CHAPTER

30 PLANT REPRODUCTIONPlanning Guide

Compression GuideTo shorten instructionbecause of time limitations,omit Section 3.

Chapter Opener

Section 1 Plant Life Cycles• Describe the life cycle of a moss.• Describe the life cycle of a fern.• Describe the life cycle of a gymnosperm.• Compare homospory and heterospory.

Section 2 Sexual Reproduction in Flowering Plants

• Identify the four main flower parts, and state the functionof each.

• Describe gametophyte formation in flowering plants.• Relate flower structure to methods of pollination.• Describe fertilization in flowering plants.

TE Activity Floral Structures, p. 614 ◆gTE Demonstration Pollen Diversity, p. 615 ◆gTE Internet Activity Pollination, p. 616 a

HBS Quick, Data, and Math Labs Observing theArrangement of Parts of a Flower* ◆g

HBS Skills Practice Labs Dissecting Flowers* ◆gANC Forensics Labs Assault at the Flower

Shop* ◆a

TE Group Activity Dispersal Methods, p. 619 ◆gSE Quick Lab Predicting Seed Dispersal,

p. 620 ◆gANC Datasheets for In-Text Labs Predicting Seed

Dispersal*gTE Internet Activity Seeds, p. 621 aTE Group Activity Germinating Bluebonnets,

p. 622 ◆gTE Activity Garden Design, p. 623 gTE Demonstration Vegetative Propagation,

p. 623 ◆gSE Exploration Lab Comparing Seed Structure and

Seedling Development, pp. 628–629 ◆gANC Datasheets for In-Text Labs Comparing Seed

Structure and Seedling Development*gHBS Inquiry and Exploration Labs Fruits and

Seeds* ◆g

OSP Parent LetterCD Student Edition on CD-ROMCD Guided Reading Audio CD

TR G33 Life Cycle of a Moss*TR G34 Life Cycle of a Fern*TR G35 Life Cycle of a Conifer*CD Visual Concepts CD-ROM

TR G36 Floral Structure*TR G37 Formation of a Female

Gametophyte*TR G38 Formation of a Male

Gametophyte*TR G39 Life Cycle of an Angiosperm*CD Visual Concepts CD-ROM

TR G40 Bread Wheat*TR G41 Bread Wheat, cont.*TR G42 Seed Structure*TR G43 Structure and Function

of Seeds*TR G44 Seed Germination*TR G45 Stems Modified for Vegetative

Reproduction*TR G46 External Structures

of Kalanchoe*TR G47 Internal Structures

of Kalanchoe*TR G48 Methods of Vegetative Plant

Propagation*CD Visual Concepts CD-ROMVID Biology Lab Video Observing the

Effect of Nutrients on VegetativeReproduction

VID Biology Lab Video Comparing Beanand Corn Seedlings

pp. 608–612

608A C H A P T E R 3 0 P l a n t R e p r o d u c t i o n

OBJECTIVES LABS, DEMONSTRATIONS, AND ACTIVITIES TECHNOLOGY RESOURCESPACING • 45 min

pp. 613–617PACING • 45 min

pp. 618–624PACING • 90 minSection 3 Dispersal and Propagation• Describe adaptations for fruit and seed dispersal.• Name the three major categories of fruits.• Compare the structure and germination of different

types of seeds.• Recognize the advantages and disadvantages of

sexual reproduction.• Describe human methods of plant propagation.

TE Demonstration Plant Display, p. 609 ◆gTE Activity Germinating Fern Spores,

p. 610 ◆gHBS Quick, Data, and Math Labs Observing a Fern

Gametophyte* ◆gHBS Quick, Data, and Math Labs Observing the

Gametophytes of Pines* ◆g

SE Chapter Highlights, p. 625SE Chapter Review, p. 626TR Graphic Organizer*gTR Concept Mapping*g

ANC Vocabulary Review*gANC Quizzes*gANC Chapter Test*gANC Chapter Test*a

SE Standardized Test Prep, p. 627OSP Test GeneratorOSP Test Item Listing

CHAPTER REVIEW, ASSESSMENT, ANDSTANDARDIZED TEST PREPARATION

PACING • 90 min

Visit go.hrw.com to find avariety of online resources.Click Holt Online Learningfor an online edition of this textbook and otherinteractive resources.

This DVD package includes: • Holt Calendar Planner• Customizable Lesson Plans• Editable Worksheets• MindPoint® Quiz Show• Holt PowerPoint® Resources

• ExamView® Version 6.0Assessment Suite

• Interactive Teacher’s Edition• Holt PuzzlePro®

Online and Technology Resources

KEY SE Student Edition OSP One-Stop Planner VID Classroom Video/DVDTE Teacher Edition TR Transparencies and * Also on One-Stop Planner

ANC Ancillary Workbook Transparency Worksheets ◆ Requires advance prepHBS Holt BioSources Lab Program CD CD or CD-ROM

TE Using the Figure Studying Pollen, p. 608ANC Science Skills Worksheet*gANC Critical Thinking Worksheet*a

TE Reading Skill Builder Interactive Reading, p. 609 bTE Using the Figure Comparing Mosses and Ferns, p. 610 bTE Inclusion Strategies, p. 610 ◆TE Skill Builder Interpreting Visuals, p. 611 g

ANC Active Reading Guide*

TE Using the Figure Ovule Formation, p. 614 gTE Using the Figure Pollen Grain Formation, p. 615 gTE Reading Skill Builder K-W-L, p. 615 bTE Skill Builder Writing Skills, p. 616 g

ANC Active Reading Guide*

TE Using the Table Classifying Fruit Types, p. 619 ◆gTE Using the Figure Seed Structures, p. 620 gTE Skill Builder Science Literacy, p. 621 aTE Skill Builder Writing Skills, p. 623 gTE Inclusion Strategies, p. 623

ANC Active Reading Guide*

TE Assessing Prior Knowledge, p. 608ANC Study Guide*g

SE Section Review, p. 612 gTE Reteaching, p. 612 ◆bTE Quiz, p. 612 g

SE Section Review, p. 617 gTE Reteaching, p. 617 bTE Quiz, p. 617 g

SE Section Review, p. 624 gTE Reteaching, p. 624 bTE Quiz, p. 624 gTE Alternative Assessment, p. 625 gTE Study Tip, p. 625 g

National Science EducationStandards

LSCell1, LSCell2, LSCell4, LSEvol1,LSMat4, LSBeh2, UCP5

LSCell1, LSCell2, LSCell4, LSEvol1,LSMat4, LSBeh2, UCP5

LSEvol1, UCP5, SI1, SI2

C H A P T E R 3 0 P l a n n i n g G u i d e 608B

SKILLS DEVELOPMENT RESOURCES REVIEW AND ASSESSMENT CORRELATIONS

Maintained by the National ScienceTeachers Association.

www.scilinks.orgClassroom CD-ROMs

• Guided Reading Audio Program• Student One Stop• Virtual Investigations• Visual Concepts• Dissection Labs

Classroom Videos

• Lab Videos demonstratethe chapter lab.

Holt Lab GeneratorCD-ROM

Search for any lab by topic, standard,difficulty level, or time. Edit any lab to fit your needs, or create your own labs.Use the Lab Materials QuickList softwareto customize your lab materials list.

608 C H A P T E R 3 0

CHAPTER 30Using the FigureStudying Pollen Have studentsexamine the picture of the twopollen grains from goose grass,Galium aparine. Goose grass iscommonly known as bedstraw. Itshairy leaves often cling to otherplants or attach to the skin orclothing of passersby. The pollengrains in this SEM are approxi-mately 100 μm wide. (about25,000 μm equals 1 in.) Tell stu-dents that pollen grains containhaploid cells produced by meio-sis. Ask students to describe theshape, size, and surface featuresof the pollen grains shown in thephotograph. Tell students thatthese types of characteristics areunique to each plant species. Askstudents to hypothesize abouthow the pollen grains shown inthis photograph are dispersed.(by wind, insects, and humans)

Visual

Assessing PriorKnowledgeReview the following conceptswith students.

Cell Reproduction (Ch. 8): Askstudents how organisms makenew cells that are exact copies of existing cells. (by the process ofmitosis) Ask them how organismsmake new cells with half thegenetic material of the parentcells. (by the process of meiosis)Ask students what results when two haploid gamete cells combine.(a zygote is formed)

GENERAL

LS

Standards Correlations

National Science Education Standards

LSCell1 Cells have particular structures that underlie their functions.

LSCell2 Most cell functions involve chemical reactions.

LSCell4 Cell functions are regulated.

LSCell 6 Cells can differentiate and form complete multicellular organisms.

LSInter3 Organisms both cooperate and compete in ecosystems.

UCP1 Systems, order, and organization

UCP2 Evidence, models, and explanation

UCP5 Form and function

SI1 Abilities necessary to do scientific inquiry

SI2 Understandings about scientific inquiry

ST1 Abilities of technological design

ST2 Understandings about science and technology

HNS1 Science as a human endeavor

Two pollen grains (yellow) have beendeposited on the stigma of a goose-grass(Galium aparine) flower. A pollen tube canbe seen growing from the pollen grain onthe right. The pollen tube provides a pathfor sperm to travel from the pollen grainto the egg so that fertilization may occur.

SECTION 1 Plant Life Cycles

SECTION 2 Sexual Reproduction in Flowering Plants

SECTION 3 Dispersal and Propagation

30CHAPTER PLANT REPRODUCTIONPLANT REPRODUCTION

608

P L A N T R E P R O D U C T I O N 609

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describesthe life cycles of seedless andnonflowering seed plants. Thissection also describes in detailthe life cycles of a moss, a fern,and a conifer.

Ask students why they thinkmosses do not grow very large asadults. (They lack vascular tissue thatoffers structural support to plants thathave vascular systems and that trans-ports water to parts of the plant that arefar from a source of water.) Logical

DemonstrationPlant Display Bring some seed-less and nonflowering seed plantsbearing reproductive structuresto class and display them. Try to include fern fronds with sori,moss or liverworts with repro-ductive structures, and cones froma conifer (pine, juniper, spruce, or fir). Discuss with students how each structure functions inreproduction. Leave the displayout while you teach this sectionand refer to each plant as theyare addressed. Visual

Interactive Reading AssignChapter 30 of the Modern BiologyGuided Reading Audio CDProgram to help studentsachieve greater success in reading the chapter.

VerbalLS

SKILLBUILDER

READINGREADING

LS

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Motivate

LS

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SECTION 1

P L A N T L I F E C YC L E SA life cycle includes all of the stages of an organism’s growth

and development. Recall that a plant’s life cycle involves two

alternating multicellular stages—a diploid (2n) sporophyte

stage and a haploid (1n) gametophyte stage. This type of life

cycle is called alternation of generations. Also recall that

the size of gametophytes and sporophytes varies among the

plant groups.

THE LIFE CYCLE OF MOSSESThe dominant form of a moss is a clump of green gametophytes.Look at the moss life cycle illustrated in Figure 30-1. Moss gameto-phytes produce gametes in two types of reproductive structures—antheridia and archegonia. An antheridium (AN-thuhr-ID-ee-uhm) is amale reproductive structure that produces hundreds of flagellatedsperm by mitosis. An archegonium (AWR-kuh-GOH-nee-uhm) is afemale reproductive structure that produces a single egg by mito-sis. During moist periods, sperm break out of the antheridia andswim to the archegonia. One sperm fertilizes the egg at the base ofan archegonium, forming a diploid zygote. Through repeatedmitotic divisions, the zygote forms an embryo and develops into a sporophyte.

SECTION 1

O B J E C T I V E S

● Describe the life cycle of a moss.● Describe the life cycle of a fern.● Describe the life cycle of a

gymnosperm.● Compare homospory and

heterospory.

V O C A B U L A R Y

antheridiumarchegoniumhomosporysorusmicrosporemegasporeheterosporyintegumentmicropyleovulepollen grainpollinationpollen tube

Capsule

Young sporophyte

Diploid(2n)

Haploid(1n)

Zygote (2n)

Spores Femalegametophyte

Germinating spores

Sperm (1n)

Archegonium Antheridium

Egg(1n)

Malegametophyte

Adultsporophyte

Adultgameto-phyte(1n)

The life cycle of mosses alternatesbetween clumps of gametophytes (thedominant generation) and a sporophytethat consists of a spore capsule on a bare stalk.

