chapter 6: the chemistry of life - jobi - homejohnbio.wikispaces.com/file/view/chap06.pdf ·...

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Unit Projects

Unit ProjectsUnit ProjectsUnit Projects

Unit 3Unit 3Advance PlanningChapter 6■ Obtain potassium peranganate

for the BioLab, mint oil forthe Activity on p. 160, andball-and-stick models for theQuick Demo and RevealingMisconceptions.

Chapter 7■ Purchase prepared slides for

Microscopy project, Portfolioactivity, and BioLab.

■ Purchase animal and plant cellmodels and an Elodea plant.

Chapter 8■ Schedule guest speakers (cell

biologist and school nurse).■ Order prepared frog blastula

slides for MiniLab and onionroot slides for BioLab.

Chapter 9■ Obtain filter paper for the

chromatography project.■ Purchase a molecular model of

a lipid and dialysis bags for theBioDigest activities.

Using the LibraryIntrapersonal Encourage studentsto find out how a cell uses energy

and make a poster showing the flow ofenergy through a cell. L2

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MicroscopyVisual-Spatial Have students exam-ine slides of different types of

human cells (muscle, nerve, skin, etc.).They can draw diagrams of each and pos-tulate why each has its unique shape.

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Final ReportHave student groups compile their find-ings about cells in reports that could bepresented to students at your local mid-dle school. L3

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The Life of a CellThe Life of a Cell

A cell is the most basic unit of livingorganisms. No matter how complex anorganism becomes, at its core is a collectionof cells. As a cell grows in size, it eventuallydivides to form two identical cells. In manyorganisms, cells work together, formingmore complex structures.

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UNIT CONTENTSUNIT CONTENTS

The Chemistry of Life

A View of the Cell

Cellular Transport and the Cell Cycle

Energy in a Cell

Unit 3Unit 3

The Life of a CellBIODIGESTBIODIGEST

UNIT PROJECTUNIT PROJECT

Use the Glencoe Science Web site for more project

activities that are connected to this unit.science.glencoe.com

BIOLOGY

Unit 3Unit 3

The Life of a Cell

Unit OverviewUnit 3 introduces students tobasic chemistry, the structure andfunction of cells, and cell ener-getics. In Chapter 6, studentslearn the basic concepts of chemistry that are important inbiology. Chapter 7 introduces cell structure and function oforganelles. This discussion isexpanded upon in Chapter 8through an in-depth view of cel-lular transport and the cell cycle.Finally, Chapter 9 acquaints stu-dents with the details of energyflow that result from photosyn-thesis and respiration.

Introducing the UnitAsk students to describe some ofthe things they see in the photo-graph of cells of the retina interms of color, shape, and othervisual characteristics. We appre-ciate the amazing variety anddetails of the visual world aroundus through the work of special-ized cells in the retina. Each reti-nal cell receives a small piece ofan image from another cell, suchas the pyramidal neuron fromanother part of the brain, andonly by working together cancells piece together all of theinformation to give an accurateview of the world around us.

Develop a Model of a CellHave students do one of the projects forthis unit as described on the GlencoeScience Web site. As an alternative, stu-dents can do one of the projectsdescribed on these two pages.

DisplayVisual-Spatial Instruct students tocollect examples of cells from maga-

zines and science journals. They shouldmake a display that describes the differ-ent parts of a cell.

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Building a ModelKinesthetic Have student groupsdesign and make a model of a cell

that they might find in any part of aplant. They may use any materials theywish. Small motors can be used to showthe motion of cell products.

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Unit ProjectsUnit ProjectsUnit Projects

Unit Projects

Unit Projects

Unit Projects

http://science.glencoe.com

Activities/FeaturesObjectivesSection

Chapter 6 OrganizerChapter 6 Organizer

Atoms and TheirInteractionsNational Science EducationStandards UCP.1, UCP.2,UCP.3; A.1, A.2; B.1-3; C.5;D.2; E.1, E.2; F.1; G.1, G.2(1 session, 1/2 block)

Water and DiffusionNational Science EducationStandards UCP.2, UCP.3,UCP.4; A.1, A.2; C.5; G.1, G.3(1 session, 1/2 block)

Life SubstancesNational Science EducationStandards UCP.1, UCP.2;A.1, A.2; B.2, B.3; C.5; E.1,E.2; G.1-3 (3 sessions, 1 block)

1. Relate the particle structure of an atomto the identity of elements.

2. Relate the formation of covalent andionic chemical bonds to the stability ofatoms.

3. Distinguish mixtures and solutions.4. Define acids and bases and relate their

importance to biological systems.

5. Relate water’s unique features to polar-ity.

6. Explain how the process of diffusionoccurs and why it is important to cells.

7. Classify the variety of organic compounds.8. Describe how polymers are formed and

broken down in organisms.9. Compare the chemical structures of car-

bohydrates, lipids, proteins, and nucleicacids, and relate their importance to liv-ing things.

Problem-Solving Lab 6-1, p. 149Careers in Biology: Weed/Pest ControlTechnician, p. 154MiniLab 6-1: Determine pH, p. 155Design Your Own BioLab: Does tempera-ture affect an enzyme reaction? p. 168

Problem-Solving Lab 6-2, p. 158MiniLab 6-2: Examine the Rate of Diffusion,p. 159

Inside Story: Action of Enzymes, p. 166BioTechnology: Are fake fats for real? p. 170

MATERIALS LIST

BioLabp. 168 timer or clock, 400-mL beaker,kitchen knife, tongs or forceps, potato,3% hydrogen peroxide, ice, hot plate,waxed paper, thermometer

MiniLabsp. 155 small beakers (4), lemon juice,household ammonia solution, liquiddetergent, shampoo, vinegar, pHpaper, pH color chartp. 159 raw potato, single-edge razorblade, beaker, forceps, metric ruler,timer or clock, potassium perman-ganate solution

Alternative Labp. 164 paper cups (4), gelatin dessertmix, fresh pineapple, canned chunkpineapple, grapes or orange sections,refrigerator, waxed paper, knife, water

Quick Demosp. 146 iron nails, copper pipe, alu-minum foil, coal or charcoal, mercurythermometerp. 150 beaker, water, table salt, 9-voltbattery, electrical wirep. 157 paper towel, bowl; cookingpot, Bunsen burner, ring standp. 163 model of methane molecule

Need Materials? Contact Carolina Biological Supply Company at 1-800-334-5551or at http://www.carolina.com

Index to National Geographic MagazineThe following articles may be used forresearch relating to this chapter:“Worlds Within the Atom,” by JohnBoslough, May 1985.

Teacher’s Corner

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The Chemistry of LifeThe Chemistry of Life

TransparenciesReproducible MastersSection

Atoms and TheirInteractions

Water andDiffusion

Life Substances

Section 6.1

Section 6.2

Section 6.3

Teacher Classroom Resources

Section Focus Transparency 12Basic Concepts Transparency 4Basic Concepts Transparency 5a, 5b

Section Focus Transparency 13

Section Focus Transparency 14Reteaching Skills Transparency 8

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Assessment Resources Additional ResourcesSpanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block SchedulingReviewing Biology: Preparing to Take the EOC Test, pp. 11-12North Carolina Teacher Resource Manual

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Chapter Assessment, pp. 31-36MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomExamView® Pro SoftwareBDOL Interactive CD-ROM, Chapter 6 quiz5 Days to the EOC Test

Section 6.2

Section 6.1

Section 6.3

Refer to pages 4T-5T of the Teacher Guide for an explanation of the National Science Education Standards correlations.

Reinforcement and Study Guide, pp. 25-26BioLab and MiniLab Worksheets, p. 27Content Mastery, pp. 29-30, 32

Reinforcement and Study Guide, p. 27Concept Mapping, p. 6BioLab and MiniLab Worksheets, p. 28Content Mastery, pp. 29-32

Reinforcement and Study Guide, p. 28Critical Thinking/Problem Solving, p. 6BioLab and MiniLab Worksheets, pp. 29-30Laboratory Manual, pp. 39-46Content Mastery, pp. 29, 31-32Tech Prep Applications, pp. 9-10 L2

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Key to Teaching StrategiesKey to Teaching Strategies

Level 1 activities should be appropriatefor students with learning difficulties.Level 2 activities should be within theability range of all students.Level 3 activities are designed for above-average students.ELL activities should be within the abilityrange of English Language Learners.

Cooperative Learning activitiesare designed for small group work.These strategies represent student prod-ucts that can be placed into a best-workportfolio.These strategies are useful in a blockscheduling format.

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The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

Animation: The Covalent BondAnimation: The Ionic BondAnimation: Enzyme ActionExploration: Acid Base TestVideo: Properties of Water

Videodisc ProgramCovalent BondingIonic BondingProperties of Water

The Infinite VoyageUnseen WorldsThe Future of the Past

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http://www.carolina.com

Section

Elements Everything—whether it is a rock,

frog, or flower—is made of sub-stances called elements. Suppose youfind a nugget of pure gold. You couldgrind it into a billion bits of powderand every particle would still be gold.You could treat the gold with everyknown chemical, but you could neverbreak it down into simpler sub-stances. That’s because gold is an ele-ment. An element is a substance thatcan’t be broken down into simplerchemical substances. On Earth, 90elements occur naturally.

Natural elements in living things

Of the 90 naturally occurring ele-ments, only about 25 are essential toliving organisms. Table 6.1 lists someelements found in the human body.Notice that only four of the 90 ele-ments—carbon, hydrogen, oxygen,and nitrogen—make up more than96 percent of the mass of a human.Each element is identified by a one-or two-letter abbreviation called asymbol. For example, the symbol Crepresents the element carbon, Carepresents calcium, and Cl representschlorine.

6.1 ATOMS AND THEIR INTERACTIONS 145

What makes a living thingdifferent from a nonlivingthing? Are the particles

that make up a rock different fromthose of a frog or a clam? The differ-ence between living and nonlivingthings may be readily apparent toyou. For example, you may haveplayed a game of basketball yesterday,something you would not expect arock to do. We know, however,that living things have a greatdeal in common with rocks,CDs, computer chips, andother nonliving objects.Both living and nonliv-ing things are composedof the same basic buildingblocks called atoms.

SECTION PREVIEW

ObjectivesRelate the particlestructure of an atom to the identity of elements.Relate the formation of covalent and ionicchemical bonds to thestability of atoms.Distinguish mixturesand solutions.Define acids and bases and relate theirimportance to biologicalsystems.

Vocabularyelementatomnucleusisotopecompoundcovalent bondmoleculeionionic bondmetabolismmixturesolutionpHacidbase

6.1 Atoms and TheirInteractions

All things are similarat the atomic level.

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Section 6.1

PrepareKey ConceptsStudents are introduced to thesubatomic particles that make upthe atoms of elements. In addi-tion, students become acquaintedwith isotopes in biology. Studentsalso study compounds and bond-ing. Students compare the prop-erties of acids and bases.

Planning■ Gather items for the Quick

Demo and demonstrations.■ Purchase sand, salt, and gelatin

for the Enrichment.■ Obtain common household

solutions for MiniLab 6-1.■ Purchase beans and toothpicks

and gumdrops or marshmal-lows for the activities.

1 FocusBellringer Before presenting the lesson, dis-play Section Focus Trans-parency 12 on the overheadprojector and have studentsanswer the accompanying ques-tions.

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LSAssessment PlannerAssessment Planner

Portfolio AssessmentMiniLab, TWE, pp. 155, 159BioLab, TWE, p. 169

Performance AssessmentMiniLabs, SE, pp. 155, 159BioLab, SE, p. 169Alternative Lab, TWE, p. 165

Knowledge AssessmentAssessment, TWE, pp. 147, 160, 162, 167

Problem-Solving Labs, TWE, pp. 149, 158Alternative Lab, TWE, p. 165Section Assessments, TWE, pp. 155, 160, 167Chapter Assessment, TWE, p. 171-173

Skill AssessmentAssessment, TWE, p. 153 BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Elements in the Human Body (percent by mass)

Oxygen65%

Carbon18.5%

Hydrogen9.5%

Nitrogen 3%

Calcium 1.5%

Phosphorus 1%

Other Elements 1.5%

Use with Chapter 6,Section 6.1

Which four elements are the most common in thehuman body?

What do you know about these four elements?

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Transparency Elements12 SECTION FOCUS

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144 THE CHEMISTRY OF LIFE

The Chemistry of Life

What You’ll Learn■ You will relate the structure

of an atom to how it interacts with other atoms.

■ You will explain how water is important to life.

■ You will compare the role of carbon compounds inorganisms.

Why It’s ImportantLiving organisms are made ofsimple elements as well as com-plex carbon compounds. Withan understanding of these ele-ments and compounds, you willbe able to relate them to howliving organisms function.

Go through the chapter andobserve the structure diagrams.Write down any questions youhave. As you read the chapter,try to answer the questionsfrom the reading material.

