9.3 Polymers

Reading StrategyIdentifying Main Ideas Before you read,copy the concept map. As you read, com-plete the map to summarize two main ideasabout polymers.

Key ConceptsWhat is one way thatpolymers can be classified?

What are three examplesof synthetic polymers?

What are four types ofpolymers that organismscan produce?

Vocabulary◆ polymer◆ monomers◆ carbohydrates◆ nucleic acids◆ amino acid◆ protein

Freight trains, like those in Figure 13, use different types of cars totransport goods. A flatcar with no sides or roof is used to haul steelbeams. Grain is carried in covered hoppers, which have a hatch at thetop and a chute at the bottom. Liquids travel in tank cars. The carson a train may be all the same type or a mixture of different types. Onaverage, about 100 cars are linked together behind the locomotive ona freight train.

Like freight trains, some molecules are built up from smaller unitslinked together. A polymer is a large molecule that forms when manysmaller molecules are linked together by covalent bonds. The smallermolecules that join together to form a poly-mer are monomers. Poly- means “many.”Mono- means “one.” In some polymers, thereis only one type of monomer. Other polymershave two or more kinds of monomers.

Polymers can be classified as naturalpolymers or synthetic polymers. Manyimportant types of biological molecules arenatural polymers. Organisms produce thesepolymers in their cells. Synthetic polymers aredeveloped by chemists in research laboratoriesand manufactured in factories. Both types ofpolymers have industrial uses. For example,silk and cotton fabrics are woven from naturalpolymer fibers, while polar fleece is made froma synthetic polymer.

a. ? polymers

b. ?

c. ?form which

can be

Carbon Chemistry 275

Figure 13 Couplers that interlocklike the fingers of your handsconnect one railroad car toanother. Many cars can be joinedtogether to form a train, becausethere is a coupler on both ends of a car. Using Analogies How isa polymer like a train?

FOCUS

Objectives9.3.1 Distinguish a monomer

from a polymer.9.3.2 Compare three examples

of synthetic polymers.9.3.3 Describe the structures and

functions of four types ofnatural polymers.

Build VocabularyWord-Part Analysis Have studentsbreak the vocabulary terms polymer,monomer, and carbohydrate into roots,prefixes, or suffixes. Students may needto use a dictionary to find the meaningsof some parts. (Monomer has the prefixmono- meaning “one.” Monomers arethe single units that make up polymers.Polymer has the prefix poly- meaning“many.” Polymers contain manymonomers. Carbohydrate has the prefixcarbo- which means it contains carbon,and the suffix -hydrate which means italso contains the components of water—hydrogen and oxygen.)

Reading Strategya. monomersb. and c. natural/synthetic

INSTRUCTBuild Reading LiteracyUse Prior Knowledge Refer to page 2D in Chapter 1, which providesguidelines for using prior knowledge.

Before students read, ask them to listdifferent fibers used to make fabrics,such as wool and polyester. Have themdiscuss which fibers they think arenatural and identify their sources.Verbal, Intrapersonal

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Reading Focus

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Carbon Chemistry 275

Print• Laboratory Manual, Investigations 9A

and 9B• Guided Reading and Study Workbook

With Math Support, Section 9.3• Transparencies, Section 9.3

Technology • iText, Section 9.3• Presentation Pro CD-ROM, Section 9.3• Go Online, NSTA SciLinks, Polymers

Section Resources

Section 9.3

Answer to . . .

Figure 13 Like a train, a polymer ismade up of single units that are joinedtogether.

276 Chapter 9

Synthetic PolymersThe properties of a polymer depend on the type and number of mono-mers in the polymer. Rubber, nylon, and polyethylene are threeexamples of compounds that can be synthesized.

Rubber The sap collected from rubber trees in tropical regions con-tains rubber. So why would a chemist make synthetic rubber? Thesupply of natural rubber is limited. During World War II, the alliescould not obtain natural rubber. Chemists worked hard to produce asynthetic rubber, using hydrocarbons from petroleum. Natural rubberand synthetic rubbers contain different monomers and have differentproperties. The tires in Figure 14A will resist wear and be less likely toleak if they are made of synthetic rubber. Rubber is used as an adhe-sive. The How It Works box on page 277 explains how adhesives work.

