ch 2 apter tools of environmental science chapter 2

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22 Tools of Environmental ScienceC H A P T E R 2

1 Scientific Methods

2 Statistics and Models

3 Making Informed Decisions

PRE-READING ACTIVITY

Key-TermFoldBefore youread this chap-

ter, create the FoldNoteentitled “Key-Term Fold”described in the Reading andStudy Skills section of theAppendix. Write a key termfrom the chapter on each tabof the key-term fold.Under each tab, writethe definition of thekey term.

This photograph shows a researcherfilming a Weddell seal in Antarctica.Although scientists often use sophis-ticated tools in their work, theirmost important tools are those theycarry with them—their senses andtheir habits of mind.

OverviewTell students that this chapter willnot focus on the physical tools ofenvironmental science, such asmicroscopes or computers. Thischapter discusses tools of the mind:the mental and conceptual toolsthat scientists use to explore andunderstand the environment. Thischapter also explains the value ofmaking informed, thoughtful deci-sions about the environment.

Using the FigureScientists have mounted cameras onthe heads of Weddell seals to gatherinformation about their habits. Theresulting film has yielded somethingunexpected: observations of theAntarctic silverfish and the Antarctictoothfish, two ecologically impor-tant species. Ask students to con-sider how these videos might helpscientists. (These videos might helpscientists learn about the huntinghabits of seals. They might also helpscientists better understand feedingrelationships.) LogicalLS

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32 Chapter 2 • Tools of Environmental Science

For information about videosrelated to this chapter, go togo.hrw.com and type in the keyword HE8 TOOV.

GENERAL

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PRE-READING ACTIVITY

ST 2c Creativity, imagination, and a good knowledge base are all required inthe work of science and engineering. (Section 1)

SPSP 6d Individuals and society must decide on proposals involving newresearch and the introduction of new technologies into society. Decisionsinvolve assessment of alternatives, risks, costs, and benefits and considerationof who benefits and who suffers, who pays and gains, and what the risks are and who bears them. Students should understand the appropriateness andvalue of basic questions—“What can happen?”—“What are the odds?”—and“How do scientists and engineers know what will happen?” (Section 1,Section 2, Section 3)

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Chapter 2 • Tools of Environmental Science 33

The word science comes from the Latin verb scire, meaning “toknow.” Indeed, science is full of amazing facts and ideas abouthow nature works. But science is not just something you know; itis also something you do. This chapter explores how science isdone and examines the tools scientists use.

The Experimental MethodYou have probably heard the phrase, “Today scientists dis-covered…” How do scientists make these discoveries? Scientistsmake most of their discoveries using the experimental method.This method consists of a series of steps that scientists worldwideuse to identify and answer questions. The first step is observing.

Observing Science usually begins with observation. Someonenotices, or observes, something and begins to ask questions. An

is a piece of information we gather using our senses—our sight, hearing, smell, and touch. To extend their senses, scien-tists often use tools such as rulers, microscopes, and even satellites.For example, a ruler provides our eyes with a standard way tocompare the lengths of different objects. The scientists in Figure 1are observing the tail length of a tranquilized wolf with the help ofa tape measure. Observations can take many forms, includingdescriptions, drawings, photographs, and measurements.

Students at Keene High School in New Hampshire haveobserved that dwarf wedge mussels are disappearing from theAshuelot River, which is located near their school. The studentshave also observed that the river is polluted. These observationsprompted the students to take the next step in the experimentalmethod—forming hypotheses.

observation

Objectives� List and describe the steps of the

experimental method.

� Describe why a good hypothesis isnot simply a guess.

� Describe the two essential parts ofa good experiment.

� Describe how scientists study subjects in which experiments are not possible.

� Explain the importance of curiosityand imagination in science.

Key Termsobservationhypothesispredictionexperimentvariableexperimental groupcontrol group datacorrelation

S E C T I O N 1

Scientific Methods

Figure 1 � These scientists are mea-suring the tail of a tranquilized wolf.What questions could these observa-tions help the scientists answer?

OverviewBefore beginning this section,review with your students theObjectives in the Student Edition.The section focuses on the experi-mental method, but it also explainsthe value of the correlation methodfor use when experiments areimpossible or unethical. Studentslearn about scientific habits ofmind, including curiosity, skepti-cism, intellectual honesty, andimagination.

Ask students, “Why might the sci-entists be measuring the wolf’s tailin Figure 1? Once they make themeasurement, how might they useit?” (The scientists might be measur-ing the tail to record characteristicsof the members of a wolf pack. Thescientists could use this informationto study how the pack changes overtime.) Logical

IdentifyingPreconceptions Scientific Methods An experi-ment may grow out of an observa-tion, but a scientist does notnecessarily know beforehand whathe or she is going to observe. Forexample, if a scientist goes to astream to make observations aboutthe population trends of a type of frog, she might discover thatanother frog species is missingfrom a lake and decide to investi-gate that species instead. Ask stu-dents, “Where would the scientistgo from there?” (Much like areporter, a scientist observes and follows observations to seek out astory. The scientist might try to findout if the frogs have disappearedfrom other bodies of water in thesurrounding area. The scientist willlook for explanations that he or shecan test.) LogicalLS

MotivateMotivate

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FocusFocus

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MISCONCEPTION ALERT

What is an Observation? Ask students to define observation and give examples.Many students may assume that observa-tions include only phenomena they can see.In fact, observations are made using all the senses. Point out that many scientificobservations must be made indirectly, aswhen studying Earth’s deep interior orstudying magma chambers inside volca-noes. Observations can also be maderemotely using robots or satellites.

• Lesson Plan• Active Reading• Section Quiz GENERAL

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Hypothesizing and Predicting Observations give us answers toquestions, but observations almost always lead to more ques-tions. To answer a specific question, a scientist may form ahypothesis. A (hie PAHTH uh sis) is a testable idea or explanation that leads to a scientific investigation. A hypothe-sis is more than a guess. A good hypothesis follows from whatyou already know and can be tested.

The Keene High School students observed two trends: thatthe number of dwarf wedge mussels on the Ashuelot River isdeclining over time and that the number of dwarf wedge musselsdecreases at sites downstream from the first study site. Thesetrends are illustrated in Figure 2. Students tested the water inthree places and found that the farther downstream they went,the more phosphate the water had. Phosphates are chemicals inmany fertilizers.

Armed with their observations, the students might make thefollowing hypothesis: phosphate fertilizer from a lawn is washinginto the river and killing dwarf wedge mussels. To test theirhypothesis, the students make a a logical statementabout what will happen if the hypothesis is correct. The studentsmight make the following prediction: mussels will die whenexposed to high levels of phosphate in their water.

It is important that the students’ hypothesis—high levels ofphosphate are killing the mussels—can be disproved. If studentssuccessfully raised mussels in water that has high phosphate levels,their hypothesis would be incorrect. Every time a hypothesis isdisproved, the number of possible explanations for an observationis reduced. By eliminating possible explanations a scientist canzero in on the best explanation with more confidence.

What is the difference between a hypothesis and aprediction? (See the Appendix for answers to Reading Checks.)��Reading Check

prediction,

hypothesis

2000

1998

Site 1 Students found manymussels in 1998 but fewer in 2000.

Site 2 Students found few mussels in 1998 and fewer in 2000.

Site 3 Students found no mussels in 1998 or 2000.

Figure 2 � The diagram below showsthe trends observed by the students atKeene High School. Site 1 is upstream.Site 3 is downstream.

QuickLABHypothesizing and PredictingProcedure1. Place a baking tray on a table,

and place a thin book underone end of the tray.

2. Place potting soil, sand, andschoolyard dirt in three piles atthe high end of the baking tray.

3. Use a toothpick to poke severalholes in a paper cup.

4. Write down a hypothesis toexplain why soil gets washedaway when it rains.

5. Based on your hypothesis, pre-dict which of the three soils willwash away most easily.

6. Pour water into the cup, andslowly sprinkle water on thepiles.

Analysis1. What happened to the differ-

ent soils?

2. Revise your hypothesis, if neces-sary, based on your experiment.


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QuickLABSkills Acquired• Predicting• Interpreting

AAnnsswweerrss1. Answers may vary. Students

should observe that fine-grainedsoils are more likely to washaway.

2. Answers may vary.

TeachTeach

MISCONCEPTION ALERT

Hypotheses Vs. PredictionsMany people confuse hypotheseswith predictions. Explain that ahypothesis is a general statementthat offers an explanation of aproblem that has been observed.Hypotheses can be supported orcontradicted by experimentation.Point out that a prediction isbased on a hypothesis. A predic-tion is meant to describe whatwill happen in a specific situation,such as during an experiment, ifthe hypothesis turns out to beright. Reinforce this distinctionby having students form hypothe-ses and then make predictionsbased on their hypotheses.

MISCONCEPTION ALERT

Laws and Theories Many students believethat if a theory is accepted by enough peoplefor a long enough period of time, the theorywill “grow up” to be a law. Emphasize thatlaws and theories are both accepted, but thatthey serve different functions. A law, such asthe law of gravity, is a concise statement offact that is accepted as true and universal.Theories, such as the theory of evolution bynatural selection, are statements that are prod-ucts of many scientific observations and mayencompass numerous hypotheses or laws. Like

a law, a theory is accepted as true, but theo-ries are much more complex. A law can becompared to a rubber ball. When droppedunder constant conditions, the ball will alwaysbounce exactly as predicted. Bouncing is theonly action the ball performs. On the otherhand, a theory can be compared to the opera-tion of a car. A car has many components, allperforming different tasks and working in uni-son. A part of the car may be improved, suchas the brakes or air bags, but the general func-tion of the car remains constant.

AAnnsswweerr ttoo RReeaaddiinngg CChheecckkA hypothesis is a testable idea orexplanation that leads to a scientificinvestigation. A prediction is a logi-cal statement about what will hap-pen if the hypothesis is correct.

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Writing Skills Have students find somethingof interest to them in the classroom, such as amodel, a fish tank, or a globe, and write downas many observations about the object as theycan in 5 minutes. Then have students switchobjects with a partner and repeat the exercise.Have them compare observations and write ashort summary of what they learned from thisexperience in their EcoLog.

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BUILDERSKILL


Experimenting The questions that arise from observations oftencannot be answered by making more observations. In this situa-tion scientists usually perform one or more experiments. An

is a procedure designed to test a hypothesis undercontrolled conditions.

Experiments should be designed to pinpoint cause-and-effectrelationships. For this reason, good experiments have two essentialcharacteristics: a single variable is tested, and a control is used. The

(VER ee uh buhl) is the factor of interest, which, in ourexample, would be the level of phosphate in the water. To test forone variable, scientists usually study two groups or situations at atime. The variable being studied is the only difference between thegroups. The group that receives the experimental treatment is calledthe In our example, the experimental groupwould be those mussels that receive phosphate in their water. Thegroup that does not receive the experimental treatment is called the

In our example, the control group would be thosemussels that do not have phosphate added to their water. If themussels in the control group thrive while most of those in theexperimental group die, the experiment’s results support thehypothesis that phosphates from fertilizer are killing the mussels.

control group.

experimental group.

variable

experiment

� Keene High School students are conducting an experiment to study the effect of phosphate levels on the growth rates of freshwater mussels.

The ExperimentalMethod In Actionat Keene High School

Keene High School studentscollected mussels (nonendangeredrelatives of the dwarf wedgemussel) and placed equal numbersof them in two aquariums. Theyensured that the conditions in theaquariums were identical—samewater temperature, food, hours of light, and so on. The studentsadded a measured amount ofphosphate to the aquarium of theexperimental group. They addednothing to the aquarium of thecontrol group.

A key to the success of an exper-iment is changing only one variable

and having a control group. Whatwould happen if the aquarium inwhich most of the mussels died hadphosphate in the water and was alsowarmer? The students would notknow if the phosphate or the highertemperature killed the mussels.

Another key to experimenting inscience is replication, or recreatingthe experimental conditions to makesure the results are consistent. In thiscase, using six aquariums—threecontrol and three experimental—

would help ensure that the resultsare not simply due to chance.

1. Applying Ideas Why did thestudents ensure that the conditionsin both aquariums were identical?

2. Evaluating Hypothesis Howwould you change the hypothesis ifmussels died in both aquariums?

CRITICAL THINKING

www.scilinks.orgTopic: Experimenting

in Science

Code: HE80556

ActivityPark it Right Here Use the fol-lowing demonstration to introducescientific methods in a fun, dra-matic way. Ask students to namesome national parks. No matterwhat park is mentioned, write“Yellowstone” on a separate pieceof paper each time a park is calledout. Crumple each paper into aball, and toss it into a clean waste-basket. After doing this severaltimes, ask a student to pick one ofthe crumpled balls. Have the studentopen the paper and concentrate onthe park name without saying italoud. Look like you are concen-trating really hard, then amazethem with your mind-reading abili-ties. When students ask how youdid it, ask them to form hypothesesand predictions about what hap-pened. Ask them how they couldtest their predictions. Explain thatthis is how science works. Peopleobserve something strange, they tryto explain their observations, theytest their explanations, and theyweed out incorrect explanationsuntil they are left with the mostlikely one. LogicalLS

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GENERAL

English Language Learners

Notable Quotes

“If I have seen further than others, it isbecause I have stood on the shoulders ofgiants.”

