section 1 sexual reproduction in seedless · pdf filesection 1 sexual reproduction in seedless...

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This lesson begins with adiscussion of alternation of genera-tions, which occurs in all plants. Itcontinues with the life cycle of amoss to introduce the reproductivestructures and life cycles of non-vascular plants. A fern is used toillustrate the reproductive structuresand life cycles of seedless vascularplants.

Place a moss and a fern on yourdesk. Instruct students to write ashort paragraph that describes amoss or fern plant. Tell them to beas descriptive as possible about theplant’s general appearance andwhere it lives.

Discussion/QuestionTell students that the sperm of anonvascular plant must swim to anegg cell for fertilization to occur.Ask students to describe environ-mental conditions that wouldenable nonvascular plants to repro-duce sexually. (Nonvascular plantsare able to reproduce sexually wher-ever moisture is abundant. Shadyareas near streams are ideal habitats.In drier habitats, nonvascular plantscan reproduce sexually after a rainfallor heavy dew.) InterpersonalTAKS 2 Bio 6D (grade 10 only), 8C TAKS 3 Bio 7B, 13A; Bio 5A, 13B

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Bellringer

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Section 1

530 Chapter 24 • Plant Reproduction

• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Quick Lab GENERAL

GENERAL

GENERAL

Chapter Resource File

• Reading Organizers• Reading Strategies

Planner CD-ROM

Section 1 Sexual Reproduction in Seedless Plants

Reproduction in Nonvascular Plants The carpet of green you often see near streams and in moist, shadyplaces is usually made up of mosses or liverworts. As you learned inthe previous chapter, these small, relatively simple plants are non-vascular plants. They do not have a vascular system for distributingwater and nutrients. Mosses and liverworts do not usually thriveoutside moist places because they must be covered by a film ofwater to reproduce sexually.

Like all plants, nonvascular plants have a life cycle called alterna-tion of generations. In this type of life cycle, a gamete-producingstage, or gametophyte, alternates with a spore-producing stage, orsporophyte. Gametophytes produce gametes (eggs and sperm) inseparate multicellular structures. The structure that produces eggsis called an (ark uh GOHN ee uhm). The structure thatproduces sperm is called an (an thuhr IHD ee uhm).Sporophytes produce spores in a sporangium. The gametophytes ofnonvascular plants are larger and more noticeable than are thesporophytes. This difference in size is very pronounced in the liver-worts, as you can see in Figure 1.

antheridiumarchegonium

Objectives● Summarize the life cycle of

a moss.

● Summarize the life cycle ofa fern.

● Compare and Contrastthe life cycle of a moss withthe life cycle of a fern.

Key Terms

archegoniumantheridiumsorus

The gametophytes of Marchantia, a common liverwort,produce male and female gametes on separate stalks.

Figure 1 Reproductive structures of a liverwort Sporophytes, which grew from archegonia under the cap of a female stalk

Archegonia under thecap of a female stalk

Femalestalks

Sporophytes

Antheridia on top of a male stalk

Malestalks

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Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 13A TEKS Bio 7B, 8C, 13A, 13B

Teacher Edition TAKS Obj 2 Bio 6D, 8C TAKS Obj 3 Bio 7B, 13ATEKS Bio 5A, 6D, 6E, 7B, 8C, 10C,13A, 13B

pp. 530–531

Transparencies

TT Life Cycle of a MossTT Life Cycle of a Fern

Chapter 24 • Plant Reproduction 531

GENERAL

Using the Figure Walk students through the moss lifecycle shown in Figure 2, startingwith the zygote. Point out that thezygote divides mitotically. Repeatedmitotic cell divisions result in amulticellular, diploid organismcalled the sporophyte. In mosses,the sporophytes are not green, andthey consist of a bare stalk toppedwith a spore capsule. Reproductivecells in the spore capsule undergomeiosis, which reduces the chromo-some number from diploid tohaploid. Point out that the sporesgrow into either male or femalegametophytes, which are haploid. Inmosses, the gametophytes are greenand have leaflike structures. Finally,point out that when fertilization (theunion of an egg and a sperm) occursand a new zygote is formed, thediploid chromosome number isrestored, and a new sporophytegeneration begins. Visual