FIGURE 30-1

609

STATE RESOURCES

For specific resourcesfor your state, visitgo.hrw.com and type inthe keyword HSHSTR.

TEACHER RESOURCES

Workbooks

Active Reading Guide (Section 1)

Technology

CNN Presents: Science in the News, Segment 20• Migrant Bees (with Critical-Thinking Worksheet)

Transparencies • G33 Life Cycle of a Moss• G34 Life Cycle of a Fern• G35 Life Cycle of a Conifer

Visual Concepts CD-ROM• Alternation of Generations, Life Cycle of Mosses,

Life Cycle of Ferns, Life Cycle of Conifers

Using the FigureComparing Mosses and FernsHave students use Figures 30-1and 30-2 to identify ways thatmosses differ from ferns. (The domi-nant structure that we recognize as theplant is the gametophyte in mosses andthe sporophyte in ferns. ) Visual

ActivityGerminating Fern Spores Obtainsome fresh, mature fern sporo-phyte fronds (available from abiological supply house). Providethe students with dissecting nee-dles, and instruct them to gentlyopen the sori and collect spores.Place the spores on a microscopeslide. Have students place around piece of filter paper on thebase of a Petri dish and saturatethe paper with distilled water.Then have students add the sporesto the dish, place the cover on thedish, label the dish, and set thedish in a lighted location. Tell students that spore germinationrequires light. Have studentsobserve their dishes under a dissecting microscope daily. Addwater as necessary to keep the filter paper moist. Germinationshould occur within 24 hours, butmay take longer. Have studentsmake daily drawings and recordtheir observations. KinestheticLS

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610 C H A P T E R 3 0

Rhizome

Roots

Sori

Frond

Diploid(2n)

Haploid(1n)

Adult sporophyte

Zygote(2n)

SporesMaturegametophyte

Sporangiumreleasing spores

Sperm(1n)

Archegonium

AntheridiumEgg(1n)

A moss sporophyte begins as a thin stalk that grows from the tipof a gametophyte. The sporophyte remains attached to the game-tophyte and depends on it for nourishment. Soon, cells at the tip ofa stalk form a sporangium, called the capsule. Cells in the capsuleundergo meiosis to form haploid spores, which are all the same.The production of one type of spore is called homospory(hoh-MAHS-puh-ree). Therefore, the life cycle of mosses is calledhomosporous (hoh-MAHS-puh-ruhs) alternation of generations. Whenthe spores are mature, the capsule splits open, and the spores arecarried away by the wind. Spores that land in favorable environ-ments may germinate and grow into new gametophytes.

THE LIFE CYCLE OF FERNSThe life cycle of a typical fern, shown in Figure 30-2, is similar to themoss life cycle. Like mosses, most ferns are homosporous. And as inmosses, the fern sporophyte grows from the gametophyte. But in thefern life cycle, the sporophyte, not the gametophyte, is the dominantgeneration. Fern gametophytes are tiny (about 10 mm, or 0.5 in., indiameter), flat plants that are anchored to the soil by rhizoids. Bothantheridia and archegonia may form on the lower surface of a ferngametophyte. When water is present, sperm released by antheridiaswim to archegonia. One sperm fuses with the egg in an archego-nium, forming a zygote, which is the first cell of a new sporophyte.

The zygote grows into an embryo and then into a young fernsporophyte through mitotic cell division. Once the sporophyte cansurvive on its own, the gametophyte will die. A mature fern sporo-phyte usually has compound leaves that are known as fronds.

The life cycle of most ferns alternatesbetween a large sporophyte (thedominant generation) and a smallgametophyte. Both the egg and spermmay be produced on the samegametophyte.

FIGURE 30-2

610

• Gifted and TalentedStudents who are gifted and talented ben-efit from opportunities to learn beyondthe confines of the classroom and toexpand their classroom learning to theworld around them. Have students con-duct research and report on the now-extinct seed ferns that were common inthe Carboniferous period. These plantshad fernlike foliage and gymnosperm-likeseeds attached to the leaf margins. (A paleobotany textbook would be agood source.)

StrategiesStrategiesINCLUSIONINCLUSION

Foot-like Ferns Ferns in the genus Davalliaare characterized by creeping stems (rhizomes) covered with coarse tan orbrown hairs that resemble animal feet.Cultivated species include D. trihomanioides(squirrel’s foot fern), D. canariensis (deer’sfoot fern), and D. fejeensis (rabbit’s foot fern).

Teaching TipReproductive Structures Pointout to students that homosporousplants, such as mosses and ferns,produce only one kind of spore.The spores can grow into either a male gametophyte or a femalegametophyte, and the male game-tophyte produces sperm cellswhile the female gametophyteproduces egg cells. Also, pointout that heterosporous plants,such as gymnosperms, producetwo different kinds of spores. The microspores grow into malegametophytes and the megasporesgrow into female gametophytes.The male gametophytes producessperm cells and the femalegametophytes produce egg cells.

Auditory

Interpreting Visuals Havestudents study the life cycle of a conifer, as illustrated inFigure 30-3. Ask them first to find the zygote in the figure. Askthem where the young sporophytegrows from the zygote. (inside amegasporangium on a female cone)Ask students to describe the relative size and photosyntheticcapacity of the sporophyte. (largeand photosynthetic) Ask them nextto note where meiosis occurs. (inmegasporangia and microsporangia of[male and female, respectively] cones)Ask where spores develop intogametophytes. (in microsporangiaand megasporangia) Ask wheregametes are produced. (in megas-porangia of female gametophytes andmicrosporangia of male gametophytes)Ask where fertilization occurs. (in ovules, inside megasporangia infemale gametophytes in female cones of sporophytes)

Teaching TipTell students that the familiar pineis a sporophyte. Like humans,pines cannot sexually reproduceuntil they are mature. Dependingon the species, pines take from 3 to more than 30 years to reachadulthood. AuditoryLS

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P L A N T R E P R O D U C T I O N 611

Fronds grow from an underground stem, or rhizome. In most ferns,certain cells on the underside of the fronds develop into sporangia.In many ferns, the sporangia are clustered together. A cluster ofsporangia is called a sorus (SOH-ruhs), plural, sori (SOH-ree). Cells insidea sporangium undergo meiosis, forming haploid spores. At matu-rity, the sporangium opens and the spores are catapulted 1 cm(0.4 in.) or more and are then carried away by air currents. Whenthe spores land, they may grow into new gametophytes.

THE LIFE CYCLE OFGYMNOSPERMS

Unlike mosses and most ferns, gymnosperms produce two types ofspores—male microspores and female megaspores. Microsporesgrow into male gametophytes, while megaspores grow into femalegametophytes. The production of different types of spores is calledheterospory (HET-uhr-AHS-puh-ree). Thus, the gymnosperm life cycleis called heterosporous (HET-uhr-AHS-puh-ruhs) alternation of generations.All seed plants, spike mosses, quillworts, and a few fern specieshave heterospory. The microspores of heterosporous plants pro-duce male gametophytes that stay attached to the much largersporophyte and develop into pollen. Pollen can be transportedthrough the air to female gametophytes. Sexual reproduction inseed plants therefore can take place independent of seasonal rainsor other periods of moisture. Figure 30-3 shows the life cycle of aconifer, the most common kind of gymnosperm.

Diploid(2n)

MEIOSIS

MEIOSIS

FERTILIZATION

Haploid(1n)

Adultsporophyte

Microspore

Male cone

Female cone

Seed

Malegametophyte(pollen grain)Microsporangium

Megaspore

Megasporangium

Pollen tube

Pollen entersmicropyle

Ovule(contains female gametophytes)

Micropyle

Integument

The life cycle of a gymnospermalternates between a large sporophyte(the dominant generation), whichproduces two types of spores in cones,and microscopic gametophytes, whichproduce gametes. Female gametophytesproduce eggs, and male gametophytesproduce sperm.

FIGURE 30-3

sorus

from the Greek soros,meaning “heap”

Word Roots and Origins

611

Oldest Living Things Bristlecone pines aresome of the oldest known living things onEarth. Pinus longaeva, the IntermountainBristlecone Pine, grows in subalpine areas ataltitudes of 9,500 to 11,500 feet in California,Nevada, and Utah. One particular tree, namedthe Methuselah tree, is over 4,600 years old. This tree was named after the father of thebiblical Noah who was said to have lived for 969 years.

TEACHER RESOURCES

Workbooks

Quick, Data, and Math Labs• Observing a Fern Gametophyte• Observing the Gametophytes of Pines

Technology

Transparencies• G37 Formation of a Female Gametophyte• G38 Formation of a Male Gametophyte

ReteachingComparing Plants Provide stu-dents with living specimens orpictures (posters) of a moss, afern, and a conifer. Show the various stages of each plant’s lifecycle. Hold up each plant specimenand ask students whether theythink the structure is haploid ordiploid. Help students arrangethe specimens according to theirstage in the plant life cycle. Gluethe specimens or pictures onto a piece of poster board in theirproper order. Have students drawarrows to indicate the cycle anddraw a line through the cycle toseparate the haploid and diploidphases. Point out to students themajor differences between the life cycles. (The gametophyte is largerin mosses; the sporophyte is larger inferns and conifers. Mosses and ferns donot produce seeds; conifers do. Mossesand ferns have swimming sperm; conifersdo not.) Kinesthetic

Quiz1.What are the multicellular

structures of a moss, a fern,and a conifer? (The multicellularstructures are the sporophyte and the gametophyte.)

2.What reproductive cells does asporophyte produce? (spores)

3.Are seed plants homosporousor heterosporous? (heterosporouswith male microspores and femalemegaspores)

GENERAL

LS

Close

Answers to Section Review

1. An antheridium is the male reproductive structurethat produces sperm. An archegonium is the femalereproductive structure that produces an egg.

2. Ferns: Most ferns are homosporous, spores arereleased from the sporophyte, the fern gameto-phyte is photosynthetic, and sperm are flagellated.Pine: A pine is heterosporous, spores are notreleased from the sporophyte, the female gameto-phyte is microscopic and within the sporophyte, and sperm lack flagella.

3. They have separate male and female cones.4. Homospory is the condition of a species that pro-

duces just one type of spore that form female andmale gametophytes; heterospory is the conditionthat produces two types of spores that form maleor female gametophytes.

5. Mosses generally live in very moist environments;they produce swimming sperm and so requirewater for fertilization of eggs. Conifers live in muchdrier environments; they produce pollen grainscontaining reproductive cells that are transportedto egg cells by the wind.

6. All the alleles of an organism can potentially besubjected to natural selection because there areno alternate alleles that can “hide” disadvanta-geous alleles.

7. Gametophytes of mosses are not very resistant toadverse environmental conditions because theyare small and require relatively large amounts ofwater for survival, and lack much surface area forabsorption of water and minerals. Gametophytes ofconifers are very small but are enclosed within ahighly resistant covering.

612 C H A P T E R 3 0

1. Distinguish between an antheridium and anarchegonium in mosses, including their struc-tures and functions.

2. List three differences between the life cycle of a typical fern and the life cycle of a pine tree (a gymnosperm).

3. Explain why a pine tree (a gymnosperm) has twodifferent types of cones.

4. What is the difference between homosporousalternation of generations and heterosporousalternation of generations?

CRITICAL THINKING

5. Evaluating Differences How do the differencesin the environments in which mosses and gym-nosperms live relate to the differences in sexualreproduction in these plants?

6. Forming Reasoned Opinions How might thepresence of a haploid generation (the gameto-phyte) in plants serve as a “filter” for naturalselection?

7. Making Comparisons Compare male andfemale gametophytes of mosses with those ofgymnosperms in terms of their resistance toharsh environmental conditions.

SECTION 1 REVIEW

In the pine (a conifer), sexual reproduction takes more than twoyears. During the first summer, a mature pine tree produces sepa-rate female and male cones. The female cones produce megaspo-rangia, while the male cones produce microsporangia. The followingspring, cells in all sporangia undergo meiosis and divide to producehaploid spores. These spores never leave the parent to developindependently. Megasporangia produce megaspores, which developinto megagametophytes, or female gametophytes. A thick layer ofcells called an integument (in-TEG-yoo-muhnt) surrounds each mega-sporangium. The integument has a small opening called themicropyle (MIE-kroh-PIEL). Together, a megasporangium and itsintegument form a structure called an ovule (AHV-yool). Two ovulesdevelop on each scale of a female cone. Microsporangia producemicrospores, which develop into microgametophytes, or male game-tophytes. A pollen grain is a microgametophyte of a seed plant.

