Chapter 4: Cell Reproduction

Explore Activity: Infer about seedgrowth, p. 95Before You Read, p. 95

Health Integration, p. 97Science Online, p. 97MiniLAB: Modeling Mitosis, p. 101Activity: Mitosis in Plant Cells, p. 103

Chemistry Integration, p. 105Problem-Solving Activity:How can chromosome numbers bepredicted? p. 107Visualizing Polyploidy in Plants,p. 108

MiniLAB: Modeling DNA Replication,p. 111Science Online, p. 113Science Online, p. 115Activity: Mutations, p. 116Oops! Accidents in Science:A Tangled Tale, p. 118

Chapter Opener

Section 1 Cell Division and Mitosis

2 sessions

1 block

1. Explain why mitosis is important.2. Examine the steps of mitosis.3. Compare mitosis in plant and animal cells.4. List two examples of asexual reproduction.

Section 2 Sexual Reproduction and Meiosis

2 sessions

1 block

1. Describe the stages of meiosis and how sex cellsare produced.

2. Explain why meiosis is needed for sexualreproduction.

3. Name the cells that are involved in fertilization.4. Explain how fertilization occurs in sexual

reproduction.

Section 3 DNA

3 sessions

1.5 blocks

1. Identify the parts of a DNA molecule and itsstructure.

2. Explain how DNA copies itself.3. Describe the structure and function of each kind

of RNA.

See p. 5T for aKey to Standards.

National ContentStandards: UCP3,A1, C1

National ContentStandards: UCP3,UCP4, C2

National ContentStandards: UCP3,UCP4, A1, C1, C2,E2, F5, G1

National State/Local

Section/Objectives Standards Activities/Features

94A CHAPTER 4 Cell Reproduction

PRODUCTS AVAILABLE FROM GLENCOETo order call 1-800-334-7344:CD-ROMNGS PictureShow: The CellNGS PictureShow: Plants: What It Means to Be GreenCurriculum KitGeoKit: Cells and Microorganisms

Transparency SetsNGS PicturePack: The CellNGS PicturePack: What It Means to Be Green

PRODUCTS AVAILABLE FROMNATIONAL GEOGRAPHIC SOCIETYTo order call 1-800-368-2728:

VideoDNA: Laboratory of Life

INDEX TO NATIONAL GEOGRAPHIC SOCIETYThe following articles may be used for research relating to this chapter:“The Rise of Life on Earth,” by RichardMonastersky, March 1998.

Teacher’s Corner

C H A P T E R C E L L R E P R O D U C T I O N44

Section Focus TransparencyTeaching TransparencyInteractive CD-ROMGuided Reading Audio

Program

Section Focus TransparencyInteractive CD-ROMGuided Reading Audio

Program

Section Focus TransparencyInteractive CD-ROMGuided Reading Audio

Program

Chapter Resources BookletFoldables Worksheet, p. 15Directed Reading Overview, p. 17Note-taking Worksheets,

pp. 31–33

Chapter Resources BookletTransparency Activity, p. 42MiniLAB, p. 3Enrichment, p. 28Reinforcement, p. 25Transparency Activity, pp. 45–46Activity Worksheet, pp. 5–6Directed Reading, p. 18Lab Activity, pp. 9–10

Chapter Resources BookletTransparency Activity, p. 43Enrichment, p. 29Reinforcement, p. 26Directed Reading, p. 18

Life Science Critical Thinking/Problem Solving, p. 19

Mathematics Skill Activities, p. 3Performance Assessment in the

Science Classroom, p. 57

Chapter Resources BookletTransparency Activity, p. 44MiniLAB, p. 4Enrichment, p. 30Reinforcement, p. 27Directed Reading, pp. 19, 20Activity Worksheet, pp. 7–8Lab Activity, pp. 11–13

Home and Community Involvement, p. 36

Lab Management and Safety,p. 58

PortfolioVisual Learning, p. 97PerformanceMiniLAB, p. 101Skill Builder Activities, p. 102ContentSection Assessment, p. 102Challenge, p. 102

PortfolioMake a Model, p. 107PerformanceSkill Builder Activities, p. 109ContentSection Assessment, p. 109Challenge, p. 109

PortfolioExtension, p. 113PerformanceMiniLAB, p. 111Skill Builder Activities, p. 115ContentSection Assessment, p. 115Challenge, p. 115

Explore Activity: soakedbean seeds, water, papertowels, self-sealing plasticbags, hand lens

MiniLAB: colored paper,poster board, markers,toothpicks, yarn, thread,glue, scissors

Activity: prepared slide ofonion root tip, microscope

MiniLAB: pencil, paper

Activity: Web sites and other resources on mutations

CHAPTER 4 Chapter Organizer 94B

Activity Materials Reproducible Resources Section Assessment Technology

C H A P T E R O R G A N I Z E R

Need materials? Contact Science Kit at 1-800-828-7777 or www.sciencekit.com on the Internet.

Chapter Resources BookletChapter Review, pp. 35–36Chapter Tests, pp. 37–40

Standardized Test Practice by The Princeton Review, pp. 23–26

MindJogger VideoquizInteractive CD-ROMVocabulary PuzzleMakersExamView Pro Test BankInteractive Lesson PlannerInteractive Teacher Edition

Performance Assessment in the Science Classroom (PASC)

End of Chapter Assessment

Blackline Masters Technology Professional Series

http://www.sciencekit.com

Hands-on Activities

Laboratory ActivitiesActivity Worksheets

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Cell Reproduction 5

Name Date Class

Lab PreviewDirections: Answer these questions before you begin the Activity.

1. Why should you examine the root tip under high and low power?

2. What is the root cap?

Reproduction of most cells in plants and animals uses mitosis and cell division. In this activity, you will study mitosis in plant cells by examiningprepared slides of onion root-tip cells.

What You’ll InvestigateHow can plant cells in different stages ofmitosis be distinguished from each other?

Materialsprepared slide of an onion root tipmicroscope

Goals■ Compare cells in different stages of mitosis

and observe the location of theirchromosomes.

■ Observe what stage of mitosis is most common in onion root tips.

Safety Precautions

Procedure1. Obtain a prepared slide of cells from an onion

root tip.2. Set your microscope on low power and

examine the onion root tip. Move the slideuntil you can see the tip of the root. Youwill see several large round cells. These cellsare called the root cap. Move your slideuntil you see the cells in the area justbehind the root cap. Turn the nosepiece tohigh power.

3. Find one area of cells where you can seethe most stages of mitosis. Count howmany cells you see in each stage and recordyour data in the table.

4. Turn the microscope back to low power.Remove the onion root-tip slide.

Mitosis in Plant Cells

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Zone of cell division L2

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Cell Reproduction 9

Name Date Class

Modeling Cell Division in EarlyDevelopment

Every person starts out as a single cell. Cell division is responsible for the development of ababy from the single cell. As the single cell begins developing, cell division results in exponentialgrowth in the number of cells present. Exponential growth is growth that occurs at an ever-increasing rate. On a graph, exponential growth is represented by a J-shaped curve.

StrategyYou will model how cell division results in exponential growth in the number of cells in a

developing human.You will determine why exponential growth cannot continue indefinitely during human

development.You will infer why uncontrolled cell division, which occurs in cancer, can be so harmful to

human health.

Materialsuncooked ricepaper cups (11)graph paper

Procedure1. Obtain a container of uncooked rice from

your teacher. Each grain of rice representsone human cell.

2. Place one grain of rice in a paper cup. Thisgrain of rice represents the single cell thatresults when sperm and egg unite.

3. Label paper cups 1 through 10, and placethem in a row next to the cup containingthe original cell. During the first 10 celldivisions, the cells in the developinghuman all have the same cell cycle length.

4. Place two grains of rice into cup 1 to represent the number of cells present afterthe original cell undergoes the first roundof mitosis. Record the number 2 in thetable in the Data and Observations section.

5. Place grains of rice into cup 2 to representthe number of cells that will be presentafter the second round of mitosis. Recordthe number of cells in your data table.

6. Repeat step 5 for cups 3 through 10.7. Using your data and graph paper, make a

line graph that shows the growth in thenumbers of cells. Label the x-axis Numberof cell divisions and the y-axis Number ofcells.

LaboratoryActivity11

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Hands-on Activities

TransparenciesSection Focus

Cell Reproduction

We typically grow for 15 to 20 years. Though most lizards don’tgrow to be as big as people, some have the potential to grow through-out their lives. This lizard is regrowing a lost tail.

Growth SpurtSection FocusTransparency11

1. In what ways have you grown in the last year? What causes a person to grow?

2. How is this similar to a lizard regrowing its tail? How is it different?

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L2Cell Reproduction

The Santa Gertrudis bull flourishes in the arid plains of Texas. TheKing Ranch developed the Santa Gertrudis by cross-breeding Brah-man cattle with Shorthorns. As you can see, the Santa Gertrudisinherited characteristics from both of its parents.

I Think He Has Your EyesSection FocusTransparency22

1. Why might ranchers have wanted to cross-breed Brahmans andShorthorns?

2. Which of the Santa Gertrudis’ traits can you identify in the Brahman and the Shorthorn?

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Brahman Shorthorn

Santa Gertrudis

L2Cell Reproduction

This unusual cat is a Devon Rex. It appeared in Devonshire,England in 1960 when a genetic change occurred among British barn cats. The Devon Rex has a small head and a curly coat.

Curly CatSection FocusTransparency33

1. Based on the picture and the description above, what do you thinka genetic change is?

2. How can cat breeders attempt to continue the characteristics ofthe Devon Rex?

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Transparencies

TeachingAssessment

Cell Reproduction

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Directions: Carefully review the diagram and answer the following questions.

Cell Reproduction

1. A cell produced by the fruit fly cell pictured above will most likely be ___.A identical to the fruit fly cellB a combination of its two parent fruit fly cells.C unable to reproduceD a genetic mutation

2. In which part of the cell are the chromosomes located?F Cell membraneG CytoplasmH Nucleus

J Mitochondrion

3. The fruit fly cell above contains eight chromosomes. How manychromosomes will cells produced by the above cell probably have?A sixteen B eight C four D sixty-four

AssessmentTransparency

Interphase

Centrioles(two parts)

Chromatin

Nuclearmembrane

Nucleolus

Cell membrane

Chromosomes

L2Cell Reproduction

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Animal Cell Division

Nucleus

Centrioles

Nucleolus

Chromosomesnot yet visible

Duplicatedchromosome

Nuclearmembranebreaks down

Spindle fiber

Chromosomes

Newnucleus

Cytoplasmseparating

Mitosis ends Mitosis begins

L2

The following designations will help youdecide which activities are appropriatefor your students.

Level 1 activities should be appropriate for students with learning difficulties.

Level 2 activities should be withinthe ability range of all students.

Level 3 activities are designed forabove-average students.

ELL activities should be within the ability range of EnglishLanguage Learners.

Cooperative Learning activities are designed for small group work.

Multiple Learning Styles logos,as described on page 22T, are used throughout to indicate strategies that address differentlearning styles.

These strategies represent studentproducts that can be placed into a best-work portfolio.

P

LS

COOP LEARN

ELL

L3

L2

L1

Key to Teaching Strategies

This is a representation of keyblackline masters available in theTeacher Classroom Resources. SeeResource Manager boxes within thechapter for additional information.

94C CHAPTER 4 Cell Reproduction


R E S O U R C E M A N A G E R

Spanish Directed Reading

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Nombre Fecha Clase

Reproducción celular 21

Satis

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Lectura dirigida para

Dominio del contenido

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SinopsisReproducción celular

Instrucciones: Completa el mapa conceptual usando los siguientes términos.

metafase telofase profase

Instrucciones: Usa los cinco términos del mapa conceptual para identificar las fases de la mitosis.

Descripción4. Las fibras del huso comienzan a desaparecer, se forma la

membrana nuclear y el citoplasma comienza a dividirse.5. Los pares de cromátides son visibles, el nucléolo y la membra-

na nuclear se desintegran y comienzan a formarse las fibras delhuso.

6. Los pares de cromátides se alinean en el centro de la célula yel centrómero de cada par se adhiere a las fibras del huso.

7. Cada centrómero se divide y cada par de cromátides se ali-nea en el centro de la célula, donde se convierten en cromo-somas idénticos.

8. La célula crece y hace copias de su material hereditario.

Fases de la mitosis

1. 2.

3.

la interfase

anafase

las cromátides no se separan

las cromátides se sitúan en polos opuestos de la célula

la división celular conduce a

conduce a una fase conocida como

los pares decromátides

se alínean en elcentro de la célula

L1

Enrichment

28 Cell Reproduction

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True to Foram

The cells of the human body are calledeukaryotic cells. Eukaryotic cells must repro-duce and divide in order to make new cells.You are familiar with the cells of your body,but millions of eukaryotic cells are completeliving organisms all by themselves. The singlecelled organism lives, feeds, and reproduces bymitosis, just like the cells in your body.

Single Cell with a ShellAn interesting type of single celled animal is

called a foraminiferan (four–am–in–if–ur–an).This very long word belongs to a very tiny ani-mal. Foraminiferans, or forams for short, arerelated to amoebas, single-celled organisms thathave no firm body shape. In contrast to amoe-bas, forams single cells are surrounded by littleshells they make from fluids on the outside oftheir bodies. These shells are called “tests.”Forams make tests of many different shapes andsizes. The Egyptian pyramids are made of stonesfilled with the circle-like foram tests. They areeasy to see since they are about as big as a dime.

