animalcules of a cell - temecula valley unified school ...web1.tvusd.k12.ca.us/gohs/myoung/bio....

The Life of aCell

Unit OverviewUnit 3 introduces students tobasic chemistry, cell structure andfunction, and cell energetics.Chapter 6 presents basic con-cepts of chemistry important inbiology. Chapter 7 introduces cell struc-ture and function.Chapter 8 expands upon the dis-cussion in Chapter 7 through anin-depth view of cellular transportand the cell cycle.Chapter 9 acquaints studentswith the details of energy flow inphotosynthesis and respiration.

Introducing the UnitAsk students to describe some ofthe things they see in the photo-graphs of cells within the unit.Lead a discussion on what knowl-edge and questions the studentshave about cells. Take notes andrevisit them after the unit is com-plete to reassess their knowledge.

A WebQuest is aninquiry-based online project inwhich all information used bystudents is obtained from theWeb. Students evaluate the infor-mation to complete the activity.Access the Unit 3 WebQuest at

Discussion As students read theunit, have them refer to the time lineabove. Ask students to consider thereasons that many cell discoveries camein short bursts (such as 1665–1674,1831–1839, and 1950–1991), followed

by longer periods of non-discovery(such as 1674–1831, and 1855–1950).Students should realize that discoveryand knowledge of cells was dependenton technology, especially advances anddevelopments in microscopes. L2

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The Life of a CellWhat You’ll LearnChapter 6

The Chemistry of Life

Chapter 7A View of the Cell

Chapter 8 Cellular Transport and the Cell Cycle

Chapter 9Energy in a Cell

Unit 3 ReviewBioDigest & Standardized Test Practice

Why It’s ImportantA cell is the most basic unit of living organisms. No matterhow complex an organism is, at its core it is a collection ofcells. In many organisms, cells work together, formingmore complex structures.

Understanding the PhotoThis is a color-enhanced image of a plant celltaken with a transmission electron micro-scope. Note the many compartments withinthe cell. These compartments keep the cell’sfunctions separated.Color-enhanced TEM Magnification: 4200�

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1620Pilgrims aboard the Mayflowerland at Plymouth, Massachusetts.

1665Robert Hooke firstdescribes andnames cells whenhe observes a slice of cork usinga hand-craftedmicroscope that magnifies 30 times.

1674The first living cells—single-celled organ-isms—are observed.They are called animalcules meaning“little animals.”

ca.bdol.glencoe.com/webquest (t)Science Museum/Science & Society Picture Library, (crossover)Biophoto Associates/Science Source/Photo Reseachers

The following standards are covered in Unit 3:Investigation and Experimentation: 1a, 1d, 1h, 1j, 1kBiology/Life Sciences: 1a, 1b, 1c, 1d, 1h, 4e, 4f, 5a

California Standards

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Pages 138–139: Inv. & Exp. 1k

http://ca.bdol.glencoe.com/webquest

http://ca.bdol.glencoe.com/webquest

Advance MaterialsPlanningThe following materials may needto be ordered a few weeks inadvance of the planned activity.

Chapter 6� Quick Demo (p. 146) 9-volt

battery, wire� Quick Demo (p. 159) ball-

and-stick models

Chapter 7� Additional Lab (p. 182)

Elodea plant, prepared slide ofhuman cheek cells

� BioLab (p. 188) preparedslides of Bacillus subtilis, frogblood, Elodea leaf

Chapter 8 � MiniLab (p. 198) iodine

solution� MiniLab (p. 209) fish mitosis

slides� BioLab (p. 214) prepared

onion root tip slides

Chapter 9 � MiniLab (p. 226) filter paper� MiniLab (p. 236) plastic

pipettes� BioDigest (p. 246) molecular

model of a lipid, dialysis bags

Building a ModelKinesthetic Ask students to build athree-dimensional model of anatom. Students should use objectsto represent protons, electrons, andneutrons. Suspend these in theappropriate place. Wire loops canrepresent energy levels.

Using the LibraryIntrapersonal Encourage studentsto find out how a cell grows anddivides. Have them design a postershowing the steps of this process.

Cells AliveVisual-Spatial Have students viewslides of different types of cells at

.They can draw diagrams of eachand postulate why each has itsunique shape.

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1776The Declaration of Independenceis signed by the SecondContinental Congress.

1950sDevelopment of the electronmicroscope allows cell biolo-gists to see organelles.1839

It is determinedthat all animalsconsist of cells.

1972A model for the struc-ture of the membranethat surrounds the cellis proposed.

1831The cell nucleusis discovered andnamed.

1945First atomic bomb explodesover Hiroshima, Japan, duringWorld War II.

1838It is determinedthat all livingplants consistof cells.

1991Molecularmotors, whichmove moleculesthrough thecell along thecytoskeleton,are discovered.

ca.bdol.glencoe.com/microscopy

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Section ObjectivesNational Science State/Local Advanced Lab and

Standards Standards Demo Planning

End of Chapter AssessmentStudent Edition

Study Guide, p. 167Content Assessment, pp. 168–169

UCP.1, UCP.2,UCP.3; A.1, A.2;B.1–3; C.5; E.1, E.2;F.1; G.1, G.2

UCP.1, UCP.2,UCP.3; A.1, A.2;B.1–4, B.6; C.5;G.1–3

UCP.1, UCP.2,UCP.3; A.1, A.2;B.1–3, B.6; C.5; E.1,E.2; F.1, F.5; G.1–3

Student Labs:Problem-Solving Lab 6.1, p. 145MiniLab 6.1, p. 151: beakers or small glasscontainers, lemon juice, prepared householdammonia solution, liquid detergent, sham-poo, vinegar, pH paper

Teacher Demonstration:Quick Demo, p. 146: beaker, salted water,wire, 9-volt battery

Student Labs: Problem-Solving Lab 6.2, p. 154MiniLab 6.2, p. 155: single-edge razor blade,raw peeled potato, forceps, cup or beaker,purple dye

Teacher Demonstration:Quick Demo, p. 153: paper towel, water

Student Labs: Additional Lab, pp. 160–161: 4 paper cupswith gelatin, fresh pineapple, knife, waxedpaper, canned chunk pineapple, grapes ororange sections, refrigeratorInvestigate BioLab, p. 164: See materialsbelow.

Teacher Demonstration:Quick Demo, p. 159: ball-and-stick model ofa methane molecule

Student Lab: Investigate BioLab, p. 164: clock or timer,400-mL beaker, kitchen knife, tongs or largeforceps, 5-mm thick potato slices, ice, hotplate, waxed paper, non-mercury thermome-ter, 3% hydrogen peroxide

Level 1 activitiesshould be appropriatefor students withlearning difficulties.

Level 2 activitiesshould be within theability range of all students.

Level 3 activitiesare designed forabove-average students.

ELL activitiesshould be within theability range ofEnglish LanguageLearners.

Cooperative Learningactivities are designedfor small group work.P

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1 session, 1/2 block

1. Relate the particle structure ofan atom to the identity of ele-ments.

2. Relate the formation of cova-lent and ionic chemical bondsto the stability of atoms.

3. Distinguish mixtures and solu-tions.

4. Define acids and bases andrelate their importance to bio-logical systems.

1 session, 1/2 block

5. Relate water’s unique featuresto polarity.

6. Explain how the process of dif-fusion occurs and why it isimportant to cells.

3 sessions, 1 block

7. Classify the variety of organiccompounds.

8. Describe how polymers areformed and broken down inorganisms.

9. Compare the chemical struc-tures of carbohydrates, lipids,proteins, and nucleic acids, andrelate their importance to liv-ing things.

10. Identify the effects of enzymes.

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Investigational &Experimentation1a

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Reproducible Masters Technology

and Transparencies

Unit 3 FAST FILE ResourcesMiniLab Worksheet, p. 3BioLab Worksheet, pp. 5–6Reinforcement and Study Guide in English,

pp. 9–10Reinforcement and Study Guide in Spanish,

pp. 13–14Transparency Worksheets, pp. 19, 23–28

Reading Essentials for Biology, Section 6.1

Section Focus Transparency 12

Basic Concepts Transparencies 4, 5a, 5b

Unit 3 FAST FILE ResourcesMiniLab Worksheet, p. 4Reinforcement and Study Guide in English, p. 11Reinforcement and Study Guide in Spanish, p. 15Concept Mapping, p. 17Transparency Worksheet, p. 20



Unit 3 FAST FILE ResourcesReal World BioApplications, pp. 7–8Reinforcement and Study Guide in English,

p. 12Reinforcement and Study Guide in Spanish, p. 16Critical Thinking/Problem Solving, p. 18Transparency Worksheets, pp. 21, 29–30


Laboratory Manual, pp. 27–34Section Focus Transparency 14

Reteaching Skills Transparency 8

Unit 3 FAST FILE ResourcesChapter Assessment, pp. 31–36Student Recording Sheet, p. 37

Reviewing Biology, pp. 11–12

Interactive Chalkboard CD-ROM: Section 6.1 PresentationTeacherWorks™ CD-ROMGuided Reading Audio Summaries MP3

Interactive Chalkboard CD-ROM: Section 6.2 PresentationTeacherWorks™ CD-ROMGuided Reading Audio Summaries MP3

Interactive Chalkboard CD-ROM: Section 6.3 PresentationTeacherWorks™ CD-ROMGuided Reading Audio Summaries MP3Virtual Labs CD-ROMVirtual Lab: Enzyme-Controlled Reactions

Interactive Chalkboard: Chapter 6 AssessmentMindJogger Videoquizzes DVD/VHSExamView® Pro Test Bank CD-ROMTeacherWorks™ CD-ROM

Transparency CD-ROM MP3 Videocassette DVD

Legend

/self_check_quiz/vocabulary_puzzlemaker/chapter_test/standardized_test

140B

ca.bdol.glencoe.com

Succeeding on National Standards CD-ROM

Indicates materials created specifically for California.

Succeeding on National Standards CD-ROM

http://ca.bdol.glencoe.com

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Short on Time?

The BioDigest at theend of this unit can be used as a(n):• preview to introduce important

unit concepts.• overview if time does not per-

mit teaching the entire chapter.• review of key unit concepts.

Understanding the PhotoAsk students to list the features ofliving things and compile a list onthe board. Brainstorm to seewhat students know about howliving things are chemically dif-ferent and similar to nonlivingmaterials. Ask them to speculateabout why early scientists thoughta mysterious force controlledchemical changes in organisms.

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Demo Using a piece of carbon(such as coal), a bottle of water, andsugar cubes, tell students that thecombination of carbon and watercontains the same elements as sugar.Mix a small amount of water in a

beaker containing some powderedpieces of coal. Sugar does not result.Ask students why you don’t getsugar when you mix water with thecoal. Help them understand that theelements (carbon in coal; hydrogen

and oxygen in water) only combineas sugar when chemical bonds form.Unlike the coal and water mixture,sugar cannot be easily separatedinto its components.

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Visit to• study the entire chapter

online• access Web Links for more

information and activities on the chemistry of life

• review content with theInteractive Tutor and self-check quizzes



What You’ll Learn� You will relate an atom’s

interactions with other atomsto its structure.

� You will explain why water is important to life.

� You will compare the role of biomolecules in organisms.

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.

This butterfly, as well as the col-orful flower, is made of atoms.Atoms also make up the break-fast you ate this morning, theair you breathe, and the pagesof this book. Why, then, are allthese things different?

Understandingthe Photo

ca.bdol.glencoe.com

Robert Lubeck/Animals Animals/Earth Scenes

This CD-ROM is an editableMicrosoft® PowerPoint®

presentation that includes:• Section presentations• Section checks• Image bank• Hot links to Biology Online• All transparencies


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BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

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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Unit 3 FAST FILE ResourcesMiniLab Worksheet, p. 3BioLab Worksheet, pp. 5–6Reinforcement and Study Guide in

English, pp. 9–10Reinforcement and Study Guide in

Spanish, pp. 13–14Transparency Worksheets, pp. 19, 23–28

Reading Essentials for Biology,Section 6.1

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

5b

1 FocusBellringerSection Focus Transparency 12SECTION PREVIEW

ObjectivesRelate the structure of anatom to the identity of elements.Relate the formation ofcovalent and ionic chemicalbonds to the stability ofatoms.Distinguish mixtures andsolutions.Define acids and bases andrelate their importance tobiological systems.