—Isaac NewtonMuch like the upper levels of a buildingdepend on the lower levels for structure,discoveries are often possible only becauseof earlier scientific findings. Ask studentsto research Newton’s three laws of motionand describe how Newton based his workon that of others. LogicalLS

The Experimental Method InAction If students have troubleidentifying the hypothesis, tellthem that the Keene High Schoolstudents hypothesized that phos-phates were killing the mussels.

AAnnsswweerrss ttoo CCrriittiiccaall TThhiinnkkiinngg1. Students ensured that the con-

ditions in the aquariums wereidentical so that they could testone variable.

2. Answers may vary. Students maysuggest testing other variables.

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Group Activity The Metric Game Point out thatmost of the measurements in thisbook use SI units. Understandingthe metric system is an essentialcomponent of scientific literacy.Divide students into teams andhave each team send a representa-tive to the board. Select an item in the room (such as a book, theboard, or water in a glass) andprovide a metric unit with whichto measure the item. Have eachteam estimate the measurement ofthe item. After measuring the item,the team with the closest estimateis awarded one point. Allow stu-dents to take turns measuring theitems so that students becomefamiliar with the meter stick, bal-ance, graduated cylinder, and othermeasuring tools. Repeat this exer-cise throughout the year. VisualLS

Teach, continuedTeach, continued

Never Cry Wolf Students may not be familiarwith naturalist Farley Mowat’s novel NeverCry Wolf. In this book, the Canadian govern-ment sent Mowat out to investigate wolves.Their hypothesis was that the growing wolfpopulation threatened people and caribou.Mowat’s data did not confirm the hypothesis.In fact, the wolves were helping to maintain a healthy caribou population. Ask students to read Never Cry Wolf, or watch the movie,and identify different aspects of the scientificmethod in Mowat’s research. LogicalLS


MISCONCEPTION ALERT

Information on the InternetThe Internet is an increasinglyimportant means not only fordisseminating scientific resultsand studies but also for linkingrelevant studies together. TheInternet also offers a lot of mis-information and bias. As a class,brainstorm a list of environmen-tal science keywords. Then havestudents use the keywords tofind examples of both unbiasedand biased information on theInternet.

Organizing and Analyzing Data Keepingcareful and accurate records is extremelyimportant in science. A scientist cannotrely on experimental results that are basedon sloppy observations or incompleterecords. The information that a scientistgathers during an experiment, which isoften in numeric form, is called

Organizing data into tables and graphicillustrations helps scientists analyze thedata and explain the data clearly to others.The scientist in Figure 3 is analyzing dataon pesticides in food. Graphs are oftenused by scientists to display relationshipsor trends in the data. Graphs are espe-cially useful for illustrating conclusionsdrawn from an experiment.

One common type of graph is called abar graph. Bar graphs are useful for com-

paring the data for several things in one graph. Figure 4 showsthe data in Table 1 in the form of a bar graph. Look at the datafor Site 3 in the bar graph. The data show that the concentrationof phosphates is higher at Site 3 than at Sites 1 and 2, and theconcentration of nitrates is lower than at Sites 1 and 2.

Drawing Conclusions Scientists determine the results of theirexperiment by analyzing their data and comparing the outcomeof their experiment with their prediction. Ideally, this comparisonprovides scientists with an obvious conclusion. But often the con-clusion is not obvious. For example, in the mussel experiment,what if three mussels died in the control tank and five died in theexperimental tank? The students could not be certain that phos-phate is killing the mussels. Scientists often use mathematical toolsto help them determine whether such differences are meaningfulor are just a coincidence. Scientists also repeat their experiments.

Repeating Experiments Although the results from a single experiment may seem conclusive, scientists look for a largeamount of supporting evidence before they accept a hypothesis.The more often an experiment can be repeated with the sameresults, in different places and by different people, the more surescientists become about the reliability of their conclusions.

Communicating Results Scientists publish their results to sharewhat they have learned with other scientists. When scientiststhink their results are important, they usually publish their find-ings as a scientific article. A scientific article includes the questionthe scientist explored, reasons why the question is important,background information, a precise description of how the workwas done, the data that were collected, and the scientist’s inter-pretation of the data.

data.

Figure 3 � This scientist is analyzinghis data with the help of a computer.

0

0.1

0.2

0.3

Site 1 Site 2 Site 3

Mill

igra

ms

per

lite

r o

f w

ater

Nitrates

Phosphates

Figure 4 � This graph and the tableabove it compare the concentrationsof phosphates and nitrates in theAshuelot River in 2000. Site 1 isupstream of Sites 2 and 3.

Pollutant Concentrations (mg/L)

Site Nitrates Phosphates

1 0.3 0.02

2 0.3 0.06

3 0.1 0.07

Table 1 �

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CONNECTIONCONNECTIONLANGUAGE ARTSLANGUAGE ARTS

GENERALNotable Quotes

“There are two possible outcomes: If the result confirms the hypothesis, thenyou’ve made a measurement. If the result is contrary to the hypothesis, then you’vemade a discovery.”

—Enrico FermiAsk students to explain the followingquote in relation to scientific methodsand the formation of a hypothesis.

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The Correlation MethodWhenever possible, scientists study questions by using experi-ments. But many questions cannot be studied experimentally. The question “What was Earth’s climate like 60 million yearsago?” cannot be studied by performing an experiment because thescientists are 60 million years too late. “Does smoking cause lungcancer in humans?” cannot be studied experimentally becausedoing experiments that might injure people would be unethical.

When using experiments to answer questions is impossible orunethical, scientists test predictions by examiningor associations between two or more events. For example, scien-tists know that the relative width of a ring on a tree trunk is agood indicator of the amount of rainfall the tree received in agiven year. Trees produce wide rings in rainy years and narrowrings in dry years. Scientists have used this knowledge to investi-gate why the first European settlers at Roanake Island, Virginia(often called the Lost Colony) disappeared and why most of thefirst settlers at Jamestown, Virginia, died. As shown in Figure 5,the rings of older trees on the Virginia coast indicate that theLost Colony and the Jamestown Colony were founded duringtwo of the worst droughts the coast had experienced in centuries.The scientists concluded that the settlers may have starvedbecause the famine made it hard to grow food.

Although correlation studies are useful, cor-relations do not necessarily prove cause-and-effect relationships between two variables. Forexample, the correlation between increasingphosphate levels and a declining mussel popula-tion on the Ashuelot River does not prove thatphosphates harm mussels. Scientists becomemore sure about their conclusions if they findthe same correlation in different places and asthey eliminate other possible explanations.

correlations,

GeologyConnection to

Coral Correlation Some geolo-gists use an interesting correla-tion to study records of pastclimates. Certain species of coralput down layers of skeleton everyyear and can live for 300 years.Coral skeletons contain the ele-ments strontium, Sr, and calcium,Ca. In some corals, the ratio ofthese elements in a layer of skele-ton correlates with local sea sur-face temperature at the time thatthe layer forms. The correlationbetween the Sr to Ca ratio andthe sea temperature provides sci-entists with one record of howEarth’s climate has changed overthe centuries.

1560 1600 1640 1680

–4

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4

Year

Dro

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JamestownDrought1606–1612

Lost ColonyDrought1587–1589 Wet

conditions

Dry conditions

Source: Science.

Figure 5 � This cross section of abaldcypress from southeasternVirginia (above) shows a record ofrainfall beginning in 1531. The graphtranslates the relative tree ring widthinto what is called a drought index,which allowed scientists to comparerainfall between different years.

Using the Figure Drought in Jamestown Thedrought severity index for theJamestown area from 1560 until1700 is shown in Figure 5. Askstudents to look for and discusspatterns in the data. Ask, “Whatdoes the data show about the‘average’ rainfall in the Jamestownarea? What conclusions can youdraw about the role of rainfallvariability on the history ofhuman settlements and civiliza-tions?” (The data shows that therainfall in any given year is likely tovary, often widely, from the average.Variability in rainfall could have con-tributed significantly to the fates ofhuman settlements and civilizations.)

Visual

Dendrochronology TutorialsDendrochronologists are scientistswho study tree rings. Because trees have annual growth cycles,scientists can determine a tree’s history by taking tree ring samples.A thick ring indicates that condi-tions were favorable for treegrowth and a thin ring can revealenvironmental stresses such asdrought. Dendrochronologists ana-lyze tree-ring data from around the world to establish a record of the Earth’s climate. There areseveral dendrochronlogy tutorialsand activities available on theInternet. Have students find thebest ones and share them with the class.

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GENERAL

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Phenology in Alaska In an attempt to study climate change, scientists have utilized the records from a yearly bettingpool in Nenana, Alaska. For most of thepast century, area residents bet yearly on when the ice of the Nenana River would crack, signaling the start of thespring thaw. Participants pay a few dollarsto enter, and the winners split the pot. Thewagering has resulted in a nearly 100-year

record of the date the river has broken upeach year. A Stanford University scientistwho researches phenology, the study of thetiming of natural events, used the records as data for a correlation study. In 2001 the ice breakup occurred, on average, 5.5 days sooner than it did in 1917. Thisindicates that the climate around Nenanahas warmed over the course of 80 years.

BRAIN FOOD

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Scientific Habits of MindScientists actually approach questions in many different ways.But good scientists tend to share several key habits of mind, orways of approaching and thinking about things.

Curiosity Good scientists are endlessly curious. Jane Goodall, pic-tured in Figure 6, is an inspiring example. She studied a chimpanzeetroop in Africa for years. She observed the troop so closely that shecame to know the personality and behavior of each member of thetroop and greatly contributed to our knowledge of that species.

The Habit of Skepticism Good scientists also tend to be skepti-cal, which means that they don’t believe everything they are told.For example, 19th century doctors were taught that men andwomen breathe differently—men use the diaphragm (the sheet ofmuscle below the rib cage) to expand their chest, whereas womenraise their ribs near the top of their chest. Finally, a female doctorfound that women seemed to breathe differently because theirclothes were so tight that their ribs could not move far enough topull air into their lungs.

Openness to New Ideas As the example above shows, skepticismcan go hand in hand with being open to new ideas. Good scien-tists keep an open mind about how the world works.

BiologyConnection to

Discovering Penicillin AlexanderFleming discovered penicillin byaccident. Someone left a windowopen near his dishes of bacteria,and the dishes were infected withspores of fungi. Instead of throw-ing the dishes away, Fleminglooked at them closely and sawthat the bacteria had died on theside of a dish where a colony ofgreen Penicillium mold had startedto grow. If he had not been acareful observer, penicillin mightnot have been discovered. Youmay find Penicillium yourself onmoldy bread.

Figure 6 � Jane Goodall is famousfor her close observations of chim-panzees—observations fueled in partby her endless curiosity.



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CONNECTIONCONNECTIONBIOLOGYBIOLOGY

GENERAL

Jane Goodall Jane Goodall isfamous for studying chimpanzeesin the Gombe Forest in Tanzania.Before she began her research in1960, people knew little aboutchimps and thought they were dan-gerous. She would spend days at atime patiently observing the chimpsin their habitat. She initially hadlittle money for her studies but wasable to survive on little food anddrink. She made the most of theresources she had, going on to beone of the most successful womanscientists in history. To learn moreabout the Gombe chimps and theresearchers studying them today,students can visit the Jane GoodallInstitute’s Center for PrimateStudies on the Internet.

GENERALNotable Quotes

“The whole of science is nothing morethan a refinement of everyday thinking.”

—Albert Einstein Discuss the quotation with students.Ask, “Are there tools of environmentalscience that are useful to people in every-day situations?” If necessary, promptthem to consider how a mechanic usesthe experimental method to diagnose aproblem with a car. LogicalLS

StrategiesStrategiesINCLUSIONINCLUSION

Have students observe people, objects, sys-tems and the environment of the classroomfor 8–10 minutes. Then have them label fournote cards with the following: “See,” “Hear,”“Smell,” and “Touch.” Students can drawor write about their observations for eachof the senses. Observations should indicatetime, date, and room conditions. This exer-cise can also be repeated, and students cancompare and discuss the results.

GENERAL

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MISCONCEPTION ALERT

Scientific Methods Point outthat the title of this section isplural. Emphasize that there isno single scientific method. Sci-entists approach problems froma variety of viewpoints. Theyconduct their research usingavailable tools, data, time, andpeople. Research often leadsscientists to develop new toolsand techniques, but the basicmethods remain unchanged.

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Intellectual Honesty A scientistmay be certain that a hypothesis is correct before it has been fullytested. But when an experimentis repeated, the results may differ from those obtained thefirst time. A good scientist willconsider the possibility that thenew results may be accurate, even if this means that the hypothesismight be wrong.

Imagination and CreativityGood scientists are not onlyopen to new ideas but able toconceive of new ideas themselves.The ability to see patterns whereothers do not, or to imaginethings that others cannot, allows agood scientist to expand the bound-aries of what we know.

An example of an imaginative and creative scientist is John Snow, shown in Figure 7. Snow was aphysician in London during a cholera epidemic in 1854. Cholera,a potentially fatal disease, is caused by a bacterium found in waterthat is polluted with human waste. Few people had indoor plumb-ing in 1854. Most people got their water from public pumps; eachpump had its own well. To find the polluted water source, Snowmade a map showing the homes of everyone who died of cholera.The map also showed the public water pumps. In this example ofa correlation study, he found that more deaths occurred around apump in Broad Street than around other pumps in the area.London authorities ended the cholera epidemic by shutting off theBroad Street pump. Using observation, imagination, and creativity,Snow solved an environmental problem and saved lives.