The male cones of a pine release huge numbers of pollen grains,as seen in Figure 30-4. Pine pollen travels on the wind, and only afew grains may land on a female cone. The pollen grains driftbetween the cone scales until they reach the ovules. The transferof pollen to ovules is called pollination. A drop of fluid at themicropyle captures the pollen grain. As the fluid dries, the pollengrain is drawn into the micropyle. After pollination, the femalegametophyte within the ovule produces archegonia and eggs.

After pollination, the pollen grain begins to grow a pollen tube, aslender extension of the pollen grain that enables sperm to reach anegg. Unlike the sperm of seedless plants, pine sperm do not have fla-gella and they do not swim to an egg. The pollen tube takes about ayear to reach an egg only a few millimeters away. During this time,two sperm develop in the pollen tube. When the pollen tube reachesan archegonium, one sperm unites with an egg to form a zygote. Theother sperm and the pollen tube die. Over the next few months, thezygote develops into an embryo as the ovule matures into a seed.

The male cones (pollen cones) of pinesproduce millions of pollen grains. Themale cones then die. Wind-pollinatedspecies typically produce large amountsof pollen. Large numbers of pollengrains increase the odds that femalecones (seed cones) will be pollinated.

FIGURE 30-4

612

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describesthe structures of flowering plants,how pollen and ovules form, andhow pollination and fertilizationoccur.

Tell students that the primaryfunction of flowers generally is topromote pollination, either bywind, water, or animals. Ask themto identify the importance of hav-ing pollen come from a differentplant than the plant being self-pollinated. (This promotes geneticvariability.) Logical

DiscussionFlower Display Provide studentswith a variety of flowers or pic-tures of flowers. Include large,colorful flowers, scented flowers,inconspicuous or small flowers,and flowers with nectaries. Makesure that some of the flowershave visible stamens and pistils.Day-old flowers are often availablefrom florists, garden centers, andgrocery stores. Have studentsexamine the flowers and discussthe diversity they observe. Askstudents to describe the adaptiveadvantage of bright coloration,large flowers, fragrance, or nec-taries. (attracts pollinators) Ask stu-dents why wind-pollinated flowersoften have small petals. (Large petalsblock air currents and waste energy asthey are not needed to attract pollinators.)

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P L A N T R E P R O D U C T I O N 613

S E X UA L R E P RO D U C T I O N

I N F L OW E R I N G P L A N T SMany flowers have bright colors, attractive shapes, and

pleasing aromas. These adaptations help ensure successful

sexual reproduction by attracting animals that will transfer

pollen. But some flowers are not colorful, large, or fragrant.

Such flowers rely on wind or water for the transfer of pollen.

PARTS OF A FLOWERRecall that early land plants lacked leaves and roots and consistedof only stems. Leaves evolved from branches of stems. Botanistsconsider flowers to be highly specialized branches and the parts ofa flower to be specialized leaves. These specialized leaves form onthe swollen tip of a floral “branch” or receptacle.

Flower parts are usually found in four concentric whorls, orrings, as shown in Figure 30-5. Sepals (SEE-puhlz) make up the outerwhorl. They protect the other parts of a developing flower beforeit opens. Petals make up the next whorl. Most animal-pollinatedflowers have brightly colored petals. The petals and sepals of wind-pollinated plants are usually small or absent.

The two innermost whorls of flower parts contain the reproduc-tive structures. The male reproductive structures are stamens(STAY-muhnz), each of which consists of an anther and a filament. Ananther contains microsporangia, which produce microspores thatdevelop into pollen grains. A stalklike filament supports an anther.The innermost whorl contains the female reproductive structures,which are called carpels (KAHR-puhlz).

SECTION 2

O B J E C T I V E S

● Identify the four main flower parts,and state the function of each.

● Describe gametophyte formationin flowering plants.

● Relate flower structure to methodsof pollination.

● Describe fertilization in floweringplants.

V O C A B U L A R Y

receptaclesepalpetalstamenantherfilamentcarpelpistilovarystylestigmaembryo sacpolar nucleitube cellgenerative cellnectardouble fertilization

PetalOvuleSepal

Receptacle

Anther

FilamentStamen

Stigma

Style

Ovary

Pistil(fused carpels)

This diagram shows a flower that has all four whorls of flower parts—sepals, petals, stamens, and carpels.Most species of flowering plants haveflowers that have both stamens andcarpels.

FIGURE 30-5

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Trends in Botany“Warm-Blooded” Flowers Scientists study-ing the sacred lotus, Nelumbo nucifera, havediscovered that this plant is able to warm upits flowers. Scientists found that as the flowerbuds open, the flower temperature increasesto an average of 32°C (90°F), even if the sur-rounding air temperature is as cool as 5°C(41°F). The flowers are pollinated by beetlesthat must warm up their bodies to about30°C (86°F) in order to fly and carry pollen to another flower. The insects do this byshivering. Scientists think that this plant’swarm flower temperature allows the beetlesto spend more time pollinating.

SECTION 2

TEACHER RESOURCES

Workbooks

Active Reading Guide (Section 2)

Quick, Data, and Math Labs• Arrangement of Parts of a Flower

Technology

Transparencies • G36 Floral Structure

Visual Concepts CD-ROM• Pollen Grain Formation, Parts of a Pollen Grain,

Ovule Formation in an Angiosperm, Parts of anAngiosperm Ovule, Parts of a Seed, Parts of aFlower, Fertilization of a Flower, Flowers andAnimal Pollinators

Using the FigureOvule Formation Take studentsthrough ovule formation step bystep, as shown in Figure 30-6.Stress the roles of meiosis andmitosis in alternation of genera-tions. Ask students if the megas-pore mother cell is haploid ordiploid. (diploid) Ask students howmany cells meiosis produces andif they are haploid or diploid. (four,haploid) Ask students what kindsof cells are produced by mitosis.(haploid if from a haploid cell, diploid iffrom a diploid cell) Visual

ActivityFloral Structures Provide stu-dents with different kinds of flow-ers. Wildflowers are preferablebecause cultivated flowers oftenlack floral parts. If using cultivatedflowers, choose Easter lilies.Avoid using daisies, chrysanthe-mums, and other compositesbecause the individual flowers ofthese plants are very tiny. Havestudents examine the flowerswith a hand lens and a dissectingmicroscope. Have studentsremove and examine the outer-most structures of the flower, andthen progressively remove andidentify the inner structures. Askstudents to make labeled draw-ings of the structures they see.

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Trends in BotanyRewards for Pollinators Scientists workingwith nine different species of insect-pollinatedflowering plants found that all of the speciesunderwent a flower-color change over time,from yellow to orange or orange-red, thatwas correlated with a loss of food rewardsfor the pollinators. Scientists concluded thatflower-color change is an adaptation thatattracts first-time visitors and provides themwith cues for associating one color with a reward.

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Micropyle

Integuments

Megasporemother cell (2n)

Megasporemother cell

Megaspores(1n)

Embryo sac(female gametophyte)

Degeneration

MITOSIS

MEIOSIS

Polarnuclei

Egg

Ovule

Megasporangium

Eight nuclei (1n)

FORMATION OF A FEMALE GAMETOPHYTE

Stigma

Style

Ovary

Pistil

One or more carpels fused together make up the structure calleda pistil (also shown in Figure 30-6). The enlarged base of a pistil iscalled the ovary. A style, which is usually stalklike, rises from theovary. The tip of the style is called the stigma. Generally, a stigma issticky or has hairs, enabling it to trap pollen grains.

GAMETOPHYTE FORMATIONIn angiosperms, gametophytes develop within the reproductive struc-tures of flowers. Embryo sacs, which are the female gametophytes inangiosperms, form within the ovary of the pistil. Pollen grains, themale gametophytes, form within the anthers of the stamens.

Embryo Sac FormationIn flowering plants, ovules form in the ovary of a pistil. As Figure30-6 shows, an angiosperm ovule consists of a megasporangiumsurrounded by two integuments. These two integuments do notcompletely enclose the megasporangium. At one end of the ovuleis the micropyle, through which a pollen tube can enter.

An ovule contains a large diploid cell called a megaspore mothercell. A megaspore mother cell undergoes meiosis and produces fourhaploid megaspores. In many species of flowering plants, only onemegaspore enlarges. The other three degenerate. The remainingmegaspore undergoes three mitotic divisions, which produce a cellthat has eight haploid nuclei. These nuclei migrate to certain loca-tions within the cell. The nuclei are initially arranged in two groupsof four, with one group of nuclei at each end of the cell.

A cross section of an immature ovulefrom a flower reveals a single large cell,a megaspore mother cell. This cellundergoes meiosis and produces fourmegaspores. One of the megasporesundergoes a series of mitotic divisionsthat results in the formation of anembryo sac (a female gametophyte).

FIGURE 30-6

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GENETICSGENETICSCONNECTIONCONNECTION

Ploidy Changes Plant life cycles exhibit analternation between diploid and haploidstages. A diploid zygote grows into a multi-cellular, diploid sporophyte, which produceshaploid spores by meiosis. The haploidspores develop into multicellular, haploidgametophytes, which produce haploidgametes by mitosis. The union of two hap-loid gametes produces a new diploid zygote.Thus, meiosis allows for combining geneticinformation from two individuals withoutincreasing the total amount of genetic infor-mation contained in the cells of an organism.

Using the FigurePollen Grain Formation Guidestudents through pollen forma-tion step by step, as shown inFigure 30-7. Ask students if themicrospore mother cell is haploidor diploid. (diploid) Ask studentshow many cells meiosis producesand if they are haploid or diploid.(four, haploid) Ask students whathappens to these cells. (Each celldivides by mitosis to produce two haploidcells, which then become surrounded bya thick wall. These two-celled structuresare pollen grains.) Visual

DemonstrationPollen Diversity Provide studentswith a variety of prepared slidesand electron micrographs ofpollen. (Prepared slides are avail-able from biological supply houses,and micrographs can be found in college biology or botany text-books.) Have students examinethe slides under microscopes andstudy the micrographs. Ask stu-dents to speculate on the adaptiveadvantages of the particular pollenshapes and surface characteristics.(Pollen with large spikes could be easilytransported by furry animals; smoothpollen could be easily transported by aircurrents; pollen arranged in packetscould be easily transported on the backsof insects.)

Visual

K-W-L Before students read thischapter, have them write shortindividual lists of all the thingsthey already Know (or think theyknow) about plant life cycles and reproduction. Ask them tocontribute their entries to a grouplist on the board or overhead projector. Then have students listthings they Want to know aboutplant life cycles and reproduction.Have students save their lists for use later in the AlternativeAssessment exercise at the end of the chapter. VerbalLS

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Anther

Microsporangium(pollen sac)

Filament

MEIOSIS

MITOSIS

Microspore mother cell (2n)

Generativecell

Pollen grain(male gametophyte)

Tubecell Tube cell

nucleus

Microspores(1n)

FORMATION OF A MALE GAMETOPHYTE

A cross section of an anther of a flowerreveals four pollen sacs (microsporangia).Microspore mother cells within themicrosporangia undergo meiosis andproduce microspores. Each microsporethen develops into a two-celled pollengrain (a male gametophyte).

FIGURE 30-7One nucleus from each group migrates to the center of the cell.These two nuclei are called polar nuclei because they came fromthe ends, or poles, of the cell. Cell walls then form around each ofthe remaining six nuclei. One of the three cells that are nearest tothe micropyle enlarges and becomes the egg. The two cells oneither side of the egg will later help attract the pollen tube towardthe egg. The function of the three cells at the other end of the cellis unclear. These five non-egg cells will eventually die after fertiliza-tion occurs.

The resulting structure, which usually contains eight nuclei andseven cells (the egg, the five non-egg cells, and the large centralcell enclosing these cells), is the embryo sac. The embryo sac isthe mature female gametophyte, or megagametophyte. Theembryo sac is another feature that is seen in angiosperms but isnot seen in gymnosperms. The surrounding integuments and theembryo sac now form a mature ovule, which may eventuallydevelop into a seed.