Brainstorming Ask students toidentify the haploid structures in aplant’s life cycle (spores, male andfemale gametophytes, eggs, andsperm). Ask which are unicellular(spores, sperm, and eggs) and whichare multicellular (male and femalegametophytes). Ask students toidentify the haploid structures in ananimal’s life cycle (egg and sperm).Ask if these are unicellular or mul-ticellular (unicellular). Ask studentsto identify the diploid structures ina plant’s life cycle (sporophyte,zygote). Ask which is unicellular(zygote) and which is multicellular(sporophyte). Ask students to iden-tify the diploid structures in ananimal’s life cycle (all stages ofdevelopment from the zygote to theadult). Ask which of these struc-tures is unicellular (zygote) andwhich are multicellular (all otherstages of development).

Interpersonal Bio 6E, 10C, 13BLS

SKILLBUILDER

READINGREADING

Bio 6E, 10C, 13BLS

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MISCONCEPTION ALERT

Spores The term spore does not have a sin-gle, concise definition as students might think.Two things are generally true of spores. First,they are unicellular; second, they have a pro-tective outer covering. In some bacteria, sporesform from regular cells when environmentalconditions are harsh. These cells lose most oftheir water and develop a protective outer

covering. Many of these bacteria also pro-duce toxins, which help the spores remainviable in harsh environments. The spores of fungi and plants are haploid, drought-resistant, and easily transported by wind orwater. The spores of fungi and plants developinto multicellular individuals (by mitotic celldivision) without fusing with another cell.

Life Cycle of a MossThe life cycle of a moss is summarized in Figure 2. Sexual reproduc-tion results in a fertilized egg, or zygote. The diploid zygote grows intoa new diploid sporophyte. As you can see, a moss sporophyte growsfrom a gametophyte and remains attached to it. The sporophyteconsists of a bare stalk with a spore capsule (sporangium) at its tip.Spores form by meiosis inside the spore capsule. Therefore, as in allplants, the spores are haploid. The spore capsule opens when thespores are mature, and the spores are carried away by wind or water.When a moss spore settles to the ground, it germinates and grows intoa “leafy” green gametophyte. Archegonia and antheridia form at thetips of the haploid gametophytes. Eggs and sperm form by mitosisinside the archegonia and antheridia. Remember, moss gametophytesgrow in tightly packed clumps of many individuals. When watercovers a clump of mosses, sperm can swim to nearby archegonia andfertilize the eggs inside them.

The word archegoniumcomes from the Greekwords archegonos,meaning “first of a race.”Knowing this makes iteasier to remember that anew and geneticallydifferent individual growsfrom an archegonium whenits egg is fertilized.

Figure 2 Moss life cycle.In mosses, a sporophyte thatconsists of a spore capsule ona bare stalk alternates with a“leafy,” green gametophyte.

An adult sporophyte produces spores within its spore capsule.

2

Gametophytesproduce gametes inside antheridia and archegonia.

4

Sperm swim toand fertilize eggs inside the archegonia.

5

A zygote develops into a new sporophyte.

1

Spores grow into male and female gametophytes.

3

Diploid (2n) Haploid (n)

GametophytesFemale

Male

AntheridiaSperm

EggArchegonia

Adultsporophyte SporesSpore capsule

(sporangium)

Germinating spore

Zygote

Young sporophyte

Fertilization

Meiosis

Mitosis

Mitosis

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GENERAL

Observing a FernGametophyteSkills AcquiredObserving, makingcomparisons, makingconclusions

Teacher’s Notes Tell students that fern gameto-phytes develop on moist soiland are very small.

Answers to Analysis1. Answers will vary but should

be consistent with the dia-grams in Figure 4.