How did drawing a map of London help John Snowsolve the cholera problem in 1854?��Reading Check

1. Describe the steps of the experimental method.

2. Name three scientific habits of mind and explaintheir importance.

3. Explain why a hypothesis is not just a guess.

4. Explain how scientists try to answer questions thatcannot be tested with experiments.

CRITICAL THINKING

5. Analyzing Methods Read the description of experi-ments. Describe the two essential parts of a goodexperiment, and explain their importance.

6. Analyzing Relationships How can a scientist be both skeptical and open to new ideas at the same time? Write a one-page story that describessuch a situation. WRITING SKILLS

READING SKILLS

S E C T I O N 1 Review

Figure 7 � John Snow (bottom) created his famous spot map (top),which enabled him to see a patternthat no one had noticed before.

Oxford St. Dean

St.Wardour St.

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Broad St.Gt. Marlborough St.

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Scale0 50 100 yards

0 50 100meters

Pump sites

Deaths from cholera

AAnnsswweerr ttoo RReeaaddiinngg CChheecckkSnow’s map helped him see that thehomes of people who died fromcholera were concentrated aroundthe Broad Street pump.

Reteaching Scientific Methods Remind stu-dents that not all questions can beanswered using scientific methods.Ask students to give examples ofquestions. Then ask students whichquestions scientists could answerand which ones they could not.

Logical

Quiz 1. Why should the results of an

experiment be repeatable? (If theresults of an experiment cannot bereplicated, scientists cannot trustthe reliability of their conclusions.)

2. Why are experiments designed tohave as few variables as possible?(Limiting variables allows scientiststo pinpoint causes and effects.)

Alternative Assessment Identifying Scientific MethodsProvide students with a copy of anarticle about an environmental issuefrom a magazine such as Discover,National Geographic, or ScientificAmerican. Have students highlightand label parts of the article thatdemonstrate the scientific method.

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AAnnsswweerrss ttoo SSeeccttiioonn RReevviieeww1. First, make observations or measurements to

gather information. Second, use these obser-vations to form a hypothesis, and make aprediction based on the hypothesis. Next,conduct an experiment to test the hypothesisunder controlled conditions. Organize andanalyze information, or data, that is gatheredfrom the experiment. Use the data to formconclusions about the original hypothesis.Repeat the experiment and share the results.

2. Sample answers: Curiosity leads scientiststo ask new questions. Skepticism leads sci-entists to question explanations they doubt.Openness to new ideas prevents scientists

from limiting their thinking. Intellectualhonesty helps ensure accurate conclusions.Imagination and creativity help scientistsconceive new ideas and explanations.

3. A hypothesis considers information gath-ered by observation, while a guess mightnot. A hypothesis is also a testable explana-tion, while a guess may not be testable.

4. Scientists study correlations, reliable associ-ations between two events, to answer ques-tions that cannot be investigated withexperiments. The more correlations thatexist between variables, the more sure scientists can be of their conclusions.

5. The two essential parts of a good experi-ment are testing only one variable andusing a control. It is important to test onlyone variable so you can be sure that thisvariable is the cause of any changes thatoccur. It is important to use a control sothat you have something to compare withthe experimental treatment.

6. Answers may vary. A skeptical scientist does not believe everything he or she istold. In being skeptical about establishedideas, a scientist is open to new ones.

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Environmental science provides a lot of data that need to beorganized and interpreted before they are useful. is thecollection and classification of data that are in the form of num-bers. People commonly use the term statistics to describe num-bers, such as the batting record of a baseball player. Sportswritersalso use the methods of statistics to translate a player’s battingrecord over many games into a batting average, which allowspeople to easily compare the batting records of different players.

How Scientists Use StatisticsScientists are also interested in comparing things, but scientistsuse statistics for a wide range of purposes. Scientists rely on anduse statistics to summarize, characterize, analyze, and comparedata. Statistics is actually a branch of mathematics that providesscientists with important tools for analyzing and understandingtheir data.

Consider the experiment in which students studied mussels tosee if the mussels were harmed by fertilizer in their water. Studentscollected data on mussel length and phosphate levels during thisexperiment. Some mussels in the control group grew more thansome mussels in the experimental group, yet some grew less. Howcould the students turn this data into meaningful numbers?

Statistics Works with Populations Scientists use statistics todescribe statistical populations. A statistical population is a groupof similar things that a scientist is interested in learning about. Forexample, the dwarf wedge mussels shown in Figure 8 are part ofthe population of all dwarf wedge mussels on the Ashuelot River.

StatisticsObjectives� Explain how scientists use statistics.

� Explain why the size of a statisticalsample is important.

� Describe three types of modelscommonly used by scientists.

� Explain the relationship betweenprobability and risk.

� Explain the importance of concep-tual and mathematical models.

Key Termsstatisticsmeandistributionprobabilitysampleriskmodelconceptual modelmathematical model

S E C T I O N 2

Statistics and Models

Figure 8 � Students found thesedwarf wedge mussel shells in amuskrat den. These mussels are partof the statistical population of alldwarf wedge mussels on theAshuelot River.

OverviewBefore beginning this section,review with your students theObjectives in the Student Edition.This section discusses statistics andexplains how scientists apply statis-tics to data. Students will also learnabout the importance of physical,graphical, conceptual, and mathe-matical models in science.

Bring in a few news clippings thatinclude statistics. Discuss the statis-tics and how they are used with theclass. Point out, in particular, adver-tisements that include statistics topromote a product. Discuss withthe class the difference betweenresponsible uses of statistics andmisleading uses of statistics.

Verbal/Visual

Group Activity That’s MY Birthday Write the 12 months of the year on the board.Ask everyone in the room to tellyou his or her birthday. If morethan one student shares a birthday,call attention to this fact. Ask stu-dents if they are surprised. Start adiscussion about the probability ofthis occurrence. Ask interested stu-dents to research why this might bethe case. (Probability is not as simpleas it seems. In a group of 23 people,there is a 50 percent chance that twowill share a birthday. In a group of40, the chance is nearly 90 percent.Have students research in the libraryor on the Internet to find the probabil-ity of a shared birthday.) LogicalLS

MotivateMotivate

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Bellringer

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Critiquing Advertorials Ask students tosearch newspapers and magazines for adverto-rials. These features often resemble magazineor newspaper content but are created by advertisers. Ask students to annotate anadvertorial with their own critique of the statements and statistics provided in the text.A good method to prepare a critique of theadvertorial is to photocopy and reduce thefeature so there is a margin of white space forstudents to work in. LogicalLS


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TT Bellringer TT Size Distribution of Dwarf Wedge

Mussels

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“Rosencrantz and Guildenstern Are Dead”In Tom Stoppard’s play, minor characters fromShakespeare’s “Hamlet” become the protago-nists. Ask students to read the first act of theplay or watch the movie of the same name. In the play, a character is tossing a coin withsome improbable results. Despite continuoustossing, the coin always comes up heads. Askstudents to interpret this scene. Ask, “Whatdoes Tom Stoppard mean to say about theworld that the characters inhabit?” (Studentsmay think that Stoppard was trying to present a

world in which the laws of logic and reason aresuspended. In truth, Rosencrantz and Guildensterninhabit a world that is determined by mathemat-ical concepts of probability. Mathematiciansdefine probability as the long-run pattern thatpredictably emerges from a series of randomoutcomes. If 100 coin flips were made, the resultscan be surprisingly uneven. Coin tosses only yieldabout a .5 probability after one thousand flips.The characters may function with free will, butthey are beholden to a fate—or a probability—that they cannot perceive.) LogicalLS


What Is the Average? Although statistical populations are com-posed of similar individuals, these individuals often have differentcharacteristics. For example, in the population of students in yourclassroom, each student has a different height, weight, and so on.

The Keene High School students measured the lengths ofdwarf wedge mussels in a population, as shown in Figure 8. Theyadded the lengths of the mussels and then divided by the numberof mussels. This gave the average length of the mussels, which instatistical terms is called the mean. The is the numberobtained by adding the data for a characteristic and dividing thissum by the number of individuals. The mean provides a singlemeasure for a given characteristic of a population. Scientists cancompare different populations by comparing their means. Themean length of the mussels in Figure 9 is about 30 mm.

The Distribution The bar graph in Figure 9 shows the lengths ofdwarf wedge mussels in a population. The pattern that the barscreate when viewed as a whole is called the distribution. A

is the relative arrangement of the members of a sta-tistical population. In Figure 9, the lengths of the individuals arearranged between 15 and 50 mm.

The overall shape of the bars, which rise to form a hump inthe middle of the graph, is also part of the distribution. The lineconnecting the tops of the bars in Figure 9 forms the shape of abell. The graphs of many characteristics of populations, such asthe heights of people, form bell-shaped curves. A bell-shapedcurve indicates a normal distribution. In a normal distribution,the data are grouped symmetrically around the mean.

How was the mean length of the dwarf wedge mus-sel population calculated? ��Reading Check

distribution

mean

50 10 15 20 25 35 4530 40 5550 60

Length (mm)

Size Distribution of Dwarf Wedge Mussels

Num

ber

of

mus

sels

0

5

10

15

20

25Figure 9 � This bar graph shows thedistribution of lengths in a populationof dwarf wedge mussels. For example,the second bar from the left indicatesthat the population studied containedfour mussels between 20 and 25 mmlong.

Venn DiagramCreate the

Graphic Organizer entitled“Venn Diagram” described in theAppendix. Label the circles with“Statistics” and “Models.” Then,fill in the diagram with the charac-teristics that eachway of interpretingthe data shares withthe other.

www.scilinks.orgTopic: Statistics in

ScienceCode: HE81452

Reteaching Distribution Students may havetrouble with the concept of distri-butions. Show them a number ofgraphs throughout the book andexplain the arrangement of data.You may want to discuss somegeneral grading strategies with stu-dents to further explain what abell-shaped curveis. Visual

Paired Summarizing Have stu-dents pair with a partner. Each stu-dent should read and summarizethe meaning of the terms distribu-tion and mean. Ask each pair toshare an example of a distributionand a mean. Interpersonal

Math Skills Ask students to createa set of data that has a mean of 12and that includes at least five num-bers. Then, ask students to create aline graph that shows the distribu-tion of this data. Ask them if thedata appears to be in a bell-shapedcurve. (Accept any set of data thathas a mean of 12.) LogicalLS

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Venn DiagramYYoouu mmaayy wwaanntt ttoo hhaavvee ssttuu--ddeennttss wwoorrkk iinn ggrroouuppss ttoo ccrreeaatteetthhiiss VVeennnn DDiiaaggrraamm.. HHaavvee oonneessttuuddeenntt ddrraaww tthhee mmaapp aanndd ffiilllliinn iinnffoorrmmaattiioonn pprroovviiddeedd bbyyootthheerr ssttuuddeennttss ffrroomm tthheeggrroouupp..

AAnnsswweerr ttoo RReeaaddiinngg CChheecckkThe students calculated the meanlength of the mussels by adding thelengths of the mussels and thendividing by the number of mussels.

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What Is the Probability? The chance that something will hap-pen is called For example, if you toss a penny, whatis the probability that it will come up heads? Most people wouldsay “half and half,” and they would be right. The chance of atossed penny coming up heads is 1⁄2, which can also be expressedas 0.5 or 50%. In fact, probability is usually expressed as a num-ber between 0 and 1 and written as a decimal rather than as afraction. Suppose the penny comes up heads 7 out of 10 times.Does this result prove that the probability of a penny coming upheads is 0.7? No, it does not. So what is the problem?

The problem is that the sample size—the number of objectsor events sampled—is too small to yield an accurate result. In sta-tistics, a is a group of individuals or events selected torepresent the population. If you toss a penny 10 times, your sam-ple size is 10. If you continue tossing 1,000 times, you are almostcertain to get about 50% heads and 50% tails. In this example,the sample is the number of coin tosses you make, while the pop-ulation is the total number of coin tosses possible. Scientists tryto make sure that the samples they take are large enough to givean accurate estimate for the whole population.

Statistics in Everyday LifeYou have probably heard, “There is a 50 percent chance of raintoday.” Figure 10 shows an example of a natural event that we oftenassociate with probability—a thunderstorm. You encounter statisticsoften and use them more than you may think. People are constantlytrying to determine the chance of something happening. A guess orgut instinct is probably just an unconscious sense of probability.

Understanding the News The news contains statistics every day,even if they are not obvious. For example, a reporter may say,

“A study shows that forest firesincreased air pollution in the city lastyear.” We could ask many statisticalquestions about this news item. Wemight first ask what the averageamount of air pollution in the city is.We could gather data on air pollutionlevels over the past 20 years and graphthem. Then we could calculate themean, and ask ourselves how differentlast year’s data are from the average.We might graph the data and look atthe distribution. Do this year’s pollu-tion levels seem unusually high com-pared to levels in other years?Recognizing and paying attention tostatistics will make you a better con-sumer of information, including infor-mation about the environment.

sample

probability.

Figure 10 � Most people are familiarwith statistics regarding the weather,such as the chance, or probability, ofa thunderstorm.