To find out more about cellchemistry, visit the GlencoeScience Web site.science.glencoe.com

READING BIOLOGYREADING BIOLOGY

6

The gold shown in this scanning-tunneling microscopepicture is made ofatoms. Atoms make up the colorful frogs andthe element gold.

ChapterChapter

BIOLOGY

Magnification:32 900�

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Theme DevelopmentUnity within diversity isstressed through the discussionthat although living things andnonliving things differ, they arealike in that all are made up ofelements. Energy should be dis-cussed along with chemical reac-tions. Be sure to stress thatalthough elements unite withother matter or break apart dur-ing chemical reactions, matter isneither created nor destroyed.

Chapter 6Chapter 6

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.Kinesthetic Meeting IndividualNeeds, p. 147; Project, p. 151;

Reteach, p. 153; Activity, p. 154Visual-Spatial Portfolio, p. 146;Extension, p. 153; Biology

Journal, pp. 157, 158; Reteach, p. 150;Tech Prep, p. 162; Check for Under-standing, p. 166

Interpersonal MeetingIndividual Needs, p. 161;

Portfolio, p. 163Intrapersonal Enrichment, pp. 148, 165; Portfolio, p. 153;

Extension, p. 160;Linguistic Biology Journal, pp. 149, 161; Portfolio, p. 159 Logical-Mathematical QuickDemo, p. 157; Activity, p. 160;

Portfolio, p. 162; Going Further, p. 169

GETTING STARTED DEMOGETTING STARTED DEMO

Direct students’ attention tothe photographs shown here.Ask students to list the featuresof living things in their journals.Also ask students to speculateand write in their journalsabout why early scientiststhought a mysterious force con-trolled chemical changes inorganisms.

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If time does not permit teach-ing the entire chapter, use theBioDigest at the end of theunit as an overview.

Glencoe’s Biology: The Dynamicsof Life contains many resourcesto assist a student’s reading skills.Each chapter contains figureswith expanded captions thatexpand on written material. WordOrigins, located along the side oftext, expand knowledge of biologyvocabulary. Glencoe’s ContentMastery Booklet helps developreading skills while reinforcingcontent. In addition, use theInteractive Tutor for Biology: TheDynamics of Life on the GlencoeWeb site to reinforce vocabulary.science.glencoe.com

READING BIOLOGYREADING BIOLOGY




Figure 6.1Trace elements areneeded in smallamounts to controlcell metabolism.

Percent by Percent by mass in mass in

Element Symbol human body Element Symbol human body

Oxygen O 65.0 Iron Fe trace

Carbon C 18.5 Zinc Zn trace

Hydrogen H 9.5 Copper Cu trace

Nitrogen N 3.3 Iodine I trace

Calcium Ca 1.5 Manganese Mn trace

Phosphorus P 1.0 Boron B trace

Potassium K 0.4 Chromium Cr trace

Sulfur S 0.3 Molybdenum Mo trace

Sodium Na 0.2 Cobalt Co trace

Chlorine Cl 0.2 Selenium Se trace

Magnesium Mg 0.1 Fluorine F trace

Table 6.1 Elements that make up the human body

Trace elementsNotice that some of the elements

listed in Table 6.1, such as iron andmagnesium, are present in livingthings in very small amounts. Suchelements are known as trace ele-ments. They play a vital role in main-taining healthy cells in all organisms,as shown by the examples in Figure 6.1. Plants obtain trace ele-ments by absorbing them through

their roots. Animals get these impor-tant elements from the foods they eat.

Atoms: The BuildingBlocks of Elements

Elements, whether they are foundin living things or not, are made upof atoms. An atom is the smallestparticle of an element that has thecharacteristics of that element.

Mammals use iodine (I), anessential element, to producesubstances that affect the ratesof growth, development, andchemical activities in the body.

AA Plants must have magnesium(Mg) in order to form thegreen pigment chlorophyll thatcaptures light energy for theproduction of sugars.

BB A trace of fluorine, anotheressential element, binds withthe surface structure of teeth,making them resistant todecay.

CC

Mg++ ions

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2 Teach

Quick DemoQuick Demo

Display various elements usingcommon objects such as ironnails, a piece of copper pipe, a piece of aluminum foil, apiece of coal or charcoal, anda mercury thermometer. Tellstudents that each material iscomposed of a different kindof element. Direct students’attention to the appropriateobject when discussing eachelement.

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PortfolioPortfolio

Diagramming Atomic StructureVisual-Spatial Have students makea detailed drawing of an aluminum

atom, showing the contents of thenucleus of the atom and the energy levelsof the electrons.

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VIDEODISCThe Secret of LifeComposition of Living

Organisms!7;5~A"

Visual LearningVisual-Spatial Discuss possi-ble dietary sources of each

element listed in Table 6.1. Havestudents redesign the table toinclude pictures that show twosources of each element listed.Have students conduct additionalresearch if necessary.

Concept DevelopmentStress that the elements carbon,hydrogen, nitrogen, oxygen,phosphorus, and sulfur are themain components of living mat-ter. All these elements form mol-ecules through covalent bonding.

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Resource ManagerResource ManagerSection Focus Transparency 12 and

MasterBasic Concepts Transparency 4 and

Master

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Electron energy levels

Nucleus

e – Nucleus8 protons (p )8 neutrons (n )

Oxygen atom

Hydrogen atom

p+

e –

e –

e –e –

e – e –

e –

+

0

e –


Figure 6.2Electrons move rapidly around atoms, forming electronclouds that have several energy levels.

The structure of an atomEach element has distinct charac-

teristics that result from the structureof the atoms that compose the element. For example, iron differsfrom aluminum because the structureof iron atoms differs from that of alu-minum atoms. Still, all atoms havethe same general arrangement. Thecenter of an atom is called thenucleus (NEW klee us) (plural,nuclei). It is made of positivelycharged particles called protons (p+)and particles that have no charge,called neutrons ( n0). All nuclei arepositively charged because of thepresence of protons.

Forming a cloud around thenucleus are even smaller, negativelycharged particles called electrons ( e–).If you’ve ever looked at a spinningfan, you’ve probably noticed that asthe fan blades turn, they appear to

form a blurry disk that occupies aspace around the center of the fan.Similarly, an electron cloud is thespace around the atom’s nucleus thatis occupied by these fast-movingelectrons. Although it is impossibleto pinpoint the exact location of anelectron because it is moving soquickly, the electron cloud is an areawhere it is most likely to be found.

Electron energy levelsElectrons travel around the nucleus

in certain regions known as energylevels, as indicated by Figure 6.2.Each energy level has a limited capac-ity for electrons. Because the firstenergy level is the smallest, it can holda maximum of only two electrons.The second level is larger and canhold a maximum of eight electrons.The third level is larger yet and canhold 18 electrons. For example,

Oxygen has two electrons in its first energylevel and six electrons in the second level.

BB

Hydrogen, the simplest atom, has justone electron in its first energy level andone proton in its nucleus.

CCAn atom has a nucleus and electrons incloudlike energy levels.

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MMEETING EETING IINDIVIDUAL NDIVIDUAL NNEEDS EEDS MEETING INDIVIDUAL NEEDS

Visually Impaired Kinesthetic To help students who arevisually impaired understand the struc-

ture of an atom, make atomic models by glu-ing marbles, jelly beans, and yarn to a pieceof cardboard. Use the yarn to outline thenucleus and the energy levels. Use marbles

for the neutrons and jelly beans for the elec-trons and protons. Allow visually impairedstudents to manipulate the model. Havepeers work with visually impaired studentsto assist in identifying the parts of themodel.

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VIDEODISCThe Secret of LifeHydrogen/Carbon Atom

Oxygen Atom

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Tying to PreviousKnowledgeRelate the discussion of thechemistry of life to the character-istics of living things discussed inChapter 1. Emphasize that thepresence of carbon is a character-istic shared by all organisms.

DisplayMake a bulletin board displaythat models the structure of anatom. Label the nucleus, protons,neutrons, and electrons of themodel. Refer to the display whendiscussing atomic structure.

Knowledge On the chalk-board, prepare a table with theheads: Particle, Location, Charge,and Symbol. Beneath the Particlehead, list: Electron, Neutron, andProton. Have volunteers come tothe chalkboard to complete thetable.

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AssessmentAssessment

the oxygen atom in Figure 6.2 has atotal of eight electrons. Two elec-trons fill the first energy level. Theremaining six electrons occupy thesecond level.

Atoms contain equal numbers ofelectrons and protons; therefore,they have no net charge. The hydro-gen (H) atom in Figure 6.2 has justone electron and one proton. Oxygen(O) has eight electrons and eight pro-tons. Figure 6.3 shows three otherelements whose properties differbecause of their atomic structure.

Isotopes of an ElementAtoms of an element sometimes

contain different numbers of neutronsin the nucleus. Atoms of the sameelement that have different numbersof neutrons are called isotopes (I suhtohps) of that element. For example,most carbon nuclei contain six neu-trons. However, some have seven oreight neutrons. Each of these atomsis an isotope of the element carbon.Scientists refer to isotopes by givingthe combined total of protons andneutrons in the nucleus. Thus, themost common carbon atom isreferred to as carbon-12 because ithas six protons and six neutrons.Other isotopes of carbon include car-bon-13 and carbon-14.

Isotopes are often useful to scien-tists. The nuclei of some isotopes,such as carbon-14, are unstable andtend to break apart. As nuclei break,they give off radiation. These iso-topes are said to be radioactive.Because radiation is detectable and


Figure 6.3The properties of anelement are deter-mined by the struc-ture of its atoms. Asyou can see, copper,gold, and carbonhave very differentproperties.

Figure 6.4Radioactive isotopes are used in medicine todiagnose and/or treat some diseases.

Radioactive iodine (I) introduced into thebody is absorbed by the thyroid gland. Bydetecting the radioactive iodine taken up, thefunction of the thyroid gland can be mea-sured. The thyroid scan on the left is normaland the scan on the right is overactive.

AA

Radiation given off when radioactive isotopesbreak apart is deadly to rapidly growing cancercells. The patient is being treated with radiationfrom a radioactive isotope of cobalt (Co).

BB

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VIDEODISCThe Infinite VoyageUnseen Worlds

Studying the Basic BuildingBlocks: The Atom (Ch. 9) 2 min.

The Scanning TunnelingMicroscope: Observing AtomicParticles (Ch. 10) 2 min.

!7~$G"

!8$.J"

EnrichmentIntrapersonal The scanningtunneling microscope (STM)

provides a three-dimensionalmap of a molecule’s surface bymeasuring the flow of electronsacross a small vacuum gap. Atungsten tip similar to a phono-graph needle is positioned a fewangstroms from the substancebeing studied. When a small volt-age is applied, some electronsjump across the gap between thetip and the surface. As the tipmoves across the surface, the cur-rent varies according to the con-tours of the atoms present. Havecapable students research thesemicroscopes and give a presenta-tion to the class.

DiscussionRadiation can penetrate and dis-rupt the functions of living cells.However, certain radioisotopeshave practical uses in medicine asdiagnostic tools. For example,radioactive iodine is used to iden-tify problems with the thyroidgland. Lead a discussion on howthe benefits of such radiationcompare with the risks of expo-sure.

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Note Internet addresses that you find useful in the space belowfor quick reference.

BIOLOGY

What information can be gained from seeing thenucleus of an atom? Looking at a model of an atom’snucleus can reveal certain information about that particularatom. Models may help predict electron number, position ofelectrons in energy levels, and how isotopes of an elementdiffer from each other.

AnalysisExamine diagrams A and B. Both are models of an atom

of beryllium. Only the nucleus of each atom is shown.

Thinking Critically1. What is the neutron number for A? For B?2. Which diagram represents an isotope of beryllium?

Explain how you were able to tell.3. How many electrons are present in atoms A and B?

Explain how you were able to tell.4. How many energy levels would be present for A and B?

How might the electrons in A and B be distributed inthese levels?

Problem-Solving Lab 6-1Problem-Solving Lab 6-1 Interpreting ScientificIllustrations

can damage or kill cells, scientistshave developed some useful applica-tions for radioactive isotopes, asdescribed in Figure 6.4.

Atomic models like those discussedin the Problem-Solving Lab on thispage help scientists and studentsvisualize the structure of atoms andunderstand complex intermolecularinteractions.

Compounds and Bonding

Water is a substance that everyoneis familiar with; however, water is notan element. Rather, water is a type ofsubstance called a compound. Acompound is a substance that iscomposed of atoms of two or moredifferent elements that are chemicallycombined. Water(H2O) is a com-pound composedof the elementshydrogen andoxygen. If youpass an electriccurrent throughwater, it breaks

down into these elements. Just as thecombined ingredients in a pizzaresult in a tasty meal, you can see inFigure 6.5 that the properties of acompound are different from thoseof its individual elements.