Review Vocabulary energy: the ability to cause

change (p. 9)

New Vocabularyelementatomnucleusisotopecompoundcovalent bondmoleculeionionic bondmetabolismmixturesolutionpHacidbase

6.1 ATOMS AND THEIR INTERACTIONS 141

Atoms: The BuildingBlocks of Rocks—and You!Using Prior Knowledge Thedifference between living andnonliving things may be readilyapparent to you. For example,these corals are responding totheir surroundings, somethingyou would not expect a rock todo. We know, however, that liv-ing things have a great deal incommon with rocks, CDs, com-puter chips, and other nonlivingobjects. Both living and nonliv-ing things are composed of thebasic building blocks called atoms.Compare and Contrast What makes a living thing different from a nonlivingthing? How are the particles that make up a rock similar to those of a coral?

Atoms and TheirInteractions6.1

Cup corals eat a juvenile octopus.

Elements Everything—whether it is a rock, frog, or flower—is made of sub-

stances called elements. Suppose you find a nugget of pure gold. Youcould grind it into a billion bits of powder and every particle would stillbe gold. You could treat the gold with every known chemical, but youcould never break it down into simpler substances. That’s because gold isan element. An element is a substance that can’t be broken down intosimpler chemical substances.

Natural elements in living thingsOf the naturally occurring elements on Earth, only about 25 are essen-

tial to living organisms. Table 6.1 on the next page lists some elementsfound in the human body. Notice that four of the elements—carbon,hydrogen, oxygen, and nitrogen—together make up more than 96 per-cent of the mass of a human body. Each element is identified by a one- ortwo-letter abbreviation called a symbol. For example, the symbol C rep-resents the element carbon, Ca represents the element calcium, and Clrepresents the element chlorine.

Jeffrey Rotman/Photo Researchers

Standard 1l Students will analyze situations and solve problems thatrequire combining and applying concepts for more than one area of science.


Using PriorKnowledgeCompare and Contrast Liv-ing things and nonliving thingsare all made of atoms. It is theway the atoms combine into dif-ferent elements that affects theirphysical and chemical propertiesand whether they are living ornonliving. The particles that forma rock and the hard outer cover-ing of a coral are made of similarsubstances that are combineddifferently.

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Visual LearningVisual-Spatial Discuss possibledietary sources of each elementlisted in Table 6.1. Have studentsredesign the table to include pic-tures that show two sources ofeach element listed. Have stu-dents conduct additional researchif necessary.

Concept DevelopmentStress that the elements carbon,hydrogen, nitrogen, oxygen,phosphorus, and sulfur are themain components of living mat-ter. All of these elements formmolecules through covalentbonding. Refer to this during thediscussion of covalent bonds onpages 145–146.

DisplayMake a bulletin board display thatmodels the structure of an atom.Label the nucleus, protons, neu-trons, and electrons of the model.Refer to the display when dis-cussing atomic structure.

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142 THE CHEMISTRY OF LIFE

Mammals use iodine (I) to producehormones, substances that affectchemical activities in the body.

A Plants use magnesium (Mg) to formchlorophyll, which captures lightenergy for sugar production.

B

Trace elements

Some of the elements listed inTable 6.1, such as iron and copper,are present in living things in verysmall amounts. Such elements areknown as trace elements. They play a vital role in maintaining healthycells in all organisms, as shown bythe examples in Figure 6.1. Plantsobtain trace elements by absorbingthem through their roots; animalsget them from the foods they eat.

Atoms: The BuildingBlocks of Elements

Whether elements are found in liv-ing things, like cup corals, mammals,or plants, or in nonliving things, likerocks, they are made of atoms. Anatom is the smallest particle of an ele-ment that has the characteristics ofthat element. Atoms are the basicbuilding blocks of all matter. The waythey are structured affects their prop-erties and their chemical behavior.

Figure 6.1Some elements that areneeded in small amountsare involved in cellmetabolism.

Table 6.1 Some Elements That Make Up the Human Body

Percent By Percent ByElement Symbol Mass in Element Symbol Mass in

Human Body Human Body

Oxygen 0 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

(l)A.B. Joyce/Photo Researchers, (r)F. Stuart Westmoreland/Photo Researchers

Table of Elements To help studentsbetter understand elements, create aPeriodic Table of Everyday Things. Havestudents bring in objects to representas many elements as possible on thePeriodic Table of Elements (coal for car-bon, an aluminum can for aluminum).

Display these in the same order as thePeriodic Table. Use photos to representhard-to-find or unsafe elements. Referto this Periodic Table throughout theyear as elements are discussed.

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Tying to PriorKnowledgeRelate 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.

ReinforcementVisual-Spatial Bring in examplesof aluminum (cans, nails, foil) andiron (steel cans, nails). Allow stu-dents to compare these objects.List their similarities and differ-ences on the board. Even thoughboth aluminum and iron are met-als, differences in their atomicstructures result in different properties.

Chalkboard ActivityTo help students organize theirinformation, draw a table withcolumns labeled: Particle, Location,Charge, and Symbol. Label therows: Electron, Neutron, andProton. Ask volunteers to come tothe chalkboard to complete thetable.

Visual LearningHelp students gain an under-standing of the relative sizes ofatoms and molecules. For exam-ple, in Figure 6.2, the averageradius of a hydrogen atom isabout 5.29 nanometers. Oxygen isabout 80% larger.

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The structure of an atomAll atoms have the same general

structure. The center of an atom iscalled the nucleus (NEW klee us)(plural, nuclei). All nuclei containpositively charged particles calledprotons ( p�). Most contain particlesthat have no charge, called neutrons(n0). All nuclei are positively chargedbecause of the presence of protons.Each element has distinct character-istics that result from the number of protons in the nuclei of the atoms that compose the element. Forexample, the element iron differsfrom the element aluminum becauseiron atoms have a different numberof protons than aluminum atoms.

The region of space surroundingthe nucleus contains extremelysmall, negatively charged particlescalled electrons (e�). The electronsare held in this region by theirattraction to the positively chargednucleus. You can visualize this region

as an electron cloud. Although it isimpossible to pinpoint the exact loca-tion of an electron, the electron cloudis the area where it is most likely to befound.

Electron energy levelsElectrons exist around the nucleus

in regions known as energy levels, asindicated in Figure 6.2A. The firstenergy level can hold only two elec-trons. The second level can hold amaximum of eight electrons. Thethird level can hold up to 18 electrons.The oxygen atom in Figure 6.2C hasa total of eight electrons. Two elec-trons fill the first energy level. Theremaining six electrons occupy thesecond energy level.

Atoms contain equal numbers ofelectrons and protons; therefore, theyhave no net charge. The hydrogen (H)atom in Figure 6.2B has just one electron and one proton. Oxygen (O)has eight electrons and eight protons.


Hydrogen atom

Oxygen atom

Nucleus 8 protons (p ) 8 neutrons (n )

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0

Nucleus 1 proton (p ) 0 neutrons (n )

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Electron energy levels

Nucleus

Figure 6.2Electrons move rapidlyaround nuclei composedof protons and neutrons. Hydrogen, the

simplest atom,has just oneelectron in itsfirst energy leveland one protonin its nucleus.

B

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

CAn atom has a nucleus and electronsin energy levels.

A

Visually Impaired To help students whoare visually impaired understand thestructure of an atom, make atomic mod-els by gluing marbles, jelly beans, driedbeans, and yarn to a piece of cardboard.Use the yarn to outline the nucleus andthe energy levels. Use marbles for the

neutrons, jelly beans for the electrons,and dried beans for the protons. Allowvisually impaired students to manipulatethe model. Have peers work with visual-ly impaired students to assist in identify-ing the parts of the model.

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EnrichmentIntrapersonal The scanning tun-neling microscope (STM) pro-vides a three-dimensional map of amolecule’s surface by measuringthe flow of electrons across a smallvacuum gap. A tungsten tip similarto a phonograph needle is posi-tioned a few angstroms from thesubstance being studied. When asmall voltage is applied, some elec-trons jump across the gap betweenthe tip 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.

An oxygenatom has a total of 8 elec-trons, 8 protons, and 8 neu-trons. The protons and neu-trons form the nucleus, twoelectrons are in the firstenergy level, and 6 electronsoccupy the second level.

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 radiation com-pare with the risks of exposure.

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Figure 6.3 shows three other elementswhose properties differ because of thenumber of protons in their nuclei.

Describe the struc-ture of an oxygen atom.

Isotopes of an ElementAtoms of the same element always

have the same number of protons butmay contain different numbers ofneutrons. Atoms of the same elementthat have different numbers of neu-trons are called isotopes (I suh tohps)

of that element. For example, mostcarbon nuclei contain six neutrons.However, some have seven or eightneutrons. Each of these atoms is an isotope of the element carbon.Scientists refer to isotopes by statingthe combined total of protons andneutrons in the nucleus. Thus, themost common carbon atom is referredto as carbon-12 because it has sixprotons and six neutrons. Otherisotopes of carbon include carbon-13and 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 andcan damage or kill cells, scientistshave developed some useful applica-tions for radioactive isotopes, asdescribed in Figure 6.4.

Atomic models like those dis-cussed in the Problem-Solving Labon the next page help scientists and students visualize the structureof atoms and understand complexintermolecular interactions.

Figure 6.4Radioactive isotopes areused in medicine to diag-nose and/or treat somediseases. Radiation givenoff when radioactive iso-topes break apart isdeadly to many rapidlygrowing cancer cells. Thispatient is being treatedwith radiation from aradioactive isotope ofcobalt (Co).

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Figure 6.3The properties of anelement are deter-mined by its atoms. Asyou can see, carbon,gold, and sulfur havevery different properties.

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Stable Isotopes Not all isotopes areunstable and radioactive. There aresome isotopes—stable isotopes—that donot decay. Like radioisotopes, stable iso-topes can be useful in biologicalresearch. Challenge advanced students

to research how stable isotopes can beused to map the location where amigrating bird was feeding as it grewnew feathers. Ask students to researchother uses for stable isotopes in scien-tific studies. L3

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Purpose Students will use models of theparticles in nuclei of beryllium topredict electron number, positionof electrons in energy levels, andhow differences in the number ofneutrons affect the element.

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

Teaching Strategies� Review the concept of isotopes

with 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 ofneutrons.

� Review the charges associatedwith each atomic particle.

Thinking Critically1. 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

AssessmentKnowledge Provide studentswith two diagrams of the nucleusfor the element fluorine. Haveone nucleus with 9 neutrons andone with 10 neutrons. Advisethem of the most common form(with 9 neutrons). Ask them toprovide the same information asthey did for beryllium. Use thePerformance Task AssessmentList for Making Observations andInferences in PASC, p. 89. L2

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Compounds and Bonding

Table salt is a substance that isfamiliar to everyone; however, tablesalt is not an element. Rather, salt isa type of substance called a com-pound. A compound is a substancethat is composed of atoms of two or more different elements that are chemically combined. Table salt(NaCl) is a compound composed ofthe elements sodium and chlorine. Ifan electric current is passed throughmolten salt in an industrial process,the salt breaks down into these ele-ments. You can see in Figure 6.5 thatthe properties of a compound aredifferent from those of its individualelements.

How covalent bonds formMost elements in nature are

found combined in the form of compounds. But how and why doatoms combine, and what is it thatholds the atoms together in a com-pound? Atoms combine with other

atoms only when the resulting compound is more stable than theindividual atoms.

For many elements, an atombecomes stable when its outermostenergy level is full, as when eightelectrons are in the second level. An exception is hydrogen, whichbecomes stable when its first energylevel is full (two electrons). How doelements fill the energy levels andbecome stable? One way is to shareelectrons with other atoms.

Interpret Scientific IllustrationsWhat can be learned by studying the nucleus of anatom? Looking at a model of the particles in an atom’snucleus can reveal certain information about that particularatom. Models may help predict electron number, the distribu-tion of electrons in energy levels, and how isotopes of an ele-ment differ from each other.

Solve the ProblemExamine diagrams A and B. Both are models of an atom ofberyllium. Only the nucleus of each atom is shown.

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

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

B? Explain how you were able to tell.4. Predict How many energy levels would be present in

atoms of A and B? How might the electrons in A and B bedistributed in these levels?