MATHPRACTICEProbability Probability is often determined by observing ratios or patterns. For example, imagine that you count200 pine trees in a forest andnotice that 40 of those trees havepine cones. What is the probabilitythat the next pine tree you comeacross will have pine cones?

Activity M&M® Samples and PopulationThe distribution of colors in a typi-cal bag of M&M’s® is available onthe Internet. Download this infor-mation for the following activity.Randomly draw five M&M’s®

from a bag and ask students tocompare the color distribution ofthese five to the distribution given.Draw 10, 20, and finally, 30 can-dies, having students consider thedistribution each time. Ask stu-dents how this exercise demon-strates the importance of samplesize in science. As an extension,students can graph the results oflarger samples.



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AAnnsswweerrss

��24000� � �1

2000� � 0.2

There is a probability of 0.2 thatthe next pine tree will have pinecones.

MATHPRACTICE

MISCONCEPTION ALERT

Probability and PossibilityThere is a difference betweenprobability and possibility.When something is possible, itcan occur. Mathematical proba-bility refers to the likelihood ofpossible events. For example, itis possible that a tornado mightsweep up a winning lotteryticket and drop it gently atsomeone’s feet on his or herbirthday, but it is not probable.

Pascal’s Triangle In 1653, French mathe-matician Blaise Pascal created “Pascal’sTriangle,” an arrangement of numbers whichdescribes simple probabilities. For example, if there are five slippers in a closet, and youwant to figure out how many different waysyou can choose two of them to wear, Pascal’sTriangle can help determine how many

different ways you can choose two objectsfrom a set of five. Pascal’s Triangle can beeasily downloaded from the Internet and isdiscussed in many upper-level math texts.Bring in a number of objects such as hats,slippers, bracelets, or ties to clearly demon-strate how Pascal’s Triangle is useful in thestudy of probability. Visual/LogicalLS

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Federal Emergency Management Agency(FEMA) After a disaster occurs, such as ahurricane, flood, drought, or terrorist attack,FEMA helps a community recover. Anotherresponsibility of FEMA is mitigation, theeffort to lessen the impact of a disaster beforeit occurs. With mitigation in mind, FEMAprovides the public with information on how to protect houses and public buildingsfrom flooding, earthquakes, and wind. This

information is based upon risks that havebeen determined by experts. The probabilityof a flood is something that can be calculatedby analyzing the geography and the historicweather and climatic patterns of a region.Mitigation is not limited to FEMA. Architectsand structural engineers also consider how to engineer buildings and other structures towithstand the forces of earthquakes, floods,and tornadoes.


Thinking About Risk In scientific terms, is the probabilityof an unwanted outcome. For example, if you have a 1 in 4chance of failing a class, the risk of failing is 1⁄4, or 0.25. Figure 11 shows a well-publicized environmental problem—oilspills. But as you can see in the pie graph, the risk of pollutionfrom large oil spills is much smaller than the risk of oil pollu-tion from everyday sources.

The most important risk we consider is the risk of death.Most people overestimate the risk of dying from sensationalcauses, such as terrorism, and underestimate the risk from com-mon causes, such as smoking. Likewise, most citizens over-estimate the risk of sensational environmental problems andunderestimate the risk of ordinary ones, as shown in Table 2.

risk

Perceptions of Risk by Experts and Ordinary Citizens

High risk Low risk

Experts ozone depletion; oil spills;global climate change radioactive materials;

water pollution

Citizens ozone depletion; global climate change;radioactive waste; water pollutionoil spills

Source: U.S. Environmental Protection Agency.

Table 2 �

Figure 11 � The graph below showsthe sources of oil that pollute theocean. The photo at left shows an oilspill off the coast of Galveston, Texas.Big oil spills are a relatively minorsource of oil pollution.

Runoff from land51.4%

Routine ship maintenance

19.4%

Big spills5.2%

Natural seeps8.8%

Offshore drilling2.2%

Air pollution13.0%

LawConnection to

Oil Tankers The Oil Pollution Actof 1990 was a response to a hugeoil spill from an oil tanker, theExxon Valdez, in Alaska in 1989.The controversial bill had beendebated for 14 years; it passedswiftly in the aftermath of the dis-aster. Under the law, all oiltankers operating in United Stateswaters must be protected withdouble hulls by 2015.

Group Activity Teaching To the Class Have stu-dents create teaching materials onprobability, statistics, and risk forother students. Split the class intothree groups. One group shoulddevise a lesson on probability,another on statistics, and a thirdon risk. Ask students to present thelessons to the class. Interpersonal

Math Skills Lightning kills about80 people each year in the UnitedStates. Those are not bad oddswhen you consider that the popula-tion is about 280 million and thatthe behaviors you choose—such as whether or not to stand next to large metal objects during incle-ment weather—play a large part inyour safety. Ask students to assumethat everyone in the United Stateshas equal risk for being struck bylightning. Ask students what anindividual’s chance of being killedwould be. (The chance of beingkilled is 80/280 million. Expressed as a probability, the chance is0.00000028, or .000028%.)

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ModelsYou are probably already familiar with models. Museums havemodels of ships, dinosaurs, and atoms. Architects build models ofbuildings. Even crash-test dummies are models. are repre-sentations of objects or systems. Although people usually think ofmodels as things they can touch, scientists use several differenttypes of models to help them learn about our environment.

Physical Models All of the models mentioned above are physicalmodels. Physical models are three-dimensional models you cantouch. Their most important feature is that they closely resemblethe object or system they represent, although they may be largeror smaller.

One of the most famous physical models was used to discoverthe structure of DNA. The two scientists who built the structuralmodel of DNA knew information about the size, shape, andbonding qualities of the subunits of DNA. With this knowledge,the scientists created model pieces that resembled the subunitsand the bonds between them. These pieces helped them figure outthe possible structures of DNA. Discovering the structure ofDNA furthered other research that helped scientists understandhow DNA replicates in a living cell. Figure 12 shows a modernmodel of a DNA molecule. The most useful models teach scien-tists something new and help to further other discoveries.

Graphical Models Maps and charts are the most common exam-ples of graphical models. Showing someone a road map is easierthan telling him or her how to get somewhere. An example of agraphical model is the map of the Denver, Colorado, area inFigure 13. Scientists use graphical models to show things such asthe positions of the stars, the amount of forest cover in a givenarea, and the depth of water in a river or along a coast.

Models

Figure 12 � This plastic model of aDNA molecule is an example of aphysical model.

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Figure 13 � This map of the Denver,Colorado, area is an example of agraphical model.

GeofactFossil-Fuel Deposits Fossil fuels,such as coal and oil, are oftenburied deep underground in particular rock formations. Wefind fossil fuels by drilling forrocks that indicate the presenceof fossil fuels and then we makemodels of where the coal or oil is likely to be found.

_ _ _ g

Discussion Giant’s Causeway Giant’sCauseway in Northern Ireland issaid to have been built by themythical giant Finn McCool.According to legend, McCool builtthe plateau, composed of about40,000 columns, to woo a ladygiant. Geologists know that whenlava cools it forms regular polygo-nal columns like the ones at Giant’sCauseway. But scientists did notknow why, until physicists AlbertoG. Rojo and Eduardo A. Jaglastarted to “play” with computermodels. “If you want to fracturea material with the least energy,hexagons are the way to do it,”explains Rojo. The scientists real-ized that they could model theirresults using simple materials. Withcornstarch, water, and tape, theyduplicated the fracturing of lava.Ask students to categorize the twotypes of models that Rojo andJagla employed. (The first modelwas a computer model, which is con-ceptual and mathematical. The sec-ond model is a physical model.)

Group Activity Modeling Lava Fractures Todemonstrate how lava behaves asit cools, mix cornstarch with waterin equal parts by volume. Spreadthe mixture onto a flat surface to adepth of one-half of an inch. Whenthe mixture dries, place a wideswath of clear tape across the topand pull up. The mix of polygonsthat appear on the plate mimicthose of Giant’s Causeway, as wellas those in the Palisades in NewJersey and in Devil’s Postpile, inCalifornia. Kinesthetic/VisualLS


Paired Reading Group students in pairs. Haveeach student read the “Models” section silentlywhile taking note of any passages he or she findsconfusing. After students finish reading, ask onestudent to summarize the section and the sec-ond student to add any ideas that were omitted.Both readers should help each other with anyparts the other person did not understand. Havethe students prepare a list of questions (withanswers) to ask the class. Students may still haveunanswered questions. Ask the class if it canprovide the answers. Verbal/InterpersonalLS

SKILLBUILDER

READINGREADING

Identifying Models Have students use theweather section of the newspaper to identifyuses of graphical, mathematical, and concep-tual models. For example, a mathematicalmodel may be used to predict the likelihood ofrain on a certain day. A graphical model, suchas a map, may be used to show the locationsof pressure fronts or storms. A conceptualmodel may be used to explain long-term trendsin the weather. LogicalLS


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Conceptual Models A is a verbal or graphicalexplanation of how a system works or is organized. A flow-chartdiagram is an example of a type of conceptual model. A flow-chart uses boxes linked by arrows to illustrate what a system con-tains and how those contents are organized.

Consider this example. Suppose that a scientist wants toknow how mercury, a poisonous metal, moves through the envi-ronment to reach people after the mercury is released from burn-ing coal. The scientist would use an understanding of mercury inthe environment to build a conceptual model, as shown in Figure14. Scientists often create such diagrams to help them understandhow a system works—what components the system contains,how they are arranged, and how they affect one another.

Conceptual models are not always diagrams. They can alsobe verbal descriptions or even drawings of how somethingworks or is put together. For example, the model of an atom asa large ball circled by smaller balls is a conceptual model of thestructure of an atom. As this example shows, an actual modelcan be more than one type. An atomic model made of plasticballs is both a conceptual model and a physical model.

How does building a conceptual model help scientists in their work? ��Reading Check

conceptual model

Figure 14 � This conceptual modelshows how mercury released fromburning coal could end up reachingpeople, where it could cause poisoning.

FIELD ACTIVITYFIELD ACTIVITY Conceptual Model Accompanyyour class outdoors. Observeyour surroundings, and writedown observations about whatyou see. In your Ecolog, draw aconceptual model of somethingyou observe. Your model shouldrepresent a system with compo-nents that interact, such as asmall community of organisms.

www.scilinks.orgTopic: Using Models

Code: HE81588

Using the Figure Mercury Sources Ask students to review Figure 14. Can they seeanother way in which people mightingest mercury besides the waysshown in the figure? (People couldconsume water contaminated bymercury.) Ask students to thinkabout why people might not beaffected by mercury directlythrough the water supply.(Untreated drinking water can becontaminated by low levels of inor-ganic mercury, but the process ofbiomagnification concentrates mer-cury in the tissues of living things.So, ingesting dangerous levels ofmercury from food represents amuch greater health risk.) Visual

Group Activity Making Models Introduce stu-dents to the concept of a scalemodel. In a scale model, there is aconstant ratio between the dimen-sions of the model and the object itrepresents. Most maps and manytoys are examples of scale models.Divide students into groups of five,and challenge the groups to makea scale map of the classroom.

Visual

AAnnsswweerr ttoo RReeaaddiinngg CChheecckkA conceptual model helps scientiststo understand a system by showingwhat components the system con-tains, how they are arranged, andhow they affect one another.

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Transparencies

TT Conceptual Model of MercuryContamination

The Periodic Table The periodic table of theelements is a conceptual model. Russianchemist Dmitri Mendeleev used the propertiesof each element to arrange and categorize allthe known elements. Scientists all over theworld have been using updated versions ofMendeleev’s periodic table since the time thatthe periodic table was first published, in1869. Ask students why the periodic table issuch an important conceptual model andwhat might happen if there were no way toclassify the elements. LogicalLS

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Mathematical Models A is one or moreequations that represents the way a system or process works.You can represent many common situations using math models.

For example, suppose that the grapes in a fruit basket athome are getting moldy. You notice that every day the mold cov-ers two more grapes. Here is a mathematical model for the num-ber of moldy grapes on Tuesday:

MTue � MMon � 2, where M � number of moldy grapes

Mathematical models are especially useful in cases with manyvariables, such as the many things that affect the weather.

Because mathematical models use numbers and equations,people may think the models are always right. But weathermodels, for example, sometimes predict rain on dry days. In fact,people are the ones who interpret data and write the equations.

If the data or the equations arewrong, the model will not be real-istic and so will provide incorrectinformation. Like all models,mathematical models are only asgood as the data that went intobuilding them.

People may think of math-ematical models as being confinedto blackboards and paper, but sci-entists can use the models to cre-ate amazing, useful images. Lookat the image of the San FranciscoBay Area in Figure 15. This is a“false color” digital satelliteimage. The satellite measuresenergy reflected from the Earth’ssurface. Scientists use mathemati-cal models to relate the amount ofenergy reflected from objects tothe objects’ physical condition.

mathematical model

1. Explain why sample size is important in determiningprobability.

2. Explain what “the mean number of weeds in threeplots of land” means.

3. Describe three types of models used by scientists.

CRITICAL THINKING

4. Analyzing Relationships Explain the relationshipbetween probability and risk.

5. Applying Ideas Write a paragraph that uses exam-ples to show how scientists use statistics.

6. Evaluating Ideas Why are conceptual and math-ematical models especially powerful?

WRITING SKILLS


Figure 15 � This is a satellite image of the San Francisco Bay Area.Scientists use mathematical modelsto understand the terrain from theway objects on the surface reflectlight. In this image, healthy vegeta-tion is red.