How covalent bonds formMost matter is in the form of com-

pounds. But how and why do atomscombine, and what is it that holds theatoms of unlike components togetherin a compound? Atoms combine withother atoms only when conditionsare right, and they do so to becomemore stable.


Figure 6.5Table salt is made from the elementssodium (Na) and chlorine (Cl). The flaskcontains the poisonous, yellow-greenchlorine gas. The lump of silver-whitemetal is the element sodium. The whitecrystals of table salt no longer resembleeither sodium or chlorine.

AA BBBeryllium nucleus Beryllium nucleus

Most common form

Proton

149

Purpose Students will use diagrams of anucleus of beryllium to predictelectron number, position ofelectrons in energy shells, andhow differences in the number ofneutrons affects the element.

Process Skillsthink critically, apply concepts,compare and contrast, defineoperationally, interpret data

Teaching Strategies■ Review the concept of isotopeswith students. Provide otherexamples for them to analyze.■ Explain or emphasize the con-cept that all atoms of the sameelement have the same electronand proton number. They maydiffer only in the number of neu-trons. ■ Review the charges associatedwith each atomic particle.

Thinking Critically

1. 5, 42. Both A and B have four pro-

tons, so they are both iso-topes of beryllium.

3. 4. Electron and proton num-bers are always the same.

4. 2. Two electrons in each level.

Knowledge Provide stu-dents with two diagrams of thenucleus for the element fluorine.Have one nucleus with 9 neutronsand one with 10 neutrons. Advisethem of the most common form(with 9 neutrons). Ask them toprovide the same information forberyllium. Use the PerformanceTask Assessment List for MakingObservations and Inferences inPASC, p. 17. L2

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Problem-Solving Lab 6-1Problem-Solving Lab 6-1

BIOLOGY JOURNAL BIOLOGY JOURNAL

Life as an Atom Linguistic Ask students to pretendthat they are a particular type of

atom. Ask them to write a paragraph ortwo describing their basic structure.Encourage the students to use theirimaginations, while retaining scientificaccuracy.

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Remember electron energy levels?For most elements, an atom becomesstable when its outermost energylevel is full, such as having eight elec-trons in the second level. An excep-tion is hydrogen, which becomes sta-ble when its first energy level is full(two electrons). How do elements fillthe energy levels and become stable?One way is to share electrons withother atoms.

For example, two hydrogen atomscan combine with each other by shar-ing their electrons, as shown inFigure 6.6. As you know, individualatoms of hydrogen contain only oneelectron. Each atom becomes stableby sharing its electron with the otheratom. The two shared electronsmove about the first energy level ofboth atoms. The attraction of the

positively charged nuclei for theshared, negatively charged electronsholds the atoms together. When twoatoms share electrons, such as hydro-gen sharing with oxygen in water, theforce that holds them together iscalled a covalent bond (koh VAY

lunt). Most compounds in organismshave covalent bonds. Examplesinclude sugars, fats, proteins, andwater.

A molecule is a group of atomsheld together by covalent bonds andhaving no overall charge. A moleculeof water is represented by the chemi-cal formula H2O. The subscript 2represents two atoms of hydrogen(H) combined with one atom of oxy-gen (O). As you will see, many com-pounds in living things have morecomplex formulas.


Figure 6.6Sometimes atoms combine by sharing electronsto form covalent bonds.

Hydrogen gas (H2) exists as two hydrogenatoms sharing electrons with each other.The electrons move around the nuclei ofboth atoms.

AA

When two hydrogensshare electrons withoxygen, they formcovalent bonds toproduce a moleculeof water.

BB

View an ani-mation of covalentbonding in thePresentation Builderof the InteractiveCD-ROM.

CD-ROM

+ +

–

–

p p

e

e

Hydrogen molecule

p+

p+

e–e–

e–

e–

e–

e–

e–

e–

e–e

Watermolecule

+

n088

p

–

150


Place a beaker of lightly saltedwater on a table where it canbe seen by students. Connectone end of a piece of wire tothe positive terminal of a 9-volt battery. Connect a secondpiece of wire to the negativeterminal of the battery. Placethe other ends of the wiresinto the water; do not allowwires to touch. Instruct stu-dents to observe the ends ofthe wires for the appearanceof bubbles. Explain that pass-ing an electric current throughwater breaks the water apart,resulting in the elements oxy-gen and hydrogen.

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VIDEODISCBiology: The Dynamicsof Life

Covalent Bonding (Ch. 17)Disc 1, Side 1 37 sec.

Ionic Bonding (Ch. 18)Disc 1, Side 145 sec.

!8rÜ"

!8|á"The Secret of LifeWater Molecule

!7;6`I"

CD-ROMBiology: The Dynamicsof Life

Animation: The Covalent BondAnimation: The Ionic BondDisc 1

Cultural DiversityKenichi Fukui and ChemicalReactions In the 1950s, Japanese chemist Kenichi Fukui(1918–1998) developed the idea that chemi-cal reactions occur as a result of interactionsof the outer-level electrons of one atom ormolecule with the outer-level electrons of

another atom or molecule. In 1981, Fukuireceived the Nobel Prize for Chemistry for hisinvestigations of the mechanisms of chemicalreactions. Discuss with students the work ofKenichi Fukui toward understanding chemi-cal interactions.

How ionic bonds formNot all atoms bond with each

other by sharing electrons.Sometimes atoms combine with eachother by gaining or losing electronsin their outer energy levels. An atom(or group of atoms) that gains orloses electrons has an electricalcharge and is called an ion. An ion isa charged particle.

A different type of chemical bondholds ions together. The bondformed between a sodium atom (Na)and chlorine atom (Cl) is a goodexample of this. A sodium atom con-tains 11 electrons, including one inthe third energy level. A chlorineatom has 17 electrons, with the outerlevel holding seven electrons. Whensodium and chlorine combine, thesodium atom loses one electron, andthe chlorine atom gains it. Thus,with eight electrons in its outer level,the chlorine ion formed is stable andhas a negative charge. Sodium haslost the one electron that was in itsthird energy level. Thus, the sodiumion is stable and has a positivecharge. The attractive force betweentwo ions of opposite charge is knownas an ionic bond. The bond betweensodium and chlorine is an ionic bond,as shown in Figure 6.7.

Ionic compounds are less abundantin living things than are covalent

molecules, but ions are important inbiological processes. For example,sodium and potassium ions arerequired for transmission of nerveimpulses. Calcium ions are necessaryfor muscles to contract. Plant rootsabsorb essential minerals in the formof ions.

Chemical ReactionsWhen chemical reactions occur,

bonds between atoms are formed orbroken, causing substances to com-bine and recombine as different mole-cules. In organisms, chemical reac-tions occur over and over inside cells.All of the chemical reactions thatoccur within an organism are referredto as that organism’s metabolism.These reactions break down andbuild molecules that are important


Figure 6.7The positive chargeof a sodium ionattracts the negativecharge of a chlorineion, and the elementscombine with anionic bond that formsexplosively, as shownin the photograph.

OriginWORDWORD

metabolism From the Greekword metabole,meaning “change.”Metabolisminvolves manychemical changes.

View an animation of ionicbonding in thePresentation Builderof the InteractiveCD-ROM.

CD-ROM

+

+

+

11p +

12 n 0

2e –8e –

e – 7e –

+Sodium atom Chlorine atom

Na Cl NaCl

Sodium + ion Chloride – ion

Ionic bond

17 p +

18 n 0

2e –8e –

11p +

12 n 0

2e –8e –

8e –

17 p +

18 n 0

2e –8e –

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ReinforcementLogical-Mathematical Givestudents several chemical

formulas related to living things,such as CO2 and C6H12O6. Havethem practice identifying the ele-ments in the compounds and thenumbers of atoms of each type ofelement shown in each formula.

Chalkboard ExampleLogical-Mathematical Writea few chemical equations on

the chalkboard and work withstudents to balance the equations.Once the equations are balanced,have students confirm the bal-ance by counting the number ofatoms of each kind on each sideof the equation. Reinforce theidea that atoms are never createdor destroyed in ordinary reac-tions. Some possible equationsare as follows.Mg + 2HCl ⇒ MgCl2 + H22C2H2 + 5O2 ⇒ 2H2O + 4CO22H2S + 3O2 ⇒ 2H2O + 2SO2

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P R O J E C TModeling

Kinesthetic Have students buildmodels of water molecules. Students

may use toothpicks and gumdrops or col-ored marshmallows to represent theatoms in the molecule.

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for the functioning of organisms.Scientists represent chemical reac-tions by writing chemical equations.Chemical equations use symbols andformulas to represent each elementor substance.

Writing chemical equationsThe events that take place when

hydrogen gas combines with oxygengas are shown in Figure 6.8. Sub-stances that undergo chemical reac-tions, such as hydrogen and oxygen,are called reactants. Substancesformed by chemical reactions, such aswater, are called products.

It’s easy to tell how many moleculesare involved in a reaction because thenumber before each chemical formulaindicates the number of molecules ofeach substance. The subscript num-bers in a formula indicate the numberof atoms of each element in a mole-cule of the substance. A molecule oftable sugar can be represented by theformula C12H22O11. The lack of anumber before a formula or under asymbol indicates that only one atomor molecule is present.

Looking at the equation in Figure 6.8, you can see that eachmolecule of hydrogen gas is com-posed of two atoms of hydrogen.


Figure 6.8This balanced equation shows two molecules of hydro-gen gas reacting with one molecule of oxygen gas toproduce two molecules of water.

Likewise, a molecule of oxygen gas is made of two atoms. Perhaps theeasiest way to understand chemicalequations is to know that atoms areneither created nor destroyed inchemical reactions. They are simplyrearranged. Therefore, an equation iswritten so that the same numbers ofatoms of each element appear onboth sides of the arrow. In otherwords, equations must always bewritten so that they are balanced.

Mixtures and SolutionsWhen elements combine to form a

compound, the elements no longerhave their original properties. Whathappens if substances are just mixedtogether and do not combine chemi-cally? A mixture is a combination ofsubstances in which the individualcomponents retain their own proper-ties. Figure 6.9 shows a mixture ofsand and sugar. If you stirred sandand sugar together, you could still tellthe sand from the sugar. Neithercomponent of the mixture wouldchange, nor would they combinechemically. You could easily separatethem by adding water to dissolve thesugar and then filtering the mixtureto collect the sand.

+

+2H2 O2 2H2O

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EnrichmentPrepare mixtures of sand andwater (suspension) and salt andwater (solution). Explain that thecontents of both containers rep-resent mixtures. Stir each con-tainer and ask students todescribe any changes theyobserve in the appearance of themixtures.

Use the observable traits of themixtures to explain that there aredifferent types of mixtures.Explain that the sand and waterrepresent a suspension—a het-erogeneous mixture consisting offinely divided particles of a solidtemporarily suspended in a liq-uid. The salt and water are asolution—a mixture in which oneor more substances are evenlydistributed in another substance.

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VIDEODISCThe Infinite VoyageThe Future of the Past

Preserving Frescoes in Florence(Ch. 1) 9 min. 30 sec.

!7-8J"


Concept MappingHave students create a concept map showing the relationships among elements,mixtures, compounds, and solutions. Thefollowing terms should be included: atoms,elements, molecules, compounds, mixtures,solutions, solvent. Students may add otherterms and should supply their own con-necting words.

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A solution is a mixture in whichone or more substances (solutes) aredistributed evenly in another sub-stance (solvent). In other words, onesubstance is dissolved in another andwill not settle out of solution. Youmay remember making Kool-Aidwhen you were younger. The sugarmolecules in Kool-Aid dissolve easilyin water to form a solution, as shownin Figure 6.10.

Solutions are important in livingthings. In organisms, many vital sub-stances, such as sugars and mineralions, are dissolved in water. The moresolute that is dissolved in a givenamount of solvent, the greater is thesolution’s concentration (strength).The concentration of a solute isimportant to organisms. Organismscan’t live unless the concentration ofdissolved substances stays within aspecific, narrow range. Organismshave many mechanisms to keep the


Figure 6.10The sugar molecules in the Kool-Aid dissolvein the water, making a solution. Here, sugaris the solute and water is the solvent.

Figure 6.9This combina-tion of sand and sugar illustrates

a mixture. Bothcomponentsretain theiroriginal properties.

concentrations of molecules and ionswithin this range. For example, thepancreas and other organs in yourbody produce substances that keepthe amount of sugar dissolved in yourbloodstream within a critical range.

Watermolecules

Sugarmolecules

Sugarcrystal

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Using Science TermsTell students to imagine they aremaking a glass of lemonade froma mix. Ask: “Which part of theresulting solution is the solute?Which is the solvent?” Thelemonade mix is the solute because itis the material being dissolved. Thewater in which the mix is dissolved isthe solvent.

3 AssessCheck for Understanding

Visual-Spatial Refer studentsto the periodic table. Pro-

vide students with a list of severalcommon elements. For each ele-ment, ask students to give thecorrect symbol and diagram theatom’s structure to show its pro-tons, neutrons, and electronenergy levels.