Shedding their ShellsWhen it comes time for a foram to repro-

duce the most common way they do it is bymitosis. The cell slips outside its test and thenucleus begins to enter prophase. This is adangerous time for the foram because itsenergy is going into mitosis and it cannotswim away from predators.

Foram MitosisWhen examined under a microscope, the

foram’s chromatids can be seen. The nuclearmembrane disappears and the chromosomesline up in the center of the cell. The foramthen goes through the rest of the stages ofmitosis: metaphase, anaphase, and telophase.Finally, there are two forams with the samegenetic material. The new cell has the exactsame genetic information as the parent cell.It therefore, uses fluids from its skin to make a shell that looks just like its parent. It feedson the same food and will, eventually, gothrough mitosis itself.

1. Are all eukaryotic cells found in large animals?

2. What are forams related to?

3. How are the forams different from their relative?

4. How big are the forams founds in the stones of the Egyptian pyramids?

5. How does a foram reproduce itself?

6. Will the offspring be different from the parent? Explain.

Meeting Individual Needs

Enrichment11

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Meeting Different Ability LevelsDirected ReadingReinforcementContent Outline

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Cell Reproduction 31

Cell Reproduction

Section 1 Cell Division and Mitosis

A. Cell division—increases the number of cells and causes many-celled _____________ to grow

1. Cells have periods of formation, growth and development, and death called _______________.

2. Interphase—most of the life of any eukaryotic cell, or cell with a nucleus, is spent in a

period of __________ and _______________.

a. Chromosome—structure in the nucleus that contains ______________ material

b. During interphase, a cell duplicates its _______________ and prepares for cell division.

c. After interphase, the nucleus divides, and then the ______________ separates to formtwo new cells.

B. Mitosis—process in which the nucleus divides to form two identical __________

1. Prophase

a. Nucleolus and ____________________ disintegrate.

b. __________ move to opposite ends of the cell.

c. ______________ begin to stretch across the cell.

2. Metaphase—pairs of ______________ line up across the center of the cell.

3. Anaphase

a. Each ______________ divides.

b. Each pair of chromatids _____________ and moves to opposite ends of the cell.

4. _________—spindle fibers disappear and a new nucleus forms.

C. Results of mitosis

1. Each cell in your body, except sex cells, has the same number of ______ chromosomes.

2. Allows growth and ____________ worn out or damaged cells

D. ____________________—a new organism is produced from one parent organism.

1. An organism with no nucleus divides into two identical organisms by ___________.

2. _______—a small, exact copy of the adult grows from the body of the parent.

3. In ________________, a whole new organism grows from each piece of the parent.

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Directions: Study the following diagrams. Then label the appropriate steps of mitosis.

1. ________________________ 2. ________________________

3. ________________________ 4. ________________________

Directions: Answer the following questions on the lines provided.5. Once chromosomes have been copied during interphase, the cell is ready to begin what process?

6. During metaphase, the centromeres attach to what structures?

7. Why doesn’t the cell membrane pinch in to divide the cytoplasm telophase in plant cells?

8. How many chromosomes does each new cell contain after mitosis if the original cell had 52

original cell chromosomes?

9. Why is mitosis a form of asexual reproduction?

10. What are three types of asexual reproduction?

11. Why are skin cells undergoing mitosis continuously?

12. What types of cells in your body are no longer undergoing mitosis?

13. What phase of the cell cycle are the types of cells in Question 12?

Cell Division and Mitosis

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OverviewCell Reproduction

Directions: Complete the concept map using the terms in the list below.

metaphase telophase prophase

Directions: Use the five terms in the concept map to identify the steps of mitosis below.

Description

4. Spindle fibers start to disappear, nuclear membrane forms,and cytoplasm begins to divide.

5. Chromatid pairs are fully visible, the nucleolus and the nuclearmembrane disintegrate, and spindle fibers begin to form.

6. Chromatid pairs line up across center of cell, the centromereof each pair attaches to spindle fibers.

7. Each chromatid pair splits at the centromere and separatesto opposite ends of the cell, where they become identicalchromosomes.

8. Cell grows and makes copies of its hereditary material.

Step of Mitosis

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Content Mastery

1. 2.

3.

interphase

anaphase

chromosomeshave separated

chromatoid pairsare now visible,

leading to

mitosis begins,which leads to

mitosis ends, andeach new cell enters

a period called

pairs of chromatoidsline up in thecenter of the

cell

Meeting Different Ability Levels

L2 L2 L1

Chapter Tests

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Chapter Test

Name Date Class

Cell Reproduction

I. Testing ConceptsDirections: Match the terms in Column II with the descriptions in Column I. Write the letter of the correct termin the blank at the left.

Directions: For each of the following, write the letter of the term or phrase that best completes the sentence.

11. Most of the life of any cell is spent in a period of cell growth and development called ______a. interphase b. metaphase c. prophase d. telophase

12. All of the following are true of animals and plant cells during mitosis EXCEPT ______.a. only animals have spindle fibers c. only plants form cell platesb. only plants have rigid cells walls d. only animals have centrioles

13. All of the following are composed of body cells EXCEPT ______.a. bone b. kidney c. liver d. sperm

14. Each human skin cell has ______ pairs of chromosomes.a. 13 b. 18 c. 23 d. 46

15. Human sex cells have ______ individual chromosomes.a. 13 b. 23 c. 33 d. 46

Column I

1. reproduction in which a new organism is produced when sex cells combine

2. cell that forms in fertilization

3. the joining of an egg and a sperm

4. a nucleic acid which carries the code for making proteins from the nucleus to the ribosomes

5. structures in the nucleus that contain hereditary material

6. formation of two nuclei with identical chromosomes

7. nuclear division that forms sex cells

8. coded instructions that control cell activity

9. segment of DNA controlling production of one protein

10. any permanent change in genetic material of a cell

Asse

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Column II

a. asexual reproduction

b. chromosomes

c. DNA

d. egg

e. fertilization

f. gene

g. sperm

h. meiosis

i. mitosis

j. mutation

k. RNA

l. sexual reproduction

m. zygote

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Chapter ReviewTest Practice Workbook

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Chapter Review

Name Date Class

Cell Reproduction

Part A. Vocabulary ReviewDirections: Use the clues below to complete the crossword puzzle.

Across2. describes cells that do not have pairs of

chromosomes

5. the joining of an egg and a sperm

7. any permanent change in a gene orchromosome of a cell

8. describes cells that have pairs ofchromosomes

9. the process in which the nucleus dividesto form two identical nuclei

10. cells formed in the male reproductiveorgans

12. type of reproduction when two sex cells,usually an egg and a sperm, come together

14. a section of DNA (on a chromosome)where instructions for making specificproteins are found

Down1. a structure in the nucleus that contains

hereditary material

3. type of reproduction when a neworganism (sometimes more than one) isproduced that has hereditary materialidentical to the parent organism

4. the code that contains all the informationthat an organism needs to grow and function

6. the cell that forms when an egg and asperm join

7. a process by which haploid sex cells areproduced

11. a type of nucleic acid that carries thecodes for making proteins from thenucleus to the ribosomes

13. cells formed in the female reproductiveorgans which contain stored food alongwith the other cell parts

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AssessmentAssessment

CHAPTER 4 Resource Manager 94D

94E CHAPTER 4 Cell Reproduction94E CHAPTER 4 Cell Reproduction

locations. The alleles may or may not be identi-cal. For example, the gene for hair color wouldbe at the same location on homologous chro-mosomes but may code for brunette on onechromosome and blonde on the other.

Animals and some plants have one pair ofsex chromosomes. In most animals, includinghumans, the sex chromosomes of the female aretruly homologous, whereas the male sex chro-mosomes are of unequal lengths and have manydifferent genes. This is reversed in birds andbutterflies, with males having the truly homo-logous sex chromosomes.

Asexual ReproductionEukaryotes, which include many protists, somefungi, and plants, reproduce asexually by mitosis.Prokaryotes, like bacteria, reproduce by fission. Depending on the organism, one orseveral new organisms can be created that aregenetically identical to, or clones of, the origi-nal organism. Most animals do not use asexualreproduction. Recently scientists have beenable to stimulate cells from adult animals todivide by mitosis and reproduce new animalsthat are clones of the organism from which thecells were taken.

Sexual Reproduction and MeiosisSexual ReproductionSex cells, or gametes, are the

result of meiosis. Because of a process thathappens at metaphase I called independentassortment, the possible combination of chro-mosomes for each sex cell varies every time sexcells form. When duplicated homologouschromosomes line up at a cell’s center duringmetaphase I, there are no rules about how a par-ticular pair is aligned relative to any other pair.The only requirement is that the alignmentresults in one half of each duplicated chromo-some moving in one direction and the other half

22S E C T I O N

Cell Division and MitosisResults of MitosisEvery species has a characteris-tic number of chromosomes in

each cell. A cat has 38 chromosomes, whereas apotato and a chimpanzee each have 48 chromo-

somes. In all sexuallyreproducing organisms,

chromosomes occur in homologous pairs.

Except for some sex chro-mosomes, homologous

chromosomes are of equallength and have the same

genes at the same relative

11S E C T I O N

The first pigs were cloned in 2000.Scientists think that organs frompigs could be transplanted intohumans.

Reuters New Media, Inc./Corbis


moving in the opposite direction duringanaphase I. The offspring formed by fertilizationhas its own unique combination of genetic mate-rial. This produces variation between parentsand offspring and may give offspring a betterchance of surviving in a changing environment.

Meiosis and Sex CellsThis process is often called reduction divisionsince the number of chromosomes in the cellsproduced is half that of the original cell. Meiosisprovides for great diversity within a speciesbecause of the many ways the chromosomes canalign during metaphase I. There are more than 8 million possible gametes that can be producedfrom the 23 pairs of human chromosomes.

In animals, meiosis results in haploid eggand sperm cells. In plants, meiosis results inhaploid spores that later produce egg andsperm cells.

DNAWhat is DNA?The information in DNA thatdetermines what an organism

will be is contained in a code dictated by theorder of subunits called nucleotides. A nucleotideconsists of the sugar deoxyribose, a phosphatemolecule, and one of the four possible nitrogenbases. A DNA molecule is two chains ofnucleotides. These two chains are antiparalleland run in opposite directions. One chain endswith a phosphate, and the other chain ends with

deoxyribose. Just as the order ofletters on this page determineswhat words you are reading, theorder of nucleotides determinesthe message on the DNA.Because DNA is copied from onegeneration to the next, anychange, or mutation, in a gene isalso preserved. If the changeoccurs in cells that becomegametes, it is passed on to futuregenerations in a process calledheredity.

A DNA ModelThe process of DNA replica-tion is directed by the enzymecalled DNA polymerase. Itmoves along the separatedDNA molecule and inserts the correct, complementarynucleotides onto the exposednitrogen bases. This happens atmany locations along the lengthof the DNA molecule simulta-neously. Otherwise the time itwould take to match up the millions of nitrogen baseswould be astronomical.

MutationsA change in a cell’sgenetic message is calleda mutation. Some muta-tions affect the messageitself, altering the sequenceof DNA nucleotides.Other classes of mutationsinvolve sequences of DNAthat can move from place to place and are oftencalled jumping genes. When a particular geneis mutated, its function is often destroyed.

H E L P I N G Y O U P R E PA R E

CHAPTER 4 Helping You Prepare 94F

For additional content background on thistopic, go to the Glencoe Science Web siteat science.glencoe.com.

33S E C T I O N

Barbara McClintock first published a paper on jumping genes in the1940s. In 1983 she received theNobel Prize for her work.

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C H A P T E R 44Cell Reproduction

Chapter Vocabularymitosis, p. 98chromosome, p. 98asexual reproduction, p. 101sexual reproduction, p. 104sperm, p. 104egg, p. 104fertilization, p. 104zygote, p. 104diploid, p. 104haploid, p. 105meiosis, p. 105DNA, p. 110gene, p. 112RNA, p. 112mutation, p. 114

What do you think?Science Journal The structures in thepicture are duplicated chromosomes,which contain genetic information forthe organism they belong to.

How does a cut on your skinheal? Why doesn’t a babychicken grow up to look like

a duck? Why do turtles, like the onein the photo to the right, and mostother animals need to have two par-ents, when a sweet potato plant canbe grown from just one potato? Inthis chapter, you will find answers tothese questions as you learn aboutcell reproduction. You also will learnwhat genetic material is and how itfunctions.

What do you think?Science Journal Look at the picturebelow with a classmate. Discuss whatyou think this might be. Here is ahint: These structures contain impor-tant information for cells. Write youranswer or best guess in your ScienceJournal.

Cell Reproduction

94

44

94 CHAPTER 4 Cell Reproduction

Stability and Change DNA controls all cell activi-ties by directing the production of proteins inliving organisms. Changes in DNA can result in evolutionary changes that are inherited.

EXPLOREACTIVITY

Purpose Use the Explore Activ-ity to introduce students togrowth; as they read the chapter,they will understand that growthis the result of mitosis.