Nylon In the 1930s, Wallace Carothers was trying to produce a syn-thetic polymer to replace silk. The polymer he produced was nylon,which has properties not found in natural polymers. Nylon fibers arevery strong, durable, and shiny. Nylon is used in parachutes, wind-breakers, fishing line, carpets, and ropes like the one in Figure 14B.

Polyethylene Plastic milk bottles, plastic wrap, and the plasticshapes in Figure 14C are made of polyethylene. This polymer formswhen ethene (or ethylene) molecules link head to tail. The number ofcarbon atoms in a polyethylene chain affects the properties of the poly-mer. The more carbon atoms in the chain, the harder the polymer is.

What determines the hardness of polyethylene?

For: Links on polymers

Visit: www.SciLinks.org

Web Code: ccn-1093

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

H

+ + hn

n

C C

H

H

C

H

H

H

H

C C

H

H

C

H

H

H

H

Figure 14 Synthetic polymers areused to make tires, ropes, andplastic objects. A About half therubber produced in the worldis used to manufacture tires. B Nylon is a good choice for arope because its fibers are strongand do not wear out easily. C The hard plastic shapes aremade from a high-densitypolyethylene polymer.Inferring At room temperature,polymers are most likely to existas which state of matter?

A B C

276 Chapter 9

Synthetic PolymersUse VisualsFigure 14 Have students look at theobjects in Figure 14. Ask, What are somephysical properties of rubber, nylon,and polyethylene? (Possible answer:Rubber resists wear. Nylon is durable andstrong. High-density polyethylene is hard.)What are some ways that each of thepolymers is used? (Possible answer:Rubber is used for tires and as an adhesive.Nylon is used for parachutes, windbreakers,fishing line, carpets, and rope. Polyethyleneis used for milk bottles and plastic wrap.)Visual, Logical

Integrate Social StudiesNatural rubber collected from trees is softand sticky. In 1839, Charles Goodyearfound that when sulfur is added to rubberand the mixture is heated, the rubber isno longer sticky. Have students researchother topics related to polymers. Possibletopics include the discovery of nylon, the discovery of artificial silk (later calledrayon) by Hilaire de Chardonnet, or theuse of polymers in the film industry.Students may also want to researchcurrent efforts to recycle plastics,including the codes used on plasticproducts. Have students use posters orcomputer graphics to prepare a report on their research. Verbal, Portfolio

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Section 9.3 (continued)

Download a worksheet onpolymers for students to complete,and find additional teacher supportfrom NSTA SciLinks.

Customize for English Language Learners

Think-Pair-ShareHave students work in pairs to think of moreanalogies for polymers. Examples include

beads in a necklace and links in a chain.Strengthen discussion skills by having studentsshare their examples with the class.

Answer to . . .

Figure 14 Polymers are most likely to be solids at room temperature.

The hardness of poly-ethylene is determined

by the number of carbon atoms in thechain. The more carbon atoms thereare, the harder the polymer is.

Synthetic AdhesivesAdhesion is the force of attraction between molecules ofdifferent substances whose surfaces are in contact. Theseforces are rarely strong enough to bind two surfacestogether. An adhesive placed between the surfaces bindsthem together. Most adhesives are synthetic polymers.The diagram illustrates how some adhesives work. Theadhesive remains liquid until the surfaces are in position.Then the adhesive sets. Interpreting Diagrams Explainthe purpose of a stabilizer in an adhesive.

Liquid adhesiveIn a typical adhesive,monomer molecules anda stabilizer are in asolvent. The stabilizerstops the monomersfrom forming asolid polymer.

Types of adhesion Adhesion can work in three

ways. Molecules of the polymer and thesurface may become physically connected.The molecules may also become attractedby intermolecular forces, or they may reactby forming covalent bonds.

Monomersjoin together.

Solid adhesiveContact with water in the

air and on the surfaces beingjoined makes the stabilizerinactive. The monomers thenbegin to join together to forma polymer. As the chain lengthens,the adhesive changes from aliquid to a solid.