2. A new sporophyte begins itsgrowth in an archegonium.This process occurs becausethe egg remains in the archego-nium, and a sperm cell swimsfrom an antheridium to thearchegonium where it fertilizesthe egg.TAKS 1 Bio/IPC 2C, 2D; Bio 13B

Math Skills Ask students to usethe information in Figure 3 to esti-mate the number of spores that onefern plant might produce. To helpthem with their calculations, havestudents assume that only half ofthe frond is visible in the photo,each sporangium produces 100spores, and one plant produces 12fronds. (A sample calculation wouldbe as follows: 260 sori per frond � 30sporangia per sorus � 100 spores persporangium � 12 fronds per plant = 9,360,000 spores per plant.)

Logical TAKS 1 Bio/IPC 2C; Bio 13BLS

BUILDERSKILL

Teach, continuedTeach, continued

Garden centers and florists often receive callsabout insects on ferns and flower arrange-ments that include fern leaves. When the fernleaves have sporangia on them, people oftenmistake the sori or sporangia for insects. Aclose look at these spore-producing struc-tures reveals that they are lined up in rowsacross from each other. Insect pests, such asscale and mealy bugs, rarely line up in suchregular patterns.

REAL WORLDREAL WORLDCONNECTIONCONNECTION

Reproduction in Seedless Vascular PlantsYou may recall that the seedless vascular plants includethe whisk ferns, horsetails, club mosses, and ferns. Theseedless vascular plants differ from the nonvascularplants because they have efficient water- and food-conducting systems of vascular tissue. Like thenonvascular plants, the seedless vascular plants thrive inmoist, shady places. They can reproduce sexually onlywhen a film of water covers the gametophyte. Eggs formin archegonia, and sperm form in antheridia. Thearchegonia and antheridia develop on the lower surfacesof the gametophytes. In most species of seedless vascularplants, both eggs and sperm are produced by the sameindividual. In some species, however, eggs and sperm areproduced by separate gametophytes.

Unlike nonvascular plants, seedless vascular plantshave sporophytes that are much larger than their gameto-phytes. Some ferns, for example, have sporophytes that areas large as trees. On the other hand, the gametophytes of

ferns are thin, green, heart-shaped plants that are less than 1 cm (0.5in.) across. The sporophytes produce spores in sporangia. In horse-tails and club mosses, sporangia develop in cones. In ferns, clusters ofsporangia form on the lower surfaces of fronds, as shown in Figure 3.A cluster of sporangia on a fern frond is called a . The wordsorus comes from the Greek word soros, meaning “a heap.”

sorus

Observing a FernGametophyte You can observe the archegonia and antheridia of a fern gametophyte with a microscope.

Materials

prepared slide of a fern gametophyte with archegonia and antheridia, compound microscope

Procedure

1. Examine a slide of afern gametophyte

under low power of a micro-scope. Move the slide untilyou can see a cluster ofarchegonia. Now, switch tohigh power, and focus on onearchegonium. Draw and labelwhat you see.

2. Switch back to low power,and move the slide until youcan see several egg-shapedstructures. These areantheridia. Now, switch tohigh power, and focus on oneantheridium. Draw and labelwhat you see.

Analysis

1. Describe the appearance ofan archegonium and anantheridium.

2. Critical ThinkingDrawing Conclusions Inwhich structure, an archego-nium or antheridium, does thegrowth of a new sporophytebegin? Explain.

Figure 3 Sori on a fernfrond. Many sori are visible on this portion of a frond froma polypody fern. Each sorusconsists of about 20–30sporangia.

Fern Gametophytes (56�)

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Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2DTAKS Obj 2 Bio 8C TAKS Obj 4 IPC 8A TEKS Bio 6E, 8C, 13BTEKS Bio/IPC 2C, 2DTEKS IPC 8A

pp. 532–533

IPC Benchmark Mini-Lesson

Biology/IPC Skills TAKS 4 IPC 8ADistinguish between physical and chemical changesin matter, such as ... stages in the rock cycle. Activity Have students use the Internet to researchhow fossils and fossil fuels are formed. As students toprepare a poster showing the stages that lead to theformation of fossils and fossil fuels.