KinestheticPreparation Soak pinto beans orother large seeds for 24 hours.Materials 2 soaked seeds, papertowels, self-sealing plastic bag,hand lensTeaching Strategy After soaking,the seeds should split easily. Ifstudents have difficulty, forcepscan be used to separate theseeds.

ObserveStudents should observe and record

the growth of a new plant from one halfof each seed. They should predict thatthe cells of the seed embryo are able touse the information needed to grow intoa plant.

LSL2

95

Most flower and vegetable seeds sprout and growinto entire plants in just a few weeks. Although

all of the cells in a seed have information and instruc-tions to produce a new plant, only some of the cells in the seed use the information. Where are these cells

in seeds? Do the following activity to find out.

Infer about seed growth1. Carefully split open two bean seeds

that have soaked in water overnight.

2. Observe both halves and record yourobservations.

3. Wrap all four halves in a moist papertowel. Then put them into a self-sealing, plastic bag and seal the bag.Wash your hands.

4. Make observations for a few days.

ObserveIn your Science Journal, describe what you observe. Hypothesize about whichcells in seeds use information about how plants grow.

EXPLOREACTIVITY

Making an Organizational Study Fold When information is grouped into clear categories, it is easier to make sense of what you are learning. Make the following Foldable to help you organize

information about cell reproduction.

1. Place a sheet of paper in front of you so the long side is at the top. Fold the paper in half from the left side to the right side and then unfold.

2. Fold in each side to the center line to divide the paper into fourths.

3. Use a pencil to draw a cell on the front of your Foldable as shown.

4. As you read the chapter, use a pen to illustrate how the cell divides into two cells. Under the flaps, list how cells divide. In the middle section, list why cells divide.

FOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

CHAPTER 4 Cell Reproduction 95

Dinah Zike Study FoldPurpose Students should use

this Foldable to diagram cells and organize informa-tion on cells and cell division as they read.

For additional help, see Foldables Worksheet p. 15 in Chapter Resources Booklet, or go to theGlencoe Science Web site at science.glencoe.com.See After You Read in the Study Guide at the end ofthis chapter.


FOLDABLESReading &Study Skills

Before You ReadBefore You Read

Per formance Have studentsrepeat the experiment usingcorn seeds and observe the newplant that grows from each seed.Use Performance Assessmentin the Science Classroom,p. 89.


S E C T I O N

11

PORTFOLIO

Visual Learning, p. 97

PERFORMANCE ASSESSMENT

MiniLAB, p. 101Skill Builder Activities, p. 102See page 122 for more options.

CONTENT ASSESSMENT

Section, p. 102Challenge, p. 102Chapter, pp. 122–123

Section Planner


Cell Reproduction

We typically grow for 15 to 20 years. Though most lizards don’tgrow to be as big as people, some have the potential to grow through-out their lives. This lizard is regrowing a lost tail.

Growth SpurtSection FocusTransparency11

1. In what ways have you grown in the last year? What causes a person to grow?

2. How is this similar to a lizard regrowing its tail? How is it different?

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Tie to Prior KnowledgeUse a diagram or trans-

parency to review the parts of acell and their functions. Explainthat mitosis involves only thenucleus.

Bellringer TransparencyDisplay the Section FocusTransparency for Section 1.Use the accompanying Trans-parency Activity Master.ELL

L2

Cell Division andMitosis

Cell Division and MitosisS E C T I O N

Why is cell division important? What do you, an octopus, and an oak tree have in common?

You share many characteristics, but an important one is that youare all made of cells—trillions of cells. Where did all of thosecells come from? As amazing as it might seem, many organismsstart as just one cell. That cell divides and becomes two, twobecome four, four become eight, and so on. Many-celled organ-isms, including you, grow because cell division increases the totalnumber of cells in an organism. Even after growth stops, celldivision is still important. Every day, billions of red blood cells inyour body wear out and are replaced. During the few seconds ittakes you to read this sentence, your bone marrow producedabout six million red blood cells. Cell division is important toone-celled organisms, too—it’s how they reproduce themselves,as shown in Figure 1B. Cell division isn’t as simple as just cuttingthe cell in half, so how do cells divide?

The Cell Cycle A living organism has a life cycle. A life cycle begins with the

organism’s formation, is followed by growth and development,and finally ends in death. Right now, you are in a stage of yourlife cycle called adolescence, which is a period of active growthand development. Individual cells also have life cycles.

■ Explain why mitosis is important.■ Examine the steps of mitosis.■ Compare mitosis in plant and

animal cells.■ List two examples of asexual

reproduction.

Vocabularymitosischromosomeasexual reproduction

Your growth, like that of many organisms, depends on cell division.

Figure 1 All organisms use cell division.

Many-celled organisms, suchas this octopus, grow by increas-ing the numbers of their cells.

Like this amoeba, a one-celled organismreaches a certain size and then reproduces.


Section 1 Cell Division and Mitosis 97

Length of Cycle The cell cycle, as shown in Figure 2, is aseries of events that takes place from one cell division to thenext. The time it takes to complete a cell cycle is not the same inall cells. For example, the cycle for cells in some bean plantstakes about 19 h to complete. Cells in animal embryos dividerapidly and can complete their cycles is less than 20 min. Insome human cells, the cell cycle takes about 16 h. Cells inhumans that are needed for repair, growth, or replacement, likeskin and bone cells, constantly repeat the cycle.

Interphase Most of the life of any eukaryotic cell—a cellwith a nucleus—is spent in a period of growth and developmentcalled interphase. Cells in your body that no longer divide, suchas nerve and muscle cells, are always in interphase. An activelydividing cell, such as a skin cell, copies its hereditary materialand prepares for cell division during interphase.

Why is it important for a cell to copy its hereditary informa-tion before dividing? Imagine that you have a part in a play andthe director has one complete copy of the script. If the directorgave only one page to each person in the play, no one wouldhave the entire script. Instead the director makes a complete,separate copy of the script for each member of the cast so thateach one can learn his or her part. Before a cell divides, a copy ofthe hereditary material must be made so that each of the twonew cells will get a complete copy. Just as the actors in the playneed the entire script, each cell needs a complete set of heredi-tary material to carry out life functions.

After interphase, cell division begins. The nucleus divides,and then the cytoplasm separates to form two new cells.

SECTION 1 Cell Division and Mitosis 97

Research Nerve cells inadults usually do not undergo mitosis. Visit theGlencoe Science Web site atscience.glencoe.comfor more information aboutnerve cell regeneration.Communicate to your classwhat you learn.

In most cells, the cell cycleis well controlled. However,cancerous cells haveuncontrolled cell division.Some cancerous cells forma mass of cells called atumor. Find out why sometumors are harmful to anorganism. Write what youfind out in your ScienceJournal.

InterphaseDNA is copied;chromosomes duplicate.

Cell grows and functions, organellesduplicate.

Cell grows andprepares for mitosis.Cytoplasm

divides.

Mitosis occurs.

Cell CycleFigure 2 Interphase is the longest part of the cell cycle. When do chromosomes duplicate?

Figure 2 Have students make anevents chain concept map thatoutlines the steps of the cellcycle as illustrated in Figure 2.

Visual-Spatial PLSL2

Cancerous tumors grow rapidly andsometimes invade healthy tissue.

Life of a Cell Have students write cre-ative stories about the life cycle of a cell from itsbeginning to its end. Have them use sectionvocabulary as they describe what happens in thecell. LinguisticLSL2

Chapter Resources Booklet

Transparency Activity, p. 42Directed Reading for Content Mastery,

pp. 17, 18

Resource Manager

Internet Addresses

Explore the Glencoe Science Web siteat science.glencoe.com to find outmore about topics in this section.

The Cell Cycle

Caption AnswerFigure 2 during interphase




MitosisMitosis (mi TOH sus) is the process in which the

nucleus divides to form two identical nuclei. Each newnucleus also is identical to the original nucleus. Mitosisis described as a series of phases, or steps. The steps ofmitosis in order are named prophase, metaphase,anaphase, and telophase.

Steps of Mitosis When any nucleus divides, thechromosomes (KROH muh sohmz) play the impor-

tant part. A chromosome is a structure in the nucleus that con-tains hereditary material. During interphase, each chromosomeduplicates. When the nucleus is ready to divide, each duplicatedchromosome coils tightly into two thickened, identical strandscalled chromatids, as shown in Figure 3.

How are chromosomes and chromatids related?

During prophase, the pairs of chromatids are fully visiblewhen viewed under a microscope. The nucleolus and the nuclearmembrane disintegrate. Two small structures called centrioles(SEN tree olz) move to opposite ends of the cell. Between thecentrioles, threadlike spindle fibers begin to stretch across thecell. Plant cells also form spindle fibers during mitosis but donot have centrioles.

In metaphase, the pairs of chromatids line up across the cen-ter of the cell. The centromere of each pair usually becomesattached to two spindle fibers—one from each side of the cell.

In anaphase, each centromere divides and the spindle fibersshorten. Each pair of chromatids separates, and chromatidsbegin to move to opposite ends of the cell. The separated chro-matids are now called chromosomes. In the final step, telophase,spindle fibers start to disappear, the chromosomes start touncoil, and a new nucleus forms.

Division of the Cytoplasm For most cells, after thenucleus has divided, the cytoplasm separates and two new cellsare formed. In animal cells, the cell membrane pinches in themiddle, like a balloon with a string tightened around it, and thecytoplasm divides. In plant cells, the appearance of a cell plate,as shown in Figure 4, tells you that the cytoplasm is beingdivided. New cell walls form along the cell plate, and new cellmembranes develop inside the cell walls. Following division ofthe cytoplasm, most new cells begin the period of growth, orinterphase, again. Review cell division for an animal cell usingthe illustrations in Figure 5.

Figure 3 DNA is copied during interphase.

An unduplicated chromosomehas one strand of DNA. Aduplicated chromosome has twoidentical DNA strands, calledchromatids, that are heldtogether at a region called thecentromere.

Figure 4The cell plate shown in this plantcell appears when the cytoplasmis being divided.

98

DuplicationChromatids

Centromere

Unduplicatedchromosome


Cell plate

Mitosis

Use an AnalogyCompare chromosome thick-

ening to a coiled telephonecord. When stretched out, thecord is long and thin, like chro-mosomes during interphase.When the cord returns to itsusual position, it shortens andthickens, like chromosomespreparing to divide.

Visual-SpatialLSL1

Answer A duplicated chromosome ismade up of two chromatids.

Reading Check

Students may assume that allcells divide. However, somecells do not divide at all. Redblood cells circulating in theblood vessels do not divide;they live for 90 days beforethey are replaced by new cells.

Most cells are not actively engagedin mitosis.Skin cells spend 15–20days in interphase.After infancy,nerve cells stay in interphase.

Visually Impaired Have selected students makethree-dimensional models of mitosis on posterboard. Display the posters in the classroom forvisually impaired students to feel.

Visual-SpatialLSL2

Historic Contributions In 1887, Edouard-Joseph-Marie van Beneden, a Belgian scientist,discovered that each species has a fixed numberof chromosomes. He also observed the forma-tion of a haploid cell. In 1956, J. Hin Tjio andAlbert Levan showed that each human cell has46 chromosomes.



Figure 5 Cell division for an animal cell is shown here. Each micrographshown in this figure is magnified 600 times.

Centriole

Nucleus

Centrioles

Nucleolus

Chromosomesnot yet visible


Nuclearmembranebreaks down

Spindle fiber

Chromosomes

Newnucleus

Cytoplasmseparating

Mitosis ends Mitosis begins

ProphaseThe chromatid pairsare now visible andthe spindle isbeginning to form.

TelophaseIn the final step,the cytoplasm is beginning to separate.

AnaphaseThe chromosomeshave separated.

MetaphaseChromatid pairs arelined up in the center of the cell.

InterphaseDuring interphase,the cell’s chromo-somes duplicate.The nucleolus isclearly visible inthe nucleus.

Quick DemoUse a microprojector to

show mitotic cell divisions inthe growth of fertilized frog eggs. The increasing numbers of cells can be readily seen dur-ing the early stages of tadpoledevelopment.

ExtensionHave students research and

report on cancer. The reportshould include how cancerrelates to mitosis and some ofthe technology used to diagnoseand treat cancer. Display writtenreports. LinguisticLSL2

The fact that chromosomesare duplicated in the nucleusduring interphase has beenhypothesized for more than ahundred years, but evidencefor the hypothesis did notappear until 1981.

Use Science WordsWord Meaning Explain that theword mitosis derives from theGreek word for “thread.” Havestudents explain the derivation.During mitosis, the replicated chromo-somes—threadlike structures—separate.Then point out that phase isanother word for “stage.” Havestudents use a dictionary to findthe meanings of the prefixesinter- (between), pro- (before), meta-(after), ana- (up), and telo- (end).