Stabilizer

Solvent

Permanent adhesionAn epoxy resin was used toattach the automobile to thebillboard. Epoxy resins areoften stored in two parts thatare mixed just before theepoxy is used. Strong bindingforces in these adhesives makethem heat- and water-resistant.

Applying the adhesive Some of

the liquid is squeezed onto one of the surfaces to be joined.

Tube

Monomermolecule

Temporary adhesionThe sticky strip on a reusablenote contains tiny dropletsfilled with adhesive. Each timeyou stick the note on an object,a few droplets burst, releasingthe adhesive, which attaches tothe object’s surface.

Carbon Chemistry 277

Synthetic AdhesivesThe invention of reusable notes began in 1968 when Dr. Spencer Silver wasattempting to make a strong adhesive.One of the adhesives he produced was just strong enough to hold paperstogether, but it was weak enough thatthe papers could be separated withoutdamage. Silver tried to develop a use for the weak adhesive, but it was hiscolleague, Art Fry, who realized theadhesive’s potential. While singing in a choir, Fry was bothered by bookmarksslipping out of pages. By applying some of the weak adhesive to paper, Fry developed a reusable bookmark that could stick to pages withoutharming them. The adhesive is nowused to produce the familiar, multi-colored reusable notes.

Interpreting Diagrams Stabilizers areused to prevent the adhesive monomersfrom forming a solid polymer.Logical

For EnrichmentHave students work in pairs and devisean experiment to compare two types of commercially-available adhesives.Remind them to start by forming ahypothesis and writing a plan for theirexperiment. Suggest that they develop a number scale for reporting how well each adhesive binds two surfacestogether. Materials may include paper,metal foil, or wooden craft sticks. Kinesthetic, Logical

FYIAlthough the terms are used inter-changeably, glue refers to naturalproducts and adhesives refersto synthetics.

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Carbon Chemistry 277

Natural PolymersAlmost all of the large molecules produced by organisms are polymers.

Four types of polymers produced in plant and animal cells arestarches, cellulose, nucleic acids, and proteins.

Starches Many animals are attracted to sweet-tasting foods. Thecompounds responsible for this sweetness are often sugars. Simplesugars have the formula C6H12O6. They can exist as straight chains orrings. The simple sugars glucose and fructose can react to form sucrose(table sugar). Glucose monomers join to form starches as shown below.

Typically, a starch contains hundreds of glucose monomers. Plantsstore starches for food and to build stems, seeds, and roots. Flour forthe bread, pasta, and tortillas shown in Figure 15 is made by grindingthe seeds of grains, such as wheat and corn. Simple sugars, slightlymore complex sugars such as sucrose, and polymers built from sugarmonomers are all classified as carbohydrates.

Cellulose The carbohydrate cellulose is the main component ofcotton and wood. It is the most abundant of all organic compoundsfound in nature. Cellulose molecules contain 3000 or more glucosemonomers. Cellulose gives strength to plant stems and tree trunks.Most animals cannot digest cellulose.

Distinguishing Sugars From Starches

Materials1 slice each of potato, ripe apple, and bread; 15 mL cornstarch; 15 mL table sugar; iodine in dropper bottle; 6 small paper plates

Procedure1. Place one sample of each food on a paper

plate. CAUTION Never eat anything in a lab.

2. Place 2 to 3 drops of iodine solution on thecornstarch. Record your observations.

3. Repeat Step 2 using sugar instead of cornstarch.

4. Place 2 to 3 drops of iodine on each of theother food samples. Record your observations.

Analyze and Conclude1. Classifying How can an iodine solution be

used to distinguish a sugar from a starch?

2. Drawing Conclusions Which of the foodsamples contained starch?

3. Predicting What other foods would turndark when tested with iodine solution?

278 Chapter 9

Figure 15 All the foods showncontain starch, which is a polymerof the simple sugar glucose.Observing Identify foods that you recognize in the photograph.

Glucose A type of starch found in plants

CH2OH

OH

OH

O

O O

CH2OH

OH

OH

O

O

CH2OH

OH

OH

O

O

CH2OH

OH

OH

O

HO OH

278 Chapter 9

Natural Polymers

Distinguishing Sugars From Starches

ObjectiveAfter completing this activity, studentswill be able to• use iodine to test for the presence

of starch in foods.