Reteaching Models Reinforce students’ com-prehension of models by dividingthe class into groups of three. Askeach group to have a representativeexplain to you what a physical,graphical, conceptual, and mathe-matical model is. Be sure to ask foran example of each.

Quiz 1. Why do murders make front-

page news, but lung cancerdeaths do not? (Answers mayvary. Students should incorporatethe idea that rare and sensationalevents receive more attention thandaily risks.)

2. Provide an example of a concep-tual model. (Answers may vary.)

AlternativeAssessment Risks Ask students to identify different risks in their lives—thingsthey are scared of or things theymay live with that do not botherthem. They should also includedangers that seem very remote as well as environmental issues.Ask students to rank the risks andthen do research to determinewhich are likely to be high risks for them and which are likely to below risks. Ask them to share theirresults with you or with the class.

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AAnnsswweerrss ttoo SSeeccttiioonn RReevviieeww1. A statistical sample needs to be large enough

to reflect a population. If a sample is not largeenough it can easily misrepresent probability.

2. The statement means that someone has deter-mined how many weeds are in each of threeplots of land, added these numbers together,and divided by three. In this case, the “mean”represents the average number of weeds in thethree plots.

3. Answers may vary. Students should includethree of the following: Physical models arethree dimensional and closely resemble theobject sor system they represent. Graphical

models, which include maps and charts, illus-trate data such as positions or amounts graphi-cally. Conceptual models show how somethingworks or how it is organized. Mathematicalmodels use one or more equations to representhow a system or process works.

4. Probability is the chance that an event willoccur. Risk is the probability of an unwantedoutcome.

5. Answers may vary.6. Answers may vary. Students may say that

conceptual and mathematical models representideas and relationships clearly and precisely.


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Writing Ask students to imagine that they livein a town with a coal-fired power plantnearby. Many people are employed by thepower plant and at a nearby coal mine. A neighboring county, which is generally more affluent, is building a wind farm to gener-ate electricity. The wind farm will be opera-tional in a few years. The press has raised thequestion of whether the existing plant shouldbe closed. Ask students to write a sentence foreach value in Table 3, explaining how it relatesto this situation. LogicalLS

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Scientific research is an essential first step to solve environmentalproblems. However, many other factors must also be considered.How will the proposed solution affect people’s lives? How muchwill it cost? Is the solution ethical? Questions like these requirean examination of which are principles or standards weconsider important. What values should influence decisions thataffect the environment? Table 3 lists some values that often affectenvironmental decisions. You might think of others as well.

An Environmental Decision-Making ModelForming an opinion about an environmental issue is often difficultand may seem overwhelming. It helps to have a systematic way ofanalyzing the issues and deciding what is important. One way toguide yourself through this process is to use a decision-makingmodel. A is a conceptual model that pro-vides a systematic process for making decisions.

Figure 16 shows one possible decision-making model. Thefirst step of the model is to gather information. In addition towatching news reports and reading about environmental issues,you should listen to well-informed people on all sides of an issue.Then consider which values apply to the issue. Explore the conse-quences of each option. Finally, evaluate all of the information tomake a decision.

Why is a decision-making model helpful for making

environmental decisions?��Reading Check

decision-making model

values,

Objectives� Describe three values that people

consider when making decisionsabout the environment.

� Describe the four steps in a simple environmental decision-making model.

� Compare the short-term and long-term consequences of twodecisions regarding a hypotheticalenvironmental issue.

Key Termsvalue

decision-making model

S E C T I O N 3

Making Informed Decisions

Explore consequences

Consider values

Gather information

Make a decision

Figure 16 � The diagram aboveshows a simple decision-makingmodel.

Values That Affect Environmental Decision Making

Value Definition

Aesthetic what is beautiful or pleasing

Economic the gain or loss of money or jobs

Environmental the protection of natural resources

Educational the accumulation and sharing of knowledge

Ethical/moral what is right or wrong

Health the maintenance of human health

Recreational human leisure activities

Scientific understanding of the natural world

Social/cultural the maintenance of human communities and their values and traditions

Table 3 �

Before beginning this section,review with your students theObjectives in the Student Edition.This section introduces the idea thatenvironmental decisions involvedifferent values that are often com-peting. Difficult decisions can bemanaged systematically by using adecision-making model.

Ask students to write down a pro-blem in their life that presented adifficult decision. Ask them to con-sider how they usually approachdecisions. Ask, “Is it by flipping acoin or by talking to your friends?How do you weigh what is impor-tant to you?” Intrapersonal

Discussion Alien Invasion Present studentswith the following scenario: Ahighly-evolved alien race hasinvaded Earth and is quicklydescending upon your home town.You are forced to evacuate imme-diately, perhaps leaving your homebehind forever. You do not knowwhere you will go or what you willdo next. There is only time to take10 items with you. Food is sup-plied on the evacuation ship. Askstudents what items they woulddecide to take. Discuss the prosand cons of each choice and comeup with a common list for theclass. Ask students what valuesinfluenced their decision. (Answersmay vary. Ethical, educational, envi-ronmental, health, and social valuesmay influence students’ choices.)

Verbal

AAnnsswweerr ttoo RReeaaddiinngg CChheecckkA decision-making model is helpfulfor making environmental decisionsbecause it provides a systematic wayof analyzing the issues and determin-ing what is important.

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A Hypothetical SituationConsider the following hypothetical example. In the town ofPleasanton, in Valley County, biologists from the local collegehave been studying the golden-cheeked warbler, shown inFigure 17. The warblers have already disappeared from mostareas around the state, and the warbler population is decliningin Valley County. The biologists warn county officials that if theofficials do not take action, the state fish and wildlife servicemay list the bird as an endangered species.

Pleasanton is growing rapidly, and muchof the new development is occurring outside

the city limits. This development is destroy-ing warbler habitat. Valley Countyalready has strict environmental controlson building, but these controls do notprevent the clearing of land.

Several groups join together to pro-pose that the county buy several hundred

acres of land where the birds are known to

Saving the Everglades: MakingInformed Decisions

Figure 17 � The map (above)shows the proposed naturepreserve, which would behome to warblers like the one pictured (right).

� The roseate spoonbill is a col-orful resident of the Everglades.

The Florida Everglades is an enor-

mous, shallow freshwater marsh.

The water in the Everglades slowly

flows from Lake Okeechobee to

Florida Bay. Much of the marsh is

filled with sawgrass, mangroves,

and other water-loving plants. It is

also home to wildlife, from 40

species of fish to panthers, alliga-

tors, and wading birds such as

herons and roseate spoonbills.

In the 1880s, marshlands were

considered wastelands. Developers

began to drain the Everglades. They

replaced marsh with houses and

sugarcane fields. Between 1940 and

1971, the Army Corps of Engineers

built dikes, canals, and pumping

stations that drained even more

water. The Corps also straightened

the Kissimmee River, which runs

into Lake Okeechobee.

Scientists have shown that what

remains of the Everglades is dying. Its

islands and mangrove swamps are

vanishing, its water is polluted with

fertilizer from farms, and its wading-

bird colonies are much smaller than

before. These effects have economic

consequences. Because much of the

Everglades’ water has been diverted

from Florida Bay into the Atlantic

Ocean, the towns of southeast

Florida are running out of fresh water

and much of the marine life in

Florida Bay has died.

In the 1990s, a commission

reported that the destruction of the

Everglades had jeopardized the

state’s tourism industry, farming, and

the economic future of south Florida.

The solution was obvious—undo

the water diversion dikes and dams

and restore water to the Everglades.

Discussion Emotions and Decision-MakingPoint out to students that it isimportant to distinguish betweenemotional arguments and factualarguments while making decisions.People often confuse the two. Havestudents come up with a list ofemotional statements and a list offactual statements and explore thedifferences between the two. Youmight also stress that emotionalarguments have value and shouldbe considered. Verbal

NIMBY NIMBY, which stands forNot In My Backyard, refers to thereaction many people have towardssomething they consider unpleasantbeing located near their homes.NIMBY may apply to things thatare dangerous, unsightly, noisy orinconvenient. Have students giveexamples of what might elicit aNIMBY response. (Examples mayinclude the proposed building ofnuclear power plants, power lines,landfills, highways, airports, or cellu-lar phone antennas.)

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CONNECTIONCONNECTIONREAL-LIFEREAL-LIFE

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Acronym Glossary Acronyms are popularin environmental science. Have studentsresearch environmental science acronyms onthe Internet so that they can create an acronymglossary. Knowledge of these acronyms willhelp students better understand articles thatrelate to environmental issues. The followingacronyms will help students get started:NGO—Non Governmental Organization—refers to organizations that do not receivegovernment funds. NIMEY—Not In MyElection Year—refers to a politician’s decision

to forestall something unpleasant for the con-stituency during an election year. GOOMBY—Get Out Of My Backyard—refers to an indi-vidual’s desire to remove an environmentalhazard from a neighborhood or community.BANANA—Build Absolutely NothingAnywhere Near Anything—refers to a personwho is opposed to any form of real estatedevelopment. LULU stands for LocallyUndesirable Land Use. Other acronymsinclude EPA, USGS, FWS, NRDC, IPCC,WWF and WMO.

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breed and save that land as a nature preserve. The groups alsopropose limiting development on land surrounding the preserve.The group obtains enough signatures on a petition to put theissue to a vote, and the public begins to discuss the proposal.

Some people who own property within the proposed pre-serve oppose the plan. These property owners have an economicinterest in this discussion. They believe that they will losemoney if they are forced to sell their land to the county insteadof developing it.

Other landowners support the plan. They fear that withoutthe preserve the warbler may be placed on the state’s endan-gered species list. If the bird is listed as endangered, the statewill impose a plan to protect the bird that will require evenstricter limits on land development. People who have land nearthe proposed preserve think their land will become more valu-able. Many residents of Pleasanton look forward to hiking andcamping in the proposed preserve. Other residents do not likethe idea of more government regulations on how private prop-erty can be used.

� The Everglades can be thought of as a shallow, slow-moving riverthat empties into Florida Bay.

EcofactThe Everglades There are 112threatened or endangered plantand animal species in the FloridaEverglades, according to the U.S.Fish & Wildlife Service.

In 2000, the $7.8 billion Everglades

Restoration Plan was signed into law.

The plan was put together by groups

that had been fighting over the

Everglades for decades: environmen-

talists, politicians, farmers, tourism

advocates, and developers. Over the

course of 5 years, members from the

groups met and crafted a plan. At

plan than without it. Already Florida

has restored 7 miles of the

Kissimmee River to its original path.

Native plants are absorbing some

of the pollution that has killed an

estimated $200 million worth of

fish and wildfowl. The Everglades

Restoration Plan is not perfect, but

the process of creating and approv-

ing it shows how science and

thoughtful negotiation can help solve

complex environmental problems.

CRITICAL THINKING

1. Analyzing Processes Explainwhy it was so difficult for people toagree on how to restore theEverglades.

2. Analyzing RelationshipsIf your county decided to build alandfill, do you think the decision-making process would resemble theEverglades example?

first people were afraid to break up

into committees for fear that other

people would make deals behind

their backs. The director instituted

social gatherings, and the members

got to know and trust each other.

In the end, no one was com-

pletely satisfied, but all agreed that

they would be better off with the

www.scilinks.orgTopic: Environmental

Decision Making

Code: HE80525

Reteaching Revisiting Einstein After dis-cussing decision-making models,ask students to think again aboutthe following quote from AlbertEinstein: “The whole of science isnothing more than a refinement ofeveryday thinking.” Ask studentsto review their comments in theirEcoLog, and ask them if they haveany further insights. How is thedecision-making model similar tothe scientific method? LogicalLS

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Saving the Everglades Muchof south Florida would be unin-habitable if it were not for theCentral and Southern FloridaProject (CS&F Project), whichwas initiated in 1948. The U.S.Army Corps of Engineers con-structed one of the largest watermanagement projects in theworld to drain portions of theEverglades in an attempt tomitigate flooding, conservewater, preserve fish and wildlife,and make land available fordevelopment. Unfortunately,the project had adverse effectson south Florida ecosystems.In 1992 the Central & SouthFlorida Project began to be re-evaluated, leading to the com-prehensive restoration effortsin place today. These effortsmust consider how to protectthe ecosystem while ensuringthat Florida’s water needs con-tinue to be met.

AAnnsswweerrss ttoo CCrriittiiccaall TThhiinnkkiinngg1. Answers may vary but students

should focus on the idea thatpeople are motivated by differ-ent values and interests. Evenwhen different groups couldagree that action had to betaken, they argued on the scopeand methods of restoration.

2. Answers may vary, but studentsshould recognize that demo-cratic community decisionsoccur when people with differ-ent values come to an agree-ment and establish trust.

StrategiesStrategiesINCLUSIONINCLUSION

Ask students to locate Key Terms in thechapter by using the Chapter Highlightsand page numbers. Students should copythe sentence where the term appears in thetext. Students can also write an originalsentence using the term. If the student hasdifficulty with writing, the student can reador compose the sentences aloud into a taperecorder. Students may use the tape or writ-ten activity as a study guide for independent or small group work.