Beryllium nucleus Beryllium nucleus

Most common form

Proton

Figure 6.5Table salt is made fromthe elements sodium (Na)and chlorine (Cl). Theflask contains the poison-ous, yellow-green chlo-rine gas. The lump ofsilver-white metal is theelement sodium. Thewhite crystals of table saltno longer resemble eithersodium or chlorine.

6.1 ATOMS AND THEIR INTERACTIONS 145Chip Clark

BBAA

Kenichi Fukui and Chemical ReactionsIn the 1950s, Japanese chemist KenichiFukui (1918–1998) developed the ideathat chemical reactions occur as a resultof interactions of the outer-level elec-trons of one atom or molecule with theouter-level electrons of another atom

or molecule. In 1981, Fukui received theNobel Prize for Chemistry for his inves-tigations of the mechanisms of chemi-cal reactions. Discuss with students thework of Kenichi Fukui toward under-standing chemical interactions. L2

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Figure 6.6Sometimes atoms combine by sharingelectrons to form covalent bonds.

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

A

When twohydrogens shareelectrons withoxygen, theyform covalentbonds to producea molecule ofwater (H2O).

B

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Hydrogen molecule

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PhysicalScience

Connection

Chemical bond-ing and theperiodic tableLiving things aremade up mainly offour elements:hydrogen, carbon,nitrogen, andoxygen. Nonmetalelements that areclose to each otheron the periodictable tend to com-bine by formingcovalent bonds. Asa result, almost allthe compoundsformed from thesefour elements arecovalently bonded.

Look at Figure 6.6A. You will seethat two hydrogen atoms can com-bine with each other by sharingtheir electrons. As you know, hydro-gen atoms contain only one elec-tron. Each atom becomes stable bysharing its electron with the otheratom. The two shared electronsmove about the nuclei of bothatoms. The attraction of the posi-tively charged nuclei for the shared,negatively charged electrons holdsthe atoms together. When twoatoms share electrons, such as twohydrogen atoms sharing electrons,

the force that holds them together iscalled a covalent (koh VAY lunt)bond. Most compounds in organ-isms have covalent bonds. Examplesinclude sugars, fats, proteins, andwater.

A molecule is a group of atoms held together by covalent bonds. It hasno overall charge. In a molecule ofwater, Figure 6.6B, two hydrogenatoms and one oxygen atom shareeight electrons. Each of the hydrogenatoms contributes one electron, andthe oxygen atom contributes six elec-trons. Thus, all three atoms are stable.

Michael P. Gadomski/Photo Researchers

Candy Ions Have students make a two-dimensional model of an ionic com-pound on a sheet of poster paper orcardboard using small pieces of candyfor electrons. Use Figure 6.7 as an

example. Try combining other atoms,like Ca and Cl or C and H. Emphasizethat no electrons are lost; they are sim-ply rearranged. L2

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Water Break Place a beaker of lightlysalted water on a tablewhere it can be seen by stu-dents. Connect one end ofa piece of wire to the posi-tive terminal of a 9-voltbattery. Connect a secondpiece of wire to the nega-tive terminal of the battery.Place the other ends of thewires into the water; do not allow wires to touch.Hydrogen gas is explosive;do not generate an exces-sive amount. Instruct stu-dents to observe the endsof the wires for the appear-ance of bubbles. Explainthat passing an electric cur-rent through water breaksthe water apart, resulting in the elements oxygen andhydrogen. Point out that ittakes energy to break thecovalent bond.

Have students researchthe chemical formula andstructure of ethane.Discuss the types of bondspresent in this molecule.In ethane (C2H6), each car-bon atom is linked to theother carbon and threehydrogen atoms by singlecovalent bonds.

Physical Science Connection

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ReinforcementLogical-Mathematical Give stu-dents several chemical formulasrelated to living things, such asCO2 (carbon dioxide) andC6H12O6 (sugar). Have thempractice identifying the elementsin the compounds and the num-bers of atoms of each type of ele-ment shown in each formula.

Chalkboard ExampleLogical-Mathematical Write afew chemical equations on thechalkboard and work with stu-dents to balance the equations.Once the equations are balanced,have students confirm the balanceby counting the number of atomsof each kind on each side of theequation. Reinforce the idea thatatoms are neither created nordestroyed in ordinary reactions.Some possible equations are: Mg � 2HCl ⇒ MgCl2 � H22C2H2 � 5O2 ⇒ 2H2O � 4CO22H2S � 3O2 ⇒ 2H2O � 2SO2

Caption Question AnswerFigure 6.7 Sodium loses oneelectron in bond formation.

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A molecule of water is representedby the chemical formula H2O. Thesubscript 2 represents two atoms ofhydrogen (H) combined with oneatom of oxygen (O). As you will see,many compounds in living thingshave more complex formulas.

How ionic bonds formNot all atoms bond with each other

by sharing electrons. Sometimesatoms combine with each other byfirst gaining or losing electrons intheir outer energy levels. An atom (orgroup of atoms) that gains or loseselectrons has an electrical charge andis called an ion. An ion is a chargedparticle made of atoms.

A different type of chemical bondholds ions together. The bond formedbetween a sodium atom (Na) andchlorine atom (Cl) in table salt is agood example of this. A sodium atomcontains 11 electrons, including onein the third energy level. A chlorineatom has 17 electrons, with the outerlevel holding seven electrons. Thesodium atom loses one electron to thechlorine atom, and the chlorine atomgains one electron from the sodiumatom. With eight electrons in itsouter level, the chloride ion formed is stable and has a negative charge.The sodium ion has eight electrons in

its outer energy level. The sodium ionis stable and has a positive charge.The attractive force between two ionsof opposite charge is known as anionic bond. The bond betweensodium and chlorine when they com-bine is an ionic bond, as shown inFigure 6.7.

Ionic compounds are less abundantin living things than are covalentmolecules, but ions are important in biological 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 ReactionsChemical reactions occur when

bonds are formed or broken, causingsubstances to recombine into differ-ent substances. In organisms, chemi-cal reactions occur inside cells. All ofthe chemical reactions that occurwithin an organism are referred to as that organism’s metabolism.These reactions break down and build molecules that are important for the functioning of organisms. Scientists represent chemical reac-tions by writing chemical equations.


metabolism fromthe Greek wordmetabole, mean-ing “change”;Metabolisminvolves manychemical changes.

+

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�Sodium atom Chlorine atom Sodium � ion Chloride � ion

Ionic bond

17 p�

17Na atom: Cl atom: 11p�

10e � e �17 p�

18Na� ion: Cl� ion:

Na Cl Na Cl

Figure 6.7The positive charge of asodium ion attracts thenegative charge of achloride ion. This attrac-tion is called an ionicbond. Use Models Howmany electrons doessodium lose in bondformation?

Metabolism Have students researchdifferent kinds of metabolism, suchas anabolism and catabolism.Challenge them to present theresults in creative ways. L3

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Modeling Have students build modelsof water molecules. Students may usetoothpicks and gumdrops or coloredmarshmallows to represent the atomsin the molecule.

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Caption Question AnswerFigure 6.8 Hydrogen gas andoxygen gas are reactants. Wateris the product.

PortfolioMixtures and Compounds Havestudents construct a table to com-pare and contrast mixtures andcompounds. Encourage studentsto reread the section entitled“Mixtures and Solutions” to findthe information needed to com-plete their tables. L2

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Writing chemical equationsThe reaction that takes place when

hydrogen gas combines with oxygengas is shown in Figure 6.8. In a chem-ical reaction, substances that undergochemical reactions, such as hydrogenand oxygen, are called reactants.Substances formed by chemical reac-tions, such as water, are called products.

It’s easy to tell how many moleculesare involved in a reaction. In a chemi-cal equation the number before eachchemical formula indicates the num-ber of molecules of each substance.The subscript numbers in a formulaindicate the number of atoms of eachelement in a molecule of the substance.

A molecule of table sugar can be repre-sented by the formula C12H22O11. Thelack of a number before a formula orunder a symbol indicates that only onemolecule or atom is present.

Looking at Figure 6.8, you can seethat each molecule of hydrogen gas iscomposed of two atoms of hydrogen.Likewise, a molecule of oxygen gas ismade of two oxygen atoms. Perhapsthe easiest way to understand chemi-cal equations is to know that atomsare neither created nor destroyed inchemical reactions. They are simplyrearranged. An equation is written sothat the same numbers of atoms ofeach element appear on both sides ofthe arrow. In other words, equationsmust always be written so that theybalance.

Mixtures and SolutionsWhen elements combine chemi-

cally to form a compound, the ele-ments no longer have their originalproperties. What happens if sub-stances are just mixed together and donot combine chemically? A mixture isa combination of substances in whichthe individual components retain theirown properties. Figure 6.9 shows amixture of sand and sugar crystals.

Figure 6.8This balanced equation shows two molecules of hydrogen gas reactingwith one molecule of oxygen gas to produce two molecules of water.Interpret Scientific Illustrations Which of the molecules shownhere are reactants? Which are products?

+

+2H2 O2 2H2O


PhysicalScience

Connection

Conservation ofmass in chemicalreactions In achemical reaction,atoms are neithercreated nordestroyed. As aresult, mass isconserved as achemical reaction.This means thatthe mass of thereactants equalsthe mass of theproducts.

Figure 6.9In this illustration of amixture, both the sandand sugar retain theiroriginal properties.

Matt Meadows

Concept Mapping Have students createa concept map poster showing the rela-tionships among elements, mixtures,compounds, and solutions. The follow-ing terms should be included: atoms,elements, molecules, compounds,

mixtures, solutions, solvent. Studentsmay add other terms and should supplytheir own connecting words. Posterscan be presented or displayed as partof a concept review. L2

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Have students reviewrules for balancing chemi-cal equations, and thenbalance the followingreaction:Cl2 � NaBr → NaCl � Br2Because there are twobromine atoms on theright side of the equation,a coefficient of 2 is placedbefore NaBr; likewise,there are two chlorineatoms on the left side ofthe equation so a coeffi-cient of 2 is placed beforeNaCl. The balanced equa-tion is:Cl2 � 2NaBr → 2NaCl � Br2


149

Using Science TermsTell students to imagine they aremaking a glass of lemonade from amix. Ask: “Which part of theresulting solution is the solute?Which is the solvent?” The lemon-ade mix is the solute because it isthe material being dissolved. Thewater in which the mix is dis-solved is the solvent.

ReinforcementPrepare mixtures of sand andwater (suspension) and salt andwater (solution). Explain that thecontents of both containers repre-sent mixtures. Stir each containerand ask students to describe anychanges they observe in theappearance of the mixtures.

Use the observable traits of themixtures to explain that there aredifferent types of mixtures.Explain that the sand and waterrepresent a suspension—a hetero-geneous mixture consisting offinely divided particles of a solidtemporarily suspended in a liquid.The salt and water are a solu-tion—a mixture in which one ormore substances are evenly dis-tributed in another substance.

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When you stir sand and sugar together,you can still tell the sand from thesugar. Neither component of the mix-ture changes; that is, the componentswould not combine chemically. Youcan easily separate them by addingwater to dissolve the sugar and then fil-tering the mixture to collect the sand.

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. You mayremember using powdered drink mixwhen you were younger. The sugarmolecules in the powdered drink mixdissolve easily in water to form a solu-tion, as shown in Figure 6.10.

Solutions are important in livingthings. In organisms, many vital substances, such as sugars and mineralions, are dissolved in water. The more

solute that is dissolved in a givenamount of solvent, the greater is thesolution’s concentration. The con-centration of a solute is important toorganisms. Organisms can’t live unlessthe concentration of dissolved sub-stances stays within a specific, narrowrange. Organisms have many mecha-nisms to keep the concentrations ofmolecules and ions within this range.For example, the pancreas and otherorgans in your body produce sub-stances such as insulin and glucagonthat keep the amount of sugar dis-solved in your bloodstream within acritical range.

Acids and basesChemical reactions can occur only

when conditions are right. A reactionmay depend on available energy, tem-perature, or a certain concentration of a substance dissolved in solution.

Figure 6.10The sugar molecules in the powdered drink mix dissolvein the water, making a solution. Here, sugar is the soluteand water is the solvent.