Math It takes 15 minutes for certain embryo cellsto divide. Have students calculate how many cells would be produced from one embryo cellafter four hours. 240 minutes divided by 15 minutes �16 cell divisions; 216 � 65, 536 cells

Logical-MathematicalLSL2


Note-taking Worksheets, pp. 31–33Enrichment, p. 28

Resource Manager

Results of Mitosis You should remember two importantthings about mitosis. First, it is the division of a nucleus. Sec-ond, it produces two new nuclei that are identical to each otherand the original nucleus. Each new nucleus has the same num-ber and type of chromosomes. Every cell in your body, exceptsex cells, has a nucleus with 46 chromosomes—23 pairs. This isbecause you began as one cell with 46 chromosomes in itsnucleus. Skin cells, produced to replace or repair your skin, havethe same 46 chromosomes as the original single cell you devel-oped from. Each cell in a fruit fly has eight chromosomes, soeach new cell produced by mitosis has a copy of those eightchromosomes. Figure 6 shows the chromosomes found in mosthuman cells and those found in most fruit fly cells.

Each of the trillions of cells in your body, except sex cells, hasa copy of the same hereditary material. Even though all actors ina play have copies of the same script, they do not learn the samelines. Likewise, all of your cells use different parts of the samehereditary material to become different types of cells.

Cell division allows growth and replaces worn out or dam-aged cells. You are much larger and have more cells than a babymainly because of cell division. If you cut yourself, the woundheals because cell division replaces damaged cells. Another waysome organisms use cell division is to produce new organisms.


Figure 6 Pairs of chromosomes are found in the nucleus of most cells. All chromosomes shownhere are in their duplicated form. Most human cells have 23 pairs of chromosomesincluding one pair of chromo-somes that help determine sex such as the XY pair above.

Most fruit fly cells have fourpairs of chromosomes. What doyou think the XX pair in fruit flieshelps determine?

1 2 3 4 5 6

13 14 15 16 17 18

7 8 9 10 11 12

19 20 21 22 (XY)

1 2

3 (XX)

Mitosis, continued

DiscussionHave students use their

knowledge of the cell cycle toinfer why even slight injuries tothe brain and spinal cord can beserious and permanent. Becausenerve cells do not undergo mitosis, dam-aged cells are not replaced, althoughsome repair does occur.

DiscussionMany nonliving things such as

icicles, stalagmites, crystals, andsand dunes appear to grow. Askstudents to give examples ofother nonliving things thatappear to grow. Possible answers:highway systems, buildings, develop-ments, shopping malls Have stu-dents distinguish between theprocesses involved in the growthof living things and the growthof nonliving things. In nonlivingthings, growth is caused by the sur-rounding environment. In living things,growth is caused by processes within theorganism.

Caption AnswerFigure 6 the sex of the organism


LAB DEMONSTRATIONLAB DEMONSTRATIONPurpose to observe asexual reproductionin a sweet potatoMaterials sweet potato with leaf buds,water, widemouthed glass jar, 4 toothpicksPreparation Obtain a sweet potato that haspurple leaf buds growing at its scarredend.

Procedure Fill a jar almost full of water,and place sweet potato with buds orscarred end up so at least half of thepotato is in water. Toothpicks can hold thepotato in place. Keep water level constantand observe for three weeks.Expected Outcome Students should observethe formation of roots and leaf growth.

What part of the sweet potato pro-duced leaves and roots? Leaves developedfrom the buds; roots grew from the bottom half ofthe sweet potato. Is this an example of sex-ual or asexual reproduction? Explain.Asexual; a new organism is produced from one parent.


Asexual ReproductionReproduction is the process by which an organism produces

others of its same kind. Among living organisms, there are twotypes of reproduction—sexual and asexual. Sexual reproductionusually requires two organisms. In asexual reproduction, a neworganism (sometimes more than one) is produced from oneorganism. The new organism will have hereditary material iden-tical to the hereditary material of the parent organism.

How many organisms are needed for asexualreproduction?

Cellular Asexual Reproduction Organisms with eukary-otic cells asexually reproduce by cell division. A sweet potatogrowing in a jar of water is an example of asexual reproduction.All the stems, leaves, and roots that grow from the sweet potatohave been produced by cell division and have the same heredi-tary material. New strawberry plants can be reproduced asexu-ally from horizontal stems called runners. Figure 7 showsasexual reproduction in a potato and a strawberry plant.

Recall that mitosis is the division of a nucleus. However, bac-teria do not have a nucleus so they can’t use mitosis. Instead,bacteria reproduce asexually by fission. During fission, anorganism whose cells do not contain a nucleus copies its geneticmaterial and then divides into two identical organisms.


Figure 7 Many plants can reproduce asexually.

Modeling MitosisProcedure1. Make models of cell division

using materials suppliedby your teacher.

2. Use four chromosomes inyour model.

3. When finished, arrange themodels in the order inwhich mitosis occurs.

Analysis1. In which steps is the

nucleus visible?2. How many cells does a

dividing cell form?

A new potato plant can grow from eachsprout on this potato.

How does the genetic material in the small strawberry plant compare to the genetic material in the large strawberry plant?

Asexual Reproduction

Answer one

Reading Check

Cloning Have students use science ref-erence books, newspapers, and the Internet toresearch cloning, a process that artificiallyreproduces an exact duplicate of a single parent.Have students write reports in their ScienceJournals on the medical uses as well as the nega-tive ethical implications of cloning technology.

LinguisticLSL2

Purpose to construct a modelof mitosis

Kinesthetic and Visual-SpatialMaterials colored paper, pos-ter board, markers, tooth-picks, yarn, thread, glue, scissorsTeaching Strategy Studentmodels should resemble mito-sis as shown in Figure 4.Analysis1. prophase and telophase2. two new cells

LSELLL2

Performance Assess students’understanding of mitosis bymaking flash cards of thestages and having studentsarrange them in the properorder. Use PASC, p. 163.

MiniLAB

Caption AnswerFigure 7 They are identical.


MiniLAB, p. 3Transparency Activity, pp. 45–46Lab Activity, pp. 9–10

Resource Manager


ReteachHave students draw the

nucleus or chromosomes on cellcycle outlines and describe whatis occurring at each stage.

Visual-Spatial

ChallengeAt one time, interphase was

called the resting stage. Whyis this not a good descriptionof interphase? A cell in interphase is carrying out all of the life processes.

LSELL

L1

Budding and Regeneration Look at Figure 8A. A neworganism is growing from the body of the parent organism. Thisorganism, called a hydra, is reproducing by budding. Budding isa type of asexual reproduction made possible because of celldivision. When the bud on the adult becomes large enough, itbreaks away to live on its own.

Could you grow a new finger? Some organisms can regrowdamaged or lost body parts, as shown in Figure 8B. Regenera-tion is the process that uses cell division to regrow body parts.Sponges, planaria, sea stars, and some other organisms can useregeneration for asexual reproduction. If these organisms breakinto pieces, a whole new organism will grow from each piece.Because sea stars eat oysters, oyster farmers dislike them. Whatwould happen if an oyster farmer collected sea stars, cut theminto pieces, and threw them back into the ocean?


Section Assessment

1. What is mitosis and how does it differ inplants and animals?

2. Give two examples of asexual reproductionin many-celled organisms.

3. What happens to chromosomes beforemitosis begins?

4. After a cell undergoes mitosis, how are thetwo new cells alike?

5. Think Critically Why is it important forthe nuclear membrane to disintegrate during mitosis?

6. Testing a Hypothesis A piece of leaf, stem,or root can grow into a new plant. Hypothesizehow you would use one of these plant parts togrow a new plant. Test your idea. For morehelp, refer to the Science Skill Handbook.

7. Solving One-Step Equations If a cell under-goes cell division every 5 min, how many cellswill there be after 1 h? Calculate and record theanswer in your Science Journal. For more help,refer to the Math Skill Handbook.

Figure 8Some organisms use cell divisionfor budding and regeneration.

Hydra, a freshwater animal,can reproduce asexually by bud-ding. The bud is a small exactcopy of the adult.

Some sea stars reproduce asexually by shedding arms. Each armcan grow into a new sea star.

Asexual Reproduction, continued

ActivityAdd one package of yeast and

one teaspoon of sugar to a .5 Lcontainer of warm water. Letthe container stand in a warmplace for a few hours. Allow stu-dents to examine microscopeslides of the mixture to observebudding in yeast cells.

Visual-Spatial

Text Question AnswersSea star numbers would increase

because of regeneration.

LSL2

Oral How is mitosis differentfrom cell division? Mitosis is thedivision of the nucleus. Cell divisionincludes mitosis and the division of thecytoplasm and its contents. Use Per-formance Assessment in theScience Classroom, p. 89.

Answers to Section Assessment1. A process in which a cell nucleus

divides into two nuclei, each ofwhich has the same genetic informa-tion; in animal cells, the cytoplasmdivides as the cell membranepinches in the middle of the cell. Inplant cells, the appearance of the cellplate indicates that the cytoplasm isbeing divided.

2. Possible answers: budding and regeneration

3. The chromosomes duplicate.4. They both have the same genetic

information.5. Otherwise, the chromosomes would

not be able to move to opposite endsof the cell.

6. Hypotheses will vary. Students mayseparate plant parts and place themin water or soil.

7. 60 minutes divided by 5 minutes �12 cell divisions; 212 � 4,096 cells

ACTIVITY 103

Write a story as if you were a cell in an onionroot tip. Describe what changes occur as yougo through mitosis. Use some of your draw-ings to illustrate the story. Share your storywith your class. For more help, refer to theScience Skill Handbook.

Reproduction of most cells in plants and ani-mals uses mitosis and cell division. In this

activity, you will study mitosis in plant cells byexamining prepared slides of onion root-tip cells.

What You’ll InvestigateHow can plant cells in different stages of mitosisbe distinguished from each other?

Materialsprepared slide of an onion root tipmicroscope

Goals■ Compare cells in different stages of mitosis

and observe the location of their chromosomes.■ Observe what stage of mitosis is most

common in onion root tips.

Safety Precautions

Procedure 1. Copy the data table in your Science Journal.

2. Obtain a prepared slide of cells from anonion root tip.

3. Set your microscope on low power and exam-ine the onion root tip. Move the slide untilyou can see the tip of the root. You will seeseveral large, round cells. These cells arecalled the root cap. Move your slide until yousee the cells in the area just behind the rootcap. Turn the nosepiece to high power.

4. Find one area of cells where you can see themost stages of mitosis. Count how many cellsyou see in each stage and record your data inthe table.

5. Turn the microscope back to low power.Remove the onion root-tip slide.

Stage of Number Percent Mitosis of Cells of Cells

Observed Observed

Prophase

Metaphase

Anaphase

Telophase

Total

Number of Root-Tip Cells Observed

Conclude and Apply1. Compare the cells in the region behind the

root cap to those in the root cap.

2. Calculate the percent of cells found in eachstage of mitosis. Infer which stage of mitosistakes the longest period of time.

78 65

23 19

12 10

7 6

120 100

Mitosis in Plant Cells

Zone of cell division

Rootcap

Purpose Students observe thestages of mitosis.

Visual-SpatialProcess Skills observing, infer-ring, comparing and contrastingTime Required 40 minutesTeaching Strategy Review thestages of mitosis before begin-ning the activity.Troubleshooting Students mayhave difficulty locating all thephases. You may want to placean onion root tip slide on themicroprojector and point outthe phases.Answers to Questions1. The cells behind the root cap are

smaller than those in the root cap.Mitosis occurs at a faster rate in cellsbehind the root cap.

2. See student page; prophase takes the longest.

LSELLL2

ACTIVITY 103

The story and drawings should include the stages inmitosis.

Performance To further assessstudents’ understanding of mito-sis, give each one a sheet of paperlisting a stage and have themdescribe what comes before andafter that stage. Use Perfor-mance Assessment in the Science Classroom, p. 163.


Reinforcement, p. 25Activity Worksheet, pp. 5–6

Resource Manager

S E C T I O N

22

PORTFOLIO

Make a Model, p. 107


Skill Builder Activities, p. 109See page 122 for more options.

CONTENT ASSESSMENT


Section Planner


Cell Reproduction

The Santa Gertrudis bull flourishes in the arid plains of Texas. TheKing Ranch developed the Santa Gertrudis by cross-breeding Brah-man cattle with Shorthorns. As you can see, the Santa Gertrudisinherited characteristics from both of its parents.

I Think He Has Your EyesSection FocusTransparency22

1. Why might ranchers have wanted to cross-breed Brahmans andShorthorns?

2. Which of the Santa Gertrudis’ traits can you identify in the Brahman and the Shorthorn?

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Brahman Shorthorn

Santa Gertrudis

Tie to Prior KnowledgeAs a review, ask students to

describe the stages in mitosis.Then tell the students that forcertain cells, the nucleus dividestwice. They will learn why inthis section.


L2

Sexual Reproduction and Meiosis

Sexual Reproduction and Meiosis

S E C T I O N

Sexual ReproductionSexual reproduction is another way that a new organism can

be produced. During sexual reproduction, two sex cells, some-times called an egg and a sperm, come together. Sex cells, likethose in Figure 9, are formed from cells in reproductive organs.Sperm are formed in the male reproductive organs. Eggs areformed in the female reproductive organs. The joining of an eggand a sperm is called fertilization, and the cell that forms iscalled a zygote (ZI goht). Generally, the egg and the sperm comefrom two different organisms of the same species. Following fer-tilization, cell division begins. A new organism with a uniqueidentity develops.