••VViissuuaallllyy IImmppaaiirreedd••LLeeaarrnniinngg DDiissaabblleedd

••DDeevveellooppmmeennttaallllyy DDeellaayyeedd

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How to Use the Decision-Making ModelThe hypothetical situation in Pleasanton can be used to illustratehow to use the decision-making model. Michael Price is a voter inValley County who will vote on whether the county should createa nature preserve to protect the golden-cheeked warbler. Thesteps Michael took to make his decision about the proposal areoutlined below.

Gather Information Michael studied the warbler issue thor-oughly by watching local news reports, reading the newspaper,learning more about golden-cheeked warblers from various Websites, and attending forums where the issues were discussed. Anexample of scientific information that Michael consideredincludes the graph of warbler population decline in Figure 18.Several of the arguments on both sides made sense to him.

Consider Values Michael made a table similar to Table 4 to clarify his thoughts. The values listed are environmental, eco-nomic, and recreational. Someone else might have thought othervalues were more important to consider.

1992 1994 1996 1998 2000 2002

Year

Nu

mb

er

of

bre

ed

ing

pair

s

Warbler Populationin the Pleasanton Area

0

20

40

30

50

10

Figure 18 � The population ofgolden-cheeked warblers in thePleasanton area has declined inrecent years.

Table 4 �

Should Valley County Set Aside a Nature Preserve?

Environmental Economic Recreational

State officials mightrestrict somerecreational activities onprivate land within thepreserve.

Taxpayers must continue to pay formaintaining the preserve.

Taxpayers lose the tax revenue that this landwould have provided if it was developed.

Other habitat outsidethe preserve may bedamaged byoverdevelopment.

Negative long-termconsequences

Large areas of thepreserve are available forhiking and picnicking.

Landowners near thepreserve may developcampgrounds with biketrails, swimming, andfishing available on landadjacent to thepreserve.

Property near the preserve increases invalue because it is near a natural area.

Businesses move to Valley County because ofits beauty and recreational opportunities,which results in job growth.

The warbler is not listed as endangered,which avoids stricter controls on land use.

The population ofwarblers increases,and the bird does notbecome endangered.

Other species oforganisms are alsoprotected.

An entire habitat ispreserved.

Positive long-termconsequences

Michael could not thinkof any negative short-term consequences.

Property owners inside the preserve area donot make as much money as if they haddeveloped their land.

Taxpayers must pay higher taxes to buypreserve land.

Environmentalcontrols are madeless strict in parts ofthe county outsidethe preserve area.

Negative short-termconsequences

Parts of the preserve aremade availableimmediately for hikingand picnicking.

Landowners whose property was bought bythe county receive a payment for their land.

Property outside the preserve area can bedeveloped with fewer restrictions.

Habitat destruction inthe nature preservearea is slowed orstopped.

Positive short-termconsequences

InterpretingStatistics What Happened to the Warblers?Ask students to analyze the data in Figure 18. Have them create atable or bar graph that shows thepopulation of warblers every twoyears. Have students brainstormways that biologists could havecollected this data. Begin a discus-sion about whether the data insuch a graph could be misleading.Encourage skepticism and imagi-nation in the class. (Biologists couldhave collected this data by surveyinga sample of the entire county areafor warblers. The data could be misleading if the scientists did notsample a representative area. Forexample, the warblers might preferto nest in certain trees or in specificareas. If the scientists sampled theland area randomly, the chances arethat their results would misrepresentthe size of the warbler population.)

Visual

Understanding Local IssuesMaking environmental decisionsinvolves a variety of people whohave different roles in the commu-nity. Have students pick a localenvironmental issue and identifysome of the people involved withit. Then encourage them to chooseone of these people and interviewthem. Have students summarizethe interviews and bring the sum-maries to class. Then have studentsdiscuss the issue using informationfrom the people involved. VerbalLS

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GENERAL

CareerCareerArchitect Architect Samuel Mockbee asked,“Does the architect have a role in addressingpolitical or economic inequities, or trans-portation issues, or environmental issues?Because I think we do.” In 1993, Mockbeeand Dennis K. Ruth started a program called the “Rural Studio” at the University of Alabama. Students work with poor, rural residents of Hale County, Alabama, to improve their quality of life by designingaffordable housing and other buildings

using materials that would otherwise end up in landfills. They work with a communityto address its needs from within. Mockbeedecided to use his talent to combine a socialcommitment to the poor with an environmen-tal focus. Have students find out more about the Rural Studio and the connectionsbetween architecture and environmental science. Students can also look for informa-tion about “Green Architecture” programs on the Internet.

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AAnnsswweerrss ttoo SSeeccttiioonn RReevviieeww1. Gathering information is important to fully

understand a problem. It is necessary to con-sider values so that a decision is made basedon what is important to the decision-maker.Exploring the consequences is importantbecause it is necessary to consider the long-term impact of a decision. It is important tomake a decision so that something can be done and the decision maker’s values can beimplemented.

2. Answers may vary, but may include the fol-lowing: Environmental values are values basedon how important nature and the environmentare to you. Economic values are values based

on monetary costs and benefits. Recreational values are values based on the importance ofleisure and having fun.

3. Answers may vary. Accept any reasonable,thoughtful answer.

4. The tables may vary but should show anunderstanding of the decision-making modeland a thoughtful exploration of an issue.

5. Answers may vary. Students may offer improve-ments such as quantifying the positive andnegative consequences to better assess the situation.


Explore Consequences Michael decided that in the short termthe positive and negative consequences listed in his table werealmost equally balanced. He saw that some people would sufferfinancially from the plan, but others would benefit. Taxpayerswould have to pay for the preserve, but all the residents wouldhave access to land that was previously off-limits because it wasprivately owned. Some parts of the county would have more pro-tection from development, and some would have less.

The long-term consequences of the plan helped Michael makehis decision. He realized that environmental values were animportant factor. The idea of a bird becoming extinct distressedhim. Also, protecting warbler habitat now would costless than doing it later under a state-imposed plan.

Michael considered that there were long-term benefits to add to the analysis as well. He had readthat property values were rising more rapidly incounties with land for recreation. He found that peo-ple would pay more to live in counties that have openspaces. Michael had found that Valley County hadvery little preserved land. He thought that creatingthe preserve would bring the county long-term eco-nomic benefits. He also highly valued the aestheticand recreational benefits a preserve would offer, suchas the walking trail in Figure 19.

Make A Decision Michael chose to vote for the naturepreserve. Other people who looked at the same table ofpros and cons might have voted differently. If you livedin Valley County, how would you have voted?

As you learn about issues affecting the environ-ment, both in this course and in the future, use thisdecision-making model as a starting point to makingyour decisions. Make sure to consider your values,weigh pros and cons, and keep in mind both the short-term and long-term consequences of your decision.

How did considering long-term conse-quences help Michael make a decision about creating anature preserve in Valley County?

��Reading Check

1. Explain the importance of each of the four steps in asimple decision-making model.

2. List and define three possible values to considerwhen making environmental decisions.

3. Describe in a short paragraph examples of twosituations in which environmental values come intoconflict with other values.

CRITICAL THINKING

4. Making Decisions Pick one of the situations youdescribed in question 3. Make a decision-making tablethat shows the positive and negative consequences ofeither of two possible decisions.

5. Analyzing Ideas Suggest how to make the deci-sion-making model presented here more powerful.


Figure 19 � Land set aside for anature preserve can benefit people aswell as wildlife.

WRITING SKILLS

Reteaching Applying the Decision-MakingModel Have students identify alocal environmental issue. Ask students to research the issue andthen prepare an environmentaldecision-making table similar toTable 4. Review and discuss thetables in class. Then have studentswrite a paragraph that describestheir decision-making model andthe decision they made. Ask stu-dents to use the model throughoutthe school year. Intrapersonal

Quiz 1. What are four values that are

very important to you when you make everyday decisions?Explain why. (Answers may vary.)

2. Why is it important to identifythe different values that influ-ence decision making? (Answersmay vary. Students should recog-nize that different values influencedecisions and these values canconflict with each other.)

AlternativeAssessment Land Use One of the most con-troversial topics in urban develop-ment is land use, the way that acity will be organized in order tobe a functional place. Ask studentsto choose a city in the UnitedStates or abroad that interests them and analyze the infrastruc-ture, including public transporta-tion, schools, public land, shoppingdistricts, and living areas. Ask stu-dents to include their findings in areport that focuses on the environ-mental characteristics of the citythey studied. Students should sup-plement their report with a mapillustrating land use in the city theychose. Verbal/Visual

AAnnsswweerr ttoo RReeaaddiinngg CChheecckkMichael found out that people arewilling to pay more to live in coun-ties with open spaces. He voted infavor of the preserve because he tookthis long-term economic benefit intoaccount.

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HighlightsCCHHAAPPTTEERR

22 HighlightsC H A P T E R 2

1 Scientific Methods

2 Statistics and Models

3 Making Informed Decisions

Key Termsobservation, 33hypothesis, 34prediction, 34experiment, 35variable, 35experimental

group, 35control group, 35data, 36correlation, 37

Main Ideas� Science is a process by which we learn aboutthe world around us. Science progresses mainlyby the experimental method.

� The experimental method involves makingobservations, forming a hypothesis, performingan experiment, interpreting data, and commu-nicating results.

� In cases in which experiments are impossible,scientists look for correlations between differ-ent phenomena.

� Good scientists are curious, creative, honest,skeptical, and open to new ideas.

statistics, 40mean, 41distribution, 41probability, 42sample, 42risk, 43model, 44conceptual model, 45mathematical

model, 46

� Scientists use statistics to classify, organize,and interpret data.

� Measures such as means and probabilitiesare used to describe populations and events.

� Statistics provides a powerful tool for evalu-ating information about the environment.

� Scientists use models, including conceptualand mathematical models, to understand thesystems they study.

value, 47decision-making

model, 47

� Making environmental decisions involvesgathering information, considering values, andexploring consequences.

� Decisions about the environment should bemade thoughtfully. Using a decision-makingmodel will provide you with a systematicprocess for making knowledgeable decisions.

� Making a table that lists positive and nega-tive short-term and long-term consequenceswill help you recognize and weigh your valuesabout an environmental decision.

Alternative Assessment Models in Our Lives Ask stu-dents to identify five models theyuse in their daily lives. Have themdescribe how they use each modeland identify whether it is a physi-cal, mathematical, conceptual, orgraphical model. Students shouldinclude examples of five modelsthey use in their Portfolio.

Decision-Making Have studentsthink of an environmental issuethat might also be an emotionalissue for them. Have them create a decision-making table thatincludes risks and use the table tohelp make a decision. Ask studentsto make persuasive use of statisticsfrom the newspaper, Internet, orbooks to support their reasoning.

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• Chapter Test• Chapter Test• Concept Review• Critical Thinking• Test Item Listing• Observation Lab• Design Your Own Lab• CBL™ Probeware Lab• Consumer Lab• Long-Term Project GENERAL

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ReviewUsing Key TermsUse each of the following terms in a separatesentence.

1. experiment2. correlation3. model4. distribution5. values

For each pair of terms, explain how the meaningsof the terms differ.

6. hypothesis and prediction7. risk and probability8. distribution and population9. sample and population

Understanding Key Ideas10. Scientists form _______ hypotheses to

answer questions.a. accurateb. shortc. mathematicald. testable

11. Risk is the _______ of a negative outcome.a. sampleb. statisticc. probabilityd. event

12. If the results of your experiment do not sup-port your hypothesis, you shoulda. publish your results anyway.b. consider the results abnormal and continue

working.c. find a way to rationalize your results.d. try another method.

13. In a population, characteristics such as sizewill often be clustered around the a. sample.b. mean.c. distribution.d. collection.

14. Models used by scientists includea. conceptual models.b. variable models.c. physical models.d. Both (a) and (c)

15. Reading scientific reports is an example ofa. assessing risk.b. considering values.c. gathering information.d. exploring consequences.

16. A conceptual model represents a way ofthinking about a. relationships.b. variables.c. data.d. positions.

17. In an experiment, the experimental treatmentdiffers from the control treatment only in the_______ being studied.a. experimentb. variablec. hypothesisd. data

18. To fully understand a complex environmen-tal issue, you may need to considera. economics.b. values.c. scientific information.d. All of the above

19. Scientists _______ experiments to make surethe results are meaningful.a. performb. repeatc. concluded. communicate

C H A P T E R 2

Imagining Examples To understand how keyterms apply to actual examples, work with a part-ner and take turns describing an environmentalproblem and explaining how the key terms relateto the problem.

STUDY TIP

ANSWERS

UUssiinngg KKeeyy TTeerrmmss1. Sample answer: The scientist

conducted an experiment to verify her hypothesis.

2. Sample answer: Storm cloudsand rain have a strong correlation.

3. Sample answer: The doctorshowed his patient a model to demonstrate how the heartworks.

4. Sample answer: To see if thereare more elderly people thanyoung people, you could look at a distribution of ages.

5. Sample answer: My motheralways considers her valuesbefore making a decision.

6. A hypothesis is a testable expla-nation for an observation, whilea prediction is an educated guessof what will happen when thehypothesis is tested.

7. A risk is the chance that anunwanted event will occur. Aprobability is the likelihood thatsomething will happen.

8. A distribution is the arrangementof the members of a populationin relation to a characteristic. Apopulation is a group of similarthings that is being studied.

9. A population is a group of simi-lar things that is being studied,while a sample is a smallergroup studied to represent thepopulation.