Skills Focus Observing, FormulatingHypotheses, Inferring

Prep Time 15 minutes

Materials 1 slice each of potato, ripe apple, bread; 15 mL cornstarch; 15 mL table sugar; iodine in a dropperbottle; 6 small paper plates

Advance Prep Cut apples, potatoes,and bread into small cubes (about 1 cm3). Place iodine solution in labeleddropper bottles.

Class Time 10–15 minutes

Safety Students should wear safetygoggles and aprons. Remind studentsnot to eat anything in the lab. Ifstudents slice their own apples andpotatoes, remind them to be carefulwhen handling sharp objects.

Teaching Tips • Do not slice the apples and potatoes

until right before class. Oxidation willcause them to turn brown, making it difficult to observe the results.

• Make sure that the apples are very ripe,but not rotten. In an unripe apple, all of the starch may not be converted tosugar, and students may get a positiveresult. Test one apple in advance.

Expected Outcome Iodine solutionchanges color in the presence of starch.Iodine will change from orange-rust tobrown or blue-black with the cornstarch,potato, and bread. Iodine will not changecolor with the sugar or the apple.

Analyze and Conclude1. Iodine will change color with starch,but not with a sugar.2. The cornstarch, potato, and breadcontain starch. 3. Possible answers include corn, flour,cereals, or any of the foods shown inFigure 15. Visual, Logical

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Section 9.3 (continued)

Starchy Root Cassava is a starchy tuber that isa food staple for many people in South America,West Africa, and the Caribbean. Cassava issimilar to the sweet potato, except that some

varieties contain prussic acid. If not prepared by grating, pressing, and heating, cassava istoxic. Tapioca is a product of cassava roots.

Facts and Figures

Carbon Chemistry 279

Nucleic Acids There are molecules in each cell of a plant or animalthat store information about its structures and functions. These mol-ecules are nucleic acids. Nucleic acids are large nitrogen-containingpolymers found mainly in the nuclei of cells. There are two types ofnucleic acid, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

The monomers in a nucleic acid are nucleotides. Figure 16A showsthe three parts of a nucleotide. The yellow circle represents a phos-phate group. The green pentagon represents deoxyribose sugar, whichhas a five-carbon ring. The purple rectangle represents an organic base.The bases in DNA are adenine, thymine, cytosine, and guanine.

When two strands of DNA line up as shown in Figure 16B, an ade-nine base always pairs up with a thymine base, and a cytosine basealways pairs up with a guanine base. These pairs of bases are arrangedlike the rungs of a ladder. The strands are held together by strong inter-molecular attractions between hydrogen atoms on one strand andnitrogen or oxygen atoms on the other strand. Figure 16C shows howthe strands twist around each other in a structure called a double helix.The order of the base pairs in a strand is a code that stores informationthat is used to produce proteins.

What are the two types of nucleic acids?

A

B

C

Phosphate

Adenine

Thymine

Cytosine

Guanine

Deoxyribosesugar

Figure 16 Nucleic acids are polymers that store thegenetic information that gives the girls in thephotograph their distinct physical characteristics. A The monomers in DNA have three components—aphosphate group, a sugar, and one of four organicbases. B Two strands of DNA are held together byintermolecular attractions between the organic bases. C The shape of DNA is like a twisted ladder. Phosphate-sugar chains form the sides of the ladder. The rungs of the ladder are pairs of bases.

A

CG

T

T A

A T

CG

GC

CG

T A

CG

CG

GC

A T

Use VisualsFigure 16 Have students examine thethree-part diagram of DNA. Ask, Whichpart of the diagram (A, B, or C) showsa single monomer of a nucleic acid?(Part A shows one nucleotide unit.) Howare Parts B and C of the diagramrelated? (Part B shows two strands of thepolymer, each containing many monomerunits. Part C shows how the strands in Part B twist to form a double helix.) Explainthat the strands of DNA need to separatewhen DNA replicates (makes copies ofitself). Ask, If the strands were heldtogether by covalent bonds instead ofintermolecular attractions, how mightthis affect DNA replication? (Becausecovalent bonds are stronger than inter-molecular attractions, more energy wouldbe required to separate the strands.)Visual, Logical

FYIRNA is different from DNA in severalways. The sugar in RNA is ribose insteadof deoxyribose. RNA contains the baseuracil instead of thymine. RNA has onlyone strand.