Pollen Grain FormationAn anther contains four microsporangia, or pollen sacs, as shownin Figure 30-7. Initially, the pollen sacs contain many diploid cells.These diploid cells are called microspore mother cells. Each ofthese microspore mother cells undergoes meiosis and producesfour haploid microspores. A microspore undergoes mitosis andproduces two haploid cells, but these cells do not separate. Athick wall then develops around the microspore. The resultingtwo-celled structure is a pollen grain, which is the male gameto-phyte, or microgametophyte. The larger of the two cells is thetube cell, from which the pollen tube will form. The generativecell, which is enclosed in the tube cell, will divide by mitosis toform two sperm.

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Pollination Methods Flowers that areinsect-pollinated are called entomophilous,which literally means “insect loving.” Plants that are wind-pollinated are calledanemophilous. Pollen produced by ento-mophilous plants is typically large, sticky,and high in protein. Pollen produced byanemophilous plants tends to be small andhave little nutritional value to insects.

Writing Skills Have studentsconduct research and report on a coevolutionary relationshipbetween a flowering plant and itspollinator. Examples include thecarrion flower and the fly; theAmerican sausage tree and bats;yuccas and the yucca moth; figtrees and fig wasps; and wasp orfly orchids and a wasp or fly.

Verbal

Teaching TipDouble Fertilization inAngiosperms Have students makea Graphic Organizer similar tothe one at the bottom of this pageto illustrate the process of doublefertilization in angiosperms. Askstudents to use the applicablevocabulary words for this section,and any other words that theywish to include. Visual

Pollination Have studentsresearch pollination by using theInternet Connect box on thispage. VerbalLS

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POLLINATIONBefore a sperm can fertilize the egg contained in an embryo sac,pollination must occur. In flowering plants, pollination occurswhen pollen grains are transferred from an anther to a stigma.Pollination that involves just one flower, flowers on the same plant,or flowers from two genetically identical plants is called self-pollination. In contrast, pollination that involves two genetically dif-ferent plants is called cross-pollination.

The pollination of flowering plants occurs in several ways.Flower structure promotes self-pollination in plants, such as peasand beans, that have flowers with petals that completely encloseboth the male and female flower parts. Some aquatic plants, suchas sea grasses, have pollen that is dispersed by water. Many plants,such as oak trees and grasses, release their pollen into the air. Theflowers of such wind-pollinated angiosperms are small and lackshowy petals and sepals. Successful wind pollination depends onfour conditions: the release of large amounts of pollen, the amplecirculation of air to carry pollen, the relative proximity of otherplants for the pollen to be transferred to, and dry weather toensure that pollen is not washed from the air by rain.

Most plants that have colorful or fragrant flowers are pollinatedby animals. Bright petals and distinctive odors attract animals thatfeed on pollen and nectar, a nourishing solution of sugars. Animalpollinators include bats, bees, beetles, moths, butterflies, mosqui-toes, monkeys, and hummingbirds. When these animals gather nec-tar, pollen sticks to their bodies. As they collect more nectar, theanimals deposit some of the pollen on other flowers. For example,as the hummingbird in Figure 30-8 collects nectar from a flower,pollen from the anthers is deposited on the hummingbird’s beakand head. When the hummingbird moves on to another flower, thepollen may be transferred to the stigma of the second flower.

FERTILIZATIONFertilization, the union of haploid gametes resulting in a diploidzygote, may follow pollination, as shown in Figure 30-9. For fertil-ization to occur in angiosperms, a pollen grain must land on astigma and then absorb moisture. The pollen grain will then ger-minate. Germination occurs when the nucleus of the tube cellcauses the tube cell to form a pollen tube that grows through thestigma and style toward the ovary. The pollen tube grows to anovule within the ovary and enters the ovule through the micropyle.After the pollen tube penetrates the embryo sac, two sperm (pro-duced from the mitotic division of the generative cell in the pollengrain) can travel through the pollen tube and reach the egg. Unlikea gymnosperm’s pollen tubes, an angiosperm’s pollen tubes usu-ally reach an egg a day or two after pollination.

These long, tubular flowers are adaptedfor pollination by hummingbirds, whichhave long beaks adapted for reachingthe nectar located deep in the flowers.

FIGURE 30-8

www.scilinks.org

Topic: PollinationKeyword: HM61177

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Graphic Organizer

Use this Graphic Organizer with Teaching Tip:Double Fertilization in Angiosperms on this page.

Pollination

Fertilization

Fertilization

Ovules with 1 egg

Flowers

Pollen grainsmake 2 sperm

Sperm (n) +

egg (n)

Sperm (n) +

2 polar nuclei (2n)

Endosperm3n

Zygote2n

EmbryoPlant(2n)

Teaching TipColor of Hybrid Fruit If a flowerof a Red Delicious apple plant ispollinated by a Yellow Deliciousapple, what would the fruit looklike? (It would look like a typical RedDelicious apple. Because a fruit is aripened ovary, which is maternal tissue,it would have the characteristics of thefemale parent.) Logical

ReteachingFlowering Plant Puzzle Havestudents construct a crosswordpuzzle using the vocabularyterms in this section. Verbal

Quiz1.What structures can be found

inside of an anther? An ovary?(An anther may contain microsporangia,microspore mother cells, microspores,pollen grains, tube cells, and genera-tive cells. An ovary may containmegasporangia, megaspore mothercells, megaspores, ovules, embryosacs, polar nuclei, egg cells, andembryos.)

2.Which is the dominant phasein a flowering plant’s life cycle?(sporophyte)

3.What happens after a pollengrain lands on a stigma? (The pollen grain germinates, and thetube cell grows into a pollen tube thatextends all the way down the stigmainto the ovary. The generative celldivides, forming two sperm cells. The sperm cells move down throughthe pollen tube and enter the ovarythrough the micropyle. One spermcell fertilizes the egg cell, forming azygote. The other sperm cell fuseswith the two polar nuclei, forming the endosperm.)

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1. Draw a generalized flower and show the fourtypes of flower parts in relation to each other.Be sure to label each structure.

2. Name the male and female gametophytes inflowering plants.

3. How do the flowers of wind-pollinated plantsdiffer from the flowers of animal-pollinatedplants?

4. Why is fertilization in flowering plants calleddouble fertilization?

CRITICAL THINKING

5. Interpreting Graphics What type of pollinationis shown in the illustration above?

6. Distinguishing Relevant Information The vastmajority of the known species of plants areangiosperms. What are some characteristics ofthis group of plants that help explain theirevolutionary success?

7. Making Comparisons How is meiosis inflowering plants like meiosis in humans?

SECTION 2 REVIEW

Endosperm

MEIOSIS

MEIOSIS

POLLINATION

OvulePistil

SeedFERTILIZATION

Endospermnucleus (3n)

Embryo sac(femalegametophyte)

Pollen grain(malegametophyte)

Embryo

Zygote (2n)

Micropyle

Sperm(1n)

Egg (1n)

Ovule

Pollen tube

Ovary

Style

Stigma

Pollengrain

Pollentube Sperm

Tubenucleus

Pollen

Anther

POLLINATION AND FERTILIZATION IN FLOWERING PLANTS

One of the two sperm fuses with the egg, forming a diploidzygote. The zygote eventually develops into an embryo. The secondsperm fuses with the two polar nuclei, producing a triploid (3n)nucleus. This nucleus then develops into tissue called endosperm.The endosperm provides nourishment for the embryo. Kernels ofcorn are mostly endosperm. In many plants, however, theendosperm is absorbed by the embryos as the seeds mature. Thisprocess of two cell fusions, which is called double fertilization, isunique to angiosperms.

In a process called double fertilization,

one sperm fuses with an egg, forming azygote. Another sperm fuses with twopolar nuclei, forming an endosperm.

FIGURE 30-9

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Answers to Section Review

1. See Figure 30-5 for a complete flower drawingshowing the sepals, petals, stamens, and carpels.

2. pollen grain (male) and embryo sac (female) 3. The flowers of wind-pollinated plants usually lack

scents, nectar, and large petals and sepals. Theflowers of animal-pollinated plants usually havescents, nectar, and large, colorful petals or sepalsthat attract animals.

4. Two sperm fuse with cells in the embryo sac. Onesperm fertilizes the egg and the other sperm fuseswith the two polar nuclei to form the endosperm.

5. self-fertilization6. Some of the characteristics of angiosperms that

help explain their evolutionary success include thefact that they do not rely on water for fertilization,they produce resistant young embryos (insideseeds) that can be dispersed to new areas, andthey recruit insects and other animals to achieveefficient pollination of their flowers.

7. Meiosis in flowering plants is like the same processin humans and other animals in that it begins with adiploid cell and results in between 1 and 4 haploidcells that have unique genotypes.

TEACHER RESOURCES

Technology

Transparencies • G39 Life Cycle of an Angiosperm

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describeshow fruits and seeds of floweringplants are dispersed, the charac-teristics of different types offruits, the structure of seeds, thechanges that occur during germi-nation, the characteristics ofasexual reproduction, and meth-ods of vegetative propagation.

Bring to class some fruits that are commonly referred to as vegetables. (Examples are anysquash such as zucchini, tomato,any pepper, and corn.) Ask stu-dents to distinguish between thebotanical definition of a fruit andvegetable. (Botanically, a fruit is aripened ovary with seeds. In more famil-iar terms, a fruit is generally sweet. Avegetable is any nonreproductive part ofa plant) Logical

DiscussionHumans as Seed Dispersers Askstudents to think of ways theymight have helped plants disperseseeds. Discuss student responsesand suggest others they mightnot mention. (Examples include car-rying burred fruits on pant legs, eatingapples and tossing the core on the ground,blowing dandelion fruits, spitting water-melon seeds, putting out seeds for birds,and not trimming weeds or mowing alawn.) Point out that many animals,small and large, participate inseed dispersal. IntrapersonalLS

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D I S P E R S A L A N D

P RO PAG A T I O NFruits and seeds normally result from sexual reproduction

in flowering plants. Fruits are adapted for dispersing, or

distributing, seeds. Seeds are adapted for the dispersal and

propagation (production of new individuals) of plants. Many

plants also propagate through asexual reproduction.

DISPERSAL OF FRUITS AND SEEDS

Recall that one property of populations is dispersion, the spatialdistribution of individuals. If individual plants are too closetogether, they must compete with each other for available water,nutrients, and sunlight. One reason for the success of the seedplants is the development of structures that are adapted for dis-persing offspring—fruits and seeds.

Fruits and seeds are dispersed by animals, wind, water, forcibledischarge, and gravity. You may have walked through a field andunwittingly collected burrs, or stickers, on your shoes or socks.These burrs are fruits, and you helped disperse them. The smell,bright color, or flavor of many fruits attract animals. When animalseat such fruits, the seeds are transported to new locations andoften pass unharmed through the animals’ digestive systems.

Fruits and seeds dispersed by wind or water are adapted forthose methods of dispersal. Orchids have tiny, dustlike seeds thatcan easily be carried by a slight breeze. Figure 30-10 shows anexample of seeds adapted for wind dispersal. Many plants thatgrow near water produce fruits and seeds that contain air cham-bers, which allow them to float. Coconuts, for example, may floatthousands of kilometers on ocean currents.

The most dramatic method of seed dispersal occurs in plantsthat forcibly discharge their seeds from their fruits. The tropicalsandbox tree, which has fruits that hurl seeds up to 100 m (328 ft),appears to hold the distance record.

Although gymnosperms do not produce fruits, their cones mayhelp protect seeds and aid in seed dispersal. Female pine conesclose after pollination and open again only when the seeds aremature. Pine seeds may be dispersed when gravity causes cones todrop and roll away from the parent tree. Pine seeds have “wings”that aid in wind dispersal.

SECTION 3

O B J E C T I V E S

● Describe adaptations for fruit andseed dispersal.

● Name the three major categories of fruits.

● Compare the structure andgermination of different types ofseeds.

● Recognize the advantages anddisadvantages of asexualreproduction.

● Describe human methods of plantpropagation.

V O C A B U L A R Y

propagationseed coatplumuleepicotylhypocotylradiclehilumdormancyclonevegetative reproductioncuttinglayeringgraftingtissue culture

Milkweed seeds have “parachutes” thathelp them drift with the wind.