ReteachKinesthetic Using gumdropand toothpick molecules,

demonstrate a chemical reactionsuch as CH4 + 2O2 ⇒CO2 +2H2O. Stress the conservation ofmatter as students tear the origi-nal molecules apart to build newmolecules.

ExtensionVisual-Spatial Ask studentsto make a display to show

the chemical formulas of tencommon substances.

Skill Give students the fol-lowing equations to balance.

N2O4 ⇒ NO2C3H8 + O2 ⇒ CO2 + H2O

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PortfolioPortfolio

Mixtures and CompoundsIntrapersonal Have students con-struct a table to compare and con-

trast mixtures and compounds. Encouragestudents to reread the section entitled“Mixtures and Compounds” to find theinformation needed to complete theirtables.

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Figure 6.11The pH scale rangesfrom 0 to 14. Lemonand tomato are acidic(pH < 7). Pure water is neutral (pH 7).Ammonia (pH 11) is basic.

0 1 2 3 4 5 6 7

NeutralMore acidic

8 9 10

Acids and basesChemical reactions can occur only

when conditions are right. For exam-ple, a reaction might depend on tem-perature, the availability of energy, ora certain concentration of a substancedissolved in solution. Chemical reac-tions in organisms also depend onthe pH of the environment. The pHis a measure of how acidic or basic asolution is. A scale with values rang-ing from 0 to 14 is used to measurepH. Indicators like pH paper describethe pH of substances like thoseshown in Figure 6.11.

Substances with a pH below 7 areacidic. An acid is any substance thatforms hydrogen ions (H+) in water.When the compound hydrogen chlo-ride (HCl) is added to water, hydro-gen ions (H+) and chloride ions (Cl–)are formed. Thus, hydrogen chloridein solution is called hydrochloricacid. This acidic solution contains anabundance of H+ ions and has a pHbelow 7.

Substances with a pH above 7 arebasic. A base is any substance thatforms hydroxide ions (OH–) in water.For example, if sodium hydroxide(NaOH) is dissolved in water, it forms

CAREERS IN BIOLOGY

Weed/Pest ControlTechnician

A career working with chemicals

does not always require aPh.D. Weed and pestcontrol technicians usechemicals to get rid of unwanted weeds,insects, and other pests.

Skills for the JobAfter high school,

most technicians receive on-the-job training in pestcontrol or take correspondencecourses to earn a degree in this field. In many states, you must pass a test to become licensed.

As a technician, you may visit homes, office buildings,restaurants, hotels, and other places where insects, animals,or weeds have become a problem. You will choose the cor-rect chemical and form, such as a spray or gas, to get rid ofor prevent infestations of flies, roaches, termites, or othercreatures. You will select different chemicals to deal withweeds. You might also set traps to catch rats, mice, moles, or other animals.

To find out more about careers in related fields, visit the Glencoe Science Web site. science.glencoe.com

LemonpH 2

TomatopH 4

WaterpH 7

EggpH 8

AntacidpH 10

MilkpH 6

BIOLOGY

154

EducationCourses in high school:chemistry, mathematics,

biology, and carpentryCollege: a degree in biology formanagers or supervisorsOther education sources: on-the-job training and correspon-dence courses

Career IssueAsk students whether weed andpest control technicians shouldtell their customers about non-chemical ways to control weedsand insects. Why or why not?

For More InformationFor more information about pestcontrol, write to:

National Pest Control Association8100 Oak StreetDunn Loring, VA 22027

4 CloseActivity

Kinesthetic Have studentsbuild a model of an element,

such as oxygen, using navy beansfor electrons, pinto beans forneutrons, and kidney beans forprotons.

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CAREERS IN BIOLOGY

MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

GiftedLogical-Mathematical Provide students with several chemical for-

mulas, including some with coefficients.Have them determine how many atomsof each element are represented in eachformula. Students can also draw diagramsgiving the molecular structure of the com-pounds.

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Exploration: Acid Base TestDisc 1

Resource ManagerResource ManagerContent Mastery, p. 30BioLab and MiniLab Worksheets,

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Determine pH The pH of a solu-tion is a measurement of how acidic or basic that solution is. An easy way to measure the pH of a solution is to use pH paper.

Procedure ! Pour a small amount (about 5 mL)

of each of the following into separate clean, small beakers or other small glass containers: lemon juice, householdammonia solution, liquid detergent, shampoo, and vinegar.

@ Dip a fresh strip of pH paper briefly into each solution andremove.

# Compare the color of the wet paper with the pH colorchart; record the pH of each material. CAUTION: Washyour hands after handling lab materials.

Analysis1. Which solutions are acids?2. Which solutions are bases?3. What ions in the solution caused the pH paper to change?

Which solution contained the highest concentration ofhydroxide ions? How do you know?

MiniLab 6-1MiniLab 6-1

sodium ions (Na+) and hydroxideions (OH–). This basic solution con-tains an abundance of OH– ions andhas a pH above 7.

Acids and bases are important toliving systems, but strong acids andbases can also be dangerous. Forexample, some plants grow well onlyin acidic soil, whereas others requiresoil that is basic. Another example,orange juice, is a common acid thatcan corrode immature teeth if theacid is not later rinsed away. The

MiniLab shown here describes howyou can investigate several householdsolutions to determine if they areacids or bases.


Household Solutions

More basic

11 12 13 14

Section AssessmentSection AssessmentUnderstanding Main Ideas1. Describe where the electrons are located in

an atom.2. A nitrogen atom contains seven protons,

seven neutrons, and seven electrons. Describe the structure of a nitrogen atom. Use a labeled drawing to help you explain this structure.

3. How does the formation of an ionic bond differ from the formation of a covalent bond?

4. What can you say about the proportion ofhydrogen ions and hydroxide ions in a solutionthat has a pH of 2?

Thinking Critically5. A fluorine atom has nine electrons. Make an

energy level diagram of fluorine. How manyelectrons would be needed to fill its outer level?

6. Interpreting Scientific Illustrations Study thediagram in Figure 6.10, which shows the processof a polar compound dissolving in water.Describe the process step-by-step. Tell what thewater molecules are doing and why. Describewhat is happening to the sugar molecules andwhy. Describe the nature of the mixture after thecompound dissolves. For more help, refer toThinking Critically in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

Experimenting HouseholdammoniapH 11

Draincleaner

pH 13

Purpose Students will determine the pHof common solutions.

Process Skillsobserve and infer, interpret data

Safety Precautions Have students wear aprons andsafety goggles. CAUTION: Bothhigh and low pH solutions caninjure the skin and eyes. Havestudents wash hands after thisactivity.

Teaching Strategies■ Use a pH paper that measuresfrom pH 0 to 14.

Expected ResultsThe approximate pH of the solu-tions are: lemon juice, pH 3;household ammonia, pH 11; liq-uid detergent, pH 10; shampoo,pH 7; and vinegar, pH 3.

Analysis1. lemon juice and vinegar2. household ammonia and liq-

uid detergent3. H+ ions and OH– ions. House-

hold ammonia contains themost OH– ions; it had thehighest pH.

Portfolio Have studentsmake a pH scale in their portfo-lios and show where each solutionfalls on the scale. Use thePerformance Task AssessmentList for Scientific Drawing inPASC, p. 55.

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Section AssessmentSection AssessmentSection Assessment1. Electrons move around the nucleus in

regions known as energy levels.2. The nucleus contains seven protons

and seven neutrons. The first energylevel contains two electrons. The nextenergy level contains five electrons.

3. Ionic bonds form as one atom gainselectrons from another or gives up

electrons to another. Covalent bondsinvolve sharing of electrons.

4. There are more hydrogen than hydrox-ide ions in an acidic solution of pH 2.

5. The diagram should show two energylevels containing two and seven elec-trons, respectively. One electron isneeded to fill the outer level.

6. Polar water molecules attract and sur-round the polar sugar molecules.Eventually, this attraction pulls themolecules of the sugar crystal apart. Asolution of a molecular substance con-sists of water molecules and solutemolecules.

155


charged hydrogen atoms of onewater molecule attract the negativelycharged oxygen atoms of anotherwater molecule. This attraction ofopposite charges between hydrogenand oxygen forms a weak bond calleda hydrogen bond. Hydrogen bondsare important to organisms becausethey help hold many large molecules,such as proteins, together.

Also because of its polarity, waterhas the unique property of being ableto creep up thin tubes. Plants in par-ticular take advantage of this prop-erty, called capillary action, to getwater from the ground. Capillaryaction and the tension on the water’ssurface, which is also a result ofpolarity, play major roles in gettingwater from the soil to the tops ofeven the tallest trees.

Water resists temperature changes

Water resists changes in tempera-ture. Therefore, water requires moreheat to increase its temperature than

do most other common substances.Likewise, water loses a lot of heatwhen it cools. In fact, water is like aninsulator that helps maintain a steadyenvironment when conditions mayfluctuate. Because cells exist in anaqueous environment, this propertyof water is extremely important tocellular functions as it helps cellsmaintain an optimum environment.

Water expands when it freezesWater is one of the few substances

that expands when it freezes. Becauseof this property, ice is less dense thanliquid water and floats as it forms in apond. Use the Problem-Solving Lab onthe next page to investigate thisproperty. Water expands as it freezesinside the cracks of rocks. As itexpands, it often breaks apart therocks. Over long time periods, thisprocess forms soil.

The properties of water make it anexcellent vehicle for carrying sub-stances in living systems. Another wayto move substances is by diffusion.

6.2 WATER AND DIFFUSION 157

p+

Hydrogen atom

Oxygen atom

Hydrogen atom

p+

e–

e–

e–

e–

e–e–

e–

e–

e–

e–

8p+

8n0

Figure 6.12Because of water’sbent shape, the pro-truding oxygen end of the molecule has aslight negative charge,and the ends with protruding hydrogenatoms have a slight positive charge.

+

+

Negatively-charged end

Positively-charged end

157

2 TeachSection


Water and ItsImportance

Water is perhaps the most impor-tant compound in living organisms.Most life processes can occur onlywhen molecules and ions are free tomove and collide with one another.This condition exists when they aredissolved in water. Water also servesas a means of material transportationin organisms. For example, blood andplant sap, which are mostly water,transport materials in animals andplants. In fact, water makes up 70 to95 percent of most organisms.

Water is polarSometimes, when atoms form

covalent bonds, they do not share theelectrons equally. The water mole-cule pictured in Figure 6.12 shows

that the shared electrons areattracted by the oxygen atom morestrongly than by the hydrogen atoms.As a result, the electrons spend moretime near the oxygen atom than theydo near the hydrogen atoms.

When atoms in a covalent bond do not share the electrons equally,they form a polar molecule. A polarmolecule is a molecule with anunequal distribution of charge; thatis, each molecule has a positive endand a negative end. Water is anexample of a polar molecule. Polarwater molecules attract each other aswell as ions and other polar mole-cules. Because of this attraction,water can dissolve many ionic com-pounds, such as salt, and many otherpolar molecules, such as sugar.

Water molecules also attract otherwater molecules. The positively

Most of us take water forgranted. We turn on thekitchen faucet at home to

get a drink and expect water tocome out of the faucet. When wehike in a forest, we expect water tobe flowing in the streams and fill-ing the lakes. Most of the time, wedon’t think about how importantwater is to our life and the life ofother organisms on Earth.

SECTION PREVIEW

ObjectivesRelate water’s uniquefeatures to polarity.Explain how theprocess of diffusionoccurs and why it isimportant to cells.

Vocabularypolar moleculehydrogen bonddiffusiondynamic equilibrium

6.2 Water and Diffusion

Water is vital to theliving world.

156

Section 6.2

PrepareKey ConceptsStudents will develop an under-standing of the properties ofwater that make it an excellentsolvent and a necessary biologicalcomponent. Students will alsostudy the process of diffusion.

Planning■ Buy a roll of paper towels for

the Quick Demo.■ Obtain marbles and plastic

container for Reteach.■ Buy potatoes for MiniLab 6-2.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 13 on the overhead pro-jector and have students answerthe accompanying questions.

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BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

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GiftedIntrapersonal Some bacteria canlive on the underside of snow. Ask

gifted students to research how thesebacteria keep from freezing.

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Logical-MathematicalAsk students to explain

the water movement as you dipthe edge of a paper towel in abowl of water.

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“Water, water everywhere…” Visual-Spatial Have students cut outpictures from magazines that illus-

trate uses of water. Ask them to prepare adisplay of their pictures. Students maywant to include industrial uses of water,uses of water by organisms, or environ-mental uses of water.