Diploid Cells Your body forms two types of cells—body cellsand sex cells. Body cells far outnumber sex cells. Your brain,skin, bones, and other tissues and organs are formed from bodycells. A typical human body cell has 46 chromosomes. Eachchromosome has a mate that is similar to it in size and shapeand has similar DNA. Human body cells have 23 pairs of chro-mosomes. When cells have pairs of similar chromosomes, theyare said to be diploid (DIH ployd).

■ Describe the stages of meiosis andhow sex cells are produced.

■ Explain why meiosis is needed forsexual reproduction.

■ Name the cells that are involved infertilization.

■ Explain how fertilization occurs insexual reproduction.

Vocabularysexual reproduction zygotesperm diploidegg haploidfertilization meiosis

Because of meiosis and sexual repro-duction, no one is exactly like you.

Figure 9A human sperm or egg contains 23 chromosomes.The chromosomes are shown in their duplicated form.

Humanegg andmany sperm

1 2 3 4 5 6

13 14 15 16

17 18

7 8

9 10 11 12

19 20 21 22 (X)


Magnification: 790�

Section 2 Sexual Reproduction and Meiosis 105

Sexual Reproduction

Answer 23 chromosomes

Meiosis and Sex Cells

Reading Check

Caption AnswerFigure 10 Fertilized cells have twicethe number of chromosomes found insex cells.

Haploid Cells Because sex cells do not have pairs of chromo-somes, they are said to be haploid (HA ployd). They have onlyhalf the number of chromosomes as body cells. Haploid means“single form.” Human sex cells have only 23 chromosomes—one from each of the 23 pairs of similar chromosomes. Com-pare the chromosomes found in a sex cell, as shown in Figure 9,to the full set of human chromosomes seen in Figure 6A.

How many chromosomes are usually in eachhuman sperm?

Meiosis and Sex CellsA process called meiosis (mi OH sus) produces haploid sex

cells. What would happen in sexual reproduction if two diploidcells combined? The offspring would have twice as many chro-mosomes as its parent. Although plants with twice the numberof chromosomes as the parent plants are often produced, mostanimals do not survive with a double number of chromosomes.Meiosis ensures that the offspring will have the same diploidnumber as its parent, as shown in Figure 10. After two haploidsex cells combine, a diploid zygote is produced that developsinto a new diploid organism.

During meiosis, two divisions of the nucleus occur. Thesedivisions are called meiosis I and meiosis II. The steps of eachdivision have names like those in mitosis and are numbered forthe division in which they occur.

SECTION 2 Sexual Reproduction and Meiosis 105

The human egg releases achemical into the surround-ing fluid that attractssperm. Usually, only onesperm fertilizes the egg.After the sperm nucleusenters the egg, the cellmembrane of the eggchanges in a way that pre-vents other sperm fromentering. What adaptationin this process guaranteesthat the zygote will bediploid? Write a paragraphdescribing your ideas inyour Science Journal.

Meiosis

Meiosis

Sperm (Haploid number = 24)

Egg (Haploid number = 24)

Fertilization

Zygote (Diploid number = 48)

Mitosis

Development

Figure 10 When sex cells join, a zygote forms. The zygote divides bycell division and develops into a new organism. Comparethe number of chromosomes present in the different cells.

With 23 pairs of chromosomes in thehuman body, there are more than 8million different combinations ofchromosomes possible for everyhuman cell formed by meiosis.

Math Have students use library references tofind the number of chromosomes in the bodycells of various plants and animals. Then havethem determine the number of chromosomes inthe sex cells of each one. The number of chromosomesin sex cells should be half the number of chromosomes inbody cells. Logical-MathematicalLSL3

The changes in the egg prevent fer-tilization by more than one sperm.

Use Science WordsWord Origin The term meiosiscomes from a Greek word for“diminution” or becoming less.Ask students what diminishes orbecomes less in meiosis. The chromosome number in each cell isdiminished.


Transparency Activity, p. 43Directed Reading for Content Mastery,

p. 18

Life Science Critical Thinking/Problem Solving, p. 19

Resource Manager


Prophase I Metaphase I Anaphase I Telophase I

Duplicatedchromosomes

Nuclear membrane Centrioles

Spindle fibersPair of duplicatedchromosomes

Meiosis I Before meiosis begins, each chromosome is dupli-cated, just as in mitosis. When the cell is ready for meiosis, eachduplicated chromosome is visible under the microscope as twochromatids. As shown in Figure 11, the events of prophase I aresimilar to those of prophase in mitosis. In meiosis, each dupli-cated chromosome comes near its similar duplicated mate. Inmitosis they do not come near each other.

In metaphase I, the pairs of duplicated chromosomes line upin the center of the cell. The centromere of each chromatid pairbecomes attached to one spindle fiber so, the chromatids do notseparate in anaphase I. The two pairs of chromatids of each simi-lar pair move away from each other to opposite ends of the cell.Each duplicated chromosome still has two chromatids. Then, intelophase I, the cytoplasm divides, and two new cells form. Eachnew cell has one duplicated chromosome from each similar pair.

What happens to duplicated chromosomes during anaphase I?

Meiosis II The two cells formed during meiosis I now beginmeiosis II. The chromatids of each duplicated chromosome willbe separated during this division. In prophase II, the duplicatedchromosomes and spindle fibers reappear in each new cell.Then in metaphase II, the duplicated chromosomes move to thecenter of the cell. Unlike what occurs in metaphase I, each cen-tromere now attaches to two spindle fibers instead of one. Thecentromere divides during anaphase II, and the chromatids sep-arate and move to opposite ends of the cell. Each chromatidnow is an individual chromosome. As telophase II begins, thespindle fibers disappear, and a nuclear membrane forms aroundthe chromosomes at each end of the cell. When meiosis II is fin-ished, the cytoplasm divides.


Figure 11 Meiosis has two divisions of the nucleus—meiosis I andmeiosis II. How many sex cells are finally formed after both divisions are completed?

Meiosis IMeiosis and Sex Cells, continued

Caption AnswerFigure 11 four

In vitro fertilization is a proce-dure that joins sperm and eggsoutside the body. Fertilizedeggs (actually two-day-oldembryos) are then implantedinto the female.

ExtensionHave students research and

report on the contribution ofAfrican American cell biologistEverett Anderson to the modernunderstanding of meiosis. Ander-son is one of the leading researchers indeveloping electron microscopic tech-niques to study meiosis.

LinguisticLSL2

Answer The duplicated chromosomesof each similar pair are pulled to oppo-site ends of the cell.

Use Science WordsWord Meaning Have students usea dictionary to find out whattriploid and tetraploid mean.Have them write an explanationof how this condition occurs.Triploid—each cell in the organism con-tains three sets of chromosomes; plantendosperm is tr iploid and normal.Tetraploid organisms have four sets ofchromosomes in each cell; these conditionsarise from total nondisjunction duringmitosis or meiosis. LinguisticLSL2

Reading Check

Learning Disabled Students who are dyslexic mayhave trouble distinguishing between the firstand second parts of meiosis. Instead of Romannumbers, as in prophase I and prophase II, useArabic numbers for easier identification(prophase 1 and prophase 2).


Enrichment, p. 29

Mathematics Skill Activities, p. 3

Resource Manager


Prophase II Metaphase II Anaphase II Telophase II

Unduplicatedchromosomes

Summary of Meiosis Two cells form during meiosis I. Inmeiosis II, both of these cells form two cells. The two divisionsof the nucleus result in four sex cells. Each has one-half thenumber of chromosomes in its nucleus that was in the originalnucleus. From a human cell with 46 paired chromosomes, meio-sis produces four sex cells each with 23 unpaired chromosomes.

Offspring get half of their chromosomesfrom one parent and half from the other.

What happens if each parent has a differentdiploid number of chromosomes?

Identifying the ProblemA zebra and a donkey can mate to pro-

duce a zonkey. Zebras have a diploid numberof 46. Donkeys have a diploid number of 62.

How can chromosome numbers be predicted?

Solving the Problem1. How many chromosomes would the

zonkey receive from each parent?2. What is the chromosome number of the

zonkey? 3. What would happen when meiosis

occurs in the zonkey’s reproductiveorgans?

4. Predict why zonkeys are usually sterile.

Problem-Solving Activity


Donkey62 Chromosomes

Zebra46 Chromosomes

Zonkey

Meiosis II Make a ModelHave students make a model

of the stages of meiosis in anorganism with three pairs ofchromosomes. Have them useshapes to distinguish the chro-mosomes. Kinesthetic

ActivityUsing one of their favorite

songs, have students write substi-tute lyrics about what happens inmeiosis. Auditory-MusicalLSL2

LSL1

Flow Chart A flow chart helps students logicallysequence events. Students will write major stagesof the sequence in large ovals and write sub-stages in smaller ovals under the larger ovals.Have students design a flow chart for a conceptin this section. Sample flow chart:

Ac tive Reading

ExtensionIn areas throughout the world,

people have similar geneticallycontrolled traits including skincolor, height, and face shape.Have students determine why.Cultures of people were unable to travelgreat distances for thousands of yearsand therefore reproduced mainly amongthemselves, so genetic instructions forsuch traits remained within given cul-tures. Logical-MathematicalLSL3

Meiosis I Meiosis II

Prophase Inuclear membrane

disintegrates; spindlefibers form

Metaphase Ipairs line up

Anaphase IChromosomes pulled

to ends of cell

Telophase ICytoplasm divides

Prophase IIchromosomes & spindle

fibers reappear

Metaphase IIchromosomes line up

Anaphase IIcentromere divides;chromatids separate

Telophase IInuclear membranes

form

National Math StandardsCorrelation to Mathematics Objectives1, 6, 8, 9

Answers1. 23 from the zebra and 31 from

the donkey2. 543. Normal sex cells would not form

because there are 8 unpaired chromosomes from the donkey.

4. Each sex cell could not have one-half the chromosomes of the original cell.

Visualizing Polyploidyin Plants

Have students examine thepictures and read the captions.Then ask the following questions.

What kinds of mistakes inmeiosis or mitosis couldresult in a polyploid plant? Amistake that caused chromosome setsnot to separate, allowing more than onefull set to be present in a cell after divi-sion to form sex cells.

What is the main advantageof bananas being triploid?Triploid plants have very small seeds, sopeople can eat bananas without remov-ing seeds.

Why wouldn’t you findtriploid peanuts in the gro-cery store? The part of a peanutplant you eat is a seed, but triploid plantshave little or no seeds.

ActivityHave students use pipe clean-

ers to model the chromosomesof one of the plants featuredhere. For example, a bananawith 3 sets of 11 chromosomes,a strawberry with 8 sets of 7 chromosomes or a peanut with4 sets of 10 chromosomes.

ExtensionHave students research the

meaning of the terms allopoly-ploidy and autopolyploidy. Havethe students find and list someexamples of plants that eachterm applies to.

VISUALIZING POLYPLOIDY IN PLANTS

Figure 12

TETRAPLOID Polyploidyoccurs naturally in manyplants—including peanutsand daylilies—due to mis-takes in mitosis or meiosis.

HEXAPLOID Modern cultivated strains ofoats have six sets of chromosomes, makingthem hexaploid (6n) plants.

OCTAPLOID Polyploid plants often arebigger than nonpolyploid plants and mayhave especially large leaves, flowers, orfruits. Strawberries are an example of octa-ploid (8n) plants.

TRIPLOID Bright yellow bananas typically come from triploid (3n) bananaplants. Plants with an odd number ofchromosome sets usually cannot repro-duce sexually and have very small seedsor none at all.

▼

▼

▼

▼

You received a haploid (n) set of chromosomes from each of your parents, making you a diploid (2n) organism. In nature, however, many plants

are polyploid—they have three (3n), four (4n), ormore sets of chromosomes. We depend on some ofthese plants for food.

108


Figure 13 Have students follow the unseparatedchromosome pair through each stage of meiosis.How did this error affect the sex cells? Somehad too many chromosomes; others not enough.


Reinforcement, p. 26

Performance Assessment in the Science Classroom, p. 57

Resource Manager


ReteachShow the phases of meiosis

out of sequence. Have studentsidentify each phase and placethe phases in order.

Visual-Spatial

ChallengeHow are the cells at the end

of meiosis different fromthose at the beginning? Theoriginal cell is diploid, and each of the new cells is haploid.

LSELLL2

Metaphase I Anaphase I Metaphase II Anaphase II Sex cells

Mistakes in Meiosis Meiosis occurs many times in re-productive organs. Although mistakes in plants, as shown in Figure 12, are common, mistakes are less common in animals.These mistakes can produce sex cells with too many or too fewchromosomes, as shown in Figure 13. Sometimes, zygotes pro-duced from these sex cells die. If the zygote lives, every cell in theorganism that grows from that zygote usually will have thewrong number of chromosomes. Organisms with the wrongnumber of chromosomes may not grow normally.


Section Assessment

1. Compare and contrast sexual and asexualreproduction.

2. What is a zygote, and how is it formed?

3. Give two examples of sex cells. Where aresex cells formed?

4. Compare what happens to chromosomesduring anaphase I and anaphase II.

5. Think Critically Plants grown from run-ners and leaf cuttings have the same traitsas the parent plant. Plants grown fromseeds can vary from the parent plants inmany ways. Suggest an explanation forwhy this can happen.