Watermolecules

Sugarmolecules

Sugarcrystal

6.1 ATOMS AND THEIR INTERACTIONS 149Aaron Haupt

Chemical Formulas: Logical-Mathematical Provide students withseveral chemical formulas, includingsome with subscripts. Examples caninclude C6H12O6 and H2SO4. Have themdetermine how many atoms of each

element are represented in each for-mula. Students can also draw diagramsgiving the molecular structure of thecompounds.

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Purpose Students will determine the pH ofcommon 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. Have stu-dents wash hands after this activity.

Teaching Strategies� Prepare the ammonia solution

ahead of time. Dilute householdammonia with water at a 1:10ratio. CAUTION: Ammonia is askin and eye irritant and isharmful if inhaled.

� 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.

Modified AssessmentPortfolio Have students make apH scale in their portfolios andshow where each solution falls onthe scale. Use the PerformanceTask Assessment List forScientific Drawing in PASC,p. 127.

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Weed/Pest ControlTechnician

A career working with chemi-cals does not always require a

Ph.D. Weed and pest control tech-nicians use chemicals to get rid ofunwanted weeds, insects, and other pests.

Skills for the JobAfter high school, most techni-

cians receive on-the-job training inpest control or take correspondencecourses to earn a degree in thisfield. In many states, you must passa test to become licensed.

As a technician, you may visithomes, office buildings, restaurants, hotels, and otherplaces where insects, animals, or weeds have become aproblem. You will choose the correct chemical and form,such as a spray or gas, to get rid of or prevent infestationsof flies, roaches, termites, or other creatures. You will selectdifferent chemicals to deal with weeds. You might also settraps to catch rats, mice, moles, or other animals.

For more careers in related fields, visit

0 1 2 3 4 5 6 7

NeutralMore acidic

8 9 10

LemonpH 2

TomatopH 4

EggpH 8

AntacidpH 10

MilkpH 6

Chemical reactions in organisms alsodepend on the pH of the environmentwithin the organism. The pH is ameasure of how acidic or basic a solu-tion is. A scale with values rangingfrom below 0 to above 14 is used tomeasure pH. Figure 6.11 shows thepH of some common substances.

Substances with a pH below 7 areacidic. An acid is any substance thatforms hydrogen ions (H�) in water.When hydrogen chloride (HCl) isadded to water, hydrogen ions (H�)and chloride ions (Cl�) are formed.Thus, hydrogen chloride in solutionwith water as a solvent is calledhydrochloric acid. This acidic solu-tion contains an abundance of H�

ions and has a pH below 7. A solutionis neutral if its pH equals 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 formssodium ions (Na�) and hydroxide ions(OH�). This basic solution containsan abundance of OH� ions and has apH above 7.

Figure 6.11Substances commonly found in the house-hold are acids and bases. Lemon andtomato are acidic (pH < 7). Pure water isneutral (pH 7). Ammonia (pH 11) is basic.


ca.bdol.glencoe.com/careers

(top, l to r)Mark Steinmetz, Mark Burnett, J. Sekowski, Mark Burnett, Aaron Haupt, (b)Aaron Haupt

Career PathCourses in high school: chem-istry, mathematics, biology, and

carpentryCollege: a degree in biology for man-agers or supervisorsOther education sources: on-the-jobtraining and correspondence courses

Career IssueAsk students whether weed and pest con-trol technicians should tell their customersabout non-chemical ways to control weedsand insects. Why or why not?

For More InformationFor more about pest control, write to:

National Pest Management Association8100 Oak StreetDunn Loring, VA 22027

Pages 150–151: Inv. & Exp. 1a

http://ca.bdol.glencoe.com/careers

151

3 Assess

1. Electrons move around the nucleus inregions known as energy levels.

2. In their drawings, the nucleus containsseven protons and seven neutrons. Thefirst energy level contains two elec-trons. The next energy level containsfive electrons and could become stableby sharing these other electrons in acovalent bond.

3. Ionic bonds form between ions as oneatom gains electrons and another givesup electrons. Covalent bonds involvethe sharing of electrons between atoms.

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

5. A solution is one type of mixturewhere the solutes are evenly distrib-uted in the solvent, but a mixture does

not have to be a solution. For exam-ple, sand and marbles together are amixture, but not a solution.

6. Sugar molecules separate from thesugar crystal. Sugar molecules (solute)are evenly distributed in the water(solvent), creating a solution.

Understanding Main Ideas1. Describe where the electrons are located in an atom.

2. A nitrogen atom contains seven protons, sevenneutrons, and seven electrons. Make a labeleddrawing of the structure of a nitrogen atom. How can this atom become stable?

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

4. What can you say about the amount of hydrogenions relative to the amount of hydroxide ions in asolution that has a pH of 2?

Thinking Critically5. Are all mixtures solutions? Are all solutions mix-

tures? Give an example.

6. Interpret Scientific Illustrations Figure 6.10shows the process of a compound dissolving inwater. Describe what is happening to the mole-cules. Describe the nature of the mixture afterthe sugar completely dissolves. For more help,refer to Interpret Scientific Illustrations in theSkill Handbook.

SKILL REVIEWSKILL REVIEW


More basic

11 12 13 14

HouseholdammoniapH 11

DraincleanerpH 13

Many of the foods you eat, such asoranges and grapefruits, are acidic.Some plants grow well only in acidicsoil, whereas others require soil that isbasic. Acids and bases are importantto living systems, but strong acids andbases can be dangerous. The MiniLabdescribes how you can investigate sev-eral household solutions to determineif they are acids or bases.

Describe the behav-ior of an acid in water.

ca.bdol.glencoe.com/self_check_quiz

ExperimentDetermine pH The pH of a solution 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 sepa-rate clean, labeled beakers or othersmall glass containers: lemon juice,prepared household ammonia solu-tion, 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 with soap after handling lab materials.

Analysis1. Evaluate Data Which solutions are acids?2. Evaluate Data Which solutions are bases?3. Draw Conclusions What ions in the solution caused the

pH paper to change color? Which solution contained thehighest concentration of hydroxide ions? How do youknow?

Household solutions

(l)Elaine Shay, (c r)Aaron Haupt

Check for UnderstandingVisual-Spatial Give students alist of common elements fromthe first 3 rows of the periodictable. For each element, askstudents to diagram theatom’s structure to show itsprotons, neutrons, and elec-tron energy levels.

ReteachKinesthetic Using gumdropand toothpick models,demonstrate a chemical reac-tion such as CH4 � 2O2 ⇒CO2 � 2H2O. Stress the con-servation of matter as stu-dents tear the original mole-cules apart to build new mol-ecules.

ResourcesFor more practice, useReading Essentials forBiology, Section 6.1.

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ExtensionVisual-Spatial Ask students tomake a display to show the chem-ical formulas of ten common substances.

Skill Give students the followingequations to balance.

N2O4 ⇒ NO2C3H8 � O2 ⇒ CO2 � H2O

Answers:N2O4 ⇒ 2NO2C3H8 � 5O2 ⇒ 3CO2 � 4H2O

When an acidis placed in water, it formshydrogen ions.

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http://ca.bdol.glencoe.com/self_check_quiz

152152


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Unit 3 FAST FILE ResourcesMiniLab Worksheet, p. 4Reinforcement and Study Guide in

English, p. 11Reinforcement and Study Guide in

Spanish, p. 15Concept Mapping, p. 17Transparency Worksheet, p. 20



1 FocusBellringerSection Focus Transparency 13

6.2SECTION PREVIEWObjectivesRelate water’s unique fea-tures to polarity.Identify how the processof diffusion occurs andwhy it is important to cells.

Review Vocabulary homeostasis: regulation of

the internal environmentof a cell or organism tomaintain conditions suit-able for life (p. 9)

New Vocabularypolar moleculehydrogen bonddiffusiondynamic equilibrium


Water—It’s One of a Kind!Finding Main Ideas Most of us take water for granted. Weturn on the kitchen faucet athome to get a drink and expect water to come out of the faucet. We don’t think about how importantwater’s properties are to life.Organize Information Asyou read this section, make a listof the properties of water. Next toeach property, write how it is impor-tant in maintaining homeostasis in living organisms.

Water and Its ImportanceWater is perhaps the most important compound in living organisms.

Most life processes can occur only when molecules and ions are free tomove and collide with one another. This condition exists when they aredissolved in water. Water also serves to transport materials in organisms.For example, blood and plant sap, which are mostly water, transportmaterials in animals and plants. In fact, water makes up 70 to 95 percentof most organisms.

Water is polarSometimes, when atoms form covalent bonds, they do not share the

electrons equally. The water molecule pictured in Figure 6.12A showsthat the shared electrons are attracted by the oxygen nucleus morestrongly than by the hydrogen nuclei. As a result, the electrons spendmore time near the oxygen nucleus than they do near the hydrogen nuclei.

When atoms in a covalent bond do not share the electrons equally, theyform a polar bond. A polar molecule is a molecule with an unequal dis-tribution of charge; that is, each molecule has a positive end and a nega-tive end. As illustrated in Figure 6.12B, water is an example of a polarmolecule. Polar water molecules attract ions as well as other polar mole-cules. Because of this attraction, water can dissolve many ionic com-pounds, such as salt, and many other polar molecules, such as sugar.

Water and Diffusion

Water is vital to the living world.

PhysicalScience

Connection

The structure ofwater moleculesWater is sometimescalled the universalsolvent because ofits ability to dis-solve a wide rangeof materials. Thisability is related tothe polarity of thewater molecule,which is due to its“V” shape as wellas the polarity ofthe hydrogen-oxygen bonds.Water moleculeswould not be polarif they were linear,with hydrogenatoms on oppositesides of the oxygenatom.

Jim Steinberg/Photo Researchers

Standard 1l Students will analyze situations and solve problems that requirecombining and applying concepts for more than one area of science.


Finding Main IdeasOrganize Information Properties of Water1. polar2. resists temperature change3. expands when it freezes

Importance in Homeostasis1. allows tops of plants to get

water from soil 2. helps prevent large tempera-

ture changes in organisms3. bottoms of lakes and ponds

won’t freeze

Have students researchexamples of polar andnonpolar molecules. Then,ask them to sketch themolecules in their sciencenotebooks, illustrating theoverall geometries andcharge distributions of themolecules. Examplesinclude ammonia (polar),sulfur dioxide (polar), car-bon dioxide (nonpolar),and methane (nonpolar).


153

2 Teach

Water molecules also attract otherwater molecules. The positivelycharged hydrogen atoms of one watermolecule 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 biomolecules,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 of polar-ity, play major roles in getting waterfrom the soil to the tops of even thetallest trees.

Water resists temperature changes

Water resists changes in tempera-ture. Therefore, water requires moreheat to increase its temperature thando most other common liquids.Likewise, water loses a lot of heat

when it cools. In fact, water is like aninsulator that helps maintain a steadyenvironment when conditions fluctu-ate. Because cells exist in an aqueousenvironment, this property of wateris extremely important to cellularfunctions as it helps cells maintainhomeostasis.

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 so it floats as it forms in abody of water. Use the Problem-Solving Lab on the next page to inves-tigate this property. Water expands asit freezes inside the cracks of rocks. Asit expands, it often breaks apart therocks. Over long time periods, thisprocess helps form soil.

The properties of water make it anexcellent vehicle for carrying sub-stances in living systems. One way tomove substances is by diffusion.

Infer why coastalcommunities usually experiencemilder temperatures than cities that are not located near large bodies of water.

6.2 WATER AND DIFFUSION 153

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Hydrogen atom

Oxygen atomHydrogen atom

In a covalent bondbetween hydrogenand oxygen, theelectrons spendmore time near theoxygen nucleus thannear the hydrogennucleus.

A

Because oxygen tends to attractthe shared electrons more stronglythan hydrogen does, the protrud-ing oxygen end of a water mole-cule has a slight negative charge,and the ends with protrudinghydrogen atoms have a slightpositive charge.

B

Figure 6.12Electrons are notshared equally in awater molecule.

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Negativelycharged end

Positivelycharged end

PhysicalScience

Connection

Density ofliquids Water ismost dense atabout 4ºC. Whenthe surface of alake cools to 4ºC,the surface watersinks and warmerwater takes itsplace. This processcontinues until allthe water hascooled to 4ºC. Onlythen can thesurface startfreezing if it iscooled further.Even if the surfaceis frozen and airtemperatures arewell belowfreezing, thewater near thebottom of the lakeis at 4ºC—warmenough for aquaticlife to survive.