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CD-ROMBiology: The Dynamics of LifeVideo: Properties of Water

Disc 1

VIDEODISCBiology: The Dynamicsof Life

Properties of Water (Ch. 19)Disc 1, Side 1, 45 sec.!8á}"

Concept DevelopmentThe solubility of oxygen in waterincreases as water temperaturedecreases. Ask students to explainwhy having water at a tempera-ture of 2°C under a sheet of icewould be important for livingorganisms in terms of oxygen sol-ubility. The water at 2°C will dis-solve more oxygen than the warmerlayers of water beneath this layer. Asthe surface of the lake is sealed by ice,the temperature of the water becomesimportant to the ability of the waterto provide enough oxygen to theaquatic organisms during winter.

Resource ManagerResource ManagerSection Focus Transparency 13 and

MasterConcept Mapping, p. 6

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Examine the Rate of Diffusion In this lab, you will place a small potato cube in a solu-tion of potassium permanganate and observe how far the dark purple color diffuses into the potato after a given length of time.

Procedure! Using a single-edge razor blade, cut a cube 1 cm on each

side from a raw, peeled potato. CAUTION: Be careful withsharp objects. Do not cut objects while holding them inyour hand.

@ Place the cube in a cup or beaker containing the purplesolution. The solution should cover the cube. Note andrecord the time. Let the cube stand in the solution forbetween 10 and 30 minutes.

# Using forceps, remove the cube from the solution andnote the time. Cut the cube in half.

$ Measure, in millimeters, how far the purple solution has diffused, and divide this number by the time youallowed your potato to remain in the solution. This is the diffusion rate.

Analysis1. How far did the purple solution diffuse?2. What was the rate of diffusion per minute?

MiniLab 6-2MiniLab 6-2 Applying Concepts

movement that Brown observed ischaracteristic of gas, liquid, and somesolid molecules.

The process of diffusionMolecules of different substances

that are in constant motion have aneffect on each other. For example, ifyou layer pure corn syrup on top ofcorn syrup colored with food color-ing in a beaker as illustrated inFigure 6.14, over time you willobserve the colored corn syrup mix-ing with the pure corn syrup. Thismixture is the result of the randommovement of corn syrup molecules.Diffusion is the net movement ofparticles from an area of higher con-centration to an area of lower con-centration. Diffusion results becauseof the random movement of particles(Brownian motion). The corn syrupin Figure 6.14 will begin to diffusein hours but will take months to mixcompletely.

Diffusion is a slow process becauseit relies on the random molecularmotion of atoms. Three key factors,concentration, temperature, andpressure, affect the rate of diffusion.The concentration of the substancesinvolved is the primary controllingfactor. The more concentrated thesubstances, the more rapidly diffu-sion occurs. For example, loose sugarplaced in water will diffuse morerapidly than will a more concentratedcube of sugar. Two external factors,temperature and pressure, can speedthe process of diffusion. An increasein temperature or agitation will cause more rapid molecular move-ment and will speed diffusion.Similarly, increasing pressure willaccelerate molecular movement and,therefore, diffusion. With commonmaterials, you can use the MiniLabshown here to learn more about dif-fusion in a cell.

6.2 WATER AND DIFFUSION 159

Figure 6.14The random movementof particles of corn syrupwill cause the coloredsample to diffuse intothe uncolored sample.

159

Purpose Students will determine the rateof diffusion of a solution.

Process Skillsmeasure in SI, collect and orga-nize data, interpret data, experi-ment, and analyze

Teaching Strategies■ Regarding safety, caution stu-dents that the solution can becaustic. If they get some on theirhands, they should wash immedi-ately. To keep the solution offtheir hands, students should setthe cube on waxed paper or foilwhen they remove it from thesolution and hold the cube withthe forceps as it is cut. Alsoremind students to cut away fromtheir body.

Expected ResultsThe color will diffuse only a fewmillimeters into the cube, theexact distance depending uponthe amount of time it is in thesolution.

Analysis1. Answers will depend on the

amount of time the cube is inthe solution.

2. The rate will be in tenths tohundredths of millimetersper minute.

Portfolio Have studentswrite a report of the MiniLab for their portfolios. Use thePerformance Task AssessmentList for Lab Report in PASC, p. 47. L2

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Why does ice float? Most liquids con-tract when frozen. Water is different; it expands. Freezing changes the density of water to that of ice, which allows ice to float. Density refers to compactness and is often described as the mass of a substance per unit of volume. A mathematical expres-sion of density would read as follows:

AnalysisExamine the following table. It shows the volume and

mass for a sample of water and ice.

Thinking Critically1. How does the density of ice compare with the density of

water? Use specific values and proper units expressingdensity in your answer. Which of the two, ice or water, isless compact? Explain your answer.

2. Are the molecules of water moving closer togethertoward one another or farther apart as water freezes?Explain your answer.

3. Explain why a glass bottle filled with water will shatter ifplaced in a freezer.

4. Explain why ice forming within a living organism mayresult in its death.

Problem-Solving Lab 6-2Problem-Solving Lab 6-2 Using NumbersDiffusion

All objects in motion have energyof motion called kinetic energy. Amoving particle of matter moves in astraight line until it collides withanother particle, much like the Ping-Pong balls shown in Figure 6.13.After the collision, both particlesrebound. Particles of matter, like thePing-Pong balls, are in constantmotion, colliding with each other.

Early observations:Brownian motion

In 1827, Scottish scientist RobertBrown used a microscope to observepollen grains suspended in water. Henoticed that the grains moved con-stantly in little jerks, as if beingstruck by invisible objects. Thismotion, he thought, was the result ofa life force hidden within the pollengrains. However, when he repeatedhis experiment using dye particles,which are nonliving, he saw the sameerratic motion. This motion is nowcalled Brownian motion. Brown hadno explanation for the motion he saw,but today we know that Brown wasobserving evidence of the randommotion of molecules. This was theinvisible “life” that was moving thetiny visible particles. The random


Figure 6.13Molecules, like thesePing-Pong balls, havekinetic energy, theenergy of motion.

Source of sample Mass (g)Volume (cm3)

Water

Ice

126

126

126

140

Data Table

Density = MassVolume

158

Purpose Students will calculate thedensities for water and ice

and will correlate this informa-tion with the fact that waterexpands as it freezes.

Process Skillscompare and contrast, draw aconclusion, measure in SI, thinkcritically, use numbers, recognizecause and effect

Teaching Strategies■ Review the equation for calcu-lating density. Provide someexamples for students to use aspractice.■ Review the use of units such ascm3 and mL if necessary. ■ Remind students that cm3 isthe same as cubic centimeters orcc.■ Review the procedure forarriving at the proper units toexpress density.

Thinking Critically

1. The density of water is 1g/cm3; density of ice is 0.9g/cm3. Ice is less compact;mass in example is the same,but volume for ice is greater.A lower density indicates agreater volume with the samemass as water.

2. farther apart. This patternaccounts for increased vol-ume.

3. Water expands as it freezesand eventually breaks glass.

4. Formation of ice crystals andthe expansion within delicatecells and tissues could dam-age a living organism.

Knowledge Have stu-dents describe the type of labora-tory equipment they would needto measure the density of seawater. Use the Performance TaskAssessment List for Designing an Experiment in PASC, p. 23.L2

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Problem-Solving Lab 6-2Problem-Solving Lab 6-2


Kinetic EnergyVisual-Spatial In their journals, havestudents draw a diagram and

describe another example of kineticenergy. You might discuss some popularchildren’s toys or microwave popcorn toget them started.

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PortfolioPortfolio

The Importance of WaterLinguistic Have students write anessay that explains why water is

important to them. Ask them to thinkabout their families’ daily use of water.Challenge them to think about what usesare especially important in view of the factthat they might someday be asked to cuttheir water use in half.

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VIDEODISCThe Secret of LifeDiffusion of Water

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Resource ManagerResource ManagerReinforcement and Study Guide

p. 27Content Mastery, pp. 30-31BioLab and MiniLab Worksheets

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Section

6.3 LIFE SUBSTANCES 161

Role of Carbon in Organisms

A carbon atom has four electronsavailable for bonding in its outerenergy level. In order to become sta-ble, a carbon atom forms four cova-lent bonds that fill its outer energylevel. Look at the illustration show-ing carbon atoms and bond types in Figure 6.16. Carbon can bond withother carbon atoms, as well as withmany other elements. When eachatom shares two electrons, a doublebond is formed. A double bond isrepresented by two bars between car-bon atoms. When each shares threeelectrons, a triple bond is formed.Triple bonds are represented by threebars drawn between carbon atoms.

Did you ever hear the saying,“You are what you eat”? It’sat least partially true because

the compounds that form the cells andtissues of your body are produced fromsimilar compounds in the foods youeat. Common to most of these foodsand to most substances in organisms isthe element carbon. The first carboncompounds that scientistsstudied came from organ-isms and were calledorganic compounds.

SECTION PREVIEW

ObjectivesClassify the variety oforganic compounds.Describe how polymersare formed and brokendown in organisms.Compare the chemicalstructures of carbohy-drates, lipids, proteins,and nucleic acids, andrelate their importanceto living things.

Vocabularyisomerpolymercarbohydratelipidproteinamino acidpeptide bondenzymenucleic acidnucleotide

6.3 Life Substances

Carbon defines living organisms.

Figure 6.16When two carbonatoms bond, they shareone, two, or three elec-trons each and form acovalent bond.

Double bond Triple bond

Single bond

161

Section 6.3

PrepareKey ConceptsStudents will examine the classesof carbon compounds present inorganisms. The structural andfunctional aspects of carbohy-drates, lipids, proteins, andnucleic acids will be studied.

Planning■ Collect potatoes, knives,

hydrogen peroxide and waxedpaper for the BioLab.

■ Purchase grocery and paperitems for the Alternative Lab.

■ Make flash cards for the Checkfor Understanding.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 14 on the overhead pro-jector and have students answerthe accompanying questions.

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BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 6,Section 6.3

How many different letters are in the words? What otherwords can you make from these letters?

Use the example to explain how only 90 natural elementscould form all the different substances on Earth.

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22

SECTION FOCUS

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Transparency Elements in DifferentCombinations14


Hearing ImpairedInterpersonal Make visual cardswith pictures of foods that are asso-

ciated with carbohydrates, lipids, and pro-teins. On each card ask what organiccompound is predominant or whatmonomers are involved. Have studentswork in groups to answer the questions.

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Summarizing CarbonLinguistic Have students write aparagraph or two summarizing the

properties of carbon and describing whycarbon is so important to living things.

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Material moving outof cell equals materialmoving into cell


Figure 6.15When a cell is in dynamic equilibriumwith its environment, materials moveinto and out of the cell at equal rates. As a result, there is no net change in concentration inside the cell.

Section AssessmentSection AssessmentUnderstanding Main Ideas1. Explain why water is a polar molecule.2. How does a hydrogen bond compare to a

covalent bond?3. What property of water explains why it can

travel to the tops of trees?4. What is the eventual result of diffusion? Describe

concentration prior to and at this point.

Thinking Critically5. Explain why water dissolves so many different

substances.

6. Inferring If a substance is known to enter a cellby diffusion, what effect would raising the tem-perature have on the cell? For more help, referto Thinking Critically in the Skill Handbook.


The results of diffusionAs the colored corn syrup contin-

ues to diffuse into the pure cornsyrup, the two will become evenlydistributed eventually. After thispoint, the atoms continue to moverandomly and collide with oneanother; however, no further change

in concentration will occur. Thiscondition, in which there is continu-ous movement but no overall con-centration change, is called dynamicequilibrium. Figure 6.15 illustratesdynamic equilibrium in a cell.

Diffusion in living systemsMost substances in and around a

cell are in water solutions where theions and molecules of the solute aredistributed evenly among water mole-cules, like the Kool-Aid and waterexample. The difference in concen-tration of a substance across space iscalled a concentration gradient.Because ions and molecules diffusefrom an area of higher concentrationto an area of lower concentration,they are said to move with the gradi-ent. If no other processes interfere,diffusion will continue until there isno concentration gradient. At thispoint, dynamic equilibrium occurs.Diffusion is one of the methods bywhich cells move substances in andout of the cell.

Diffusion in biological systems isalso evident outside of the cell andcan involve substances other thanmolecules in an aqueous environ-ment. For example, oxygen (a gas)diffuses into the capillaries of thelungs because there is a greater con-centration of oxygen in the air sacs ofthe lungs than in the capillaries.

160

3 AssessCheck for UnderstandingQuiz students orally about theimportance of water to livingorganisms and test their under-standing of each of the propertiesof water.

ReteachVisual-Spatial In a clear con-tainer with a lid, place

10–15 marbles of one color. Ontop of those marbles, place anequal number of different col-ored marbles. Ask students topredict what will occur if youshake the container continuously.Like diffusion, the marbles willeventually disperse among eachother, reaching an equilibrium ofmixed color.

ExtensionIntrapersonal Have studentsresearch how rapidly mole-

cules can actually move over aparticular distance.

Knowledge Have studentslist the properties of water andgive an example of how eachproperty is useful in a livingorganism.