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Carbon Chemistry 279

Answer to . . .

Figure 15 Answers may includewaffles, bread, pasta, oats, tortillas,rice, and cereal.

RNA and DNA

280 Chapter 9

Section 9.3 Assessment

Reviewing Concepts1. Describe a way that polymers can

be classified.

2. Name three synthetic polymers.

3. What are four types of polymers that canbe found in the cells of organisms?

4. What are the three parts of a nucleotide?

5. What holds the bases together in DNA?

6. What two functional groups are found inamino acids?

Critical Thinking7. Using Analogies Which natural polymers

are like a train with identical freight cars andwhich are like a train with a mixture ofdifferent cars?

8. Inferring There is another system forclassifying carbohydrates that uses thecategories monosaccharides, disaccharides,and polysaccharides. Where would youplace glucose, sucrose, and cellulose inthis classification system? Give a reason foryour answer.

Compare-Contrast Paragraph Write aparagraph comparing natural and syntheticpolymers in general. How are they similar?How are they different?

Proteins Recall that organic acids contain a –COOH group andorganic bases, or amines, contain an –NH2 group. There is one sub-stituted hydrocarbon that contains both groups. An amino acid is acompound that contains both carboxyl and amino functional groupsin the same molecule. There are about 20 amino acids that your bodyneeds to function.

Your cells can manufacture some, but not all, of the amino acids.For example, your body can make glycine, but not phenylalanine. Theessential amino acids that your body cannot make must come fromfoods like those in Figure 17.

Your cells use amino acids as the monomers for constructing pro-tein polymers. A protein is a polymer in which at least 100 amino acidmonomers are linked through bonds between an amino group and acarboxyl group. The instructions for making proteins are stored inDNA. Proteins make up the fibers of your muscles, your hair andfingernails, and the hemoglobin in your blood. Your body may con-tain as many as 300,000 different proteins.

H

H H

C

H

N

O

C OH

Glycine Phenylalanine

H H

C

H

N

O

C OHC

H

H

Figure 17 The foods shown areall good protein sources.Classifying Group the foods intothree or four categories.

280 Chapter 9

Build Science SkillsComparing and Contrasting Havestudents compare and contrast proteinsand nucleic acids. Ask, What do thesetwo types of polymers have in com-mon? (Both have important biologicalfunctions, and the monomers of both are acids.) How do these two types of polymers differ? (The monomers in nucleic acids are nucleotides. Themonomers in proteins are amino acids.)Logical

Integrate HealthEggs, milk, meat, and fish usually containall the essential amino acids. Individualplant foods do not. A strict vegetarianmust eat a combination of foods toobtain all the essential amino acids. Havestudents research and prepare postersshowing foods (such as beans and rice)that provide the complete set of essentialamino acids.Visual

ASSESSEvaluateUnderstandingHave students write down the followinglist of polymers: polyethylene, starch,cellulose, nucleic acids, and proteins.Then, have students identify themonomers for each polymer.

ReteachUse the equation in the text on pp. 276 and 278 to compare a synthetic and a natural polymer.

Paragraphs should include the following.Similarities: made up of smaller moleculescalled monomers that are linked togetherby covalent bonds. Differences: syntheticpolymers are developed by chemists;organisms produce natural polymers.

If your class subscribes to iText, use it to review key concepts in Section 9.3.

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Section 9.3 (continued)

7. Starches and cellulose are like trains withidentical cars, and proteins and nucleic acidsare like trains with a mixture of different cars. 8. Glucose is a monosaccharide because itsmolecules are single sugar units. Sucrose is adisaccharide because its molecules containtwo glucose units linked together. Cellulose is a polysaccharide because it contains manyglucose units linked together.

Section 9.3 Assessment

1. The two main types of polymers are naturaland synthetic.2. Rubber, nylon, and polyethylene3. Starches, cellulose, nucleic acids, and proteins4. Organic base, phosphate group, and a sugar5. Strong intermolecular attractions6. Amino acids contain a carboxyl group andan amino group.