FIGURE 30-10

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SECTION 3

Fire-triggered Seed Dispersal In someplants, especially of the genus Pinus, seeddispersal is triggered by fire. Fire causes thecones to open and release its seeds. The firemust be just the right temperature. If it is toohot, the seeds are killed, and if it is too coolthe trigger does not function. This strategyenables a species to survive in areas wherefires are common.

TEACHER RESOURCES

Workbooks

Active Reading Guide (Section 3)

Technology

Transparencies • G42 Seed Structure • G43 Structure and Function of Seeds• G44 Seed Germination

Visual Concepts CD-ROM• Parts of a Seed, Development of a Fruit, and

Parts of Plants Eaten as Food

Group ActivityDispersal Methods Providegroups of students with a varietyof seeds and fruits. Include tinyseeds (carrots, lettuce), large seeds(pea), tiny fruits (grain), and largefruits (pineapple, watermelon).Also, try to include monocot seeds(grasses/corn), and dicot seeds(beans and peanuts). Include animal-dispersed burred fruits(cockle-burr), animal-dispersedbrightly colored fruits (apples,red peppers), wind-dispersedfruits (dandelion, maple), and awater-dispersed fruit (coconut).Ask students to arrange the fruitsand seeds according to their likelymethod of dispersal (wind, water,or animal), and have them inferwhat the specific agent of dispersalis. Ask students to speculate onthe advantages of the differentadaptations. (For example, tiny seedsmay be an adaptation that fits more seedsinside the fruit and facilitates wind dispersal.) Logical

Teaching TipFruit Color Advantages Askstudents to explain the adaptiveadvantage of fruits remaining greenuntil the seeds are mature andthen turning colors, such as red,orange, or yellow. (Green fruits arecamouflaged with the foliage aroundthem and are usually not sweet. Thus,they are less likely to be eaten by animals.Red, orange, or yellow fruits contrastwith green foliage and may be sweet totaste, inviting animals to eat the fruitcontaining the ripe seeds.) Logical

Using the TableClassifying Fruit Types Providestudents with a variety of fruittypes, and have them classify thefruit by using the key in Table 30-1.The following fruits can also beused: honeylocust, bean (legumes);delphinium (follicle); any grain(caryopsis); pecan, walnut (nuts);zinnia (achenes); okra, azalea(capsules); peach, plum, olive(drupes); quince (pome); blue-berry, cranberry (berries); lime(hesperidium); squash, muskmelon(pepos); blackberry (aggregatefruit). Ask students to think ofother examples of fruits that fitinto each category. Visual LS

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Major categories and types of fruits

Simple fruit—formed from one pistil of a single flower

A. Dry at maturity

1. Usually splits opena. Legume—splits along two sides to form two halvesb. Follicle—splits along one sidec. Capsule—splits in a variety of other ways

2. Usually does not split opena. Grain—thin ovary wall fused to seed coatb. Nut—thick, woody ovary wall not fused to single seedc. Achene—thin ovary wall not fused to single seedd. Samara—like an achene but with a thin, flat wing

B. Fleshy at maturity and usually not opening

1. Usually contains only one seeda. Drupe—stony inner layer around the seed

2. Usually contains many seedsa. Pome—core with seeds surrounded by papery ovary walls;

outer part formed from sepalsb. Typical berry—thin skinc. Pepo—berry with a thick, hard rindd. Hesperidium—berry with leathery, easily removed skin

Aggregate fruit—formed from several pistils of a single flower

A. Dry at maturity

B. Fleshy at maturity

Multiple fruit—formed from several flowers growing together

A. Dry at maturity

B. Fleshy at maturity

Examples

pea, peanut, black locustmilkweed, columbinepoppy, tulip

corn, wheatoak, chestnutsunflower, dandelionash, elm, maple

cherry, coconut, pecan

apple, pear

grape, tomato, bananawatermelon, cucumberorange, grapefruit, lemon

tulip tree, magnolia

raspberry, strawberry

sweetgum, sycamore

pineapple, fig

TYPES OF FRUITSBotanists define a fruit as a mature ovary. Many different types of fruits have evolved among the flowering plants. Figure 30-11shows examples of some of these fruit types. Fertilization usuallyinitiates the development of fruits. Fruits protect seeds, aid in theirdispersal, and often delay their sprouting. Fruits are classifiedmainly on the basis of two characteristics: how many pistils orflowers form the fruit, and whether the fruit is dry or fleshy. Table30-1 presents a classification system for fruits. Notice that fruitswith common names that include “nut” or “berry” may not beactual nuts or berries. For example, a peanut is actually a legume,not a nut. You may have heard the fleshy seeds of ginkgo, juniper,and yew trees referred to as berries. These names are misleadingbecause ginkgo, juniper, and yew trees are gymnosperms, which donot form fruits.

A pea pod is a simple fruit. A raspberryis an aggregate fruit. A pineapple is amultiple fruit.

FIGURE 30-11

TABLE 30-1 Fruit Classification

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AGRICULTUREAGRICULTURECONNECTIONCONNECTION

Seed Production Some crops are grownspecifically for their seeds, and seed pro-duction is an important industry withinagriculture. There are seed certificationagencies whose function is to certify seeds.The requirements for the production of certified seed are much stricter than thosefor the same crops grown for consumption.Certified seed must be genetically uniform,clean, and free of contamination with weed seeds.

Using the FigureSeed Structures Ask students toexamine Figure 30-12 and askthem what structures monocotand dicot seeds have in common.(plumule, hypocotyl, radicle, cotyledon,seed coat) Ask them to comparethe corn kernel with the beanseed with respect to nutrientstorage. (corn kernel—endosperm,bean seed—cotyledons)

Predicting Seed DispersalTime Required 30 minutes

Safety Instruct students not toeat the fruit.

Procedural Tips Provide at least10 fruits from which students canchoose. Include some fruits thatare commonly considered vegeta-bles, such as tomatoes or wholegreen beans. Cut open hard fruitsfor students. Students will alsoneed a balance or scale.

Answers to Analysis Students’hypotheses may vary. Each hypothesisshould be reasonable and testable. Forexample, one hypothesis might be thatapples (or other fleshy fruits) are eatenby an animal and the seeds are dispersedafter traveling through the animal’sdigestive system. Students should beable to describe a test for their hypothe-sis and predict the outcome.

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STRUCTURE OF SEEDSA seed is a plant embryo surrounded by a protective coat calledthe seed coat. The structure of seeds differs among the majorgroups of seed plants—angiosperms, which include monocots anddicots, and gymnosperms. To understand some of the differences,examine the seeds shown in Figure 30-12.

Look at the bean seed in Figure 30-12a, which has been opened toreveal the structures inside. Most of the interior of a bean seed isfilled by two large, fleshy cotyledons (seed leaves), which are part ofthe embryo. Recall that dicots have two cotyledons in theirembryos. Therefore, beans are dicots. A mature bean seed has noendosperm. The endosperm was absorbed by the fleshy cotyledons.

Between the two cotyledons of a bean seed are the parts thatmake up the rest of the embryo. The shoot tip, along with anyembryonic leaves, is called the plumule (PLOO-MYOOL). The epicotyl(EP-I-KAHT-uhl) extends from the plumule to the attachment point ofthe cotyledons. The hypocotyl (HIE-poh-KAHT-uhl) extends from theattachment point of the cotyledons to the radicle. The radicle isthe embryonic root. Along the concave edge of the seed, beneaththe radicle, is the hilum (HIE-luhm), which is a scar that markswhere the seed was attached to the ovary wall.

Now examine the corn kernel in Figure 30-12b. Technically, acorn kernel is a fruit, but the seed occupies almost the entire ker-nel. The wall of the fruit is very thin and is fused to the seed coat.A single umbrella-shaped cotyledon is pressed close to theendosperm. The cotyledon of a monocot seed does not store nutri-ents, as bean cotyledons do. Instead, it absorbs nutrients from theendosperm and transfers them to the embryo.

Finally, look at the pine seed in Figure 30-12c. A pine seed con-tains a sporophyte embryo that has needle-like cotyledons. Theembryo is surrounded by tissue of the female gametophyte. Likethe triploid endosperm of angiosperm seeds, the haploid tissue ofthe female gametophyte functions as a source of nourishment forthe embryo.

(c) PINE SEED (GYMNOSPERM)(a) BEAN SEED (DICOT)

Wing

Seed coat

Embryowithcotyledons

Radicle

Femalegametophytetissue (1n)

Hypocotyl

Radicle

Seed coatCotyledons

Plumule

Hilum

(a) A bean seed has two cotyledons and no endosperm. (b) A corn kernelcontains a single seed, which has onecotyledon and endosperm. (c) A pineseed has cotyledons and tissue from the female gametophyte.

FIGURE 30-12

Predicting Seed Dispersal

Materials five different fruits,balance or scale

Procedure1. Create a data table that has at

least five rows. Your table shouldhave six columns with the fol-lowing headings: “Fruit name,”“Fruit type” (from Table 30-1),“Dry/fleshy,” “Seed mass ingrams,” “Whole fruit mass ingrams,” and “Dispersalmethod.”

2. Examine your fruits, and fill inyour data table. Discuss withyour group how characteristicsof fruits and seeds might relateto dispersal methods.

Analysis Form a hypothesis abouta dispersal method for one of thefruits you have examined. Describehow you might test your hypothesis.

Quick Lab

(b) CORN KERNEL (MONOCOT)

Plumule

Hypocotyl

Endosperm (3n)

Radicle

Seed coat fused to fruit wall

Cotyledon

Epicotyl

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Poisonous Plants A common misconcep-tion people have about poisonous plantsis that, if one part of the plant is edible,then all parts will be edible. Many plantshave some poisonous parts and somenonpoisonous parts. For example, rhubarb(Rheum officinale) has edible stems butpoisonous leaves. Many plants in thegenus Prunus, such as cherries, have edible fruits and poisonous leaves, twigs,and seeds. The castor bean plant (Ricinuscommunis), on the other hand, has poisonous seeds while other parts of the plant are nonpoisonous.

MISCONCEPTION ALERT

Apomictic Seeds Not all seeds form as aresult of the fusion of a sperm and egg nucleus.Asexual formation of an embryo (in a seed)is called apomixis. One way that apomicticseeds form is by development from an eggnucleus in which meiosis has been disrupted;this sometimes occurs in apples. Apomicticseeds may also form by early division of asexually-formed embryo to form a secondembryo within the same seed coat; this oftenhappens in citrus plants.

TEACHER RESOURCES

Workbooks

Datasheets for In-Text Labs• Predicting Seed

Dispersal GENERAL

Teaching TipDormancy Hormone Many seedsthat exhibit dormancy contain a hormone in the seed coat thatinhibits growth of the embryo.Ask students what must happenin these seeds before they cangerminate. (The hormone must bewashed away or broken down.)

Logical

Science Literacy Have studentsinvestigate and write a brief reporton the rapidly expanding area ofplant patents. United States lawallows a person who develops anew plant type (not just discoversa naturally occurring new type)to apply for a patent on that plant.A patented plant cannot be prop-agated and sold without the per-mission of the patent holder andwithout payment of royalties tothis person. There are a numberof horticultural plants that havepatents on them, such as EricaSunset heather. Verbal

Seeds Have students researchseeds by using the InternetConnect box on this page.

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P L A N T R E P R O D U C T I O N 621

SEED GERMINATIONMany plants are easily grown from seeds. Although its embryo isalive, a seed will not germinate, or sprout, until it is exposed to cer-tain environmental conditions, The delay of germination oftenassures the survival of a plant. For example, if seeds that mature inthe fall were to sprout immediately, the young plants could bekilled by cold weather. Similarly, if a plant’s seeds were to sprout allat once and all of the new plants died before producing seeds, thespecies could become extinct. Many seeds will not germinate evenwhen exposed to conditions ideal for germination. Such seedsexhibit dormancy, which is a state of reduced metabolism in whichgrowth and development do not occur. The longevity of dormantseeds is often remarkable. A botanist once germinated lotus seedsthat were almost 1,000 years old.

Conditions Needed for GerminationEnvironmental factors, such as water, oxygen, and temperature,can trigger seed germination. Most mature seeds are very dry andmust absorb water to germinate. Water softens the seed coat andactivates enzymes that convert starch in the cotyledons orendosperm into simple sugars, which provide energy for theembryo to grow. As the embryo begins to grow, the softened seedcoat cracks open. This enables the oxygen needed for cellular res-piration to reach the embryo. Many small seeds need light forgermination. This adaptation prevents the seeds from sprouting ifthey are buried too deeply in the soil. In addition, some seeds ger-minate only if exposed to temperatures within a certain range.