4 CloseActivity

Logical-Mathematical Place awatch glass containing mint

oil on the front desk. Have stu-dents discuss how the moleculesof mint are reaching them. Besidesdiffusion, which is a slow process, aircurrents are also carrying the mole-cules to their noses. L2

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Section AssessmentSection AssessmentSection Assessment1. The oxygen and two hydrogens do not

share the electrons equally (electrons aremore often near the oxygen). As a result,the oxygen is negatively charged and thehydrogens are positively charged.

2. Hydrogen bonds are very weak com-pared with covalent bonds.

3. capillary action

4. The particles will reach dynamic equilib-rium.

5. Because water molecules are polar andattract other charged particles, watereasily dissolves many substances.

6. An increase in temperature causes anincrease in kinetic energy and the rate ofdiffusion of the substance into the cell.

H OH

HOH

HOH

H

OH

H

OH H

OH

HOH

H2O

H OH

OH

H

H2O

Condensation

Subunits

Subunits

Hydrolysis

Polymer

Starch

Glucosesubunits

Glycogen

Glucosesubunits

carbon, hydrogen, and oxygen with aratio of about two hydrogen atomsand one oxygen atom for every car-bon atom.

The simplest type of carbohydrateis a simple sugar called a monosac-charide (mahn uh SAK uh ride).Common examples are the isomersglucose and fructose. Two monosac-charide molecules can link togetherto form a disaccharide, a two-sugarcarbohydrate. When glucose andfructose combine by a condensationreaction, a molecule of sucrose,known as table sugar, is formed.

The largest carbohydrate mole-cules are polysaccharides, polymerscomposed of many monosaccharidesubunits. The starch, glycogen, andcellulose pictured in Figure 6.19 areexamples of polysaccharides. Starchconsists of highly branched chains ofglucose units and is used as food stor-age by plants in food reservoirs suchas seeds and bulbs. Mammals storefood in the liver in the form of glyco-gen, a glucose polymer similar to


Figure 6.18Condensation and Hydrolysis

Figure 6.19Look at the structural differences among the polysaccha-rides starch, glycogen, and cellulose. Notice that all threeare polymers of glucose.

Polymers are formed by condensationand can be broken by hydrolysis, thereaction that occurs when water isintroduced to a polymer.

AA

The silk produced by thesecaterpillars is a protein, abiological polymer formedby condensation reactions.

BB

Glucosesubunits

Crosslinkbonds

Cellulose

Potato

Liver

Cotton

163

When carbon atoms bond to eachother, they can form straight chains,branched chains, or rings. In addi-tion, these chains and rings can havealmost any number of carbon atomsand can include atoms of other ele-ments as well. This property makes ahuge number of carbon structurespossible. In addition, compoundswith the same simple formula oftendiffer in structure. Compounds thathave the same simple formula butdifferent three-dimensional struc-tures are called isomers (I suh murz).The glucose and fructose moleculesshown in Figure 6.17 have the samesimple formula, C6H12O6, but differ-ent structures.

Molecular chainsCarbon compounds also vary

greatly in size. Some compoundscontain just one or two carbonatoms, whereas others contain tens,hundreds, or even thousands of car-bon atoms. These large moleculesare called macromolecules. Proteinsare examples of macromolecules inorganisms. Cells build macromole-cules by bonding small molecules

together to form chains called poly-mers. A polymer is a large moleculeformed when many smaller mole-cules bond together.

Condensation is the chemical reac-tion by which polymers are formed.In condensation, the small moleculesthat are bonded together to make apolymer have an –H and an –OHgroup that can be removed to formH–O–H, a water molecule. The sub-units become bonded by a covalentbond as shown in Figure 6.18.

Hydrolysis is a method by whichpolymers can be broken apart.Hydrogen ions and hydroxide ionsfrom water attach to the bondsbetween the subunits that make upthe polymer, thus breaking the poly-mer as shown in Figure 6.18.

The structure of carbohydratesYou may have heard of runners

eating large quantities of spaghetti orother starchy foods the day before arace. This practice is called “carbohy-drate loading.” It works because car-bohydrates are used by cells to storeand release energy. A carbohydrateis an organic compound composed of


OriginWORDWORD

polymerFrom the Greekwords poly, meaning“many,” and meros,meaning “part.” Apolymer has manybonded subunits(parts).

hydrolysisFrom the Greekwords hydro, mean-ing “water,” andlysis, meaning “tosplit or loosen.” In hydrolysis, molecules are splitby water.

Figure 6.17The differentarrangement ofhydrogen and oxy-gen atoms aroundeach carbon atomgives glucose andfructose moleculesdifferent chemicalproperties. When glucose and fructosecombine, they formthe disaccharidesucrose, also knownas table sugar.

OH

OH

CH2OH CH2OH

Glucose

O

HOOH

OH

O HHOCH2

Fructose

Sucrose

O

HO

+ +

OH

O H2O

CH2OH

O

HOOH

OH

CH2OH

HOCH2O

HO

162

Visual LearningFigure 6.17 Direct students’attention to the illustration. Askthem what compound in additionto sucrose is formed when glu-cose and fructose combine. water

Knowledge Have volun-teers draw a model of a carbonatom on the chalkboard. Haveone student draw the protons, asecond student draw the neu-trons, and a third student add theelectrons in their correct energylevels. Ask students to use themodel to explain how many elec-trons are needed to make the car-bon atom stable. four Havestudents predict how manyhydrogen atoms could form cova-lent bonds with the carbon atom.four Ask what the formula for thismolecule would be. CH4

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PortfolioPortfolio

Planning Logical-Mathematical Have stu-dents make a daily meal plan that

contains very low levels of lipids.P

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Visual-Spatial Have the students pre-pare a chart of the foods they had

for breakfast and lunch. They should listthe organic ingredients (carbohydrates,lipids, proteins, and nucleic acids) in eachfood they ate.

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Use a ball-and-stick model of amethane molecule (CH4) toshow students the regulartetrahedron arrangementformed by the bonds of carbonatoms. Contrast the arrange-ment of the atoms in themethane molecule to those ina molecule of water.

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VIDEODISCThe Secret of LifeCarbon Bonds

!7;6~B"

Exploring NutrientsInterpersonal Have groups of studentsresearch and prepare a presentation on

one of the following: sugars and other nutri-tive sweeteners in processed foods, choles-terol in the diet, saturated and unsaturated

fats in the diet, or the functions of proteinssuch as keratin, actin, myosin, insulin, andcollagen. Encourage creativity in the presen-tations. For example, students might enact askit they have scripted in their portfolio.

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PortfolioPortfolio

VIDEODISCThe Secret of LifeMonosaccharide

Disaccharide

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Using Science TermsLinguistic Have studentslook up the meanings of the

prefix “hydro” and the suffix“lysis” in a dictionary. Hydro-refers to water, and lysis means tobreak down. Ask students to relatethe meanings of these word partsto the word hydrolysis. Remindstudents that during hydrolysispolymers are broken down by theaddition of water.

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Section Focus Transparency 14and Master

Critical Thinking/ProblemSolving, p. 6 L3

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2 Teach

composed of carbon, hydrogen, oxy-gen, nitrogen, and usually sulfur. Thebasic building blocks of proteins arecalled amino acids, shown in Figure6.21a. There are 20 common aminoacids. These 20 building blocks, invarious combinations, make literallythousands of proteins. Therefore,proteins come in a large variety ofshapes and sizes. In fact, proteins varymore in structure than any other classof organic molecules.

Amino acids are linked togetherwhen an –H from one amino acidand an –OH group from anotheramino acid are removed to form awater molecule. The covalent bondformed between the amino acids, likethe bond labeled in Figure 6.21b, iscalled a peptide bond. The numberand order of amino acids in proteinchains determine the kind of protein.

Many proteins consist of two ormore amino acid chains that are heldtogether by hydrogen bonds.

Proteins are the building blocks ofmany structural components oforganisms, as illustrated in Figure6.22. Proteins are also important inthe contracting of muscle tissue,transporting oxygen in the blood-stream, providing immunity, regulat-ing other proteins, and carrying outchemical reactions.

Enzymes are important proteinsfound in living things. An enzyme isa protein that changes the rate of achemical reaction. In some cases,


Figure 6.22Proteins make upmuch of the structureof organisms, such ashair, fingernails,horns, and hoofs.

Figure 6.21Each amino acid contains a central carbon atom to which areattached a carboxyl group, a hydrogen atom, an amino group(–NH2), and a group (–R) that makes each amino acid different (a).Amino acids are linked together by peptide bands (b).

H Hydrogen atom

CarboxylAmino group NH2 — C — COOH group

R Variable group

Peptidebond

H H H

NH2 — C — C ——— N — C — COOH

R O R

a b

EnrichmentIntrapersonal Have studentsresearch the differences in

the structures of starch, glycogen,and cellulose to determine howthere can be more than one poly-mer of glucose.

Using an AnalogyTo increase understanding ofhow only 20 amino acids can cre-ate such a variety of proteins,relate the 20 naturally occurringamino acids to the letters of thealphabet. Elicit from studentswhy the letters of the alphabetcan be used to create such a largenumber of words. Relate thisphenomenon to how a similarnumber of amino acids can createso many different proteins.

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grapes in half, or choose three orangeslices. Set these aside on waxed paper.

3. Add the following to each cup. Makesure the fruits are submerged.Cup 1—nothingCup 2—canned pineapple chunksCup 3—fresh pineapple chunksCup 4—grape halves or orange slices

4. Set cups in the refrigerator. Check thecups at the end of the period.

Expected ResultsStudents should observe that the gelatin towhich the fresh pineapple was addedremained liquefied.Analysis

1. What was the purpose of cup 1? Control2. Gelatin is a protein. Bromelin is a pro-

tein-digesting enzyme. What hap-pened to the bromelin in the cannedpineapple? It was destroyed by heatduring the canning process.

Knowledge Ask students thisquestion: Based on this activity, what can you conclude about which fruitshave enzymes that act on protein? Usethe Performance Task Assessment Listfor Analyzing the Data in PASC, p. 27.L2

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165

starch but more highly branched.Cellulose is another glucose polymerthat forms the cell walls of plants andgives plants structural support.Cellulose is also made of long chainsof glucose units hooked together inarrangements somewhat like a chain-link fence.

The structure of lipidsIf you’ve ever tried to lose weight,

you may have wished that lipids (fats)never existed. Lipids, however, areextremely important for the properfunctioning of organisms. Lipids areorganic compounds that have a largeproportion (much greater than 2 to1) of C–H bonds and less oxygenthan carbohydrates. For example, alipid found in beef fat has the for-mula C57H110O6.

Lipids are commonly called fats

and oils. They are insoluble in waterbecause their molecules are nonpolar.Recall that a nonpolar molecule isone in which there is no net electricalcharge and, therefore, lipids are notattracted by water molecules. Cellsuse lipids for energy storage, insula-tion, and protective coatings. In fact,lipids are the major components ofthe membranes that surround all liv-ing cells. Lipids are also used in foodpreparation as discussed in theBioTechnology feature. The most com-mon type of lipid, shown in Figure6.20, consists of three fatty acidsbound to a molecule of glycerol.

The structure of proteinsProteins are essential to all life.

They provide structure for tissues andorgans and carry out cell metabolism.A protein is a large, complex polymer


CH2 CH2O

O

C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3CH CH

CH2 CH2O

O

C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3CH CH

CH2 CH2CH CH2O

O

C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

Glycerol

Unsaturated fatty acid

Unsaturated fatty acid

Saturated fatty acid

Double bond

Double bond

Figure 6.20Glycerol is a three-carbon molecule thatserves as a backbonefor the lipid mole-cule. Attached to theglycerol are threefatty acids.

The carbon atoms in saturatedfatty acids cannot bond with anymore hydrogen atoms.

AA

The carbon atoms in unsaturatedfatty acids can bond with morehydrogen atoms.

BB

Meat

Butter

Peanut butter

Revealing MisconceptionsStudents often think moleculesare flat, two-dimensional struc-tures because the formulas inbooks are flat. Show studentsstructural models of various mol-ecules so they can observe thethree-dimensional appearance ofmolecules.

Visual LearningFigure 6.20 Ask students to useFigure 6.20 to answer the follow-ing questions. (a) What com-pound serves as the backbone forlipid molecules? glycerol (b) Howdo the bonds in saturated fats dif-fer from those in unsaturatedfats? Saturated fats have singlebonds; unsaturated fats have doublebonds.

Alternative LabWhat fruits contain enzymes thatact on protein?

Purpose Students will investigate the effect of theenzyme bromelin on gelatin.

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Safety PrecautionsRemind students to use caution with theknife.PreparationOne pineapple should be enough for 20students working in groups of four. A 6-ounce box of gelatin makes enough for 2groups. Make gelatin and pour 100 mL intoeach paper cup. Use hot/cold cups largeenough to hold 200 mL.