Answers to Section Review

1. First, a zygote grows into a sporophyte bymitotic cell division. Next (2), the sporophyteforms spores following meiotic cell division.Then (3), the spores grow into gametophytesby mitotic cell division. After the gametophytesform eggs and sperm by mitotic cell division(4), eggs are fertilized by sperm and a newzygote forms (5).

2. First, a zygote grows into a sporophyte bymitotic cell division. Next (2), the sporophyteforms spores following meiotic cell division.Then (3), the spores grow into gametophytesby mitotic cell division. After the gametophytesform eggs and sperm by mitotic cell division

Bio 13B

(4), eggs are fertilized by sperm and a newzygote forms (5).

3. Spores are responsible for the dispersal of seed-less plants. Spores are drought-resistant and canbe transported in the air or in water.

4. In mosses, the gametophyte is dominant; inferns, the sporophyte is dominant. Mossesform separate male and female gametophytes,while ferns form a gametophyte that producesboth eggs and sperm.

5. A. Incorrect. The antheridium produces sperm.B. Correct. C. Incorrect. The sporangium pro-duces spores. D. Incorrect. There are nostructures for conducting water in the mossplant. Bio 13B

Bio 13B

TAKS 3 Bio13A; 13B

Bio 13B

ReteachingSummarize the life cycles of mossesand ferns. Emphasize that all plantsalternate between a haploid phaseand a diploid phase in their lifecycles. Tell students that in mossesand ferns, the multicellular formsin both phases are visible with theunaided eye. Point out that thegametophyte phase in mosses isdominant and that the sporophytesare not photosynthetic. Also pointout that the sporophyte phase isdominant in ferns but that theyoung sporophytes are dependenton the gametophytes. Verbal

Quiz1. What is the name of the single-

celled, haploid reproductivestructure of plants? (spore)

2.What is the meaning of thephrase alternation of genera-tions? (It means that plants have alife cycle that alternates betweenhaploid and diploid phases.)

3. What is the name of the struc-ture that makes up the first stageof a new plant’s life cycle?(zygote)

AlternativeAssessmentPoster Have student groups makeposters that depict the life cycles ofmosses and ferns. Suggest that theyuse color-coding to identify thestructures common to the life cyclesof these two groups. (Both have azygote, a sporophyte, spores, a game-tophyte, antheridia, archegonia, eggs,and sperm.) Students also can usecolor-coding to highlight the differ-ences between the life cycles ofmosses and ferns. (Mosses have sep-arate male and female gametophytes,while ferns have both antheridia andarchegonia on each gametophyte.)

Verbal

Bio 6E, 13BCo-op LearningLS

GENERAL

GENERAL

TAKS 2 Bio 8C; Bio 6E, 13BLS

CloseClose


Life Cycle of a FernThe life cycle of a fern is summarized in Figure 4. A fertilized egg, orzygote, grows into a new sporophyte. The diploid sporophyte producesspores by meiosis. The haploid spores fall to the ground and grow intohaploid gametophytes. Fern gametophytes produce gametes by mito-sis—eggs in archegonia and sperm in antheridia. Sperm swim toarchegonia and fertilize the eggs inside them.

Figure 4 Fern life cycle.In ferns, a large sporophytewith leaves called frondsalternates with a small, green,heart-shaped gametophyte.

Maturegametophyte

Youngsporophyte

Adultsporophyte

Sporangium

Lowersurface

Antheridium

Archegonium

Spores

2

MeiosisMitosis

Mitosis

Mitosis


Fertilization

An adult sporophyte produces spores in clusters of sporangia. 3 The spores grow into a

gametophyte.

4 Gametophytes produce gametes inside antheridia and archegonia.

5 Sperm swim to the archegonia and fertilize eggs.

1 A zygote develops into a new sporophyte.

Sperm Egg

Zygote

Frond

Rhizome

Roots

Section 1 Review

List five major steps in the life cycle of a moss.