Answer to . . .

Figure 17 Possible answers include:seafood, meat, beans, and nuts.

Carbon Chemistry 281

Should People ConserveFossil Fuels?

Fossil fuels are still abundant. People can continue to use the known supply of fossilfuels at current rates for many years. New technologymakes finding and extracting oil, coal, and naturalgas easier. For example, in 1978 scientists thoughtthere was about 648 billion barrels of oil remainingworldwide. However, with new discoveries andimproved technology, optimists now think there maybe as much as 3 trillion barrels remaining. Even ifthe use of oil increased, scientists would still haveseveral hundred years to develop alternative fuels andnew refining processes. In addition, technologies arereducing the amount of sulfur dioxide and nitrogenoxides released when fossil fuels are burned.

Fossil fuels must be conserved. Advances in technology will serve only to speed up therate at which oil is extracted from oil reserves. Theamount of oil available for consumers will rise, andpeople will feel no need to conserve. At some point,production will decrease as supplies dwindle. Theemissions produced when fossil fuels burn put societyas a whole at risk. Despite more efficient methods ofcombustion, more than 6 billion tons of carbondioxide was released into the atmosphere in 1997.Developing alternative sources of energy now willreduce pollution in the future. These alternatives alsofree fossil fuels for use in the production of plastics,paints, medicines, and other essential materials.

1. Defining the Issue In your own words,describe the issue that needs to be resolvedabout the use of fossil fuels.

2. Analyzing the Viewpoints List threearguments made by those who think that fossilfuels do not need to be conserved. List threearguments made by people who think that fossilfuels must be conserved.

3. Forming Your Opinion Should peopleconserve fossil fuels? Did you find any convincingargument for or against conservation?

The Viewpoints

Research and Decide

For: More on this issue

Visit: PHSchool.com

Web Code: cch-1090

Many people depend on fossil fuels such as petroleum, or crude oil. Nearly28 billion barrels of oil was consumed in 2002. More than 14 billion barrelswas used to supply energy for automobiles, airplanes, and other means oftransportation. Fractions of crude oil are also used to produce plastics, dyes,fertilizers, solvents, aerosols, explosives, paints, soaps, and medicines.

Scientists estimate that annual consumption of oil will increase to38.6 billion barrels by 2020. Scientists disagree about how much of theremaining supply should be used. Some scientists say that there is morefossil fuels remaining than predicted and that there is no crisis. Otherssuggest that scientists must quickly develop alternative sources of energy fortransportation, such as solar power, hydrogen fuel cells, or fuels made fromplants. Alternative energy sources would reduce the use of fossil fuels andlimit the amount of pollution during their combustion.

4. Role-Playing You manufacture a product thathas parts made from synthetic polymers. Thepolymers are made from compounds found in oil.Your costs would increase without the polymers.Write a letter to your senator stating your point ofview on funding alternative energy research.

Carbon Chemistry 281

Should People ConserveFossil Fuels?BackgroundIndustrialized societies are highlydependent on fossil fuels. These fuelsprovide the energy for heating, cooling,and lighting commercial and residentialbuildings; operating industrial machineryand home appliances; and transportinggoods and people. A reduction in thesupply of fossil fuels or an increase intheir cost would have a major impact onthe economy of an industrialized society.In these countries the availability and useof fossil fuels is an important domesticand foreign policy issue. The effect onthe environment of the combustion offossils fuels is also an important issue. So is the extraction, refining, andtransporting of fossil fuels.

Answers1. Should fossil fuels be conserved? 2. Acceptable answers againstconservation include: Reserves aregreater than previously thought; tech-nology makes finding and extractingfuels easier; scientists have time todevelop alternative technologies;technologies have reduced the emissionof sulfur and nitrogen oxides when fossilfuels are burned. Acceptable answers infavor of conservation include: Advancesin technology will increase the rate ofconsumption; eventually production willdecrease; despite more efficient methodsof combustion, tons of carbon dioxideare still released into the atmosphere.3. Students should present arguments to support their decisions.4. Acceptable answers will includepersuasive reasoning to explain thechosen point of view.

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Have students further research the issues related to this topic.