Materialspaper cups (4) with gelatin, fresh pineap-ple, knife, waxed paper, canned chunkpineapple, refrigerator, grapes or orangesectionsProcedure Give students the following directions.

1. Number the cups 1 to 4.2. Select 3 chunks of canned pineapple.

Cut 3 chunks of fresh pineapple thesame size as the canned chunks. Cut 3164

The BioLab at theend of the chaptercan be used at thispoint in the lesson.

INVESTIGATEINVESTIGATE


Animation: Enzyme ActionDisc 1


Reteaching Skills Trans-parency 8 and Master

Laboratory Manual, pp. 39-42 L2

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enzymes increase the speed of reac-tions that would otherwise occur soslowly you might think they wouldn’toccur at all.

Enzymes are involved in nearly allmetabolic processes. They speed thereactions in digestion of food.Enzymes also affect synthesis of mole-cules, and storage and release ofenergy. How do enzymes act like alock and key to facilitate chemicalreactions within a cell? Read theInside Story to find out. The BioLab atthe end of this chapter also experi-ments with enzymes.

The structure of nucleic acidsNucleic acids are another impor-

tant type of organic compound that isnecessary for life. A nucleic acid(noo KLAY ihk) is a complex macro-molecule that stores cellular informa-tion in the form of a code. Nucleicacids are polymers made of smallersubunits called nucleotides.

Nucleotides consist of carbon,hydrogen, oxygen, nitrogen, andphosphorus atoms arranged in threegroups—a base, a simple sugar, and aphosphate group—as shown inFigure 6.23. You have probablyheard of the nucleic acid DNA,which stands for deoxyribonucleic

acid. DNA is the master copy of anorganism’s information code. Theinformation coded in DNA containsthe instructions used to form all of anorganism’s enzymes and structuralproteins. Thus, DNA forms thegenetic code that determines how anorganism looks and acts. DNA’sinstructions are passed on every timea cell divides and from one genera-tion of an organism to the next.

Another important nucleic acid isRNA, which stands for ribonucleicacid. RNA is a nucleic acid thatforms a copy of DNA for use in mak-ing proteins. The chemical differ-ences between RNA and DNA areminor but important. A later chapterdiscusses how DNA and RNA worktogether to produce proteins.


Figure 6.23Each nucleic acid isbuilt of subunitscalled nucleotidesthat are formed froma sugar moleculebonded to a phos-phate group and anitrogen base.

Section AssessmentSection AssessmentUnderstanding Main Ideas1. List three important functions of lipids in living

organisms.2. Describe the process by which polymers in

living things are formed from smaller molecules.

3. How does a monosaccharide differ from a disaccharide?

Thinking Critically4. Enzymes are proteins that facilitate

chemical reactions. Based on your knowledge of enzymes, what might the result be if

one particular enzyme malfunctioned or was not present?

5. Making and Using Tables Make a table com-paring polysaccharides, lipids, proteins, andnucleic acids. List these four types of biologicalsubstances in the first column. In the next twocolumns, list the subunits that make up each substance and the functions of each in organ-isms. In the last column, provide some examplesof each from the chapter. For more help, refer toOrganizing Information in the Skill Handbook.


P

O

OHO

HO

OCH2

OH OH

NH2O N

NPhosphate Ribosesugar Nitrogen

base

View an animation of enzymeaction in the Presen-tation Builder of theInteractive CD-ROM.

CD-ROM

ReteachThe concept of large polymersbeing composed of repeatingunits of monomers can be rein-forced by having students listitems that are composed ofsmaller units, such as beads mak-ing up a necklace, chain links, jig-saw puzzle pieces, or lettersmaking up words.

ExtensionLinguistic Encourage above-level students to read The

Double Helix by James Watson(Atheneum, 1968), which tells thestory of the discovery of theDNA structure.

Knowledge Prepare ahandout showing structural for-mulas for lipids, proteins, carbo-hydrates, and nucleic acids. Askstudents to identify the type oforganic compound shown in eachdiagram.

4 CloseDiscussionAsk students to explain the differ-ences between saturated andunsaturated fats. Saturated fats arecomposed of lipids containing fattyacids with only single bonds.Unsaturated fats are composed offatty acid chains of carbon with dou-ble bonds. L2

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After thereaction, the enzymereleased is in itsoriginal shapeand can go on tocarry out the samereaction again andagain. In doing so,enzymes increase thespeed at which chemicalreactions occur without beingaltered themselves by the reaction.

44

Each substrate fits into an area ofthe enzyme called the active site. Thisfitting together is often compared to a lock-and-key mechanism. However,

the enzyme changes shape a littleto fit with the substrate. The

enzyme-substrate complexputs stress on the sub-

strate due to the bind-ing of the substrate to

the enzyme.

22


Action of Enzymes

A n enzyme enables molecules, called substrates, to undergo a chemical change to

form new substances, called products. The enzyme works due to an area on its surface that fits the shape of the substrate, called an active site. When the substrate fits the active site, it causes the enzyme to alter its shape slightly as shown below.

Critical Thinking How can an enzyme participate over and over in chemical reactions?

Lysozyme structure

INSIDESSTORTORYY

INSIDESubstrate

Activesite

Enzymes act on specific substrates, such as sucrose, a disaccharide made up of glucose and fructose bonded together.

11

The products arereleased; in this casethe sucrose bonds arehydrolyzed, releasingglucose and fructose.

33

H2O

Glucose Fructose

Substrate (Sucrose)

Active sites

Active site

Enzyme

Enzyme

Products

166

IINSIDENSIDESSTORTORYY

INSIDE

Purpose Students will study the wayenzymes function in a reaction.

Teaching Strategy■ Ask students to make an anal-ogy of a lock and key to howenzymes function. Studentsshould also describe where theanalogy fails. Even though thelock and key fit together specifi-cally, the lock does not changeshape when the key fits in thekeyhole.

Visual LearningVisual-Spatial Show a com-puterized video sequence of

lysozyme activity in a cell.

Critical ThinkingThe enzyme is not changed bythe reaction. Once it releases thesubstrate, the enzyme can bind toanother substrate. This processcan be repeated over and over.

3 AssessCheck for Understanding

Visual-Spatial Use flashcards containing the names

of monomers on one side and thecorresponding polymer on theother side. First, show studentsthe polymer name (e.g., protein)and then have them respond withthe appropriate monomer name(amino acid), and vice versa.

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Section AssessmentSection AssessmentSection Assessment1. long-term energy storage, insulation,

protective coatings2. Polymers form when one monomer

loses an H+ ion and another loses anOH– to form water. A covalent bondforms between the monomers.

3. A disaccharide is made of two simplesugars called monosaccharides.

4. The chemical reaction would proceedextremely slowly.

5. Subunits and functions: polysaccha-rides, monosaccharides—for energystorage and structural components;lipids, glycerol, and fatty acids—forlong-term energy storage; proteins,amino acids—structure and enzymes;

nucleic acids, nucleotides—store infor-mation in cells. Examples: polysaccha-rides—starch, glycogen, and cellulose;lipids—animal fats and vegetable oils;proteins—muscle proteins, immunityproteins, enzymes; nucleic acids—DNA and RNA.

167

VIDEODISCThe Infinite VoyageThe Future of the Past

Winterthur Museum: New CleaningTechniques of Old Paintings (Ch. 5)

6 min.

VIDEODISCThe Secret of LifeStructure of DNA

!7;>jI"!7U`H"


Reinforcement and StudyGuide, p. 28

Content Mastery, pp. 31, 29-32

Laboratory Manual, pp. 43-46 L2

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PLAN THE EXPERIMENTPLAN THE EXPERIMENT

1. Decide on a way to test yourgroup’s hypothesis. Keep theavailable materials in mind.

2. When testing the activity ofthe enzyme at a certain tem-perature, consider the lengthof time it will take for thepotato to reach that tempera-ture, and how the temperaturewill be measured.

3. To test for peroxidase activity,add 1 drop of hydrogen perox-ide to the potato slice andobserve what happens.

4. When heating a thin potatoslice, first place it in a smallamount of water in a beaker.Then heat the beaker slowly sothat the temperature of thewater and the temperature ofthe slice are always the same.Try to make observations atseveral temperatures between10°C and 100°C.

Check the PlanDiscuss the following points

with other groups to decide on thefinal procedure for your experiment.1. What data will you

collect? How will you record them?

2. What factors should be controlled?

3. What temperatures will you test?

4. How will you achieve those tem-peratures?

5. Make sure your teacher has approved your experimental plan before you proceed further.

6. Carry out your experiment. CAUTION: Be care-ful with chemicals and heat.Wash hands after lab.


Going FurtherGoing Further

Changing Variables To carry this experi-ment further, you may wish to use hydrogenperoxide to test for the presence of peroxi-dase in other materials, such as cut pieces of different vegetables. Also, test raw beefand diced bits of raw liver.

To find out more about enzymes, visit the

Glencoe Science Web site.science.glencoe.com

1. Checking Your HypothesisDo your data support or rejectyour hypothesis? Explain yourresults.

2. Analyzing Data At what temperature did peroxidase work best?

3. Identifying Variables What fac-tors did you need to control inyour tests?

4. Recognizing Cause and Effect Ifyou’ve ever used hydrogen perox-ide as an antiseptic to treat a cutor scrape, you know that it foamsas soon as it touches an open

wound. How can you account forthis observation?

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

BIOLOGY

YOUR OWNDESIGN

YOUR OWNDESIGN

1. Students should explainwhether their data support orreject their hypotheses.

2. Between 20°C–50°C3. Answers may include the

amount of time each potatowas exposed to the tempera-ture, the sizes of the potatoslices, and the amount of per-oxide added.

4. Human tissue contains per-oxidase, so the hydrogen per-oxide is broken down andreleases oxygen.

Error AnalysisAdvise students that potato slicesmust reach the desired tempera-ture they are testing, which willtake time. Samples need to beremoved and observed carefullyfor bubbles.

Portfolio In their portfo-lios, have students summarize theresults, especially the cold treat-ment. Discuss how results dif-fered between cool pieces testedimmediately and those allowed towarm to room temperature. Usethe Performance Task AssessmentList for Evaluating a Hypothesisin PASC, p. 31.


ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

169

Data and ObservationsCooling will not deactivate the enzymes butcan slow the overall reaction. Potato slicesheated over 70ºC will not generate oxygenbubbles.

Going FurtherGoing Further

Logical-MathematicalAsk students why vegeta-

bles are boiled for a short timebefore freezing. One reason isthat boiling inactivatesenzymes that begin to breakdown the other molecules inthe vegetables.

Does temperature affectan enzyme reaction?

T he compound hydrogen peroxide, H2O2, is a by-product of meta-bolic reactions in most living things. However, hydrogen peroxide is

damaging to delicate molecules inside cells. As a result, nearly all organ-isms contain the enzyme peroxidase, which breaks down H2O2 as it isformed. Potatoes are one source of peroxidase. Peroxidase speeds up thebreakdown of hydrogen peroxide into water and gaseous oxygen. Thisreaction can be detected by observing the oxygen bubbles generated.

YOUR OWNDESIGN

YOUR OWNDESIGN

ProblemDoes the enzyme peroxidase work

in cold temperatures? Does peroxi-dase work better at higher tem-

peratures? Does peroxidasework after being frozen orboiled?

HypothesesMake a hypothesis regarding how

you think temperature will affect therate at which the enzyme peroxidasebreaks down hydrogen peroxide. Con-sider both low and high temperatures.

ObjectivesIn this BioLab, you will:■ Observe the activity of an enzyme.■ Compare the activity of the enzyme

at various temperatures.

Possible Materialsclock or timer ice400-mL beaker hot platekitchen knife waxed papertongs or large forceps thermometer5-mm thick potato slices3% hydrogen peroxide

Safety PrecautionsBe sure to wash your hands before

and after handling the lab materials.Always wear goggles in the lab.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

YOUR OWNDESIGN

YOUR OWNDESIGN

168

Time Allotment One class period

Process Skillsform a hypothesis, design anexperiment, interpret data, recog-nize cause and effect

Safety PrecautionsStudents should wear aprons andsafety goggles. Remind studentsto use caution with heat sourcesand handle glassware with tongs.

■ Obtain potatoes, knives,hydrogen peroxide, and waxedpaper.

Alternative MaterialsPieces of raw liver can be usedinstead of potato.

Possible Hypotheses■ If temperatures are very high

or very low, the enzymes willbe deactivated.

■ If the temperature is raised,the speed at which the enzymewill work will increase.

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Teaching Strategies■ Discuss the factors that might affect therate of a reaction controlled by an enzyme. ■ Students who cool the potato to low tem-peratures should be sure to run the testwhile the potato is still cool.■ Allow groups to discuss how their re-sults differed when different experimental procedures were used.