Capillary Action Ask stu-dents to explain the watermovement as you dip theedge of a paper towel in abowl of water.

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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 thewarmer layers of water beneaththis layer. As the surface of thelake is sealed by ice, the tem-perature of the water becomesimportant to the ability of thewater to provide enough oxy-gen to the aquatic organismsduring winter.

English Language Learners: Visual-Spatial Have students cut out picturesfrom magazines that illustrate uses ofwater. Ask them to prepare a displayof their pictures. Students may wantto include industrial uses of water,uses of water by organisms, or envi-ronmental uses of water.

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Have students find thedensity of water at 1°Cincrements for the tem-perature range 0°C to 10°C, and then describeany patterns in these data.The densities of waterincrease from 0°C (ice) toabout 4°C, and thendecrease from 4°C to 10°C.


Because water resistschanges in temperature, areasaround large bodies of water usu-ally will also have milder tempera-tures when compared to townsthat are farther away from thewater.

154

Purpose Students will calculate the densitiesfor water and ice and will correlatethis information with the fact thatwater expands 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 is thesame as cubic centimeters or cc.

■ Review the procedure forarriving at the proper units toexpress density.

Thinking Critically1. The density of water is 1 g/cm3;

density of ice is 0.9 g/cm3. Iceis less compact; mass in exam-ple is the same, but volumefor ice is greater. A lowerdensity indicates a greatervolume with the same massas water.

2. farther apart; This patternaccounts for increased volume.

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.

Modified AssessmentKnowledge Have students makea list of materials that they thinkwill float in water (are less densethan water). Students can test thesematerials to see if their predictionsare accurate. Use the PerformanceTask Assessment List forDesigning an Experiment inPASC, p. 95. L1

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Figure 6.13Like these table tennis balls, atoms and molecules havekinetic energy, the energy of motion. Describe Whathappens when two balls collide?

DiffusionAll objects in motion have energy of

motion called kinetic energy. A mov-ing particle of matter moves in astraight line until it collides withanother particle, much like the tabletennis balls shown in Figure 6.13.After the collision, both particlesrebound. Particles of matter, like thetable tennis 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 being struckby invisible objects. This motion, hethought, was the result of a life forcehidden within the pollen grains.However, when he repeated his exper-iment using dye particles, which arenonliving, he saw the same motion.This motion is now called Brownianmotion. Brown had no explanation forthe motion, but today we know thatBrown was observing evidence of therandom motion of atoms and mole-cules. The random movement thatBrown observed is characteristic ofgases, liquids, and some solids.

Use NumbersWhy does ice float? Mostliquids contract when fro-zen. Water is different; itexpands. The density ofwater changes when iceforms, allowing ice to float.Density refers to compact-ness and is often describedas the mass of a substanceper unit of volume. A math-ematical expression of den-sity would read as follows:

Solve the ProblemExamine the following table. It shows the volume and mass for a sample of water and ice.

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

density of water? Use specific values and proper unitsexpressing density in your answer. Which of the two, ice or water, is less compact? Explain your answer.

2. Think Critically Are the molecules of water moving closer together or farther apart as water freezes? Explain.

3. Infer Explain why a glass bottle filled with water mightshatter if placed in a freezer.

4. Recognize Cause and Effect Explain why ice formingwithin a living organism may result in its death.

Density � MassVolume

Data Table

Source of Sample Volume (cm3) Mass (g)

Water 126 126

Ice 140 126

(t)Matt Meadows, (b)Aaron Haupt

Caption Question AnswerFigure 6.13 When two balls col-lide, they bounce back from eachother in different directions.

InquiryActivity Have students mix a variety ofliquids with a polar liquid like water andobserve what happens. Allow students tochoose the liquids for their explorations.Have them make predictions before test-ing the liquids. (Food coloring can helpdistinguish clear liquids.) What do stu-dents observe? What questions do theyhave about polarity and liquids? L1

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Purpose Students will determine the rateof diffusion of a solution.

Process Skillsmeasure in SI, collect and organ-ize data, interpret data, experi-ment, and analyze

Teaching Strategies■ Prepare a dark purple dye solu-

tion by using food coloring, dyetablets, or highly-concentratedpowdered drink mix.

■ Caution students that the solu-tion can stain. To keep thesolution off their hands, stu-dents should set the cube onwaxed paper or foil when theyremove it from the solutionand hold the cube with the for-ceps as it is cut. Also remindstudents to cut away from theirbodies.

Expected ResultsThe color will diffuse only a fewmillimeters into the cube, the exactdistance depending upon theamount of time it is in the solution.

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.

AssessmentPortfolio Have students write areport of the MiniLab for theirportfolios. Use the PerformanceTask Assessment List for LabReport in PASC, p. 119. L2

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6.2 WATER AND DIFFUSION 155

The process of diffusionParticles 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 that the colored corn syruphas mixed with the pure corn syrup.This mixture is the result of the ran-dom movement of corn syrup andwater molecules. Diffusion is the netmovement of particles from an areaof higher concentration to an area of lower concentration. Diffusionresults because of the random move-ment of particles (Brownian motion).

Diffusion is a slow process becauseit relies on the random motion ofatoms and molecules. You will seeevidence that the corn syrup inFigure 6.14 has begun to diffusewithin hours but it will take monthsto mix completely if undisturbed.

Three key factors—concentration,temperature, and pressure—affect the rate of diffusion. The concentra-tion of the substances involved is the primary controlling factor. The more concentrated the sub-stances, the more rapidly diffusionoccurs because there are more collisions between the particles ofthe substances. Two external fac-tors—temperature and pressure—canchange the rate of diffusion. Anincrease in temperature increasesenergy and will cause more rapidparticle motion. This will increasethe rate of diffusion. Similarly, in-creasing pressure will accelerate particle motion and, therefore, diffu-sion. With common materials, youcan use the MiniLab shown here tolearn more about diffusion in a cell.

Explain why diffu-sion is a slow process.

Figure 6.14The random movementof molecules of cornsyrup and water willcause the uncoloredsample to diffuse intothe colored sample.

Apply ConceptsInvestigate the Rate of Diffusion In thislab, you will place asmall potato cube in asolution of purple dyeand observe how farthe dark purple colordiffuses into thepotato after a givenlength 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.

@ Use forceps to carefully place the cube in a cup or beakercontaining the purple solution. The solution should coverthe cube. Note and record the time. Let the cube stand inthe solution for between 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 hasdiffused, and divide this number by the number of min-utes you allowed your potato to remain in the solution.This is the diffusion rate.

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

Aaron Haupt

Diffusion is aslow process because it relieson the random movement ofatoms and molecules.

Research Bacteria: IntrapersonalSome bacteria can live on snow. Askstudents to research how these bac-teria keep from freezing. L3

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ExtensionIntrapersonal Have students re-search how rapidly molecules canactually move over a particulardistance.

Knowledge Have students listthe properties of water and givean example of how each propertyis useful in a living organism. L2

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1. The oxygen and two hydrogens do notshare the electrons equally (electronsare more strongly attracted to the oxy-gen). As a result, the oxygen is nega-tively charged and the hydrogens arepositively charged.

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

3. capillary action4. The particles will move from areas of

high concentration to low concentra-tion until they reach dynamic equilib-rium. After this point, there is no fur-ther concentration change.

5. An increase in temperature causes anincrease in kinetic energy which, inturn, increases the rate of diffusion ofthe substance into the cell.

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

156


The results of diffusionAs the pure corn syrup continues

to diffuse into the colored cornsyrup, the two will become evenlydistributed eventually. After thispoint, the molecules continue tomove randomly and collide with oneanother; however, no further changein concentration will occur. This

condition, 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 solute are dis-tributed evenly among water mole-cules, as in the powdered drink mix and water example. The differ-ence in concentration of a substanceacross space is called a concentrationgradient. Because ions and mole-cules diffuse from an area of higherconcentration to an area of lowerconcentration, they are said to movewith the gradient. If no other pro-cesses interfere, diffusion will con-tinue until there is no longer aconcentration gradient. At this point,dynamic equilibrium occurs. Diffu-sion is one of the methods by whichcells move substances in and out ofthe 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.

Material moving outof cell equals materialmoving into cell

Figure 6.15When a cell is in dynamic equilibrium with itsenvironment, materials move into and out ofthe cell at equal rates. As a result, there is nonet change in concentration inside or outsidethe cell.


Understanding 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 the cellular process

of diffusion? Describe concentration prior to andat this point.

Thinking Critically5. If a substance is known to enter a cell by diffu-

sion, what effect would raising the temperaturehave on the cell? Why does it have this effect?

6. Get the Big Picture Explain why water dissolvesso many different substances. For more help, referto Get the Big Picture in the Skill Handbook.


Check for UnderstandingQuiz students orally aboutthe importance of water toliving organisms and test theirunderstanding of each of theproperties of water.

ReteachVisual-Spatial In a clear con-tainer with a lid, place 10–15marbles of one color. On topof those marbles, place anequal number of differentcolored marbles. Ask studentsto predict what will occur ifyou shake the container con-tinuously. Like diffusion, themarbles will eventually dis-perse among each other,reaching an equilibrium ofmixed color.


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157


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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Transparency Elements in DifferentCombinations14

Unit 3 FAST FILE ResourcesReal World BioApplications, pp. 7–8Reinforcement and Study Guide in

English, p. 12Reinforcement and Study Guide in

Spanish, p. 16Critical Thinking/Problem Solving, p. 18Transparency Worksheets, pp. 21, 29–30


Laboratory Manual, pp. 27–34Section Focus Transparency 14

Reteaching Skills Transparency 8

1 FocusBellringerSection Focus Transparency 14

Double Bond Triple Bond

Life Substances6.3

Figure 6.16When two carbon atomsform a covalent bond,they can share one, two,or three electrons each.

Single Bond

SECTION PREVIEWObjectivesClassify the variety oforganic compounds.Describe how polymers areformed and broken down inorganisms.Compare the chemicalstructures of carbohydrates,lipids, proteins, and nucleicacids, and relate theirimportance to living things.Identify the effects ofenzymes.

Review Vocabulary organism: anything that

possesses all the charac-teristics of life (p. 6)

New Vocabularyisomerpolymercarbohydratelipidproteinamino acidpeptide bondenzymenucleic acidnucleotide

6.3 LIFE SUBSTANCES 157

The Role of Carbon in OrganismsA carbon atom has four electrons available for bonding in its outer

energy level. In order to become stable, a carbon atom forms four cova-lent bonds that fill its outer energy level. Look at the model showing car-bon atoms and bond types in Figure 6.16. Carbon can bond with othercarbon atoms, as well as with many other elements. When each atomshares two electrons, a double bond is formed. A double bond is repre-sented by two bars between carbon atoms. When each atom shares threeelectrons, a triple bond is formed. Triple bonds are represented by threebars between carbon atoms.

Carbohydrates Lipids

Proteins NucleicAcids

Classify As you read Section 6.3, draw the structure and list the characteristics of carbohydrates, lipids, proteins, and nucleic acids under the appropriate tab.

Biomolecules Make the following Foldable to help you compare the structures and functions of four types of organic compounds called biomolecules.

Label each tab.

Draw a mark at the midpoint of a sheet of paper along the side edge. Then fold the top and bottom edges in to touch the midpoint.

Fold in half from side to side.

Open and cut along the inside fold lines to form four tabs.

STEP 1

STEP 3

STEP 2

STEP 4

Standard 1h Students know most macromolecules (polysaccharides,nucleic acids, proteins, lipids) in cells and organisms are synthesized from a small collectionof simple precursors.


FOLDABLES™For an additional Foldablesactivity idea, see the Chapter 6Foldables page in Unit 3 FAST

FILE Resources.

158

Have students search for anddefine other words with theroot “poly” as a part of theword, such as polygon, poly-dactyl, polypeptide, and polygraph.

PortfolioExploring Nutrients Have groupsof students present research onone of the following: sugars andother sweeteners in processedfoods; cholesterol, saturated fatsand unsaturated fats in the diet;the functions of proteins such askeratin, actin, collagen, andinsulin. Encourage creativity inpresentations. For example, stu-dents might enact a skit they havescripted in their portfolio.

Caption Question AnswerFigure 6.17 Water is the addi-tional product.

