posted one of the claims in Step 1. It is your goal as a reporter to provide information to other citizens so that they can make informed decisions. As you think about your interview, complete Steps 2a–d.

a. Review the Process of Inquiry handout and Steps 2b–d before you begin.

b. Develop at least 10 questions that you would ask the researcher making the claim in the headline. Record these questions in your science notebook.

c. At least 3 of your questions should focus on the “design investigation” stage of the Process of Inquiry handout. Address the other stages on the handout with your remaining questions.

d. When developing your questions, consider the criteria you used when you designed the investigation in the activity Small Problem? Be sure that your questions help you determine the following:• There is evidence that supports the claim.• All the information is presented. Nothing seems to be

ignored or deleted from the data.• The data are reliable and appropriate.• The research is reasonable and the investigation is fair.• The researcher or group of researchers is credible and

reliable. 3. Get together with other students in your class who chose the

same headline. Share your questions. Are they similar? 4. Compile a list of the 10 best questions from the discussion in

Step 3 and record them in your science notebook.

Reflect and Connect Work individually and answer the following questions in your science notebook. 1. Use what you’ve learned in this chapter to write answers to

the 10 best questions you recorded in your science notebook. Imagine that you are the researcher. Keep in mind the characteristics of a scientific investigation and how this type of investigation resulted in the claim the researcher made.

Base your answers on your understanding about the process of scientific inquiry and designing scientific investigations. For example, the question you developed might be for the researcher who claimed that showering daily increases life span. Suppose your question was, “How many people were involved in the study?” The answer could be, “One thousand people were involved in the study over the past 20 years.” This addresses a large sample size.


Public Health Careers

SIDE

BAR

34

2. Find a science-related article in your local newspaper, a tabloid, or a magazine. Use the article and perform the tasks in Questions 2a–c.

a. Critically review the article. b. Describe whether the article presents a scientific and valid

argument. c. Do you believe the article? Why or why not?

When you wake up in the morning,

you may hear the radio announcer tell

you that it is a clear day. The public health

department is around to monitor air quality

and the pollution level. It also develops

programs to address air quality.

Next, you step into the shower. It is

good to know that public health employees

monitor the quality of the water you use

for your shower and especially the water

you drink. Did you know that one of the

top 10 great achievements in public health

began in 1945 when fluoride was added to

drinking water in the United States? This

simple act safely and inexpensively benefits

both children and adults. Fluoridation

prevents tooth decay in both children and

adults as well as reduces tooth loss in adults.

You get a fluoride treatment on your teeth

every time you drink water from a tap that is

monitored by public health employees.

As you get in the car to ride to school,

you buckle your seat belt to keep you safe

en route. Public health efforts have been

successful in changing personal behavior

in vehicles. These include widespread use

How has public health influenced the areas you see in this collage?



of seat belts, child safety restraints, and

motorcycle helmet use. On your ride to

school, you pick up breakfast from your

favorite fast-food chain. You see a sign

posted that indicates the restaurant was

rewarded 95 out of a possible 100 points by

local public health inspectors, so you know

the food is prepared safely.

Public health is important to many facets

of our lives. We see the work of public

health officials in regulations protecting us,

from unsafe food preparation to smoke-free

environments, to the safe water that we

drink every day.

Because public health

is involved in the safety

of so many different parts

of our lives, many career

opportunities are available.

These career choices range

from research scientists to

nurses to journalists. Have

you ever thought of being a

journalist working in the area

of public health?

Can you work under very

tight deadlines? Can you write

well? Do you think you would

enjoy “chasing a story,” which

involves some basic research

as well as tracking down

and interviewing the experts? If so, you

may want to consider a career as a health

communications journalist.

George Strait (no, not the country-

and-western singer!) is an award-winning

health and science reporter. His under-

graduate degree in science helped in his

understanding of the scientific process and

method and how to interpret data from

scientific studies. This is exactly what you are

learning in this chapter.

In 1984, George Strait was named the

chief medical reporter for World News

Tonight. At that time, there were no other

specialized medical reporters on any

television network. Strait appeared regularly

on ABC’s World News Tonight and Nightline.

During that time, he received broadcast

journalism’s highest award, the Alfred I.

duPont Award, two times. He was presented

the awards for his groundbreaking series

on women’s health and a

documentary on AIDS in

minority communities.

Strait says there are

three basic requirements

to being a good health

reporter: curiosity, the

ability to write a coherent

sentence, and the ability

to tell a good story. He

goes on to say, “Health

reporting is really a

question of finding

information and assessing

it. It requires trying to

ferret out the truth and

trying to fairly present

what you learn.”

Can you look at a scientific report and tell

if the data are valid? Do you know the right

questions to ask a scientist so that you can

decide if her claims are believable? If so, you

are on your way

to being a good

health and science

journalist.

George Strait is a broadcast journalist with a background in science. Can you determine if the science claims from research are valid or deceptive?