Some seeds germinate only after being exposed to extreme con-ditions. For example, animals often swallow the seeds of fruits theyeat, as shown in Figure 30-13. Acids in the digestive system wearaway the hard seed coat. The seeds may germinate after passingthrough the digestive systems of these animals. As an addedbonus, the seed is deposited with a bit of natural fertilizer.

dormancy

from the Latin dormire,meaning “to sleep”

Word Roots and Origins

Many animals eat apples or other fruits.The seeds are swallowed and areexposed to acids as they pass throughthe animal’s digestive system. The acidswear away the seed coat. Once the seedis on the ground, water and oxygen canenter the seed and enable the growingembryo to break out.

FIGURE 30-13

www.scilinks.org

Topic: SeedsKeyword: HM61370

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Kola Nuts Kola nuts are cultivated in the West Indies, West Africa, and SouthAfrica. They are the fruits of severaltypes of evergreen trees. People who livein African countries call the nuts guruor goora nuts, and they chew them likegum. Kola nuts are also used to makecola soft drinks and medicines. The nuts contain caffeine, a stimulant, andtheobromine, a toxic alkaloid.

CulturalAwarenessCulturalAwareness

Seeds can remain viable for years if they are kept dry and cold. The record for seedviability is held by a species of Lupinus.Some seeds of the genus Lupinus, foundburied in arctic ice and dated at 11,000 yearsold, germinated when supplied with waterand warm temperatures.

TEACHER RESOURCES

Technology

Transparencies • G40 Bread Wheat• G41 Bread Wheat (cont.)

Group ActivityGerminating BluebonnetsObtain seeds of Texas bluebon-nets (Lupinus texensis). Have stu-dents divide the seeds into twogroups (100 seeds per group),and give each group of students acookie sheet. Have the studentsplace their seeds on the cookiesheet. (CAUTION: Have studentswear protective gloves when han-dling the hot container, and becareful when pouring the boilingwater so that the water does notspill.) Heat 1 L of water on a hotplate or in a microwave oven.Then, have one group (the treat-ment group) pour boiling waterover the seeds to cover them.Have the other group (the controlgroup) pour room-temperaturewater over their seeds. Have stu-dents place the treatment seedtray in a freezer and place thecontrol tray on a counter in theclassroom. Have them removethe tray from the freezer the nextday, allow the water to thaw, andpour off the water. They shouldalso pour the water off the controlseeds. Have them repeat all ofthese procedures two moretimes. Then, have the studentsplant the seeds in pots or out-doors, labeling them appropri-ately. When a high percentage of the treatment seeds have ger-minated, have students collectdata for both groups of seeds.(They should find less than 20 percentgermination in the control group andaround 80 percent germination in thetreatment group.) Kinesthetic

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622 C H A P T E R 3 0

Other seeds, including apple seeds, must be exposed to near-freezing temperatures for several weeks before they sprout. This tem-perature requirement prevents the seeds from germinating in the falland thus ensures that the seedlings will not be killed by the cold tem-peratures of winter. The cold temperatures cause chemical changeswithin the seed. These changes enable the embryo to grow.

Process of GerminationFigure 30-14 compares germination in corn and bean seeds. The firstvisible sign of seed germination is the emergence of the radicle. Inbeans, the entire root system develops from the radicle. In corn,most of the root system develops from the lower part of the radicle.Soon after the radicle breaks the seed coat, the shoot begins to grow.

In some seeds, such as bean seeds (Figure 30-14a), thehypocotyl curves and becomes hook-shaped. Once the hookbreaks through the soil, the hypocotyl straightens. This straight-ening pulls the cotyledons and the embryonic leaves into the air.The embryonic leaves unfold, synthesize chlorophyll, and beginphotosynthesis. After their stored nutrients are used up, theshrunken bean cotyledons fall off.

In contrast, the cotyledon of the corn seed (Figure 30-14b)remains underground and transfers nutrients from the endospermto the growing embryo. Unlike the bean shoot, the corn cotyledonremains below ground. The corn plumule is protected by a sheaththat pushes through the soil. Once the sheath has broken throughthe soil surface, the plumule grows up through the sheath and thefirst leaf unfolds.

(a) During the germination of a beanseed, the cotyledons and seed coatemerge, and the plumule is protected by a hook in the hypocotyl. (b) Duringthe germination of a corn seed, thecotyledon and seed coat remain belowground and the plumule is protected bya sheath.

FIGURE 30-14Plumule

Cotyledon

Radicle

Endosperm

Protectivesheath

First leaf

Firstleaves

Radicle

Hypocotyl

Seedcoat

Cotyledons

(a) BEAN SEED GERMINATION

(b) CORN SEED GERMINATION

www.scilinks.org

Topic: Seed GerminationKeyword: HM61366

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AGRICULTUREAGRICULTURECONNECTIONCONNECTION

Fruit Tree Grafting Many commercial fruittrees, such as those that produce apples andcitrus fruits, are composed of one variety of a species grafted onto another variety.The root stock is often that of a hardy varietythat can withstand harsh environmentalconditions and is resistant to common diseases. The scion, or the part that isgrafted onto the root stock, is a variety thathas desirable characteristics (such as flavor,color, early fruit set), but it is not alwayswell adapted to the environmental conditionsunder which it is grown.

ActivityGarden Design Have studentsdesign a garden that includesboth sexually and asexuallyreproducing plants and displaytheir designs on poster boards.Students may wish to use maga-zines or plant catalogs to cut outpictures of plants used in theirdesign, or they may draw simpleschematics, similar to landscap-ing plans. Have students includethe name of each plant and how it reproduces in table format.

Visual

Writing Skills Have studentswrite a short story about disper-sal of a seed. Ask them to choosea particular kind of plant, andwrite the story in the first personas though the writer were a seedinside a fruit. Have them beginwith the formation of the zygote,its maturation into a seed, itsrelease or picking, its transportand/or consumption, its transportthrough an animal’s digestive system (if appropriate), its depo-sition in the soil, and then thebeginning of the seedling’s growthand new life as a green plant.

Verbal

DemonstrationVegetative Propagation Providestudents with examples of plantsthat propagate vegetatively fromspecialized structures. Any of theexamples given in Table 30-2would be suitable. Ask studentswhat plant organs could be pro-duced from these specializedstructures. (all) Ask students whatkind of tissue is contained in thestems that enables them to pro-duce new roots, stems, andleaves. (meristematic) Ask studentshow plants benefit from vegetativepropagation. (It requires less energythan producing flowers and fruits.)

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P L A N T R E P R O D U C T I O N 623

ASEXUAL REPRODUCTIONRecall that asexual reproduction is the production of an individualwithout the union of gametes. Elaborate technology has recentlyyielded some success in the asexual reproduction of mammals tocreate clones, or exact duplicates of organisms. But people whocreate clones of themselves are still the subjects of science fictionmovies and books. However, asexual reproduction to create clonesis common in the plant kingdom.

Asexual reproduction can be an advantage to individuals thatare well-adapted to their environment. Many new individuals canbe produced in a short time, which enables the clones to spreadrapidly and fill available space. A disadvantage of asexual repro-duction is the lack of genetic variation among the offspring. All ofthe offspring are genetically identical. Thus, the clones have thesame tolerance to an environment and are attacked by the samediseases and pests. Many of our plant cultivars are clones.

In nature, plants reproduce asexually in many ways, includingthe development of spores and vegetative reproduction.Vegetative reproduction is asexual reproduction involving vegeta-tive (nonreproductive) parts of a plant, such as leaves, stems, orroots. Many structures specialized for vegetative reproductionhave evolved in plants. Table 30-2 lists some of these structures.One example of vegetative reproduction is shown in Figure 30-15.

PROPAGATION OF PLANTSBY HUMANS

People often use vegetative structures to propagate plants. Manyspecies of plants are vegetatively propagated by humans from thestructures described in Table 30-2. People have also developedseveral methods of propagating plants from other vegetative parts,such as roots and even tissue samples. These methods include lay-ering, grafting, and using cuttings and tissue cultures.

TABLE 30-2 Plant Structures Adapted for Vegetative Reproduction

New plants are vegetatively reproducedfrom the stolons (runners) of an airplaneplant, also called a spider plant.

FIGURE 30-15

Name

Stolon(runner)

Rhizome

Bulb

Tuber

Description

horizontal, aboveground stem that produces leaves and roots atits nodes; a new plant can grow from each node

horizontal, belowground stem that produces leaves and roots at its nodes; a new plant can grow from each node

very short, underground monocot stem with thick, fleshy leavesadapted for storage; bulbs divide naturally to produce new plants

underground, swollen, fleshy stem specialized for storage; thebuds on a tuber can grow into new plants

Examples

strawberry, airplane (spider)plant, Boston fern

ferns, horsetails, iris, ginger,sugar cane

tulip, daffodil, onion, garlic,hyacinth

potato, caladium, Jerusalemartichoke

623

• Hearing ImpairedStrategiesStrategiesINCLUSIONINCLUSION

Students who are hearing impaired may beuncomfortable with public speaking. Thesestudents could be given a choice to partici-pate in a quiet activity that allows them toexpress their creativity visually. Methodsto use for the commercial propagation ofcrops depend on the characteristics of thecrop plant and the grower’s resources.

Have students select a crop plant, either afood plant or an ornamental, and investi-gate the requirements for the productionof this crop. Ask students to graphicallyillustrate a production plan for the cropand include in it their decision aboutwhether it would be best to propagate it byseed or vegetatively.

ReteachingSummarizing Plant PropagationHave students prepare a sum-mary of this section, writing oneparagraph on seed and fruit dis-persal and germination, and asecond paragraph on vegetativereproduction. Ask students tomake sure that they include all of the major points in each subsection. Verbal

Quiz1.How would a large fruit likely

be dispersed? (by an animal) How would a small fruit likelybe distributed? (by a small animal or by wind)

2.What kind of fruit is a pea pod?(a legume—a dry, simple fruit)What kind of fruit is an apple?(a pome—a fleshy, simple fruit)

3.What plant organ is most com-monly involved in asexualreproduction? (the stem)

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Answers to Section Review

1. wind, water, and animals2. simple fruit—pea (legume); aggregate fruit

(strawberry); multiple fruit—pineapple3. A bean seed has two nutrient-storing cotyledons.

The epicotyl forms a hook, protecting the plumuleas it emerges. A corn seed has one cotyledon,nutrient-storing endosperm, and a sheath that protects the plumule.

4. Asexual propagation quickly produces plants thatare identical to the parent, requires only one parent,and does not require pollination. Sexual reproductionis often slow, often requires two plants, and dependson wind, water, or animals for pollination.

5. Answers may vary. Refer to Table 30-2.

6. Sample answer: Seed dormancy prevents seedsfrom germinating before conditions are optimal for survival.

7. Sample answer: Delaying color development untilfruit maturity assures that the seeds will be capableof germinating where they are deposited.

8. Sample answer: Large seeds may have largeamounts of endosperm that will provide them witha source of energy until they emerge above thesurface of the soil and begin photosynthesizing.Small seeds have much smaller amounts of energy;adaptations may prevent them from sprouting ifthey are planted too deeply.

624 C H A P T E R 3 0

1. Name three common methods of fruit and seeddispersal.

2. Name one fruit from each of the three majorcategories of fruit.

3. How do the structure and germination of a beanseed and a corn seed differ from each other?

4. Compare asexual reproduction with sexualreproduction.

5. Make a table that compares structures andmethods for propagation of plants by humans.

CRITICAL THINKING

6. Justifying Conclusions How might seeddormancy be an evolutionary advantage?

7. Applying Information Many fruits are greenuntil they are mature. How might this be anadvantage in terms of seed dispersal by animals?

8. Evaluating Information Instructions on packetsof large seeds state that they should be planteddeeply. Instructions on packets of small seedsstate that they should be planted shallowly. Whyare these instructions different?

CuttingsIn some plants, roots will form on a cut piece of a stem, or shootswill form on a piece of a root. Pieces of stems and roots that are cutfrom a plant and used to grow new plants are called cuttings. Plantssuch as African violets can be grown from leaf cuttings, which willform both roots and shoots. Cuttings are widely used to propagatehouseplants, ornamental trees and shrubs, and some fruit crops.