UUnnddeerrssttaannddiinngg KKeeyy IIddeeaass10. d11. c12. a13. b14. d15. c16. a17. b18. d19. b


53

Review

Section Questions1 1, 2, 6, 10, 12, 17, 19–21, 28, 33,

35–372 3, 4, 7–9, 11, 13, 14, 16, 22, 23,

29–323 5, 15, 18, 24, 34, 38

Assignment Guide

CCHHAAPPTTEERR

22


ReviewShort Answer20. Explain the statement, “A good scientist is

one who asks the right questions.”

21. Explain the role of a control group in a scien-tific experiment.

22. How are statistics helpful for evaluating infor-mation about the environment?

23. Explain why environmental scientists usemathematical models.

24. How does making a table help you evaluatethe values and concerns you have whenmaking a decision?

Interpreting GraphicsThe graph below shows the change in size of ashoreline alligator population over time. Use thegraph to answer questions 25–27.

25. What happened to the density of alligatorsbetween 1986 and 1988?

26. What happened to the trend in the alligatorconcentration between 1994 and 1998?

27. How many times greater was the alligatorpopulation in 1986 than it was in 2000?

Concept Mapping28. Use the following terms to create a concept

map: control group, experiment, experimen-tal group, prediction, data, observations,conclusions, and hypothesis.

Critical Thinking29. Drawing Conclusions What does a scientist

mean by the statement, “There is an 80percent probability that a tornado will hitthis area within the next 10 years”?

30. Making Inferences How does a map ofDenver allow you to navigate around the city?

31. Evaluating Assumptions Are complicatedmodels always more accurate? Write a para-graph that uses examples to explain youranswer.

32. Interpreting Statistics Explain what the following statement proves: “We sampledpet owners and found that three out of fivesurveyed own dogs and two out of five surveyed own cats.”

Cross-Disciplinary Connection33. Language Arts The word serendipity, which

means “luck in finding something acciden-tally,” came from a Persian fairy tale calledThe Three Princes of Serendip. In the story,each of the princes discovers something byaccident. Research and write a short reporton a serendipitous discovery about the envi-ronment.

Portfolio Project34. Make a Poster Choose an environmental

issue in your area. You can choose a real-lifeproblem that you have heard about on thenews, such as improving the sewage system orbuilding a new landfill, or you can choose aproject that you think should be considered.Research the issue at your school or locallibrary. Prepare a poster listing the groups ofpeople likely to be involved in the decisionand the factors that may be taken into con-sideration, including economic, social, andenvironmental factors.

WRITING SKILLS

WRITING SKILLS

C H A P T E R 2

0

4

8

12

16

20

1985 1990 1995 2000

Year

Alli

gat

ors

per

kilo

met

er o

f sh

ore

line

?

? ?SShhoorrtt AAnnsswweerr20. When an observation warrants

further examination, a good sci-entist knows what questions toinvestigate to fully understandthe observation.

21. In an experiment, the controlgroup provides a standard to com-pare with the experimental treat-ment. The control group providesa set of data unaffected by thevariable or with the variable at a baseline value.

22. Statistics help people quantifyand analyze different kinds ofinformation, including informa-tion about the environment.

23. Environmental scientists usemathematical models to expressquantifiable relationships in themost precise form possible.

24. Making a table can help in a decision-making situationby organizing all the positive and negative consequences of a decision for comparison.

IInntteerrpprreettiinngg GGrraapphhiiccss25. The density of the alligator popu-

lation fell drastically—from almost22 per kilometer of shoreline toabout 3 per kilometer of shoreline.

26. The alligator concentrationincreased. In 1994 there was lessthan one alligator per kilometer.In 1998 there were almost 5 alli-gators per kilometer.

27. The alligator population wasmore than five times greater in 1986.

CCoonncceepptt MMaappppiinngg28. Answers to the concept mapping

questions are on pp. 715–720.


54

CCrriittiiccaall TThhiinnkkiinngg29. The scientist means that there is an 8 out of

10 chance that a tornado will strike the areaover the next 10 years.

30. Answers may vary, but students should recog-nize that a map is a graphical model of the citythat illustrates the relative size and location ofstreets and landmarks.

31. No, complicated models are not necessarilymore accurate. Adding detail to a model is only justified if that detail truly reflects relevant aspects of the system in question.

32. The statement proves very little because it doesnot state the sample size in relation to thepopulation size. It only proves that 60% ofthose surveyed own dogs and 40% own cats.

CCrroossss--DDiisscciipplliinnaarryy CCoonnnneeccttiioonn33. Answers may vary.

PPoorrttffoolliioo PPrroojjeecctt34. Answers may vary.

ReviewCCHHAAPPTTEERR

22


Read the passage below, and then answerthe questions that follow.

Jane and Jim observed a group of male but-terflies by the roadside. Jane said that thisbehavior was called puddling and that thebutterflies were counting each other to see ifthere was room to set up a territory in thearea. Jim said he did not think butterfliescould count each other and suggested the but-terflies were feeding on nitrogen in the sand.Jane agreed that the butterflies appeared to befeeding, but she said that they may not befeeding on nitrogen, because female butterfliesneed more nitrogen than males.

Jim and Jane decided to perform someexperiments on the butterflies. They put outtrays full of sand in an area where butterflieshad been seen. Two trays contained onlysand. Two contained sand and water, twocontained sand and a salt solution, and twocontained sand and a solution containingnitrogen. Butterflies came to all the trays, butthey stayed for more than 1 min only at thetrays that contained the salt solution.

1. Which of the following statements is atestable hypothesis about the experiment?a. Male butterflies mate with female

butterflies.b. Salt is a compound and nitrogen is

an element.c. Butterflies are never seen in groups

except on sandy surfaces.d. Butterflies are attracted to salt.

2. Which of the following conclusions issupported by the observations Jane andJim made? a. Male butterflies can count each other.b. The butterflies were probably feeding

on nitrogen in the sand. c. The butterflies were probably feeding

on salts in the sand.d. Female butterflies need less nitrogen

than male butterflies.

MATH SKILLS

This table shows the results of an experimentthat tested the hypothesis that butterflies are attracted to some substances but not to others.Twenty-four trays containing four substanceswere placed in random order on a sandbank tosee if butterflies landed on the trays. The numberof butterflies that landed on each type of trayand stayed for more than 5 min during a 2 hperiod was recorded in the table. Use the data inthe table below to answer questions 35–36.

35. Evaluating Data Do the results in the tableshow that butterflies are attracted to saltsolution but not any other substance? Whyor why not? What other data would youlike to see to help you evaluate the resultsof this experiment?

36. Analyzing Data Are there any controlsshown in this table?

WRITING SKILLS

37. Communicating Main Ideas How is theexperimental method an important scientifictool?

38. Writing Persuasively Write a letter to theeditor of your local paper outlining youropinion on a local environmental issue.

Butterfly Feeding Preferences

Sugar Nitrogen Saltsolution solution Water solution

Number of 5 87 7 403butterfliesattracted

READING SKILLS

MMaatthh SSkkiillllss35. No, butterflies do not appear to

be attracted only to salt solution,because 87 stayed for more than5 minutes at the nitrogen solu-tion. How the butterflies behavedafterwards and whether any diedmight be interesting data. Theexperiment should be repeatedbefore the results are evaluated.Data on combinations of ingredi-ents might also be helpful.

36. Yes, the tray with water func-tions as the control. The only dif-ference between this tray and theothers is in the substances thatare dissolved in the water.

WWrriittiinngg SSkkiillllss37. Answers may vary. The experi-

mental method is an importantscientific tool because it providesa method for using observationsto provide explanations for phe-nomena in the natural world. Theexperimental method allows peo-ple to study the impact of a vari-able as objectively as possible.

38. Answers may vary.

RReeaaddiinngg SSkkiillllss1. d2. c


55


CC H A P T E R 2 Standardized Test PrepUnderstanding ConceptsDirections (1–4): For each question, write on aseparate sheet of paper the letter of the correctanswer.

1 How would a scientist categorize a testableexplanation for an observation?A. a correlation B. an experimentC. a hypothesis D. a prediction

2 What happens when an observation is submitted for peer review?F. The article is proofread before it is

published.G. A professor gives a lecture based on a

published article.H. The results are looked at closely by other

scientific experts.I. Information on the experimental design

is included in published works.

3 Which of the following is an example of ascientist’s physical model?A. a crash-test dummy for a car companyB. a diagram of the structure of an atomC. a map of Denver, Colorado D. a satellite image of South America

4 What attribute of a skeptic would contribute to a good scientific mind?F. willingness to travelG. empathetic natureH. desire to conduct experimentsI. continual questioning of observations

Directions (5–6): For each question, write a shortresponse.

5 A penny is tossed and comes up heads 7out of 10 times. Is the probability that itwill be heads on the next toss 70%? Whyor why not?

6 A mean is the number obtained by addingup the data for a given characteristic of astatistical population, and dividing the sumby the total number of individuals in thegiven population. Why do scientists calcu-late the mean of a statistical population?

Reading SkillsDirections (7–9): Read the passage below. Thenanswer the questions.

We use statistics everyday. Weather expertsreport the forecast in terms of probabilities,such as “There is a 50 percent chance of raintoday.” People are constantly guessing the possibility that something will or will not happen. A guess is one of the ways we expressprobability.

In scientific terms, risk is the probability of an unwanted outcome. Most people over-estimate the risk of dying from sensationalcauses, such as terrorism, and underestimatethe risk from common causes such as smoking.Likewise, most citizens overestimate the risk ofsensational environmental problems such as oilspills, and underestimate the risk of ordinaryones, like ozone depletion. However, whendecisions must be made on proposals affectingthe environment, it is important that all thebenefits and risks of the possible action arecalculated.

7 Assess which of the following expertswould perceive as having the highest risk.A. the threat of global climate changeB. the radioactivity from the waste of a

nuclear power plantC. the possibility of a tidal wave reaching a

highly populated land massD. the danger of widespread water pollution

8 How would a scientist define the term risk?F. the likelihood of something goodG. a chance eventH. the probability of an unwanted outcomeI. a benefit that is overestimated

9 How could a decision-making model behelpful for estimating the benefits and risksof a proposal?A. It would eliminate uncertainty.B. It would create a digital image.C. It would predict the outcome of the

decision.D. It would allow consideration of all the

variables.

Interpreting Graphics

F.G.H.I.

A.B.C.D.

F.G.H.I.

A.B.C.D.

56

Estimated TimeTo give students practice undermore realistic testing conditions,allow them 30 minutes to answerall of the questions in this practicetest.

56 Chapter 2 • Standardized Test Prep

Standardized Test Prep

11. A12. F13. C

Answers1. C2. H3. A4. I5. Answers will vary. See Test Doctor for detailed

scoring rubric.6. Answers will vary. See Test Doctor for detailed

scoring rubric.7. A8. H9. D

10. H

Question 3 Answer A is the cor-rect choice. Answers B, C, and Dare incorrect because they are allexamples of images. Although sci-entists use maps, diagrams, andsatellite images for scientific study,these tools are not physical repre-sentations.

Question 5 Full-credit answersshould include the followingpoints:

• no; every time a penny is tossed,the probability of its outcome isindependent of the tosses thathave come before

• the probability of heads or tailsis always 50%

Question 6 Full-credit answersshould include the followingpoints:

• the mean is a numerical measurefor a given population

• the mean allows scientists tocompare characteristics of differ-ent populations

hes08TE_c02_56-57_STP 8/24/06 1:41 PM Page 56

TestProbability is thechance of an outcomeoccurring. The highestprobability occurs inthe group with thelargest number of individuals.

Interpreting GraphicsDirections (10–13): For each question below, record the correct answer ona separate sheet of paper.

The bar graph below shows the distribution of lengths in a population ofdwarf wedge mussels. Use this graph to answer questions 10 through 13.

Size Distribution of Dwarf Wedge Mussels

0 What type of distribution does this bell-shaped curve depict?F. asymmetricG. correlativeH. normalI. random

q How many mussels are less than 25 mm in length?A. 6B. 9C. 12D. 15

w Determine the total size of this statistical population of dwarf wedgemussels.F. 60G. 70H. 80I. 90

e What is the most likely size predictable for a mussel randomly drawnfrom this population?A. 15–20 mmB. 25–30 mmC. 30–35 mmD. 40–45 mm

50 10 15 20 25 35 4530 40 5550 60Length (mm)

Nu

mb

er

of

mu

ssels

0

5

10

15

20

25

57

Standardized Test Prep

Chapter 2 • Standardized Test Prep 57

Question 10 Answer H is the cor-rect choice because a bell curverepresents a normal distribution.Answer F is incorrect becauseasymmetric curves are dramaticallyasymmetrical, while this curve isonly slightly asymmetrical. AnswerG is incorrect because a correlativecurve most resembles a straightline. Answer I is incorrect becauserandom distributions have no dis-tinct shape or pattern.

Question 13 Answer C is correct.Students struggling with this typeof question may benefit from prac-ticing calculating probability. Forexample, ask students what theprobability would be of a rolling a6 on a six-sided die. Then ask stu-dents what the probability ofrolling a 6 would be if two of thesides on the die were 6.

hes08TE_c02_56-57_STP 8/24/06 1:41 PM Page 57

Skills Practice LabObservation

CCHHAAPPTTEERR

22Scientific InvestigationsA scientist considers all the factors that might be responsible forwhat he or she observes. Factors that can vary and that can bemeasured are called variables. The variable that you experimentallymanipulate is the independent variable. The variable that youthink will respond to this manipulation is the dependent variable.