Possible Procedures■ Students may place a piece of potato on

ice for 5 minutes, boil a second piece for5 minutes, and allow a third piece ofpotato to sit at room temperature for 5minutes. Each potato will then be testedfor enzyme activity.


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Chapter 6 AssessmentChapter 6 Assessment

SUMMARYSUMMARY

Section 6.1

Section 6.2

Section 6.3

Vocabularyacid (p. 154)atom (p. 146)base (p. 154)compound (p. 149)covalent bond (p. 150)element (p. 145)ion (p. 151)ionic bond (p. 151)isotope (p. 148)metabolism (p. 151)mixture (p. 152)molecule (p. 150)nucleus (p. 147)pH (p. 154)solution (p. 153)

Atoms andTheirInteractions

Main Ideas■ Water is the most abundant compound in living

things.■ Water is an excellent solvent due to the polar

property of its molecules.■ Particles of matter are in constant motion.■ Diffusion occurs from areas of higher concen-

tration to areas of lower concentration.

Vocabularydiffusion (p. 159)dynamic equilibrium

(p. 160)hydrogen bond (p. 157)polar molecule (p. 156)

Water andDiffusion

Main Ideas■ All organic compounds contain carbon

atoms. ■ There are four principal types of organic

compounds that make up living things:carbohydrates, lipids, proteins, and nucleicacids.

Vocabularyamino acid (p. 165)carbohydrate (p. 162)enzyme (p. 165)isomer (p. 162)lipid (p. 164)nucleic acid (p. 167)nucleotide (p. 167)peptide bond (p. 165)polymer (p. 162)protein (p. 164)

Life Substances

CHAPTER 6 ASSESSMENT 171

1. What are the basic building blocks of all matter?a. electrons c. atomsb. protons d. molecules

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 2. Which feature of water explains why waterhas high surface tension?a. water diffuses into cellsb. water’s resistance to temperature changesc. water is a polar moleculed. water expands when it freezes

Main Ideas■ Atoms are the basic building blocks of all

matter.■ Atoms consist of a nucleus containing protons

and neutrons. The positively charged nucleus issurrounded by a cloud of rapidly moving, nega-tively charged electrons.

■ Atoms become stable by bonding toother atoms through covalent or ionicbonds.

■ Components of mixtures retain theirproperties—components of solutions do not.

171

Main IdeasSummary statements can be used bystudents to review the major con-cepts of the chapter.

Using the VocabularyTo reinforce chapter vocabulary, usethe Content Mastery Booklet andthe activities in the Interactive Tutorfor Biology: The Dynamics of Life onthe Glencoe Science Web site.science.glencoe.com


All ChapterAssessment

questions and answers have beenvalidated for accuracy and suitabil-ity by The Princeton Review.


Chapter Assessment, pp. 31-36MindJogger VideoquizzesExamView® Pro SoftwareBDOL Interactive CD-ROM, Chapter 6

quiz

1. c2. c

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS

VIDEOTAPEMindJogger Videoquizzes

Chapter 6: The Chemistry of LifeHave students work in groups as they playthe videoquiz game to review key chapterconcepts.

In 1996, the Federal Food and DrugAdministration (FDA) approved the use of a

new fat substitute called Olestra. Other fat substi-tutes may contain fewer calories than fat, but theybreak down when exposed to high temperatures.Olestra can withstand the high temperaturesneeded to produce fried foods like potato chips.

If it isn’t fat, what is it? Most fat substitutesare molecules that are similar to fat but do nothave fat’s high calorie content. The oldest fatsubstitutes are based on carbohydrates and areused in salad dressings, dips, spreads, candy, andother foods.

Protein-based fat substitutes are also com-mon. The proteins go through a process calledmicroparticulation, in which they are formedinto microscopic round particles. This roundshape gives the substances a pleasing smoothness.Protein-based fat substitutes can be used in somecooked foods, but not fried foods.

A fat substitute made from fat Unlikeother fat substitutes, Olestra is based on actualfat molecules. It is made by surrounding a sugarmolecule, sucrose, with six to eight fatty acidmolecules. Naturally occurring dietary fats aremade of a glycerol molecule with three fattyacids attached. Because Olestra contains manyfatty acid molecules, the digestive system cannotbreak it down and it passes through the bodyundigested.

Olestra does have drawbacks. As Olestrapasses through the digestive system, it can absorband carry some fat-soluble vitamins and nutri-ents. These include vitamins A and E, plus betacarotene, which has been shown to help preventsome forms of cancer.

Fat substitutes will not replace natural fatsentirely, but products like Olestra give food

scientists some options when they are developingreduced-fat and reduced-calorie foods.


Are fake fatsfor real?

Most of us love snacks like chips, cookies, candy, fries, and ice cream. But these foods aretypically high in fat, and most of us also realize that limiting our consumption of fat is

one of the keys to a healthy lifestyle.

TechnologyTechnologyBIOBIO

1. What are some of the pros and cons ofincluding foods made with Olestra in yourdiet? Do you think it’s a good idea to eatfoods made only with fat substitutes ratherthan true fats? Why or why not?

2. Set up a blind taste test to compare chips orother snack foods made with naturally occur-ring fats to snacks made with different fatsubstitutes. Record class preferences. Howmany tasters could tell the differencebetween “fake” fats and “real” fats?

For more information on food technology, visit the Glencoe

Science Web site.science.glencoe.com

INVESTIGATING THE TECHNOLOGYINVESTIGATING THE TECHNOLOGY

Snack foods made with fat substitutes

BIOLOGY

170

Purpose Students learn about themolecular structure of

dietary fats and fat substitutes.They also learn about some ofthe health effects that can resultfrom the consumption ofprocessed foods.

BackgroundOlestra is made by Procter &Gamble and has the trade nameOlean™. Olestra prevents theabsorption of fat-soluble nutri-ents because of its large numberof fatty acid molecules. Thenutrients are absorbed by theOlestra molecules, and becausethese are not digested, neitherare the nutrients.

Teaching Strategies■ On the chalkboard, draw a dia-gram of a sucrose molecule, aglycerol molecule, and a fattyacid molecule. Point out that allare formed from carbon, hydro-gen, and oxygen atoms. Simplediagrams that use letter symbolsfor each atom and straight linesto signify chemical bonds can befound in an introductory chem-istry textbook.

Investigating the Technology

1. Olestra contributes fewercalories and fats, which ishelpful to people who arewatching their weight orneed to limit fats because ofcholesterol problems or heartdisease. But Olestra also pre-vents the body from obtain-ing certain nutrients fromfood, which could have nega-tive health consequences.Fats are an essential part of ahealthy diet, so replacing allfats with fat substitutes couldpresent a health risk.

2. To conduct a “blind” tasting,have someone who is not par-ticipating in the test put a

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sample of each product in a separatecontainer and give it an identifying let-ter or number. Tasters are not allowedto see the product packages or learnwhether each sample contains true fatsor fat substitutes until after they haverecorded their taste preferences. CAUTION: Advise students who havehad adverse reactions to Olestra not toparticipate in the blind taste test.

Going FurtherGoing FurtherGoing Further

Have students conduct research to findout which nutrients Olestra prevents thebody from absorbing and why they areessential. Encourage students to find outabout the long-term health effects ofOlestra and other fat substitutes. L3

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For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web site.science.glencoe.com

CD-ROM


CHAPTER 6 ASSESSMENT 173

and black material, how do you know thesubstance was not an element?

25. Interpreting Data The following graphcompares the abundance of four elements inliving things to their abundance in Earth’scrust, oceans, and atmosphere. Which ele-ment is the most abundant in organisms?What can you say about the general composi-tion of living things compared to nonlivingmatter near Earth’s surface?

26. Designing an Experiment The enzyme per-oxidase triggers the breakdown of hydrogenperoxide to form water and oxygen gas.Design an experiment that measures the rateof the reaction.

27. Concept Mapping Complete the conceptmap by using the following vocabulary terms:protein, amino acid, peptide bond.

THINKING CRITICALLYTHINKING CRITICALLY

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

Two students were studying the effect oftemperature on two naturally occurringenzymes. The graph below summarizestheir data.

Using a Graph Study the graph and answerthe following questions.1. At what temperature does the maximum

activity of enzyme B occur?a. 0° c. 60°b. 35° d. 70°

2. At what temperature do both enzymeshave an equal rate of reaction?a. 10° c. 45°b. 20° d. 60°

3. Which of the following descriptions bestexplains the patterns of temperatureeffects shown on this graph?a. Each enzyme has its own optimal

temperature range.b. Both enzymes have the same optimal

temperature ranges.c. Each enzyme will function at room

temperature.d. Both enzymes are inactivated by

freezing temperatures.4. Designing an Experiment Design an

experiment to test the optimal pH ofenzyme B.

Perc

ent a

bund

ance

(num

bers

of a

tom

s)

C H O N Others

10

0

20

30

40

50

Abundance of Four Elements

In living things

In Earth's crust, oceans, andatmosphere

Rate

s of r

eact

ion

Temperature (°C)

Enzyme BEnzyme A

0 20 40 60 80 100

Effects of Temperature on TwoNaturally Occuring Enzymes

1.A(n)is

made of

2. linkedby 3.

173

25. Hydrogen is the most abundantelement in organisms. Livingthings contain much morehydrogen and carbon, abouthalf the oxygen, and similaramounts of nitrogen whencompared with nonliving sub-stances.

26. Possible answers might includecounting the bubbles given offor collecting and measuring thevolume of oxygen given off.

27. 1. Protein; 2. Amino acids; 3.Peptide bonds

THINKING CRITICALLYTHINKING CRITICALLY


1. d2. c3. a4. Place an equal amount of

enzyme and substrate atdifferent pH levels andassess the rate of the reac-tion at each pH.

e–

e–

e–

e–

e–

e–

e– e–e–

e–

e–

e–e–e–e–

e–

e–

e–

e–e–


3. Which of the following describes an isotope ofthe commonly occurring oxygen atom whichhas 8 electrons, 8 protons, and 8 neutrons?a. 8 electrons, 8 protons, and 9 neutronsb. 7 electrons, 8 protons, and 8 neutronsc. 8 electrons, 7 protons, and 8 neutronsd. 7 electrons, 7 protons, and 8 neutrons

4. Which of the following will form a solution?a. sand and water c. salt and waterb. oil and water d. salt and sand

5. Which of the following applies to a watermolecule?a. Water is a nonpolar molecule.b. The atoms in water are bonded by ionic

bonds.c. The weak bond between two water mole-

cules is a covalent bond.d. Water molecules have a negatively charged

end and a positively charged end.6. Which of the following carbohydrates is a

polysaccharide?a. glucose c. sucroseb. fructose d. starch

7. Which of the following pairs is unrelated?a. sugar—carbohydrateb. fat—lipidc. amino acid—proteind. starch—nucleic acid

8. An acid is any substance that forms ________in water.a. hydroxide ions c. hydrogen ionsb. oxygen ions d. sodium ions

9. Which of these is NOT made up of proteins?a. hair c. fingernailsb. enzymes d. cellulose

10. Which of the following is NOT a smallersubunit of a nucleotide?a. phosphate c. ribose sugarb. nitrogen base d. glycerol

11. An enzyme ________ chemical reactions.12. A calcium atom has

20 protons and ________ electrons.

13. A ________ bond involves sharing of electrons.14. The first energy level of an atom holds

________ electrons; the second energy levelholds 8 electrons.

15. In a water molecule, each ________ atomshares one electron with the single ________atom.

16. A substrate fits into an area of an enzymecalled the ________.

17. Hydrogen, chlorine, and sodium are examples of ________.

18. Long chains of amino acids connected toeach other by a ________ bond form a________.

19. Diffusion is the process in which moleculesmove from a ________ concentration to a________ concentration.

20. The positively charged ________ atoms ofone water molecule attract the negativelycharged ________ atom of another watermolecule to form a hydrogen bond.

21. A magnesium atom has 12 electrons. When itreacts, it usually loses two electrons. Howdoes this loss make magnesium more stable?

22. Explain why water and a sponge would notbe effective in cleaning up a grease spill.

23. Explain why carbon is the most critical ele-ment to living things.

24. If heating a white substance produces a vapor

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

172 CHAPTER 6 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

When Eliminating, Cross It OutCross out choices you’ve eliminated with your pencil. List the answer choice letters on the scratch paper and cross them out there. You’ll stop yourself from choosing an answer you’vementally eliminated.

172

3. a4. c5. d6. d 7. d8. c9. d

10. d11. speeds12. 20 13. covalent14. 215. hydrogen; oxygen16. active site17. elements18. peptide; protein19. high; low20. hydrogen; oxygen

21. The underlying energy level is afilled level.

22. Water is a polar molecule; it willnot attract the nonpolar grease.

23. Carbon is the building blockelement of the four basic sub-stances (carbohydrates, lipids,proteins, and nucleic acids)found in all known livingorganisms.

24. The substance was a compoundbecause two new substanceswere formed by the chemicalreaction.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS



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