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When carbon atoms bond to eachother, they can form straight chains,branched chains, or rings. Thesechains and rings can have almost anynumber of carbon atoms and caninclude atoms of other elements aswell. This ability to bond in so manyways makes a huge number of carbonstructures possible. In addition,compounds with the same chemicalformula often differ in structure.Compounds that have the samechemical formula but different three-dimensional structures are called isomers (I suh murz). The glucoseand fructose molecules shown in Figure 6.17 have the same formula,C6H12O6, but different structures.

Molecular chainsCarbon compounds vary greatly

in size. Some compounds containjust one or two carbon atoms,whereas others contain tens, hun-dreds, or even thousands of carbonatoms. These large organic com-pounds are called biomolecules.Proteins are examples of biomole-cules that are found in organisms.Cells build biomolecules by bondingsmall molecules together to form

chains called polymers. A polymeris a large molecule formed whenmany smaller molecules bondtogether.

Many polymers are formed by achemical reaction known as condensa-tion. In condensation, the small mole-cules that are bonded together tomake a polymer have an –H and an–OH group that can be removed toform H–O–H, a water molecule. Thesubunits become bonded by a covalentbond, as shown in Figure 6.18. Thesepolymers can be broken apart byhydrolysis. Hydrogen and hydroxylgroups from water attach to the bondsbetween the subunits that make up thepolymer, thus breaking the polymer asshown in Figure 6.18.

The structure of carbohydratesYou may have heard of runners eat-

ing large quantities of spaghetti orbread the day before a race. Thispractice is called “carbohydrate load-ing.” It works because carbohydratesare used by cells to provide energy. A carbohydrate is a biomoleculecomposed of carbon, hydrogen, and oxygen with a ratio of about twohydrogen atoms and one oxygen atomfor every carbon atom.


polymer from theGreek words poly,meaning “many,”and meros, mean-ing “part”; A poly-mer has manybonded subunits(parts).hydrolysis fromthe Greek wordshydro, meaning“water,” and lysis,meaning “to splitor loosen”; Inhydrolysis, mole-cules are split bywater.

Figure 6.17The different arrange-ment of hydrogen (–H)and hydroxide (–OH)groups around eachcarbon atom gives glu-cose and fructose mole-cules different chemicalproperties. When glu-cose and fructose com-bine, they form thedisaccharide sucrose,also known as tablesugar. Use ModelsWhat other productis formed in this reaction?

OH

OH

CH2OH CH2OH

Glucose

O

HOOH

OH

O HHOCH2

Fructose

Sucrose

O

HO

+

OH

O H2O

CH2OH

O

HOOH

OH

CH2OH

HOCH2O

HO

+

Hearing Impaired: InterpersonalMake cards with pictures of foodsthat are associated with carbohy-drates, lipids, and proteins. On eachcard ask what organic compound ispredominant or what monomers areinvolved. Have students work ingroups to answer the questions.

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CD-ROM Students will determinethe effects of substrate concentra-tions and pH in Enzyme-ControlledReactions.

159

The simplest type of carbohydrateis a simple sugar called a monosac-charide (mah noh SA kuh ride).Common examples are the isomersglucose and fructose. Two monosac-charide molecules can combine toform a disaccharide, a two-sugar car-bohydrate. When glucose and fruc-tose link together 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 branched chains of glu-cose units and is used as energy stor-age by plant cells and as foodreservoirs in seeds and bulbs.Mammals store energy in the liver inthe form of glycogen, a highlybranched glucose polymer. Celluloseis another glucose polymer thatforms the cell walls of plants andgives plants structural support.Cellulose is made of long chains of glucose units linked together in arrangements somewhat like achain-link fence.

H

OH H

OH

HOH

H2O

H OH

OH

H

H2O

Condensation

Subunits

HydrolysisPolymer

Figure 6.18Many polymers are formed by condensation andcan be broken by hydrolysis, the reactions thatoccur when water is added to or removed from a polymer.

Figure 6.19Look at the structural differences among the polysaccharides starch,glycogen, and cellulose. Notice that all three are polymers of glucose.Compare and Contrast What are some similarities and differencesbetween these polysaccharides?

Potato

Liver

Cotton


Glucosesubunits

Glucosesubunits

Glucosesubunits

Crosslinkbonds

(t c)Aaron Haupt, (b)C. Allan Morgan/Peter Arnold, Inc.

Starch

Glycogen

Cellulose

Carbon Bonds Use a ball-and-stick model of amethane molecule (CH4) toshow students the regulartetrahedron arrangementformed by the bonds of car-bon atoms. Contrast thearrangement of the atomsin the methane molecule tothose in a molecule ofwater.

Caption Question AnswerFigure 6.19 starch—made ofbranched chains of glucose,used by plants for energy stor-age; glycogen––highly branchedchains of glucose, used by ani-mals for energy storage; cellu-lose––long chains of glucoselinked together like a chain-linkfence, used for structural sup-port in plants

EnrichmentIntrapersonal Have students re-search the differences in thestructures of starch, glycogen, andcellulose to determine how therecan be more than one polymer ofglucose. L3

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Planning a Healthy Menu: Logical-Mathematical Have students make aweekly meal plan that contains low lev-els of lipids. Challenge them to calcu-late totals of saturated and unsaturat-ed fats by carefully reading the nutri-tional labels provided on packaged

foods. A healthy diet should get nomore than 30% of calories from fat. Nomore than 10% of those fat caloriesshould be from saturated fats. SeeBioChallenges and Enrichment for addi-tional activities.

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What fruits contain enzymesthat act on protein?

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

Safety Precautions Use caution with the knife.

PreparationOne pineapple should be enough for 20students in groups of four. A 6-ounce boxof gelatin makes enough for 2 groups.Make gelatin; pour 100 mL into each cup.Use hot/cold cups that can hold 200 mL.

Materials paper cups (4) with gelatin, fresh pineapple,knife, waxed paper, canned chunk pineap-ple, grapes or orange sections, refrigerator

Procedure 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

The structure of lipidsLipids are large biomolecules that

are made mostly of carbon andhydrogen with a small amount ofoxygen. Fats, oils, waxes, and steroidsare all lipids. They are insoluble inwater because their molecules arenonpolar and are not attracted bywater molecules.

A common type of lipid, shown in Figure 6.20, consists of threefatty acids linked with a molecule of glycerol. A fatty acid is a longchain of carbon and hydrogen. Ifeach carbon in the chain is bondedto other carbons by single bonds,the fatty acid is said to be saturated.If a double bond is present in thechain, the fatty acid is unsaturated.

Fatty acids with more than onedouble bond are polyunsaturated.

Lipids are very important for theproper functioning of organisms. Cellsuse lipids for energy storage, insula-tion, and protective coverings. In fact,lipids are the major components of themembranes that surround all livingcells. To learn more about lipids in your body, read the Biotechnologyfeature at the end of this chapter.

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 polymercomposed of carbon, hydrogen, oxy-gen, nitrogen, and sometimes sulfur.

Figure 6.20Glycerol is a three-carbon molecule thatserves as a backbonefor a lipid molecule.Attached to the glyc-erol are three fattyacid groups.


CH2 O

O

CH2C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3CH CH

CH2 CH2O

O

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

CH O

O

CH2 CH2CH2C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

Glycerol

Unsaturated fatty acid group

Polyunsaturated fatty acid group

Saturated fatty acid group

Double bond

Double bonds

The carbon atoms in saturatedfatty acid groups, like thosefound in some meat and dairyproducts, cannot bond with anymore hydrogen atoms.

A

The carbon atoms in unsaturatedand polyunsaturated fatty acidgroups can bond with morehydrogen atoms when thedouble bonds are broken. Thesetypes of lipids can be found insome vegetable oils.

B

Meat

Butter

Peanut butter

(tl b)Aaron Haupt, (tr)Elaine Shay

Students sometimes think ofmolecules as structures thatare flat and two-dimensional.

Uncover theMisconceptionBecause students often lookat flat, two-dimensional struc-tures in textbooks, they maynot envision molecules in theirthree-dimensional structure.

Demonstrate theConceptShow structural models ofmolecules so students canobserve the three-dimensionalappearance of molecules. Ifyou don’t have these avail-able, you may be able to bor-row them from a collegechemistry department ormake a model of a simplemolecule using colored poly-styrene balls to representatoms and toothpicks to rep-resent bonds holding theatoms together.

Assess NewKnowledge Give students toothpicks andpolystyrene balls (or coloredmarshmallows) and ask themto make a three-dimensionalmodel of a simple compoundsuch as carbon dioxide.

Pages 160–161: Biology/Life Sciences 1a, 1b, 1h, 4e,4f*, 5a

Using an AnalogyTo increase understanding of howfewer than 25 amino acids can cre-ate such a variety of proteins, relatethe naturally occurring amino acidsto the letters of the alphabet. Elicitfrom students why the letters of thealphabet can be used to create sucha large number of words. Relatethis phenomenon to how a similarnumber of amino acids can createso many different proteins.

The BioLab atthe end of thechapter can beused at thispoint in the lesson.

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 unsaturated fats?Saturated fats have singlebonds; unsaturated fats havedouble bonds.

EnrichmentAmino Acids There is evidencethat there are additional aminoacids, like pyrrolysine and seleno-cysteine, that help build proteins.Have students research the dis-covery of these amino acids andhow they work. L3

P3 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 gelatinwith fresh pineapple remained liquefied.

Analysis1. What was the purpose of cup 1? control2. Gelatin is a protein. Bromelin is a pro-

tein-digesting enzyme. What happenedto the bromelin in the canned pineap-ple? It was destroyed by heat during thecanning process.

AssessmentKnowledge Ask students this question:“Based on this activity, what can you con-clude about which fruits have enzymesthat act on protein?” Use the PerformanceTask Assessment List for Analyzing theData in PASC, p. 99. L2

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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

Figure 6.22Proteins, such as thosefound in hair, finger-nails, horns, and hoofs,make up much of thestructure of organisms.

AA BB

Figure 6.21(A) Each amino acid contains a central carbon atom to which are attached a carboxyl group(–COOH), a hydrogen atom, an amino group (–NH2), and a variable group (–R) that makeseach amino acid different. (B) Amino acids are linked together by peptide bonds.

The basic building blocks of proteinsare called amino acids, shown inFigure 6.21A. There are about 20common amino acids. These buildingblocks, in various combinations, makeliterally thousands of proteins.

Amino acids are linked togetherwhen an –H from the amino group ofone amino acid and an –OH groupfrom the carboxyl group of 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.

Proteins come in a large variety ofshapes and sizes. The number andsequence of amino acids that make upa protein are important in determin-ing its shape. Certain amino acids areacidic, some are basic, and some arenot charged. These properties causethe amino acids to attract or repeleach other in different ways. Theamino acid chain that makes up theprotein twists and turns as the aminoacids interact. Many proteins consistof two or more amino acid chains that are held together by hydrogenbonds. The ultimate three-dimensionalshape that the protein folds into isextremely important to the function-ing of the protein. If the sequence ofamino acids in the protein were tochange, the protein might fold differ-ently and not be able to carry out itsfunction in the cell.

Proteins are the building blocks ofmany structural components of organ-isms, as illustrated in Figure 6.22.Proteins are also important in the con-tracting of muscle tissue, transportingoxygen in the bloodstream, providingimmunity, regulating other proteins,and carrying out chemical reactions.

Enzymes are important proteinsfound in living things. An enzyme isa protein that changes the rate of achemical reaction. In some cases,enzymes increase the speed of reac-tions that would otherwise occurslowly.

Enzymes are involved in nearly allmetabolic processes. They speed the reactions in digestion of food.The activities of enzymes depend onthe temperature, ionic conditions,and the pH of the surroundings.

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Enzymes acton specific sub-strates, such assucrose, adisaccharidemade up ofglucose andfructose bondedtogether.

A

+H2OGlucose Fructose

Substrate (sucrose)

Active sites

Active sites

Enzyme

Enzyme

Products

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

C

Action of EnzymesFigure 6.23An enzyme enables molecules, called substrates, toundergo a chemical change to form new substances,called products. The enzyme has an area called an activesite on its surface that fits the shape of the substrate.When the substrate binds to the active site, the enzymealters its shape slightly as shown below. Enzymes changethe rate of a reaction but they do not change theamount of end product. Critical Thinking Carefully eval-uate this model. What is another way that enzymeactivity could be represented?