You can practice the scientific method as it relates to everydayobservations, such as the observation that bread dough riseswhen it is baked. According to a bread recipe, you dissolve apackage of yeast in warm water and add flour, corn syrup, salt,and oil. Yeast is a microorganism that plays an important role inmaking bread. Yeast obtains energy by converting sugar to alco-hol and carbon dioxide gas in a process called fermentation. Thecarbon dioxide forms bubbles, which make the bread dough rise.But what role, if any, does temperature play in this process? Inthis investigation, you will work as part of a team to try toanswer these questions. Together, you will form a hypothesis andconduct an experiment that tests your hypothesis.

Procedure1. Restate the question relating temperature to fermentation in

yeast as a hypothesis.

2. Set up three test tubes containing yeast, water, and cornsyrup stoppered with a gas-delivery tube. Label the testtubes “A”, “B”, and “C”. Place each test tube in a waterbath of different temperature. Place tube A in a water bathcooled by a few ice cubes, place tube B in room-tempera-ture water, and place tube C in a warm water bath.

Objectives� Formulate

a hypothesis about the relationshipbetween temperature and fermen-tation by yeast.

� Test yourhypothesis.

� Analyze your data.� Explain whether your data support

or refute your hypothesis.

Materialsbeakers, 100 mL (3)

beakers, 400 mL (3)

clock

delivery tubes, rubber or

plastic (3)

graph paper

ice cubes

solution of yeast, corn syrup,

and water

stoppers, no. 2, one-hole (3)

test tubes, 20 mm � 200 mm (3)

thermometer

USING SCIENTIFIC METHODS

USING SCIENTIFIC METHODS

Skills Practice Lab: OBSERVATIONC H A P T E R 2

� Step 3 Carbon dioxide bubbleswill be released from the delivery tube.

3. Allow the apparatus to sit for 5 min.Then place the open end of the deliverytube under water and begin to collectdata on gas production. For the next10 min, count the number of gas bub-bles released from each tube, andrecord your data in the table on thenext page.

4. Prepare a graph of data by placing timeon the x-axis and the total number of gasbubbles released on the y-axis. Plot threecurves on the same graph, and label eachwith the temperature you recorded foreach test tube. Compare your graph withthat of three other teams before handingin your report.

SCIENTIFIC INVESTIGATIONS

Teacher’s Notes

Time Required one 45-minute class period

Lab Ratings

TEACHER PREPARATION

STUDENT SETUP

CONCEPT LEVEL

CLEANUP

Skills Acquired• Predicting• Experimenting• Measuring• Collecting Data• Classifying• Organizing and Analyzing Data• Communicating

The Scientific MethodIn this lab, students will: • Make Observations• Ask Questions• Test the Hypothesis• Analyze the Results• Draw Conclusions• Communicate the Results

MaterialsThe materials listed are for a groupof 3 to 4 students. For each work-ing group, you will need two icecubes.

E A S Y H A R D

58


Tips and TricksThis lab could be a 2-day activity; the firstday could focus on hypotheses writing prac-tice, and the second day could be used tocomplete the lab. Large empty jars may besubstituted for 400 mL beakers. To preparethe yeast liquid, add 1 tbsp dry active yeastand 200 mL corn syrup to 1 L warm water.Combine the ingredients 15–20 minutes

before class. Note that sugar will be providedin the corn syrup. To assure consistency, youwill want to make sure that each test tubecontains the same level of yeast solution. Testtubes should be filled about halfway. Usingwater temperatures around 4°C–10°C,20°C–25°C, and 40°C–45°C will providegood results.

hes08TE_c02_58-59_Lab 8/24/06 11:42 AM Page 58


Analysis 1. Classifying Data Which set of conditions is most similar to

the conditions for the bread dough in the recipe? Why weretwo other conditions used in this experiment?

2. Classifying Data What was the independent variable in thisexperiment? Explain your answer.

3. Classifying Data What was the dependent variable in thisexperiment? Explain your answer.

Conclusions4. Drawing Conclusions Write a conclusion for this exper-

iment. Describe how the independent and dependentvariables are related. Tell how the data supports yourconclusion.

5. Evaluating Results What does temperature have to dowith making bread dough rise?

6. Evaluating Methods Why did you compare your results with those of other teams before writing yourconclusions?

7. Applying Conclusions Science is not just something you know but also something you do. Explain thisstatement in light of what you have learned in this investigation.

1. Designing Experiments Formulate a new hypothesis about the effect of different types of sugar on carbon dioxide production by yeast. Test your new hypothesisunder controlled conditions. Did your results support your hypothesis? Research the types of sugar you used,and write a short explanation for your findings.

Extension

� Recording Data Count the number of bubbles produced undereach experimental condition andrecord the data in a table.

Carbon Dioxide Bubbles Released by Yeast

Time (min) 1 2 3 4 5 6 7 8 9 10

Tube A:_____

Tube B:_____

Tube C:_____ DO NOT WRITE IN THIS BOOK

AAnnsswweerrss ttoo AAnnaallyyssiiss1. The solution sitting in the warm

bath is most similar to the recipeconditions. The other conditionswere used to test the role of tem-perature in fermentation.

2. The independent variable was thetemperature of the liquid bath,because the temperature is theonly quality that varies betweenthe three beakers of yeast liquid.

3. The dependent variable in thisexperiment was the number of gasbubbles produced. The number ofcarbon dioxide bubbles is a meas-ure of the rate at which the yeastare fermenting the sugar solution.

AAnnsswweerrss ttoo CCoonncclluussiioonnss4. Answers may vary, but students

will probably find higher watertemperatures correlate positivelywith the rate of fermentation.

5. Yeast becomes active in warmconditions. Active yeast fermentssugars in bread dough, creatingalcohol and carbon dioxidebubbles. These bubbles makethe dough rise.

6. You should compare results withthe results of other teams becausethis practice is similar to repeatingthe experiment.

7. Answers may vary, but afterperforming this experiment stu-dents should have confidence in their abilities to use scientificmethods to actively makediscoveries.

AAnnsswweerrss ttoo EExxtteennssiioonn1. Answers may vary.

59

• Datasheets for In-Text Labs• Lab Notes and Answers


Catherine CummingsCurrituck County School System

Currituck, North Carolina

TEACHER

TESTED& APPRO

VED

Holt Lab Generator CD-ROM

Search for any lab by topic, standard, difficulty level, or time.Edit any lab to fit your needs, orcreate your own labs. Use the LabMaterials Quicklist software tocustomize your lab materials list.

hes08TE_c02_58-59_Lab 8/24/06 11:42 AM Page 59


A TOPOGRAPHIC MAP OF KEENE, NEW HAMPSHIRE

M A P S K I L L S

Topographic maps use contour lines to indicateareas that share a common elevation. Where thelines are close together, the terrain is steep. Wherethe lines are far apart, the landscape is flat. Inthis map, the Ashuelot River flows downhill fromSite 1 to Site 3. Use the map to answer the ques-tions below.

1. Using a Key Use the scale at the top of the map to calculate the distance between Sites 1 and 2 andbetween Sites 2 and 3.

2. Understanding Topography Are the hills to theeast and west of the town of Keene more likely to

drain into the river around Site 3 or Site 2? Explainyour answer.

3. Identifying Trends Which site is more likely to bepolluted? Explain your answer.

4. Analyzing Data Trace the sections of the AshuelotRiver between each site to determine the length ofstream between each site.

5. Interpreting Landforms A flood plain is an areathat is periodically flooded when a river overflows itsbanks. Interpret the contour lines to locate the floodplain of the Ashuelot River.

EARTH SCIENCE CONNECTION

60

AAnnsswweerrss ttoo MMaapp SSkkiillllss1. The distance between Site 1 and Site 2 is

approximately 3.5 km. The distance betweenSite 2 and Site 3 is approximately 3.1 km.

2. The hills are more likely to drain to Site 3because many of the tributaries of the AshuelotRiver flow into the river downstream from Site 2.

3. Site 3 is the most likely to be polluted becauseit is downstream from the other sites. In addi-tion, Site 3 is located in downtown Keene.

4. Accept any measurement between 8 km and 9 km.

5. Answers may vary. The flood plain of theAshuelot River is widest south of Site 2. Alarge swamp begins in this area.

A TOPOGRAPHIC MAP OFKEENE, NEW HAMPSHIRE

Discussion Contour Intervals Reproduce amountainous portion of a contourmap on the board. Discuss with stu-dents where the steepest slopes are(where the lines are closest together.)Then change the contour intervalby erasing every other contour line.Point out to students that the con-tour interval is now twice as large.Discuss with students the advan-tages and the disadvantages of amap with a larger contour interval.(The map may seem easier to read,but detail is lost.)

Visual

Group Activity Contour Mapping Give eachgroup a small bucket, a piece of clear, stiff plastic to cover thebucket, a ruler, a felt-tip pen, andsome clay. Have groups create alandform out of the clay and placeit in the bucket. Then have groupsplace the plastic over the bucketand mark the edges for alignmentpurposes. Groups should trace theoutline of the bottom of the “hill”onto the plastic and then pour 1cm of water into the bucket. Afterreplacing the plastic sheet andaligning the corner marks, havestudents trace the waterline on theplastic. Students should repeat thisuntil they reach the top of the hill.

Visual/KinestheticLS

LS

GENERAL


Transparencies

TT Topographic Map of Keene, NewHampshire

Maps in ActionMaps in Action

hes08TE_c02_60_MIA 8/25/06 4:41 PM Page 60


BATS AND BRIDGES

What Do You Think?Many bridges in the UnitedStates could provide roostingplaces for bats. Do you thinkcommunities should try toestablish colonies of batsunder local bridges? Howshould communities make this decision, and what infor-mation would they need tomake it wisely?

A large colony of Mexican free-tailed bats lives under the CongressAvenue Bridge in Austin, Texas.These bats eat millions of insects anight, so they are welcome neigh-bors. Communities around the coun-try and around the world havelearned of the bats and have askedAustin for help in building bat-friendly bridges. But all that the peo-ple of Austin knew was that the batsappeared after the Congress AvenueBridge was rebuilt in the 1980s.What attracted the bats? The peopleof Austin had to do a little research.

A Crevice Will DoIn the wild, bats spend the daysleeping in groups in caves or increvices under the flaking bark ofold trees. They come back to thesame place every day to roost.Deep crevices in tree bark are rarenow that many of our old forestshave been cut down, and manybats are in danger of extinction.

In the 1990s, the Texas Depart-ment of Transportation and BatConservation International, a non-profit organization located inAustin, set out to discover whatmade a bridge attractive to bats.They collected data on 600bridges, including some that hadbat colonies and some that didnot. They answered the followingquestions: Where was the bridgelocated? What was it made of?How was it constructed? Was itover water or land? What was thetemperature under the bridge?How was the land around thebridge used?

Some Bridges are BetterStatistical analysis of the data revealed a number of differencesbetween bridges occupied by batsand bridges unoccupied by bats.Which differences were importantto the bats and which were not?The researchers returned to the

Congress Avenue Bridge in Austinto find out. Crevices under thebridge appeared to be crucial, andthe crevices had to be the right size.Free-tailed bats appeared to prefercrevices 1 to 3 cm wide and about30 cm deep in hidden corners ofthe bridge, and they preferredbridges made of concrete, not steel.

The scientists looked again attheir data on bridges. They dis-covered that 62 percent of bridgesin central and southern Texas thathad appropriate crevices wereoccupied by bats. Now, the TexasDepartment of Transportation isadding bat houses to existingbridges that do not have crevices.These houses are known as TexasBat-Abodes, and they can makeany bridge bat friendly.

Bat Conservation Internationalis collecting data on bats and bridgeseverywhere. Different bat speciesmay have different preferences. ATexas Bat-Abode might not attractbats to a bridge in Minnesota orMaine. If we can figure out whatfeatures attract bats to bridges, wecan incorporate these features intonew bridges and make morebridges into bat-friendly abodes.

� Mexican free-tailed bats leave their roost under the Congress AvenueBridge in Austin, Texas, to hunt for insects.

61

BATS AND BRIDGES

BackgroundPeople have discussed the idea ofattracting bats to artificial roostssince at least 1900, when Dr.Charles Campbell designed andinstalled bat boxes in San Antonio,Texas. Dr. Campbell installed thebat homes in an attempt to reducethe population of malarial mosqui-toes in the area. The importance ofpreserving and creating bat habitathas gained popularity since the1980s, largely due to the efforts of Bat Conservation International.

Bats on the Web There arenumerous Internet sites that offerinformation on bats. Have studentsfind a bat Web site and researchthe topic of their choice. Studentsmay learn how to build a bat house,research how sonar works, orinvestigate the ecological role thatcertain bat species play. Have stu-dents share their findings with theclass.

AAnnsswweerrss ttoo WWhhaatt DDoo YYoouu TThhiinnkk??Answers may vary according to student’s opin-ions, but should take into consideration personalvalues, community values, and the decision-making models.

GENERAL

Society & the EnvironmentSociety & the Environment

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ch 2 apter tools of environmental science chapter 2

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