6. Making and Using Tables Make a table tocompare mitosis and meiosis in humans.Vertical headings should include: What Type ofCell (Body or Sex), Beginning Cell (Haploid orDiploid), Number of Cells Produced, End-ProductCell (Haploid or Diploid), and Number of Chromosomes in Cells Produced. For more help,refer to the Science Skill Handbook.

7. Communicating Write a poem, song, oranother memory device to help you rememberthe steps and outcome of meiosis. For morehelp, refer to the Science Skill Handbook.

Figure 13This diploid cell has four chromo-somes. During anaphase I, onepair of duplicated chromosomesdid not separate. How many chromosomes does each sex cellusually have?

Meiosis and Sex Cells, continued

ActivityShow students pictures of

karyotypes with abnormal num-bers of chromosomes and havethem find the abnormalities.

Visual-Spatial

Caption AnswerFigure 13 two

LSELL

L2

Content Write these chromo-some numbers on the board:horse—66; pig—40; cat—38;potato—48; dog—78; corn—20.How many chromosomeswould be in a cell of eachorganism produced by mitosisand meiosis? horse—66, 33; pig—40, 20; cat—38, 19; potato—48, 24;dog—78, 39; corn—20, 10 UsePASC, p. 101.

Answers to Section Assessment1. Sexual reproduction: offspring is

produced when sex cells combine;asexual reproduction: geneticallyidentical offspring produced fromone parent.

2. A zygote is the cell that forms whensperm fertilizes an egg.

3. sperm cells—form in male reproductive organs; egg cells—

form in female reproductive organs

4. Anaphase I—duplicated chromo-some pairs separate and move toopposite ends of the cell; anaphaseII—chromatids separate and moveto opposite ends of the cell.

5. Plants produced by asexual reproduc-tion are the result of mitosis, which

duplicates the genetic material of theparent. Plants grown from seeds havea combination of traits from theirparents, because seeds are producedby sexual reproduction.

6. See table.7. Allow students to share their memory

devices with the class.

Feature Mitosis Meiosis

Type of cell Body cell Sex cell

Beginning cell Diploid Diploid

Number of cells Two Fourproduced

End-product Diploid Haploid

Number of Same as Half thechromosomes original cell original cell

Feature Mitosis Meiosis

S E C T I O N

33

PORTFOLIO

Extension, p. 113


Try at Home MiniLAB, p. 111Skill Builder Activities, p. 115See page 122 for more options.

CONTENT ASSESSMENT


Section Planner


Cell Reproduction

This unusual cat is a Devon Rex. It appeared in Devonshire,England in 1960 when a genetic change occurred among British barn cats. The Devon Rex has a small head and a curly coat.

Curly CatSection FocusTransparency33

1. Based on the picture and the description above, what do you thinka genetic change is?

2. How can cat breeders attempt to continue the characteristics ofthe Devon Rex?

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Tie to Prior KnowledgeStudents should be familiar

with template systems, such askeys and locks and peg-and-holegames. Ask for other examples.Use this knowledge to explainthat DNA in the nucleus servesas a template for RNA.


L2

Nucleus


Proteins

DNA


DNA S E C T I O N

What is DNA? Why was the alphabet one of the first things you learned

when you started school? Letters are a code that you need toknow before you learn to read. A cell also uses a code that isstored in its hereditary material. The code is a chemical calleddeoxyribonucleic (dee AHK sih ri boh noo klay ihk) acid, orDNA. It contains information for an organism’s growth andfunction. Figure 14 shows how DNA is stored in cells that havea nucleus. When a cell divides, the DNA code is copied andpassed to the new cells. In this way, new cells receive the samecoded information that was in the original cell. Every cell thathas ever been formed in your body or in any other organismcontains DNA.

Discovering DNA Since the mid-1800s, scientists have known that thenuclei of cells contain large mole-

cules called nucleic acids. By 1950, chemists had learned whatthe nucleic acid DNA was made of, but they didn’t understandhow the parts of DNA were arranged.

■ Identify the parts of a DNA molecule and its structure.

■ Explain how DNA copies itself.■ Describe the structure and

function of each kind of RNA.

VocabularyDNA RNAgene mutation

DNA helps determine nearly everything your body is and does.

Figure 14DNA is part of the chromosomesfound in a cell’s nucleus.

Each chromosomeis composed of a longstrand of DNA wrappedaround proteins, likethread wrapped arounda spool.

The large DNA mole-cule, called a double helix,looks like a twisted ladder.The sides of the ladder aremade of smaller sugar-phosphate molecules.

DNA

Section 3 DNA 111

What is DNA?

A

A

A

A

A

A A

A

Adenine

T

T

TT

T

T

Thymine

C

C

C

Cytosine

C

C

C

GG

G

G

Guanine

GG

G

G

Phosphate Sugar (deoxyribose)

A

DNA’s Structure In 1952, scientist Rosalind Franklin dis-covered that DNA is two chains of molecules in a spiral form. Byusing an X-ray technique, Dr. Franklin showed that the largespiral was probably made up of two spirals. As it turned out, thestructure of DNA is similar to a twisted ladder. In 1953, usingthe work of Franklin and others, scientists James Watson andFrancis Crick made a model of a DNA molecule.

A DNA Model What does DNA look like? According to theWatson and Crick DNA model, each side of the ladder is made upof sugar-phosphate molecules. Each molecule consists of thesugar called deoxyribose (dee AHK sih ri bohs) and a phosphategroup. The rungs of the ladder are made up of other moleculescalled nitrogen bases. Four kinds of nitrogen bases are found inDNA—adenine (AD un een), guanine (GWAHN een), cytosine(SITE uh seen), and thymine (THI meen). The bases are repre-sented by the letters A, G, C, and T. The amount of cytosine incells always equals the amount of guanine, and the amount ofadenine always equals the amount of thymine. This led to thehypothesis that these bases occur as pairs in DNA. Figure 14shows that adenine always pairs with thymine, and guaninealways pairs with cytosine. Like interlocking pieces of a puzzle,each base bonds only with its correct partner.

What are the nitrogen base pairs in a DNA molecule?

SECTION 3 DNA 111

Modeling DNA ReplicationProcedure1. Suppose you have a seg-

ment of DNA that is sixnitrogen base pairs inlength. On paper, using theletters A, T, C, and G, writea combination of six pairsremembering that A and Tare always a pair and C andG are always a pair.

2. Duplicate your segment ofDNA. On paper, diagramhow this happens and showthe new DNA segments.

AnalysisCompare the order of bases ofthe original DNA to the newDNA molecules.

The rungs of the ladder are pairednitrogen bases. Notice that the pairs fittogether much like puzzle pieces.

Purpose to model DNA repli-cation Visual-SpatialMaterials pencil and paperTeaching Strategy Make surestudents understand that theyare to make up a samplestrand of DNA, then makethe complementary strand,then split the two strands andmake those complementarystrands, so they can see thatthe new strands are identicalto the original.Analysis

Answers will vary with the baseschosen, but bases should be in thesame order as the original DNA.

LSL2

Performance Draw and labelone strand of DNA. Have students draw the complemen-tary strand. Use PASC, p. 127.

MiniLAB

Answer Adenine pairs with thymine,and guanine with cytosine.

Reading Check

Learning Disabled Use unifix cubes to demon-strate the various bases. Have students maketheir own models of base pairs, using a differentcolor for each base. KinestheticLSELLL2


Transparency Activity, p. 44MiniLAB, p. 4

Home and Community Involvement, p. 36

Resource Manager

What is DNA? continued

Use an AnalogyStudents are probably familiar

with Morse code. Morse codeuses only two symbols—the dotand the dash—in combinationsto represent numbers and lettersof the alphabet. DNA has foursymbols. The order of nitrogenbases, rather than the sequenceof dots and dashes, expresses theinformation needed for lifeprocesses.

DiscussionHow can you predict the

base sequence of a secondstrand of DNA? by knowing thebase pairing rules and the sequence ofthe original DNA strand

Original DNA molecule

Step 1Enzyme separatesDNA sides

Step 2New bases pair withbases on original DNA.

Step 3Two new identical DNA molecules are produced.

A

A A

A

A A

A

A

A

C

C

C

C

CC

T

T

T

T

T

T

T

T

T

G

GG

G

G

GG

Copying DNA When chromosomes are duplicated beforemitosis or meiosis, the amount of DNA in the nucleus is dou-bled. The Watson and Crick model shows how this takes place.The two sides of DNA unwind and separate. Each side thenbecomes a pattern on which a new side forms, as shown inFigure 15. The new DNA has bases that are identical to those ofthe original DNA and are in the same order.

GenesMost of your characteristics, such as the color of your hair,

your height, and even how things taste to you, depend on thekinds of proteins your cells make. DNA in your cells stores theinstructions for making these proteins.

Proteins build cells and tissues or work as enzymes. Theinstructions for making a specific protein are found in a genewhich is a section of DNA on a chromosome. As shown in Figure 16, each chromosome contains hundreds of genes.Proteins are made of chains of hundreds or thousands ofamino acids. The gene determines the order of amino acids in aprotein. Changing the order of the amino acids makes a differ-ent protein. What might occur if an important protein couldn’tbe made or if the wrong protein was made in your cells?

Making Proteins Genes are found in the nucleus, but pro-teins are made on ribosomes in cytoplasm. The codes for mak-ing proteins are carried from the nucleus to the ribosomes byanother type of nucleic acid called ribonucleic acid, or RNA.


Chromosome 7

Diabetes

Williams-Beuren syndromePhysical- and mental-development disorder

Cystic fibrosis

Pendred syndromeA form of deafness

Obesity

Figure 16This diagram shows just a few ofthe genes that have been identi-fied on human chromosome 7.The bold print is the name thathas been given to each gene.

Figure 15DNA unzips when it is about to becopied. A protein called an enzymehelps unzip the DNA.


Genes

An individual’s complete set ofgenetic material is its genome.In early 2001, it was announcedthat a working draft of thehuman genome had beenmapped. The knowledgegained from the project will be a basis for studying human diseases and accelerating biomedical research.

DNA as Evidence Have students researchthe use of DNA technology in law enforcementand write a report in their Science Journals.Have them use the Internet, news maga-zines, reference books, and interview forensicscientists. LinguisticLSL2

When students hear about the “codeof life,” they are hearing about theorder of nitrogen bases in DNA.

Math The DNA code is written in four “letters”and the cell “reads” the code in groups of three.Have students determine how many differentways the four “letters” (A, T, G, and C) can bearranged in groups of three. There are 64 possiblecombinations. Logical-MathematicalLSL2

Text Question AnswerI t could cause ser ious health

problems.

Section 3 DNA 113

CC

C

C

C

C

C

CG GG G

G G

G

GU

UU

U

U

U

U

AA

A

A

A

AA

tRNA

Amino acidsGrowing protein

Ribosome

Chemical bond forms

DNA

mRNA

mRNA

Nucleus

Ribonucleic Acid RNA is made in the nucleus on a DNApattern. However, RNA is different from DNA. If DNA is like aladder, RNA is like a ladder that has all its rungs sawed in half.Compare the DNA molecule in Figure 14 to the RNA moleculein Figure 17. RNA has the bases A, G, and C like DNA but hasthe base uracil (U) instead of thymine (T). The sugar-phosphatemolecules in RNA contain the sugar ribose, not deoxyribose.

The three main kinds of RNA made from DNA in a cell’snucleus are messenger RNA (mRNA), ribosomal RNA (rRNA),and transfer RNA (tRNA). Protein production begins whenmRNA moves into the cytoplasm. There, ribosomes attach to it.Ribosomes are made of rRNA. Transfer RNA molecules in thecytoplasm bring amino acids to these ribosomes. Inside theribosomes, three nitrogen bases on the mRNA temporarilymatch with three nitrogen bases on the tRNA. The same thinghappens for the mRNA and another tRNA molecule, as shownin Figure 17. The amino acids that are attached to the two tRNAmolecules bond. This is the beginning of a protein. The codecarried on the mRNA directs the order in which the amino acidsbond. After a tRNA molecule has lost its amino acid, it canmove about the cytoplasm and pick up another amino acid justlike the first one. The ribosome moves along the mRNA. NewtRNA molecules with amino acids match up and add aminoacids to the protein molecule.

SECTION 3 DNA 113

Figure 17Cells need DNA, RNA, and aminoacids to make proteins.

DNA in the nucleus is used to make RNA.RNA carries the code for aprotein from the nucleusto the ribosome.

At the ribosome, theRNA’s message is translatedinto a specific protein.

Data Update The HumanGenome Project was begun in 1990. One of its goals is to identify all of the genes on human chromosomes.To find out how the project is progressing, visit the Glencoe Science Web site atscience.glencoe.com.Communicate to your classwhat you learn.

Figure 17 Have students make anevents chain concept map tooutline the stages of proteinsynthesis. Visual-SpatialLSL2

History Have students study the history of DNAresearch. Then using poster board, studentsshould draw and label a timeline showing theevents of DNA research since DNA was firstremoved from a cell nucleus in 1869.

Visual-Spatial and KinestheticLSL2


Enrichment, p. 30Directed Reading for Content Mastery,

pp. 19, 20

Cultural Diversity, p. 19

Resource Manager

Internet Addresses


Make a ModelHave students draw a cell on

poster board and make a modeldemonstrating protein synthesisusing materials such as craftsticks, beads, yarn, and so on.