LayeringIn some species, such as raspberries, roots form on stems wherethey make contact with the soil. People often stake branch tips tothe soil or cover the bases of stems with soil to propagate suchplants. The process of causing roots to form on a stem is calledlayering. Air layering, wounding a stem and placing moist peatmoss around the wound, is another common form of layering.

GraftingGrafting is the joining of two or more plant parts to form a singleplant. In grafting, a bud or small stem of one plant is attached tothe roots or stems of a second plant. The vascular cambium ofboth parts must be aligned for a graft to be successful. Graftingenables the desirable characteristics of two cultivars to be com-bined. Grafting is used to propagate virtually all commercial fruitand nut trees and many ornamental trees and shrubs.

Tissue CultureFigure 30-16 shows plants grown by tissue culture, the production ofnew plants from pieces of tissue placed on a sterile nutrient medium.Unlike most animal cells, plant cells contain functional copies of allthe genes needed to produce a new plant. Thus, it is possible for awhole plant to regrow from a single cell. Millions of identical plantscan be grown from a small amount of tissue. Tissue culture is usedin the commercial production of orchids, houseplants, cut flowers,fruit plants, and ornamental trees, shrubs, and nonwoody plants.

Tissue culture can be used to growround-leaved sundews, Droserarotundifolia. The jelly in the Petri dish isa sterile soil substitute that containsneeded nutrients.

FIGURE 30-16

SECTION 3 REVIEW

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TEACHER RESOURCES

Technology

Transparencies • G45 Stems Modified for

Vegetative Reproduction• G46 External Structures ofKalanchoë

• G47 Internal Structures ofKalanchoë

• G48 Methods of Vegetative Plant Propagation

AlternativeAssessmentK-W-L Have students return totheir lists of things they Want toknow about plant life cycles andreproduction described in theReading Skill Builder activity onthe opening page of this chapter.Have students place check marksnext to questions that they areable to answer. Students shouldfinish by making a list of whatthey have Learned. Have studentsidentify unanswered questions aswell as any new questions theymay have. Logical

Study TipSuggest to students that they prepare a table for each sectionof the chapter that summarizesthe chapter information. Theircategories for rows could be subsections within each section,different groups of plants, or anyother way of organizing the infor-mation that seems useful to them.They could fill in their tables sim-ply by adding a summary of theimportant points that fit on eachrow, or information separatedinto a category that is not used to separate rows. Verbal LS

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P L A N T R E P R O D U C T I O N 625

Plant Life CyclesSECTION 1

CHAPTER HIGHLIGHTS

antheridium (p. 609)archegonium (p. 609)homospory (p. 610)sorus (p. 611)

microspore (p. 611)megaspore (p. 611)heterospory (p. 611)

integument (p. 612)micropyle (p. 612)ovule (p. 612)

pollen grain (p. 612)pollination (p. 612)pollen tube (p. 612)

Vocabulary

propagation (p. 618)seed coat (p. 620)plumule (p. 620)epicotyl (p. 620)

hypocotyl (p. 620)radicle (p. 620)hilum (p. 620)dormancy (p. 621)

clone (p. 623)vegetative

reproduction (p. 623)cutting (p. 624)

layering (p. 624)grafting (p. 624)tissue culture (p. 624)

Vocabulary

receptacle (p. 613)sepal (p. 613)petal (p. 613)stamen (p. 613)anther (p. 613)

filament (p. 613)carpel (p. 613)pistil (p. 613)ovary (p. 613)

style (p. 613)stigma (p. 613)embryo sac (p. 614)polar nuclei (p. 615)

tube cell (p. 615)generative cell (p. 615)nectar (p. 616)double fertilization (p. 617)

Vocabulary

● Plants have a life cycle called alternation of generations,

in which a multicellular haploid gametophyte stagealternates with a multicellular diploid sporophyte stage.

● In the moss life cycle, a spore develops into a leafy greengametophyte that produces eggs in archegonia andflagellated sperm in antheridia. A moss sporophyte growsfrom a fertilized egg.

● In the fern life cycle, a spore develops into a small, flatgametophyte that produces eggs in archegonia and

flagellated sperm in antheridia. A fern sporophyte growsfrom a fertilized egg.

● In the gymnosperm life cycle, a large sporophyteproduces two types of spores, and microscopicgametophytes produce gametes. Nonflagellated spermreach an ovule through a pollen tube.

● Mosses and most ferns are homosporous (produce onlyone type of spore). All seed plants as well as a few otherspecies are heterosporous (produce male microsporesand female megaspores).

Sexual Reproduction in Flowering PlantsSECTION 2

● Flowers are reproductive structures. Most flowers consistof four parts—protective sepals, colorful petals, pollen-producing stamens, and egg-containing carpels.

● An immature ovule contains a megaspore mother cellthat undergoes meiosis and produces four megaspores.One of the megaspores divides by mitosis to form anembryo sac.

● Pollen grains form in stamens. Microspore mother cells inpollen sacs undergo meiosis and produce microspores,each of which develops into a pollen grain.

● Many flowering plants have flowers adapted for animalpollination or for wind pollination.

● In double fertilization, one sperm combines with the eggto form a zygote. A second sperm combines with twopolar nuclei to form the endosperm.

Dispersal and PropagationSECTION 3

● Fruits and seeds are dispersed by animals, wind, water,forcible discharge, and gravity. Many fruits and seeds areadapted for a particular type of dispersal.

● The three major categories of fruits are simple,aggregate, and multiple.

● The structure of seeds differs among the major groups ofseed plants. Seeds need water, oxygen, suitable

temperatures, and sometimes light to germinate. Delayedgermination often assures the survival of a plant.

● Asexual reproduction enables plants to spread rapidly ina favorable environment but can result in a lack ofgenetic variation among offspring.

● Human methods of plant propagation include usingcuttings, layering, grafting, and tissue culture.

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Answer to Concept Map

The following is one possible answerto Chapter Review item 19.

SECTION 0CHAPTER HIGHLIGHTS

microspores

microspore mother cells

contains cells called

that undergo meiosis to form

that divide by mitosis to form

Anther that is part of the stamen

pollen grains that are made of

tube cell

generative cell

and

TEACHER RESOURCES

Workbooks

• Study Guide• Vocabulary Review• Science Skills• Critical Thinking• Quizzes• Chapter Test• Chapter Test

Technology

Transparencies• Graphic Organizer• Concept Mapping

One-Stop Planner CD-ROM• Concept Mapping

Worksheet GENERAL

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ANSWERS

Using Vocabulary1. a. A megaspore develops into a

female gametophyte. A microsporedevelops into a male gametophyte. b. The transfer of pollen from anthersto stigmas is pollination. The processof two sperm cell fusions with boththe egg and with two polar nuclei isdouble fertilization. c. A sepal is partof the outermost whorl of flowerparts. A petal is part of the whorl offlower parts inside the sepals.

2. a. Homospory is the condition of aplant that produces just one type ofspore, while heterospory is the condi-tion of a plant that produces differenttypes of spores. b. The polar nucleiare located in the center of an embryosac. c. The integument is the layer ofcells that surrounds each megaspo-rangium. The micropyle is the openingin the integument through which thetube cell enters the embryo sac.

3. When dormancy of a seed breaks, theroot radicle and then the plumuleemerge through the seed coat.

4. The carpel is the part of a flower thatcontains the ovary which, after fertil-ization, enlarges to become a fruit.

Understanding Key Concepts5. The antheridium produces and

releases sperm and the archegoniumproduces an egg cell.

6. sporophyte7. The male gametophytes within the

sporophytes of seed plants developinto pollen grains that can be trans-ported through the air.

626 C H A P T E R 3 0

CHAPTER REVIEW

USING VOCABULARY1. For each pair of terms, explain how the meanings

of the terms differ.a. microspore and megasporeb. pollination and double fertilizationc. sepal and petal

2. For each pair of terms, explain the relationshipbetween the terms.a. homospory and heterosporyb. polar nuclei and embryo sacc. integument and micropyle

3. Use the following terms in the same sentence:dormancy, plumule, radicle, and seed coat.

4. Word Roots and Origins The word carpel isderived from the Greek word karpos, whichmeans “fruit.” Using this information, explain whythe term carpel is a good name for the structurethat the term describes.

UNDERSTANDING KEY CONCEPTS5. Name the sexual reproductive structures in a

moss life cycle, and describe the function of each.

6. Identify the dominant stage in the life cycle of a fern.

7. Summarize the adaptation that allows gym-nosperms to sexually reproduce in the absenceof environmental moisture.

8. Explain how heterospory can be an advantageover homospory.

9. Describe the roles of the parts of a flower that donot participate directly in reproduction.

10. Describe the roles of the parts of a flower that doparticipate directly in reproduction.

11. Distinguish between embryo sac formation andpollen grain formation.

12. Draw a diagram showing the events and plantstructures involved in angiosperm pollination.

13. Distinguish the process of fertilization in gym-nosperms from the process of fertilization inflowering plants.

14. Identify one example of a plant structure that isan adaptation for fruit or seed dispersal.

15. Describe the two characteristics used for classify-ing fruits.

16. Explain the advantage of the hypocotyl hook thatthe embryos of some seeds form as the plantemerges after germination.

17. Explain why asexual reproduction can be anadvantage for plants that are well-adapted totheir environment.

18. Compare two methods of plant propagation usedby humans.

19. CONCEPT MAPPING Use the following terms to create a concept map that

describes male reproductive structures in flower-ing plants: anther, generative cell, microsporemother cell, stamen, microspore, pollen grain,and tube cell.

CRITICAL THINKING20. Recognizing Relationships In many flowers with

both stamens and pistils, the stigma is locatedwell above the anthers. What might be the valueof such an arrangement?

21. Analyzing Information Following the self-pollination of some plants, the pollen tubes diebefore reaching ovules. What is the significanceof this event?

22. Justifying Conclusions If you were to discover anew type of rose, would you use vegetative partsor seeds to propagate the rose and produce largenumbers of identical plants? Justify your answer.

23. Interpreting Graphics In the photograph below,the houseplant on the left shows a Sansevieriatrifasciata, which has yellow-edged leaves. A sec-tion of the leaf, or a leaf cutting, can be used toproduce new plants. However, as shown on theright side of the photograph, only shoots with all-green leaves and no yellow edges will form.How do you explain this?

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CHAPTER REVIEW

8. Heterosporous plants are more likely to be cross-fertilized, which promotes genetic variation.

9. The sepals of a flower surround and protect theother parts of a flower while they mature. Thepetals attract animal pollinators.

10. A stamen produces and releases pollen, whichcontains a cell that develops into sperm. Thecarpel produces one or more egg cells inside itsone or more ovaries.

11. Ovule formation begins with meiotic division of amegaspore mother cell and results in the produc-tion of a single embryo sac containing a singleegg. Pollen grain formation begins with meioticdivision of a microspore mother cell and results in the production of four pollen grains.

12. See Figure 30-9.13. Fertilization in conifers occurs more than a year

after pollination. One sperm fuses with the egg inan ovule while the other sperm dies. Fertilizationin flowering plants occurs within a few days ofpollination. Two sperm fuse with cells in theembryo sac; one sperm fuses with the egg andthe other sperm fuses with the two polar nuclei.

14. Sample answer: Seeds of fleshy fruits, such asmulberry, are dispersed by birds.

15. number of flowers and pistils, fleshy or dry atmaturity, dry fruit splits open at maturity or not,and number of seeds

ANSWERS

P L A N T R E P R O D U C T I O N 627

Standardized Test PreparationDIRECTIONS: Choose the letter of the answer choicethat best answers the question.

1. The production of a single type of spore is a char-acteristic of the life cycles of which kinds ofplants?A. mosses and most fernsB. most ferns and gymnospermsC. mosses and most gymnospermsD. mosses, most ferns, and gymnosperms

2. Why is sexual reproduction in gymnosperms andother seed plants independent of seasonal rains?F. These plants grow only near streams and

rivers.G. Pollinators or wind carry the sperm to the

eggs.H. Fertilization occurs inside structures within

the spores.J. Fertilization always involves eggs and sperm

of the same plant.

INTERPRETING GRAPHICS: The illustration belowshows the four concentric whorls of a typical flower.Use this illustration to answer the question thatfollows.