Substrate

Activesite

Lysozyme action

Each substrate fits into theactive site. This fitting togetheris often compared to a lock-and-key mechanism. However,

the enzyme changes shape a little to fit with the

substrate. The enzyme-substrate complex putsstress on the substratedue to the binding ofthe substrate to theenzyme.

B

After the reaction, the enzyme releasedis in its original shape and can go on to carryout the same reaction again and again. Indoing so, enzymes change the speed atwhich chemical reactions occur withoutbeing altered themselves by the reaction.

D

The shape of a pro-tein is determined by the numberand sequence of amino acids andwhether the protein is made of oneor more chains of amino acids. Theinteractions between the aminoacids fold the protein into its finalthree-dimensional shape.

PurposeStudents will study the wayenzymes function in a reaction.

Teaching StrategyAsk students to make an analogy ofa lock and key to show howenzymes function. Students shouldalso describe where the analogyfails. Even though the lock and keyfit together specifically, the lockdoes not change shape when thekey fits in the keyhole.

Visual LearningReinforce the idea that an enzymecan be used repeatedly withoutbeing changed. Use clay for theenzyme and plastic buildingblocks that can snap together asthe substrate. Demonstrate eachstep of Figure 6.23 using thesematerials. If materials allow, havestudents work with you. At theend of the reaction, the clay can bereturned to its original shape, likean enzyme would.

Critical ThinkingEncourage students to describeenzyme activity in their ownwords. Discuss the strengths andweaknesses of the model asillustrated in the text. Challengestudents to formulate their ownenzyme action model to sharewith the class.

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1. long-term energy storage, insulation,protective coatings

2. In condensation, one monomer losesan H� ion and another loses an OH� toform water. A covalent bond formsbetween the monomers.

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

4. Like other nucleic acids, DNA is com-posed of smaller nucleotides consist-ing of a phosphate group, a simplesugar, and a nitrogenous base.

5. 1. Enzymes; 2. protein; 3. nucleic acids;4. nucleotides

6. The chemical reaction would not pro-ceed at the same rate.

7. Carbohydrates Energy storage Starch, glycogen,Monosaccharides Structural components cellulose

Lipids Energy storage Animal fats, Glycerol vegetable oilsFatty acids

Proteins Structure Muscle proteins, Amino acids Enzymes immunity,

and enzymesNucleic acids Store information DNA & RNANucleotides in cells

Check for UnderstandingVisual-Spatial Prepare ahandout showing structuralformulas for lipids, proteins,carbohydrates, and nucleicacids. Ask students to identifythe type of biomoleculeshown in each diagram.

ReteachThe concept of large poly-mers being composed ofrepeating units of monomerscan be reinforced by havingstudents list items that arecomposed of smaller units,such as beads making up anecklace, chain links, jigsawpuzzle pieces, or letters mak-ing up words.


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3 Assess

ExtensionLinguistic Encourage above-levelstudents to read The Double Helix byJames Watson (Atheneum, 1968),which tells the story of the discov-ery of the DNA structure.

Knowledge Use flash cards con-taining the names of monomerson one side and the correspon-ding polymer on the other side.First, show students the polymername (e.g., protein) and then havethem respond with the appropri-ate monomer name (amino acid),and vice versa.

P

ELLL1

P

AssessmentAssessmentMODIFIED

L3

P

How do enzymes act like a lock and keyto facilitate chemical reactions within acell? Examine Figure 6.23 to find out.The BioLab at the end of this chapteralso experiments with enzymes.

Identify what deter-mines the shape of a protein.

The structure of nucleic acidsNucleic acids are another important

type of organic compound that is nec-essary for life. A nucleic (noo KLAY ihk)acid is a complex biomolecule thatstores cellular information in the formof a code. Nucleic acids are polymersmade of smaller subunits callednucleotides.

Nucleotides consist of carbon,hydrogen, oxygen, nitrogen, andphosphorus atoms arranged in threegroups—a nitrogenous base, a sim-ple sugar, and a phosphate group—as shown in Figure 6.24. You haveprobably heard of the nucleic acidDNA, which stands for deoxyri-bonucleic acid. DNA is the mastercopy of an organism’s informationcode. The information coded inDNA contains the instructions used

to form all of an organism’s enzymesand structural proteins. Thus, DNAforms the genetic code that deter-mines how an organism looks andacts. DNA’s instructions are passedon every time a cell divides and fromone generation of an organism tothe next.

Another important nucleic acid isRNA, which stands for ribonucleicacid. RNA is a nucleic acid thatforms a copy of DNA for use inmaking proteins. The chemical dif-ferences between RNA and DNAare minor but important. A laterchapter discusses how DNA andRNA work together to produce proteins.

Understanding Main Ideas1. List three important functions of lipids in living

organisms.

2. Describe the process by which many polymers inliving things are formed fromsmaller molecules.

3. How does a monosaccharide differfrom a disaccharide?

4. Describe the basic components ofDNA (deoxyribonucleic acid).

5. Complete the concept map byusing the following vocabularyterms: nucleotides, protein,enzymes, nucleic acids.

Thinking Critically6. Enzymes are proteins that facilitate chemical reac-

tions. Based on your knowledge of enzymes, whatmight the result be if one particular enzyme mal-functioned or was not present?

7. Make and Use Tables Make a table comparingpolysaccharides, lipids, proteins, and nucleic acids.List these four types of biomolecules in the firstcolumn. In the second column, list the subunitsthat make up each substance. In the third column,describe the functions of each of these organiccompounds in living organisms. In the last column,provide some examples of each from the chapter.For more help, refer to Make and Use Tables inthe Skill Handbook.



P

O

OHO

HO

OCH2

OH OH

NH2O N

NPhosphate

Sugar Nitrogenousbase

made of

breakdown

to form

1.

2.

3.

4.


Figure 6.24Each nucleic acid isbuilt of subunits callednucleotides that areformed from a sugarmolecule bonded to aphosphate group and a nitrogenous base.


Before YouBegin

The compound hydrogenperoxide, H2O2, is a by-product of metabolic reac-tions in most living things.However, hydrogen perox-ide is damaging to delicatemolecules inside cells. As a result, nearly all organ-isms, such as potatoes, contain the enzyme perox-idase, which speeds up thebreakdown of H2O2 intowater and gaseous oxygen.You will detect this reac-tion by observing the oxy-gen bubbles generated.

Does temperature affectan enzyme reaction?

ProblemDoes the enzyme peroxidase work in cold temperatures?Does peroxidase work better at higher temperatures? Doesperoxidase work after being frozen or boiled?

HypothesesMake a hypothesis regarding how you think temperaturewill affect the rate at which the enzyme peroxidase breaksdown hydrogen peroxide. Consider both low and high temperatures.

ObjectivesIn this BioLab, you will:� Investigate the activity of an enzyme.� Compare the activity of the enzyme at various

temperatures.

Possible Materialsclock or timer ice400-mL beaker hot platekitchen knife non-mercury thermometertongs or large forceps or temperature probe5-mm thick potato slices 3% hydrogen peroxide

Safety PrecautionsCAUTION: Be sure to wash your hands with soap before andafter handling the lab materials. Always wear goggles in thelab. Use only GFCI protected circuits for electrical devices.

Skill HandbookIf you need help with this lab, refer to the Skill Handbook.

1. Decide on a way to test your group’s hypothesis. Chooseyour materials from those available.

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

PLAN THE EXPERIMENTPLAN THE EXPERIMENT

PREPARATIONPREPARATION

Matt Meadows

164

PROCEDUREPROCEDURE

Teaching Strategies� Discuss the factors that might affect

the rate of a reaction controlled by anenzyme.

� Students who cool the potato to lowtemperatures should be sure to run thetest while the potato is still cool.

� Allow groups to discuss how their re-sults differed when different experi-mental procedures were used.

Possible Procedures� Students may place a piece of potato

on ice for 5 minutes, boil a secondpiece for 5 minutes, and allow a thirdpiece of potato to sit at room tempera-ture for 5 minutes. Each potato willthen be tested for enzyme activity.

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.Use hot plates with even surfacesso hot liquids cannot easily tipover.

Obtain potatoes, knives, hydro-gen peroxide, and waxed paper.

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, thespeed at which the enzyme willwork will increase.

PREPARATIONPREPARATION

Refer to the Texas SafetyStandards for safety practices inthe lab and field.

Pages 164–165: Biology/Life Sciences 1b Inv. & Exp. 1a, 1c, 1d

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE


1. Identify Effects Describe your observations of the effects of peroxidase on hydrogen peroxide.

2. Check Your Hypothesis Do your data sup-port or reject your hypothesis? Explain.

3. Analyze Data At what temperature did per-oxidase work best?

4. Recognize Cause and Effect If you’ve everused hydrogen peroxide as an antiseptic totreat a cut or scrape, you know that it foamsas soon as it touches an open wound. Howcan you account for this observation?

5. What factors did you needto control in your tests? What might havecaused errors in your results?

ERROR ANALYSIS

Change Variables To carry this experimentfurther, you may wish to use hydrogen per-oxide to test for the presence of peroxidasein other materials, such as cut pieces of dif-ferent vegetables. Also, test raw beef anddiced bits of raw liver.

Web Links To find out more about enzymes, visitca.bdol.glencoe.com/enzymes

3. To test for peroxidase activity, add 1 drop of hydrogenperoxide to the potato slice and observe what happens.CAUTION: Hydrogen peroxide is a skin and eye irritant.

4. When heating a thin potato slice, first place it in asmall amount of water in a beaker. Then heat thebeaker slowly so that the temperature of the water andthe temperature of the slice are always the same. Try to make observations at several temperatures between10°C and 100°C.

Check the PlanDiscuss the following points with other groups to decide on the final 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 temperatures? 5. Make sure your teacher approves your experimental

plan before you proceed further.6. Carry out your experiment. CAUTION: Be careful with

chemicals and heat. Do not heat hydrogen peroxide.7. Clean all equipment as

instructed by your teacher and return everything to itsproper place. Wash your hands thoroughly.

CLEANUP AND DISPOSAL

Matt Meadows

1. Students should describe the number of bubbles pro-duced and their approximate duration.

2. Students should explainwhether their data supportor reject their hypotheses.

3. between 20°C–50°C4. Human tissue contains per-

oxidase, so the hydrogenperoxide is broken down andreleases oxygen.

5. Factors tocontrol may include theamount of time that eachpotato was exposed to thetemperature, the sizes of thepotato slices, and theamount of peroxide added.Answers for errors in resultsmay include incompleteheating of the potato beforetesting.

AssessmentPortfolio In their portfolios,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. 103. L2

P

ERROR ANALYSIS

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

165

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

Students should carefully clean and putaway all equipment. Make sure students

wash their hands thoroughly with soap ordetergent after handling hydrogen peroxideand cleaning up. Peroxide of 3% concentra-tion or less can be poured down the drain.

CLEANUP AND DISPOSAL

Change Variables Ask stu-dents why vegetables areboiled for a short timebefore freezing. One reasonis that boiling inactivatesenzymes that begin tobreak down the other mol-ecules in the vegetables.

http://ca.bdol.glencoe.com/enzymes

166

Purpose Students learn about two classesof lipoproteins and how they aremeasured.

BackgroundCholesterol is transported throughthe body by large molecules calledlipoproteins. Technology used toseparate lipoprotein classes is basedon specific physical properties ofmatter. Centrifugation is based ondensity, while electrophoresis isbased on electrical charge.

Teaching Strategies� Help students understand that

blood is a mixture. It serves asthe body’s transport mecha-nism, and a variety of sub-stances needed or discarded bythe body must be dissolved init. Have students brainstorm alist of substances that are car-ried by blood.

� Explain that technology is usedto separate substances based onspecific physical and chemicalproperties. Give examples ofmixtures that must be separatedby scientists and engineers, andhave students hypothesize possi-ble methods used to separatethem. (Examples: petroleumproducts spilled into water,gasoline from undergroundstorage tanks dissolved into soil.)

The technologies described in this arti-cle are used by biologists to examinesubstances other than lipoproteins.Research centrifugation and elec-trophoresis to determine other uses ofthese technologies by biologists.