Topic: public health careersGo to: www.scilinks.orgCode: 2Inquiry35


36

� Figure 1.16 Antibiotic-resistant bacteria. The bacteria that are sensitive to antibiotics die out. What happens to the bacteria that survive?

coloniesof

bacteria

only theresistantbacteriasurvive

resistantbacterialive and

reproduce

Killing Germs? Digging Deeper As you discovered in the investigation Small Problem?, bacteria and other microorganisms are everywhere. Some of these bacteria cause disease. Scientists have made great strides in developing products that

kill bacteria (figure 1.15). The death rate due to infection has decreased as the use of antibiotics increased. People now know about good hygiene and the importance of sterilizing medical supplies. All these seem like great advances in medical science. But are they? Are there problems that could arise from using antibacterial products?

Not all bacteria are harmful. For example, E. coli bacteria live in the intestinal tract of humans and other organisms. These bacteria aid digestion by helping break down foods. We use another bacteria, Streptococcus thermophilus, to culture yogurt. However, a specific strain of E. coli found in contaminated beef and other products is often lethal and group A Streptococcus causes strep throat and other illnesses. Antibacterial products cannot single

out harmful bacteria. These products kill both the harmful and the beneficial bacteria.

Our attempts to get rid of unwanted bacteria are creating a new situation. Bacteria that are sensitive to antibiotics die. But some bacteria are no longer affected by antibiotics. They are resistant to antibiotics. Many scientists believe our overuse of antibiotics and antibacterial products causes antibiotic-resistant strains of bacteria to evolve. This means random changes in these bacteria’s genetic material allow them to survive. Then they reproduce and pass on their resistance through their genetic material. (See figure 1.16.) Read the sidebar Antibiotics to learn more about how antibiotics work and how people misuse them.

� Figure 1.15 Antibacterial products. These products are used to get rid of unwanted bacteria. Is there some danger in this?



Is our everyday use of antibacterial products contributing to the evolution of resistant bacteria? Advertisers claim we need these products to stop the spread of disease. Do these products do what advertisers claim?

In Killing Germs? Digging Deeper, you will have an opportunity to demonstrate your understanding of scientific inquiry. You do this by designing and conducting a scientific investigation using antibacterial products. What you have learned throughout this chapter will help you decide what questions to ask, what tools to use, how to design a scientific investigation, how to organize your data, and how to answer your question using evidence. You will then present your findings to the rest of the class. You will work with a team for this activity.


materials as needed to conduct an investigation focusing on antibacterial products, such as the following:

• access to an incubator or warm location• 3 pairs of latex gloves• 3 pairs of safety goggles• petri dishes• petri dishes with nutrient agar• test tubes• sterile swabs• selected antibacterial or disinfectant products• source of bacteria• filter paper• water• scissors• permanent markers

10% bleach solution

30% bleach solution

sticky notes (3 different colors)

3 Scientific Investigation Report handouts

3 Killing Germs? Digging Deeper Scoring Rubric handouts


38

! Cautions

Wear safety goggles and gloves during your investigations. All materials that have come into contact with bacteria should be disposed of properly. Soak materials in 30% bleach solution, drain, and throw in the regular trash. Wipe down your work area with 10% bleach solution before and after the investigation. Wash your hands after the investigation.

Process and Procedure Manufacturers have introduced many products to the market recently that they claim “kill germs,” such as antibacterial and disinfectant products.

1. With your team, think of as many products as you can that have claims similar to those of the antibacterial products pictured in figure 1.15. Write your list in your science notebook.

2. Identify scientifically testable questions you might ask about the products on your list.

Think of as many questions as you can and record them in your science notebook.

3. Choose 1 question from your list in Step 2 for your team to investigate.

Your team must agree on the question to investigate. Discuss the options and justify why you would choose that particular question. Consider how you would design an investigation to answer that question, what background information you need, and if you have access to the necessary equipment and supplies.

4. Review the handout Killing Germs? Digging Deeper Scoring Rubric so that you understand how your teacher will grade your investigation. Discuss any questions you have with your team and your teacher.

5. In your science notebook, answer the following questions: a. What is the question you are investigating? b. What is your rationale? How will this investigation test your

question? c. What is your hypothesis? d. What is the design of your investigation?

Record this as a step-by-step procedure. As a team, determine 1 design for your investigation. If you have several ideas, discuss the pros and cons of each design and make sure each member of your team agrees. Justify why you made each decision in your design. Include a list of materials you will use and safety precautions you will take.



Wear safety gloves and

goggles during your

investigations.

e. What type of data will you collect? f. How will you organize and analyze your data? g. What is your explanation (conclusion) and what evidence

supports your explanation? h. What new questions or ideas do you have? Which might you

pursue? 6. After you have designed your investigation, show your teacher

your procedure for approval. 7. After you have approval from your teacher, conduct your

investigation. Record your observations and data in an organized and useful way.

8. Analyze and discuss the results with your teammates. As you discuss your results, answer Questions 8a–d.

a. How can you explain the results of your investigation? b. Did the results help you answer your question? c. What conclusion can you reach based on your investigation? d. How confident are you that your results answer the question

you chose? Explain your answer.