3. In which whorl are the male reproductivestructures found?A. 1B. 2C. 3D. 4

4. Pollination in flowering plants is said to takeplace when which of the following occurs?F. when insects ingest nectarG. when pollen lands on a stigmaH. when a sperm fuses with an eggJ. when a spore leaves a sporangium

DIRECTIONS: Complete the following analogy.

5. Generative cell : pollen grain :: egg cell :A. ovaryB. carpelC. receptacleD. embryo sac

INTERPRETING GRAPHICS: The illustration belowshows the structure of a corn kernel, which is amonocot seed. Use this illustration to answer thequestion that follows.

6. Which structure of the corn kernel is theendosperm, the source of nutrients?F. 1G. 2H. 3J. 4

SHORT RESPONSEA seed will not germinate until it is exposed to certainenvironmental conditions.

List two environmental factors that influence seedgermination, and describe the mechanisms by whichthey trigger the germination process.

EXTENDED RESPONSEDouble fertilization is unique to angiosperms.

Part A What cells participate in double fertilization,and what products do they form?

Part B What are the evolutionary advancementsseen only in angiosperms, and what advan-tages do they confer?

If you are not sure about thespelling of certain words when answering the short- or extended-response questions, look at the questionto see if the same word appears in the question.

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16. The hook protects the plumule by pushing asidethe soil and pulling the plumule through the soil so that the cotyledons stay folded around it or sothat the plumule’s leaves stay folded together.

17. Asexual reproduction is more rapid and producesexact copies of the parent.

18. Layering involves the formation of roots on intactstems. Propagation by cuttings involves the for-mation of roots on a piece of stem, shoots on apiece of root, or shoots and roots on a detachedleaf. Grafting involves joining pieces of two genet-ically distinct plants. Tissue culture involves thegrowth of small bits of plant tissue in a lab.

19. The answer to the concept map is found at thebottom of the Chapter Highlights page.

Critical Thinking20. In flowers in which the stigma is elevated above

the anthers, cross-pollination is more likely tooccur. Cross-pollination increases genetic varia-tion in offspring.

21. The death of pollen tubes prevents fertilization bykeeping sperm from reaching the egg.

22. The new rose should be propagated vegetativelyto produce large numbers of identical plants.

23. A shoot developing from the green part of the leafwill produce an all-green shoot. To retain the yel-low leaf edge during propagation, cut off a pieceof the rhizome containing at least one leaf.

SECTION 0Standardized TestPreparation

Teaching TipTo provide practice under realistic test-ing conditions, give students 20 minutesto answer the Standardized TestPreparation questions.

1. A2. G3. C4. G5. D6. F

Short ResponseWarm temperatures, water, and oxygenare required for germination. Warm tem-peratures are required for the metabolicactivities of growth. Water softens theseed coat so that it easily opens and itactivates enzymes that convert starch inthe endosperm into sugars. Oxygen isneeded for the breakdown of sugars andthe release of energy in the process ofaerobic respiration.

Extended ResponsePart A The egg cell fuses with a sperm

cell to produce a zygote. The two polarnuclei fuse with the second spermcell to produce endosperm.

Part B Angiosperms are unique in pro-ducing flowers and fruits. Flowersattract animal pollinators that makecross-pollination highly efficient. Fruitsprovide many mechanisms for thedispersal of seeds.

Question 2 Students may select incorrectAnswer F because they may forget thatseed plants do not require water for fertil-ization. They may select incorrect AnswerH if they forget that fertilization occursoutside the sporophyte. Also, incorrectAnswer J may be selected if they forgetthat fertilization may involve eggs andsperm of different plants.

EXPLORATION LAB

Time RequiredThree 30-minute class periods over five days

Ratings

TEACHER PREPARATION

STUDENT SETUP

CONCEPT LEVEL

CLEANUP

Safety CautionsRemind students to wear safety goggles, gloves, and a lab apron at alltimes during the lab.Caution students about Lugol’s iodinesolution, which can cause eye, nose,and throat irritation. If Lugol’s iodinesolution gets on skin or clothing, rinse itoff with water. Lugol’s solution stainsskin and may stain clothes perma-nently. If Lugol’s iodine solution gets inthe eyes, flush it out immediately withwater for 15 minutes and get medicalattention. If it is swallowed (and theperson is conscious), give the personone or two glasses of water to drink,induce vomiting, and call a physicianimmediately.Caution students to use scalpels carefully to avoid injuring themselvesand others.

Materials and EquipmentUse the Lab Materials QuicklistSoftware on the Biology LabGenerator CD-ROM to create a customized list of materials for this lab.

E A SY HAR D

Procedural Tips1. Soak seeds in water prior to the lab. This will

allow the seed coats to be removed easily.

2. For Part A, prepare about one and a half times asmany seeds as needed for the size of your class,as some seeds might be unusual in shape andbecause students might destroy seeds beforethey are finished making their observations.

3. Provide each lab group with a dropper bottlecontaining Lugol’s iodine solution.

4. Each lab group will need a scalpel, two rubberbands, two 150 mL beaders, a medicine dropper,a glass-marking pen, a metric ruler, and a micro-scope slide. Each lab group will need access to astereomicroscope or a compound light microscope.

Answers to Background

1. A seed is made up of an embryo, stored nutrients,and a seed coat.

2. Like the parent plant, the embryo is a sporophyte. It has roots, a stem, and leaves.

3. Monocots have one cotyledon, flowers with partsin multiples of three, leaves with parallel veins, andstems with scattered vascular bundles. Dicotshave two cotyledons, flowers with parts in multi-ples of four or five, leaves with netted veins, andstems with vascular bundles arranged in rings.

4. First, the seed swells as it takes up water. Next, theembryo’s root emerges, followed by emergence ofthe shoot tip.

628 C H A P T E R 3 0

Comparing Seed Structure andSeedling Development

■ Observe the structures of dicot and monocot seeds.■ Compare the structure of dicot and monocot embryos.■ Compare the development of dicot and monocot

seedlings.

■ safety goggles■ lab apron■ protective gloves■ 1 pea seed soaked overnight■ 6 bean seeds soaked overnight■ 6 corn kernels soaked overnight■ stereomicroscope■ scalpel■ Lugol’s iodine solution in dropper bottle■ paper towels■ 2 rubber bands■ 2 150 mL beakers■ glass-marking pen■ metric ruler■ microscope slide and cover slip■ medicine dropper■ compound light microscope

Background

1. What are the parts of a seed?2. In what ways are seeds like their parent plant?3. How do monocotyledons and dicotyledons differ?4. What changes occur as a seed germinates?

Seed Structure

1. Obtain one each of the following seeds—pea, bean,and corn.

2. Remove the seed coats of the pea and bean seeds. Openthe seeds, and locate the two cotyledons in each seed.

3. Using the stereomicroscope, examine the embryos ofthe pea seed and the bean seed.

4. In your lab report, draw the pea and bean embryosand label all of the parts that you can identify.

5. CAUTION Put on alab apron, safety

goggles, and gloves. In this lab, you will be work-ing with a chemical that may irritate your skin orstain your skin and clothing. If you get a chemicalon your skin or clothing, wash it off at the sinkwhile calling to your teacher. If you get a chemicalin your eyes, immediately flush it out at the eye-wash station while calling to your teacher. Use thescalpel carefully to avoid injury. Examine a cornkernel, and find a small, oval, light-colored area thatshows through the seed coat. Use the scalpel to cutthe kernel in half along the length of this area. Placea drop of iodine solution on the cut surface.

6. Use the stereomicroscope to examine the cornembryo. In your lab report, sketch the embryo andlabel all the parts that you can identify.

Seedling Development

7. Set five corn kernels on a folded paper towel. Roll upthe paper towel, and put a rubber band around theroll. Stand the roll in a beaker with 1 cm of water inthe bottom. The paper towel will soak up water andmoisten the corn. Keep water at the bottom of thebeaker, but do not allow the corn kernels to be cov-ered by the water.

PART B

PART A

SAFETY

MATERIALS

OBJECTIVES

EXPLORATION LAB

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Answers to Analysisand Conclusions

1. Corn shoots are protected by asheath as they push through the soil.Bean shoots are protected by a hookin the embryonic stem that pushesthrough the soil before the cotyledons.

2. Cotyledons are the first leaves toappear on a bean seedling.

3. The black color indicates that starchis contained in the corn kernel. Youmight expect to find starch in a cornkernel because much of the kernelis a nutrient for the embryo, andstarch is the main storage form ofcarbohydrates.

4. Yes. The distance between the markshas changed at the tips of the stemsand the tips of the roots.

5. Embryonic leaves and roots wereobserved in all seeds on the third day.

6. Peas and beans have two cotyledons,while corn has one. Corn seeds haveendosperm, while mature bean andpea seeds do not. The shoots of peasand beans hook as they germinate,while a corn shoot grows straight up.

7. Nutrients are stored in the endospermof the corn kernel and in the cotyledonsof the beans and peas. The iodine testfor starch confirms this.

8. The seedlings grow at the tips of theirroots and stems.

9. Corn seeds have only one cotyledonand thus are monocotyledons, whilebean seeds have two cotyledons andthus are dicotyledons.

Answers to Further InquiryAnswers may vary. Accept anyreasonable experiment design.

P L A N T R E P R O D U C T I O N 629

8. Repeat step 7 with five bean seeds.9. After three days, unroll the paper towels and examine

the corn and bean seedlings. Use a glass-marking pento mark the roots and shoots of the developingseedlings. Starting at the seed of the corn and atthe cotyledon node of the bean, make a mark every0.5 cm along the root of each seedling. And againstarting at the seed of the corn and at the cotyledonnode of the bean, make a mark every 0.5 cm along thestem of each seedling. Measure the distance from thelast mark on the root to the root tip of each seedling.Also measure the distance from the last mark on thestem to the shoot tip of each seedling. Record thesedata in your lab report.

10. Draw a corn seedling and a bean seedling in your labreport. Using a fresh paper towel, roll up the seeds,place the rolls in the beakers, and add fresh water tothe beakers.

11. Make a data table similar to the one shown below inyour lab notebook. Expand your table by addingcolumns under each “Roots” and “Stems” head toaccount for every section of the roots and stems ofyour seedlings.

12. After two days, reexamine the seedlings. Measure thedistance between the marks, and record the data inyour data table.

13. CAUTION Use the scalpel carefully to avoidinjury. Using the scalpel, make a cut about 2 cm

from the tip of the root of a bean seedling. Place theroot tip on a microscope slide and add a drop ofwater. Place a cover slip over the root tip. Using acompound light microscope on low power, observe theroot tip. In your lab report, draw the root tip.

14. Clean up your materials and wash yourhands before leaving the lab.

Analysis and Conclusions

1. What protects the tips of corn shoots as they pushthrough the soil? What protects the bean shoots?

2. What types of leaves first appear on the beanseedling?

3. What substance does the black color in the corn kernelindicate? Why might you expect to find this substancein the seed?

4. Examine the data you recorded for steps 9 and 12. Hasthe distance between the marks changed? If so, wherehas it changed?

5. What parts of the embryo were observed in all seedson the third day?

6. How does the structure and development of the cornkernel differ from the structure and development ofthe pea and bean seeds?

7. What was the source of nutrients for each seedembryo? What is your evidence?

8. Describe the growth in the seedlings you observed.9. Corn and beans are often cited as representative

examples of monocots and dicots, respectively. Relatethe seed structure of each to the terms monocotyledonand dicotyledon.

Further Inquiry

Design an experiment to find out how monocots and dicotscompare in general plant growth and in the structure oftheir leaves and flowers.

CORN AND BEAN SEEDLING GROWTH AFTER TWO DAYS

Corn seedlings

Roots Stems

Seed to Root tip to Seed to Shoot tip tofirst mark last mark first mark last mark

Bean seedlings

Roots Stems

Seed to Root tip to Seed to Shoot tip tofirst mark last mark first mark last markSeedling

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TEACHER RESOURCES

Workbooks

Datasheets for In-Text Labs• Comparing Seed Structure and Seedling

Development

Skills Practice Labs• Dissecting Flowers

Inquiry and Exploration Labs• Fruits and Seeds

Forensics Labs• Assault at the Flower Shop

Technology

Biology Lab Video (with Manual)• Comparing Bean and Corn Seedlings

GENERAL

GENERAL