Visual-Spatial

ActivityOn the board or an overhead

transparency, write the sequencefor one strand of DNA. Havestudents copy the sequence andwrite the corresponding sequencefor mRNA and tRNA.

Visual-Spatial

ExtensionHave students choose one of

the following DNA pioneers fora written report: Francis Crick,James Watson, Barbara McClin-tock, Maurice Wilkins, MarthaChase, A.D. Hershey, RosalindFranklin. Linguistic PLSL2

LSL2

LSL2




Controlling Genes You mightthink that because most cells in anorganism have exactly the samechromosomes and the same genes,they would make the same proteins,but they don’t. In many-celledorganisms like you, each cell usesonly some of the thousands of genesthat it has to make proteins. Just aseach actor uses only the lines fromthe script for his or her role, eachcell uses only the genes that directthe making of proteins that it needs.For example, muscle proteins aremade in muscle cells, as representedin Figure 18, but not in nerve cells.

Cells must be able to controlgenes by turning some genes off andturning other genes on. They do thisin many different ways. Sometimesthe DNA is twisted so tightly that noRNA can be made. Other times,chemicals bind to the DNA so that itcannot be used. If the incorrect pro-teins are produced, the organismcannot function properly.

MutationsSometimes mistakes happen when DNA is being copied.

Imagine that the copy of the script the director gave you wasmissing three pages. You use your copy to learn your lines. Whenyou begin rehearsing for the play, everyone is ready for one ofthe scenes except for you. What happened? You check your copyof the script against the original and find that three of the pagesare missing. Because your script is different from the others, youcannot perform your part correctly.

If DNA is not copied exactly, the proteins made from theinstructions might not be made correctly. These mistakes, calledmutations, are any permanent change in the DNA sequence of agene or chromosome of a cell. Some mutations include cells thatreceive an entire extra chromosome or are missing a chromo-some. Outside factors such as X rays, sunlight, and some chemi-cals have been known to cause mutations.

When are mutations likely to occur?


Figure 18Each cell in the body producesonly the proteins that are neces-sary to do its job.

Cells in the iris of the eye produce proteins needed for eye color.

Muscle cells produce proteins that help make muscles move.

Cells in the stomach produce proteins necessary to digest food.

Mutations

Any agent that can cause achange in DNA is a mutagen.Mutagens can be radiation,chemicals, or even high tem-peratures. Asbestos, cyanide,and formaldehyde are highlyreactive compounds found inbuildings and the environmentthat can interact with DNAand cause changes.

Effec ts of Mutation Have studentsresearch and write a report on mutations. Havethem give examples of mutations, indicatewhether the mutation is harmful, benign, orbeneficial, and include the cause of themutation. LinguisticLSL2

Students may think that anymutation that might occur dur-ing duplication is harmful.More often than not, muta-tions have no effect on thecharacteristics of the organism.Some mutations, in fact, areadaptive, providing the organ-ism with traits that make it better suited to its environ-ment; these mutations play amajor role in evolution. Anexample of a beneficial muta-tion in bacteria is antibioticresistance.


Reinforcement, p. 27Lab Activity, pp. 11–13

Reading and Writing Skill Activities, p. 51

Resource Manager

Answer when DNA is being copied

Reading Check

Section 3 DNA 115

ReteachHave students make a drawing

of DNA replication and proteinsynthesis. Visual-Spatial

ChallengeWhy does the mutation of

a sperm or egg cell have apotential for different resultsfrom that of a body cell? Amutation in a reproductive cell will affectoffspring. A mutation in a body cell willaffect only the individual.

LSL2

SECTION 3 DNA 115

Figure 19 Because of a defect on chromosome 2,the mutant fruit fly has short wingsand cannot fly. Could this defect betransferred to the mutant’s offspring?Explain.

Section Assessment

1. How does DNA make a copy of itself?

2. How are the codes for proteins carried from the nucleus to the ribosomes?

3. A single strand of DNA has the basesAGTAAC. Using letters, show a matching DNA strand from this pattern.

4. How is tRNA used when cells build proteins?

5. Think Critically You begin as one cell.Compare the DNA in one of your brain cellsto the DNA in one of your heart cells.

6. Concept Mapping Using a network tree con-cept map, show how DNA and RNA are alike andhow they are different. For more help, refer tothe Science Skill Handbook.

7. Using a Word Processor Use a word processorto make an outline of the events that led up tothe discovery of DNA. Use library resources tofind this information. For more help, refer tothe Technology Skill Handbook.

Research Visit the Glencoe Science Web site atscience.glencoe.com formore information about whatgenes are present on thechromosomes of a fruit fly.Make a poster that shows oneof the chromosomes andsome of the genes found onthat chromosome.

Results of a Mutation Genes control the traits you inherit.Without correctly coded proteins, an organism can’t grow,repair, or maintain itself. A change in a gene or chromosomecan change the traits of an organism, as illustrated in Figure 19.

If the mutation occurs in a body cell, it might or might notbe life threatening to the organism. However, if a mutationoccurs in a sex cell, then all the cells that are formed from thatsex cell will have that mutation. Mutations add variety to aspecies when the organism reproduces. Many mutations areharmful to organisms, often causing their death. Some muta-tions do not appear to have any effect on the organism, andsome can even be beneficial. For example, a mutation to a plantmight cause it to produce a chemical that certain insects avoid.If these insects normally eat the plant, the mutation will help theplant survive.

Oral What are the three kindsof RNA and their functions?Messenger RNA, transfer RNA, and ribo-somal RNA; mRNA is copied from DNAand moves from the nucleus to a ribo-some; tRNA carries amino acids to ribo-somes; rRNA makes up ribosomes. UsePerformance Assessment inthe Science Classroom, p. 89.

Answers to Section Assessment1. The two sides unwind and separate;

a complementary strand is formedfor each, and the resulting double-stranded DNA has one original strandand one new strand.

2. The codes are carried by mRNA fromthe nucleus to the ribosome.

3. TCATTG

4. The tRNA in the cytoplasm bringsamino acids to the ribosomes.There,three nitrogen bases on the mRNAtemplate match with three bases onthe tRNA.The amino acids bond, andprotein synthesis begins.

5. The DNA is identical.

6. Answers should be similar to thetable for question 16 in the ChapterAssessment.

7. Students should be sure to includethe contributions of Miescher,Griffith, Avery, Hershey, Chase,Chargraff,Wilkins, Franklin, Crick,and Watson.

Caption AnswerFigure 19 yes, if it affects reproductivecells

Internet Addresses




Recognize the ProblemInternet Students will use Inter-net sites that can be accessedthrough the Glencoe ScienceWeb site. They will observegenetic traits and mutations inanimals.Non-Internet S ources Collectbooks describing animals andtheir genetic traits.

Time Requiredabout three days

PreparationInternet Access the Glencoe Science Web site to run throughthe steps that students willfollow.Non-Internet Have students usebooks to select an animal andone of its traits to investigate.

Form a Hypothesis

Possible HypothesesMost students will select a phe-notype to hypothesize about.For example, a tiger’s white furis a mutation that can become acommon trait.

Mutations can result in dominant or recessive genes.A recessive characteristic can appear only if an organism has two recessive

genes for that characteristic.However, a dominant characteristic can appear if an organism has one or two dominant genes for that characteristic. Why do some mutations result in more common traitswhile others do not?

Recognize the ProblemHow can a mutation become a common trait?

Form a HypothesisForm a hypothesis about how a mutation can become a common trait.

Mutations

Data SourceGo to the Glencoe

Science Web site at science.glencoe.com for more information on commongenetic traits in different animals, reces-sive and dominant genes, and data fromother students.

Goals■ Observe traits of various animals.■ Research how mutations become

traits.■ Gather data about mutations.■ Make a frequency table of your

findings and communicate them to other students.


Fantail Pigeon

White tiger


Internet Addresses

Explore the Glencoe Science Web site at science.glencoe.comto find out more about topics in this activity.


Activity Worksheet, pp. 7–8

Lab Management and Safety, p. 58

Resource Manager



Test Your Hypothesis

Analyze Your Data

Draw Conclusions

Do1. Make sure your teacher approves

your plan before you start.

2. Visit the Glencoe Science Web sitefor links to different sites aboutmutations and genetics.

3. Decide if a mutation is beneficial,harmful, or neither. Record yourdata in your Science Journal.

Plan1. Observe common traits in various

animals, such as household pets or animals you might see in a zoo.

2. Learn what genes carry these traitsin each animal.

3. Research the traits to discoverwhich ones are results of mutations.Are all mutations dominant? Are anyof these mutations beneficial?

3. Make a chart that compares reces-sive mutations to dominant muta-tions. Which are more common?

4. Share your data with other studentsby posting it on the Glencoe ScienceWeb site.

1. Record in your Science Journal a listof traits that are results of mutations.

2. Describe an animal, such as a pet oran animal you’ve seen in the zoo.Point out which traits are known tobe the result of a mutation.

4. Mutations occur every day but weonly see a few of them. Infer howmany mutations over millions ofyears can lead to a new species.

1. Compare your findings to those ofyour classmates and other data on theGlencoe Science Web site. What weresome of the traits your classmatesfound that you did not? Which werethe most common?

2. Look at your chart of mutations. Are allmutations beneficial? When might amutation be harmful to an organism?

3. How would your data be affected if youhad performed this activity when oneof these common mutations firstappeared? Do you think you would seemore or less animals with this trait?

ACTIVITY 117

Find this Use the Internet activity on the Glencoe Science Web site at

science.glencoe.com. Post your data in the table provided. Combine your data with that of other students and make a chart that shows all of the data.

Siberian Husky’s eyes

Test Your Hypothesis

Teaching StrategyHave students use animal popu-lation data to see how often thatmutation is found.

Analyze Your Data1. Answers will vary. Color can result

from a mutation.2. Answers will depend upon animals

chosen.3. Answers will vary, but dominant

genes are not necessarily morecommon.

4. Students may need help postingdata.

Draw Conclusions1. Answers will vary. Remind students

that the most common traits may bethe result of mutations.

2. Answers will vary. Have studentsthink about the mutation they areinvestigating and how helpful orharmful it is to the animal.

3. If you had investigated the mutationwhen it first appeared, you may have seen fewer animals with thetrait.With the passage of time, youcan determine if the mutation isbeneficial.

4. Organisms with mutations may bebetter suited to a particular environ-ment.These traits would be passedon to their offspring. Many mutationsmay lead to a new species.

ACTIVITY 117

Oral Students describe mutations theyresearched and discuss how helpful they are toanimals. Show pictures of animals with themutation. Use Performance Assessment inthe Science Classroom, p. 143.

Have students use the Internet to collect pictures of theanimal they are investigating. Have them find picturesthat show the mutation.


Accidentsin SCIENCE

SOMETIMES GREAT DISCOVERIES HAPPEN BY ACCIDENT!

A TangledHow did a scientist get

chromosomes to separate?

Thanks to chro-mosomes, eachof us is unique!

118


Content BackgroundCytogenetics is the branch of

science that studies heredityboth through genetics and stud-ies of the cell. In 1956, modernhuman cytogenetics began,thanks to the discovery of thenumber of human chromosomespresent in each cell of the body.As early as 1905, scientists haddetermined that chromosomesare found in pairs, and in 1915,Thomas Hunt Morgan discov-ered that genes were found onchromosomes. It was not until1952 that Dr. Hsu’s workoccurred, and 1953 when Wat-son and Crick used RosalindFranklin’s work to determine thestructure of DNA. Studies ofhuman chromosomes and geneshave progressed at an astoundingrate since that time. Scientistshave determined the particularchromosome that carries thegene for many human diseasesand other traits.

DiscussionExplain what type of mis-

take the lab technician in Dr. Hsu’s lab might havemade while mixing the solu-tion that caused mysteriousbehavior of the chromo-somes. Possible answer:The technicianeither added too little of the solute to aset amount of water, or too much waterto a set amount of solute, causing thesolution to have a higher water contentthan the cells.

“Genetics and Genetic Engineering,” by Lisa Yount,Facts on File, Inc., 1997.

The Big Idea, by Paul Strathern. New York: Doubleday, 1999.

The History of Genetics, by Robert Snedden. NewYork: Raintree Steck-Vaughn Publishers, 1995.

Resources for Teachers and Students

As students research

the history of research on human chromosomes, have them

consider the rate at which discoveries occurred then and

now. Point out that the Human Genome Project has

increased the knowledge of genetics at an amazing rate.

V iewed under a microscope, chro-

mosomes in cells sometimes look a

lot like tangled spaghetti. That’s

why during the early 1900s, scientists had

such a hard time figuring out how many

chromosomes are in each human cell.

Imagine then, how Dr. Tao-Chiuh Hsu (dow

shew•SEW) must have felt when he looked

into a microscope and saw “beautifully scat-

tered chromosomes.” The problem was, Hsu

didn’t know what he had done to separate

the chromosomes into countable strands.

“I tried to study those slides and set up

some more cultures to repeat the miracle,”

Hsu explained. “But nothing happened.”