List five major steps in the life cycle of a fern.

Critical Thinking Forming ReasonedOpinions Which reproductive structures, gametesor spores, are responsible for the dispersal (spread)of seedless plants? Justify your answer.

Critical Thinking Analyzing InformationWhat are the major differences between the mosslife cycle and the fern life cycle?

What is the function of anarchegonium? A to produce sperm C to produce sporesB to produce eggs D to conduct water

TAKS Test PrepTAKS Test Prep

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13B

13A 13B

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OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This lesson introducesreproduction in seed plants, includ-ing seed structure and formation.Discussion of the reproductivestructures and life cycle of gym-nosperms features a coniferousplant. The lesson on reproductivestructures and the life cycle ofangiosperms includes a discussionof insects in the fertilization processand the formation of endosperm bydouble fertilization.

Give each student five differentkinds of seeds and have them listsimilarities and differences.Examples include various beans,peas, maple seeds, pine seeds,coconuts, and poppy. Remind themof the discussion about pollendispersal at the beginning of thechapter and point out that seedsare also adapted to different meansof dispersal, including wind, water,and ingestion and elimination byanimals. This exercise can lead intoa discussion of seed structure andfunction. TAKS 2 Bio 13A; Bio 13B

Bellringer

FocusFocus

Section 2


Transparencies

TT BellringerTT Seed Plant GametophyteTT Seed Structure

• Lesson Plan• Directed Reading• Active Reading GENERAL

GENERAL


• Reading Organizers• Reading Strategies

Planner CD-ROM

Section 2 Sexual Reproduction in Seed Plants

Reproductive Structures of Seed Plants Reproduction in seed plants (gymnosperms and angiosperms) isquite different from reproduction in seedless plants. For one thing,you need a microscope to see the gametophytes of seed plants, asFigure 5 shows. Also, spores are not released from seed plants. Thespores remain within the tissue of a sporophyte and develop intotwo kinds of gametophytes—male gametophytes, which producesperm, and female gametophytes, which produce eggs. The tinygametophytes of seed plants consist of only a few cells. A malegametophyte of a seed plant develops into a , which hasa thick protective wall. A female gametophyte of a seed plant de-velops inside an (AHV yool), which is a multicellular structurethat is part of the sporophyte. Following fertilization, the ovule andits contents develop into a seed.

Because the gametophytes of seed plants are very small, seed plantsare able to reproduce sexually without water. Wind and animalstransport pollen grains to the structures that contain ovules. Thetransfer of pollen grains from the male reproductive structures of aplant to the female reproductive structures of a plant is called

. When a pollen grain reaches a compatible female repro-ductive structure, a tube emerges from the pollen grain. This tube,called a , grows from a pollen grain to an ovule andenables a sperm to pass directly to an egg.

pollen tube

pollination

ovule

pollen grain

Objectives● Distinguish the male and

female gametophytes of seedplants.

● Describe the function ofeach part of a seed.

● Summarize the life cycle ofa conifer.

● Relate the parts of a flowerto their functions.

● Summarize the life cycle ofan angiosperm.

Key Terms

pollen grainovulepollinationpollen tubeseed coatcotyledonsepalpetalstamenantherpistilovarydouble fertilization

The tiny gametophytes of seed plants develop within specialized structures thatform in the reproductive parts of a flower.

Figure 5 Seed plant gametophytes

Male reproductivestructure

Female reproductivestructure

A pollen grain consists of only two or three cells.

Pollen grains are transferred to a femalestructure during pollination.

The female gametophytewithin an ovule consists ofonly seven cells.