A small amount of materialis placed in a test tube, theninserted into a centrifuge.The centrifuge spins the testtube rapidly, forcing theparts of the mixture to sepa-rate by density, like the partsof an oil and vinegar saladdressing when left unshak-en. Electrophoresis is alsoused to separate compo-nents. However, rather thanbeing separated by density,materials are separatedbased on electrical charge.

The “Good” Newsand the “Bad”News AboutCholesterol

About 10 percent of people ages 12 to 19 have blood cholesterol levels which put

them at risk later in life for developing heart disease––the leading cause of death in theUnited States. Biotechnology can help scientistsunderstand the link between cholesterol andheart disease.

Cholesterol is critical to certain body func-tions, including the formation of cell membranesand some hormones. Cholesterol is a lipid; itwill not dissolve in a watery liquid like blood.However, blood must absorb it so that it can betransported. Molecules called lipoproteins arethe water-soluble “packages” that transport cho-lesterol and other lipids to the tissues where theyare needed.

Are all lipoproteins created equal? Lipo-proteins vary in density and function. High-density lipoproteins (HDL) and low-densitylipoproteins (LDL) have both been studiedextensively. HDL carries excess cholesterol fromtissues and blood vessels to the liver where thecholesterol is discarded from the body. HDL isoften called “good cholesterol” because higherlevels of this substance appear to provide someprotection against coronary artery disease. LDL(“bad cholesterol”) deposits cholesterol in bodytissues and on blood vessel walls. While bodytissues need some cholesterol, excess buildup on arterial walls can lead to blockages and heart disease.

Using technology To measure the amount ofHDL and LDL in the blood, the lipoproteinsmust be separated. A blood sample is spun athigh speed in a centrifuge for a long period oftime. This process of centrifugation causes thedensest lipoproteins to settle to the bottom.

Each type of lipoprotein is then measured withan electrophoresis system. Electrophoresis isbased on the principle that lipoproteins, like allproteins, have an electric charge. The bloodsample is placed in a gel and an electric currentis applied. The lipoproteins migrate through thegel and each quantity is measured.

Changes in thinking Scientists once thoughta person with a total cholesterol level below200 milligrams per deciliter (mg/dL) was lesslikely to develop heart disease. Research hasshown that the ratio of LDL to HDL, not thetotal amount of cholesterol, is a more accuratemeasure of the risk of heart disease. Based onthis research, a person with a total cholesterollevel below 200 mg/dL still may be at risk forheart disease.

Proactive measures Elevated cholesterol levels can begin in childhood so it is vital toform healthy habits early in life. A diet low in fat and cholesterol––including a variety of fruits,vegetables, and whole grains––can help keepLDL levels low. To keep HDL levels high,maintain a healthy weight, exercise regularly,and refrain from smoking. A healthy lifestyle inthe teenage years can help reduce the risk ofdeveloping heart disease later on.

Think Critically Explain how a centrifuge works.How do electrophoresis and centrifugation differ?


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An electrophoresis system is used to separate lipoproteins.

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Key ConceptsSummary statements can beused by students to review themajor concepts of the chapter.

For additional helpwith vocabulary,have students

access the VocabularyPuzzleMaker online at

Visit /self_check_quiz/vocabulary_puzzlemaker/chapter_test/standardized_test

ca.bdol.glencoe.com

ca.bdol.glencoe.com/vocabulary_puzzlemaker

FOLDABLES™Have students use theirFoldables to review the contentof Section 6.3.

Pages 166–167: Inv. & Exp. 1m

Section 6.1STUDY GUIDESTUDY GUIDE

CHAPTER 6 ASSESSMENT 167

Atoms andTheirInteractions

Vocabularyacid (p. 150)atom (p. 142)base (p. 150)compound (p. 145)covalent bond (p. 146)element (p. 141)ion (p. 147)ionic bond (p. 147)isotope (p. 144)metabolism (p. 147)mixture (p. 148)molecule (p. 146)nucleus (p. 143)pH (p. 150)solution (p. 149)

Section 6.3

Vocabularydiffusion (p. 155)dynamic equilibrium

(p. 156)hydrogen bond (p. 153)polar molecule (p. 152)

Vocabularyamino acid (p. 161)carbohydrate (p. 158)enzyme (p. 161)isomer (p. 158)lipid (p. 160)nucleic acid (p. 163)nucleotide (p. 163)peptide bond (p. 161)polymer (p. 158)protein (p. 160)

Water andDiffusion

Life Substances

Section 6.2

To help you review bio-molecules, use the OrganizationalStudy Fold on page 157.

ca.bdol.glencoe.com/vocabulary_puzzlemaker

Key Concepts� Atoms are the basic building blocks of all

matter.� Atoms consist of a nucleus containing pro-

tons and usually neutrons. The positivelycharged nucleus is surrounded by rapidlymoving, negatively charged electrons.

� Atoms become stable by bonding to otheratoms through covalent or ionic bonds.

� Components of mixtures retain their properties.

� Solutions are mixtures in which the com-ponents are evenly distributed.

� Acids are substances that form hydrogenions in water. Bases are substances thatform hydroxide ions in water.

Key Concepts� 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 con-

centration to areas of lower concentration.

Key Concepts� All organic compounds contain carbon

atoms. � There are four principal types of organic

compounds, or biomolecules, that make upliving things: carbohydrates, lipids, pro-teins, and nucleic acids.

� The structure of a biomolecule will helpdetermine its properties and functions.

167

Use the ExamView®Pro Test Bank CD-ROM to:• Create multiple versions of tests• Create modified tests with one mouse click for inclusion students• Edit existing questions and add your own questions• Build tests aligned with state standards using built-in

State Curriculum Tags• Change English tests to Spanish with one mouse click and vice versa

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Questions andanswers have been

aligned and verified by ThePrinceton Review.

1. atom 3. diffusion2. metabolism 4. enzyme

5. C 8. C 11. B6. D 9. D 12. B7. D 10. D 13. B

14. Enzymes have an area ontheir surface called the activesite that fits the shape of thesubstrate. When the sub-strate fits into the active site,the enzyme alters its shapeslightly, putting stress on thesubstrate, causing the reac-tion to proceed more rapidly.

15. In a water molecule, theoxygen atom attracts theelectrons more stronglythan the hydrogen atoms.The electrons spend moretime near the oxygen atom,giving that end a slightlynegative charge and thehydrogen atoms a slightlypositive charge, makingwater polar. Because it is apolar molecule, water dis-solves ionic compounds andother polar molecules,moves through capillaryaction, and has a high sur-face tension.

16. Because diffusion dependson random particle motion,an increase in temperatureincreases the random move-ment of the particles. Diffu-sion occurs more rapidly.

17. No. The liquids in thebeaker are oil and water.Oil is insoluble in water sothey cannot form a solution.

Evaluating Open-Ended QuestionsOpen-ended assessment questions aregraded by using a multilevel rubricthat guides you in assessing a stu-dent’s knowledge of a particular con-cept. The following rubric is a samplescoring device.

168

18. In sickle-cell anemia, thehemoglobin error causesred blood cells to becomesickle-shaped. This clogsblood vessels and preventsoxygen delivery to tissues.

168 CHAPTER 6 ASSESSMENT ca.bdol.glencoe.com/chapter_test

Review the Chapter 6 vocabulary words listed inthe Study Guide on page 167. Match the wordswith the definitions below.

1. the smallest particle of an element that hasthe properties of that element

2. all of the chemical reactions within anorganism

3. the net movement of particles from an areaof higher concentration to an area of lowerconcentration

4. a protein that changes the rate of a chemicalreaction

5. 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

6. Which of the following carbohydrates is apolysaccharide?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. sugarB. nitrogenous base D. glycerol

11. The calcium atom shown herehas 20 protons. How many electrons does it have?A. 10 C. 40B. 20 D. 80

12. A(n) ________ bond involves sharing of electrons.A. ionic C. hydrogenB. covalent D. molecular

13. The first energy level of an atom holds amaximum of ________ electrons.A. 8 C. 16B. 2 D. 32

14. Open Ended Explain how substrates andenzymes fit together.

15. Open Ended Discuss how the structure of awater molecule affects its properties.

16. Open Ended Explain why an increase intemperature would increase the rate of diffusion of substances into or out of cells.

17. Interpret Scientific Illustrations Is theliquid in the beakerclassified as a solu-tion? Explain youranswer.

18. Many geneticdisorders are caused by proteins that aremade incorrectly in the body. Visit

to investigate theprotein error in hemoglobin that causessickle cell anemia. How does the error in the hemoglobin affect the capacity of redblood cells to deliver oxygen to the tissues?Communicate your conclusions to the class.

REAL WORLD BIOCHALLENGE

Oil

Water

ca.bdol.glencoe.com


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CHAPTER ASSESSMENT CHAPTER 6 The Chemistry of Life 37

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by

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AssessmentStudent Recording Sheet

Name Date Class

Chapter

6Chapter Chapter AssessmentChapter Assessment

Use with pages 168–169of the Student Edition

Standardized Test Practice

Vocabulary ReviewWrite the vocabulary words that match the definitions in your book.

1. _________________________ 3. _______________________

2. _________________________ 4. _______________________

Understanding Key ConceptsSelect the best answer from the choices given and fill in the corresponding oval.

5. 10.

6. 11.

7. 12.

8. 13.

9.

Constructed ResponseRecord your answers for Questions 14–16 on a separate sheet of paper.

Thinking CriticallyRecord your answers for Question 17 on a separate sheet of paper.18. Follow your teacher’s instructions for presenting your BioChallenge answer.REAL WORLD BIOCHALLENGE

Part 1 Multiple ChoiceSelect the best answer from the choices givenand fill in the corresponding oval.

19.

20.

21.

22.

23.

Part 2Constructed Response/Grid InRecord your answers for Questions 24 and 25 on a separate sheet of paper.

A B C D A B C D

A B C D A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

169

19. D 22. A20. C 23. B21. A24. Living things are composed

primarily of hydrogen, car-bon, and oxygen. Nonlivingthings are made of agreater variety of elements.

25. Carbon is the building blockelement of the four basicsubstances (carbohydrates,lipids, proteins, and nucleicacids) found in all knownliving organisms.

Answer Sheet A practiceanswer sheet can be found on p. 37 of Unit 3 FAST FILE

Resources.

CHAPTER 6 ASSESSMENT 169

Constructed Response/Grid InThe graph at the right compares the abundance of four ele-ments in living things to their abundance in Earth’s crust,oceans, and atmosphere. Use it to answer questions 24 and25. Record your answers on your answer document.

24. Open Ended Compare the general composition of living things to nonliving matter near Earth’s surface.

25. Open Ended Explain why carbon is the most critical element to living things even though it is not the most abundant.

Perc

ent

abu

nd

ance

(nu

mb

ers

of

ato

ms)

ElementsC H O N Others

10

0

20

30

40

50

Abundance of Four Elements

In livingthings

In Earth'scrust, oceans,and atmosphere

ca.bdol.glencoe.com/standardized_test

Multiple ChoiceTwo students were studying the effect of tempera-ture on two naturally occurring enzymes. Study thegraph of their data to answer questions 19–21.

19. At what temperature does the maximumactivity of enzyme B occur?A. 0°B. 35°C. 60°D. 75°

20. At what temperature do both enzymes havean equal rate of reaction?A. 10°B. 20°C. 50°D. 60°

21. Which description best explains the patternsof temperature effects shown?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.

Use the table to answer questions 22 and 23.

22. Which element listed above would have fourelectrons in its outer energy level?A. A C. CB. B D. D

23. Which two items listed above are isotopes ofthe same element?A. A and BB. C and DC. B and CD. A and D

Rat

es o

f re

acti

on

Temperature (C˚)0 20 40 60 80 100

Effects of Temperature on TwoNaturally Occuring Enzymes

Enzyme A

Enzyme B

Element Number of Protons Number of Neutrons

A 6 6

B 7 7

C 20 40

D 20 41

1b

1b

1b

The assessed California standard appears next to the question.

SCORE CRITERIA4 A correct solution that is sup-

ported by well-developed,accurate explanations.

3 A generally correct solution,but may contain minor flaws inreasoning.

SCORE CRITERIA2 A partially correct interpretation

and/or solution to the problem.1 A correct solution with no sup-

porting evidence or explanation. 0 An incorrect solution or no

solution is given.

California Standards Practice

Pages 168–169: Biology/Life Sciences 1b, 1h

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