Remember, to answer this question, consider how well you controlled the variables in the investigation. Discuss any sources of error.

9. Write a lab report on your own of your investigation.

Use what you learned about writing a lab report from the explore/explain activity. You may want to review the Scientific Investigation Report handout.

10. Prepare a visual presentation of your investigation with your team to share with the class. This could be a poster, a computer presentation, or a slide show. Look at the rubric to guide you.

11. Present your investigation to the class. Your classmates will be looking for good qualities of your investigation, ways to improve your investigation, and questions to ask you.

12. After each group presents, get together with your team for a research critique. Decide on 1 strength of the investigation, 1 way to improve it, and 1 question you have about it. Write the “strength” comment on 1 color of sticky note (designated by your teacher), the “improvement” comment on another color, and the “question” on a third color. Post your notes in the area designated by your teacher.

13. At the conclusion of each presentation, discuss the critique statements as a class. The presenters should answer questions from their classmates and address ways to improve their investigation with their own ideas.


AntibioticsSI

DEBA

R

40

Why is it that sometimes when you feel

awful, and you go to the doctor, the doctor

does not give you an antibiotic? It could

be that you have a virus. Antibiotics do not

work on viruses.

Both bacterial and viral infections can

make you sick, but bacteria and viruses are

very different. Bacteria are single-celled

microscopic organisms about 1/100th the

size of a human cell, or 1 micrometer long.

Bacteria are normally found in our bodies

and in our environment, including in plants,

animals, soil, and water. Most bacteria

are helpful, but some harmful bacteria

can cause infections. Common bacterial

infections include strep throat, urinary tract

infections, and diarrhea that is caused by

Escherichia coli bacteria. Bacteria also cause

diseases, such as tuberculosis and anthrax.

See the figure for the three most common

shapes of bacteria.

A virus is 20–100 times smaller than a

bacterium. Viruses consist only of a particle

of DNA or RNA surrounded by a protective

protein coat, or capsid (see figure on p. 41).

Viruses survive only by infecting living cells.

Most biologists classify viruses as infectious

particles rather than living organisms.

Common viral infections are colds, flu

(influenza), and mono (mononucleosis).

Other examples of viruses include chicken

pox, herpes, rabies, Ebola, Asian bird flu,

and AIDS.

Antibiotics kill or inhibit the growth of

bacteria by interfering with the normal

functions of bacteria. Antibiotics do this

without harming the host organism

(humans or other animals). Each antibiotic

affects a unique site within a bacterial

cell. Penicillin kills bacteria by attaching

to their cell walls and destroying a key

part of the wall. Erythromycin attacks the

cell components responsible for making

proteins. Other similar antibiotics include

tetracycline, streptomycin, and gentamicin.

Antibiotics do not work on viruses because

they work on

parts of bacteria

that viruses do

not have, such

as a cell wall.

� Bacterial cells. These are the three most common shapes of bacterial cells. (a) Cocci (spheres) 51,000�; (b) bacilli (rods) 24,000�; and (c) spirochetes (corkscrew) 700�.

Topic: antibioticsGo to: www.scilinks.orgCode: 2Inquiry40

a.

b.

c.



needed, such as at a patient’s request or

for a cold (viral infection). Patients may

make the mistake of using only part of

their antibiotic prescription and saving the

remaining doses for later use.

Misuse of antibiotics can lead to the

evolution of new strains of bacteria

that cannot be killed by currently used

antibiotics. These bacteria are called

antibiotic-resistant bacteria. Antibiotic

resistance occurs when bacterial DNA

spontaneously mutate. Out of the millions

of bacteria living in your body, one might

acquire a mutation that makes it resistant to

an antibiotic. If you take an antibiotic, the

susceptible bacteria will die, but the resistant

bacteria might survive. A resistant bacteria

cell will multiply without competition

from susceptible bacteria. If the bacteria

causing your illness are antibiotic resistant,

an antibiotic will not cure you. Antibiotic

resistance is a major health care problem.

Antibiotic resistance is inevitable

because mutations allow bacteria to

evolve. However, people can do things to

help decrease the number of bacteria that

become resistant. For example, people can

reduce the spread of resistant bacteria by

washing their hands. Doctors can prescribe

antibiotics only when absolutely necessary,

and patients can use them appropriately.

People also can avoid overusing antibacterial

products. By limiting the situations in which

antibiotic-resistant

bacteria thrive,

people can use

antibiotics to treat

disease-causing

bacterial infections

successfully.

Viruses only exist within the host cell and

do not carry out their own biochemical

reactions.

Unfortunately, doctors and patients

misuse antibiotics. Doctors sometimes

prescribe antibiotics when they are not

� Structure of a virus. Viruses are made of DNA or RNA and a protein coat. The electron micrograph (a) shows a virus that infects bacteria magnified 94,500 times. The diagram shown in (b) is of the same type of virus.

proteincoat(“head”)

DNA

tail

tailfibers

Go to: www.scilinks.orgTopic: antibiotic resistanceCode: 2Inquiry41aTopic: super bugsCode: 2Inquiry41b

a.

b.


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