For three months, Hsu toiled in the lab,

changing every variable he could think of to

make the chromosomes separate again.

In April 1952, he reduced the amount of salt

and increased the amount of water in the

solution used to prepare the cells for study,

and his efforts were finally rewarded. Hsu

quickly realized that the chromosomes

separated because of osmosis.

Osmosis is the movement of water mole-

cules through cell membranes. This move-

ment occurs in predictable ways. The water

molecules move from areas with higher con-

centrations of water to areas with lower con-

centrations of water. In Hsu’s case, the

solution had a higher concentration of water

than the cell did. So water moved from the

solution into the cell and the cell swelled until

it finally exploded. The chromosomes sud-

denly were visible as separate strands.

What made the cells swell the first time?

Apparently, a lab technician had mixed the

solution incorrectly. “Since nearly four

months had elapsed, there was no way to

trace who actually had prepared that particu-

lar [solution],” Hsu noted. “Therefore, this

heroine must remain anonymous.”

Tale

The Real Count

Although Hsu’s view of the chromosomeswas fairly clear, he mistakenly estimated thenumber of chromosomes in a human cell. Heput the count at 48, which was the numberthat most scientists of the day accepted. By1956, however, other scientists improvedupon Hsu’s techniques and concluded thatthere are 46 chromosomes in a human cell.Because chromosomes contain the genesthat determine each person’s characteris-tics, this discovery helped scientists betterunderstand genetic diseases and disorders.Scientists also have a better idea of whyevery person, including you, is unique.

For more information, visitscience.glencoe.com

CONNECTIONS Research Until the 1950s, scientists believedthat there were 48 chromosomes in a human cell. Research the developments that led scientists to the conclusion that the human cellhas 46 chromosomes. Use the Glencoe Science Web site to get started.

These chromo-somes are mag-nified 500 times.

OOPS! ACCIDENTS IN SCIENCE 119

ActivityHave students work in teams

to research the major discover-ies in the field of genetics. Haveeach team display their resultson a timeline made on a longpiece of paper. Students shouldbe encouraged to include dis-coveries from early researchuntil present times, and toinclude the names of the scien-tists who made the discoveries.

Analyze the EventAsk the students to brainstorm

what other positive or negativeeffects a mistake in making a labsolution could have. Poss ibleanswers: In some cases a mistake couldresult in better than expected results or adiscovery that would not have otherwisebeen made. Negative results couldinclude work that can’t be repeated, theneed to re-do the entire experiment,skewed results, or potential f ire or poisoning hazards. Point out to students that because Dr. Hsu’sresults were due to a mistake ittook him months to find thecause of the good results. Ingeneral, mistakes of this type in the lab bring only negativeoutcomes.

CONNECTIONS

Internet Addresses

Explore the Glencoe Science Web site at science.glencoe.comto find out more about topics in this feature.



ChapterStudy Guide

44

120 CHAPTER STUDY GUIDE

After students have read the chapter and completed

the Foldable described in Before You Read, havethem do the activity on the student page.


FOLDABLESReading &Study Skills

After You ReadAfter You Read

PreviewStudents can answer the ques-

tions in their Science Journals.Discuss the answers as you gothrough the chapter. Linguistic

ReviewStudents can write their

answers, then compare themwith those of other students.

Interpersonal

ReteachStudents can look at the illus-

trations and describe details thatsupport the main ideas of thechapter. Visual-Spatial

Answers toChapter ReviewSECTION 14. Cell division produces new bone cells

to replace damaged ones.

SECTION 24. 26

SECTION 34. It has a mutation that affects its

number of wings.

LS

LS

LS

120 CHAPTER STUDY GUIDE

4. Meiosis ensures that off-spring produced by fer-tilization have thesame number of chro-mosomes as their par-ents. If the diploidnumber of a frog is 26,how many chromosomesdoes this tadpole have?

Section 3 DNA 1. DNA—the genetic material of all organ-

isms—is a large molecule made up of twotwisted strands of sugar-phosphate mole-cules and nitrogen bases.

2. All cells contain DNA. The section of DNAon a chromosome that directs the makingof a specific protein is a gene.

3. DNA can copy itself and is the pattern fromwhich RNA is made. Messenger RNA, ribo-somal RNA, and transfer RNA are used tomake proteins.

4. Sometimes changes inDNA occur. Perma-nent changes in DNAare called mutations.Why does this fruit flyhave four wings insteadof the normal two?

Section 1 Cell Division and Mitosis1. The life cycle of a cell has two parts—

growth and development and cell division.Cell division includes mitosis and the divi-sion of the cytoplasm.

2. In mitosis, the nucleus divides to form twoidentical nuclei. Mitosis occurs in four continuous steps, or phases—prophase,metaphase, anaphase, and telophase.

3. Cell division in animal cells and plant cellsis similar, but plant cells do not have centri-oles and animal cells do not form cell walls.

4. Organisms use celldivision to grow, toreplace cells, and forasexual reproduc-tion. Asexual repro-duction producesorganisms with DNAidentical to the par-ent’s DNA. Fission,budding, and regen-eration can be usedfor asexual reproduction. How would celldivision help heal this broken bone?

Section 2 Sexual Reproduction and Meiosis

1. Sexual reproduction results when a malesex cell enters the female sex cell. This eventis called fertilization, and the cell that formsis called the zygote.

2. Before fertilization, meiosis occurs in thereproductive organs, producing four hap-loid sex cells from one diploid cell.

3. During meiosis, two divisions of thenucleus occur.

To help you review cellreproduction, use theOrganizational Study Fold

about the cell you made at the beginning ofthe chapter.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Study GuideChapter Study GuideChapter 44

ChapterStudy Guide

44

Using Vocabulary1. Egg, sperm2. Mitosis3. DNA or RNA4. gene5. haploid6. asexual reproduction7. chromosome8. Meiosis9. Fertilization, meiosis, or sexual

reproduction10. mutation

See student page.

CHAPTER STUDY GUIDE 121

Vocabulary Wordsa. asexual i. meiosis

reproduction j. mitosisb. chromosome k. mutationc. diploid l. RNAd. DNA m. sexual e. egg reproductionf. fertilization n. spermg. gene o. zygoteh. haploid

Using Vocabulary Replace each underlined word in the follow-

ing statements with the correct vocabulary word.

1. Muscle and skin cells are sex cells.

2. Digestion produces two identical cells.

3. An example of a nucleic acid is sugar.

4. A cell is the code for a protein.

5. A diploid sperm is formed during meiosis.

6. Budding is a type of meiosis.

7. A ribosome is a structure in the nucleusthat contains hereditary material.

8. Respiration produces four sex cells.

9. As a result of fission, a new organism develops that has its own unique identity.

10. An error made during the copying of DNAis called a protein.

Be a teacher—organize a group of friends andinstruct each person to review a section of thechapter for the group. Teaching helps you remem-ber and understand information thoroughly.

Study Tip

Think of four ways that organisms can use mitosis and fill out the spider diagram below.

Mitosis

GrowthAsexual

reproduction

Cell replacement Regeneration

Study GuideChapter XXXX Study GuideChapter

used for used for

used forused for

44

CHAPTER STUDY GUIDE 121

ChapterAssessment

44

11. TAGGCAG12. UAGGCAG13. No; in order for a mutation to be

passed to offspring, the mutationmust take place in a sex cell.

14. the copying of chromosomes ininterphase; the separation of thecopies at anaphase; the separationof two new cells at telophase

15. This could happen if nondisjunction(failure of like chromosomes orchromatids to separate) occurs during anaphase I or II.

1. D2. D3. B4. C5. A6. A7. D8. D9. C

10. B

Choose the word or phrase that best answersthe question.

1. Which of the following is a double spiralmolecule with pairs of nitrogen bases?A) RNA C) proteinB) amino acid D) DNA

2. What is in RNA but NOT in DNA?A) thymine C) adenineB) thyroid D) uracil

3. If a diploid tomato cell has 24 chromo-somes, how many chromosomes will thetomato’s sex cells have?A) 6 C) 24 B) 12 D) 48

4. During a cell’s life cycle, when do chromo-somes duplicate?A) anaphase C) interphaseB) metaphase D) telophase

5. When do chromatids separate during mitosis?A) anaphase C) metaphaseB) prophase D) telophase

6. How many chromosomes are in the originalcell compared to those in the new cellsformed by cell division?A) the same amount C) twice as manyB) half as many D) four times as many

7. What can budding, fission, and regenera-tion be used for?A) mutationsB) sexual reproductionC) cell cyclesD) asexual reproduction

8. What is any permanent change in a gene ora chromosome called?A) fission C) replicationB) reproduction D) mutation

9. What does meiosis produce?A) cells with the diploid chromosome

numberB) cells with identical chromosomesC) sex cellsD) a zygote

10. What type of nucleic acid carries the codesfor making proteins from the nucleus to the ribosome?A) DNA C) proteinB) RNA D) genes

11. If the sequence of bases on one side ofDNA is ATCCGTC, what is the sequence on its other side?

12. A strand of RNA made using the DNA pattern ATCCGTC would have what basesequence? Look at Figure 14 for a hint.

13. Will a mutation in a human skin cell bepassed on to the person’s offspring?Explain.

14. What occurs in mitosis that gives the newcells identical DNA?

15. How could a zygote end up with an extrachromosome?

16. Classifying Copy and complete this tableabout DNA and RNA.

122 CHAPTER ASSESSMENT

DNA RNA

Number of Strands

Type of Sugar

Letter Names of Bases

Where Found

DNA and RNA

2 1

deoxyribose ribose

G, A, C, T G, A, C, U

nucleus nucleus & cytoplasm

Chapter 1515 Assessment Chapter 44

122 CHAPTER ASSESSMENT

Portfolio Encourage students to place in theirportfolios one or two items of what they con-sider to be their best work. Examples include:• Visual Learning, p. 97• Make a Model, p. 107• Extension, p. 113

Performance Additional performance assess-ments, Performance Task Assessment Lists, andrubrics for evaluating these activities can befound in Glencoe’s Performance Assessmentin the Science Classroom.

Chapter Planner

ChapterAssessment

44

21. Cards should be sequenced asshown in Figure 11. If interphase is included, it should come beforeprophase I. Use PerformanceAssessment in the ScienceClassroom, p. 163.

16. See student page.17. See student page.18. Student answers should reflect

the information in Section 2 and Figure 11.

19. Incorrect division can result in anincorrect number of chromosomes,often leading to abnormal offspring.

20. The order of events given for meio-sis should reflect Figure 11 andformation of the zygote, Figure 10.The cell at the beginning of meiosisis diploid.The four cells at the end of meiosis are all haploid.

CHAPTER ASSESSMENT 123

17. Concept Mapping Complete the eventschain concept map of DNA synthesis.

18. Comparing and Contrasting Meiosis is two divisions of a reproductive cell’snucleus. It occurs in a continuous series of steps. Compare and contrast the steps of meiosis I to the steps of meiosis II.

19. Forming Hypotheses Make a hypothesisabout the effect of an incorrect mitotic division on the new cells produced.

20. Concept Mapping Make an events chainconcept map of what occurs from inter-phase in the parent cell to the formation ofthe zygote. Tell whether the chromosome’snumber at each stage is haploid or diploid.

21. Flash Cards Make a set of 11 flash cardswith drawings of a cell that show the differ-ent stages of meiosis. Shuffle your cards andthen put them in the correct order. Givethem to another student in the class to try.

Two new molecules of DNA form.

DNA unwinds.

Go to the Glencoe Science Web site at science.glencoe.com or use the Glencoe Science CD-ROM for additionalchapter assessment.

TECHNOLOGY

Each side becomes a pattern.

AssessmentChapter 1515

A scientist studied the reproduction ofhuman skin cells. The scientist examinedseveral skin cells using a microscope. Thetable below summarizes what she learned.

Use the information in the table toanswer the following questions.

1. What process is taking place in all ofthe cells?A) cell divisionB) fertilizationC) cytoplasm divisionD) chromosome separation

2. Which is the correct order of thestages, from first to last, in the cell division of a skin cell?F) 3, 4, 1, 2 H) 1, 2, 4, 3G) 1, 3, 2, 4 J) 2, 1, 3, 4

3. Since the process described in the tableproduces two new identical cells,before it begins the chromosomes inthe cell must _____ .A) divide in half C) duplicateB) find a mate D) disintegrate

AssessmentChapter

Test Practice

Cell Phase of Division Characteristic

Skin Cells

1

2

3

4

Anaphase

Telophase

Prophase

Metaphase

Chromosomeseparation

Cytoplasmdivision

Visiblechromosomes

Chromosomesline up

44

CHAPTER ASSESSMENT 123

Reproducible Masters

Chapter Resources BookletChapter Review, pp. 35–36Chapter Tests, pp. 37–40Assessment Transparency Activity, p. 47

Glencoe Science Web siteInteractive TutorChapter Quizzes

Glencoe Technology

Assessment TransparencyInteractive CD-ROM Chapter QuizzesExamView Pro Test BankVocabulary PuzzleMaker SoftwareMindJogger Videoquiz DVD/VHS

Resources

The Test-Taking Tip was writtenby The Princeton Review, thenation’s leader in test preparation.1. A2. F3. C


Documents

Chapter 4: Cell Reproduction