Ovules

Pollen grains

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Teacher Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 13ATAKS Obj 5 IPC 4BTEKS Bio 6E, 8C, 10C, 13A, 13BTEKS IPC 4B

pp. 534–535

A Sunflower Seed is Not Just a Seed Asunflower seed is a dry fruit (called an achene)with a seed inside. The edible part is the actualseed, which consists mainly of cotyledons. Acorn kernel is also not just a seed but a dryfruit (called a caryopsis) with a seed inside. Theouter covering of a corn kernel is not easilyremoved, as is the outer covering of a sun-flower seed. The edible part of the corn fruit is the whole kernel. Bio 13B

ActivityGymnosperm Flash Cards Havestudents write the key terms for thissection on separate note cards.Then, have them write a definitionon the back of each card as theyread the section. Have studentsdivide their cards into three groups:characteristics of gymnosperms only(none found only in gymnosperms);characteristics of angiosperms only(sepal, petal, stamen, anther, pistil,ovary, double fertilization); and char-acteristics of both gymnosperms andangiosperms (pollen grain, ovule, pol-lination, pollen tube, seed coat, cotyle-don). Have students use their cardsfor the Reteaching exercise.

Verbal

Teaching TipOrigins of Embryos Tell studentsthat in some plants, such as citrus,the embryo contained within the seeddoesn’t always develop from a fertil-ized egg. Instead, it develops fromother cells in the ovule. Plants thatgrow from such embryos are identi-cal to their female parent.

Reading Organizer As studentsread about the plant life cycles inthis chapter, have them developcycle concept maps. Verbal

Group ActivityDissecting Seeds Bring a varietyof seeds to class, including at leastone type of gymnosperm seed(pine, spruce, fir), one type of dicotseed (bean, pea, melon, squash),and one type of monocot seed(corn, wheat, iris). Make a longitu-dinal cut through at least one seedof each type. Have students exam-ine the whole and opened seedsusing their unaided eyes and a dis-secting microscope. Ask students tocompare the characteristics of thethree different types of seeds.

Visual TAKS 2 Bio 8CCo-op LearningLS

Bio 6E, 10C, 13BLS

GENERALSKILLBUILDER

READINGREADING

Bio 6E, 10C, 13B

TeachTeach

LS

MotivateMotivate


did you know?

SeedsAs you learned in the previous chapter, seeds contain the embryos ofseed plants. A plant embryo is a new sporophyte. A seed forms froman ovule after the egg within it has been fertilized. The outer celllayers of an ovule harden to form the as a seed matures.The tough seed coat protects the embryo in a seed from mechanicalinjury and from a harsh environment. The seed coat also preventsthe embryo from immediately growing into a young plant by keep-ing out water and oxygen. Deprived of water and oxygen, theembryo stops growing and cannot resume its growth until waterand oxygen can pass through the seed coat. Often, a seed must beexposed to cold temperatures, or the seed coat must be damaged,before the seed can take in water and oxygen. Thus, seeds enable theembryos of seed plants to survive conditions that are unfavorablefor plant growth for long periods of time.

Seeds also contain tissue that provides nutrients to plant embryos.In gymnosperms, this nutritious tissue is part of the femalegametophyte. The seeds of angiosperms, however, develop a nutri-tious tissue called endosperm. Endosperm originates at the sametime an egg is fertilized. In some angiosperms, such as corn andwheat, endosperm is still present in mature seeds. In otherangiosperms, such as beans and peas, the nutrients in theendosperm have already been transferred to the embryo by the timea seed is mature.

Leaflike structures called (kah tuh LEE duhnz), orseed leaves, are a part of a plant embryo. Cotyledons function in thetransfer of nutrients to the embryo. The embryos of gymnospermshave two or more cotyledons. For example, pine embryos have eightcotyledons. In the flowering plants, the embryos of monocots haveone cotyledon, and the embryos of dicots have two cotyledons. Thestructure of three types of seeds is shown in Figure 6.

cotyledons

seed coat

Interpreting GraphicsAfter reading the chapter,trace or make a sketch ofFigure 6 without the labels.On separate pieces ofpaper, write down thelabels. Without referring toyour book, match the labelswith the correct parts ofyour sketch.

Seeds have many similarities and differences in structure.

Figure 6 Seed structure

Wing

Seed coat

Cotyledons

Embryonicroot

Female gametophyte (n)

Embryo

Seed coat

Seed coat fused to ovary wall

Endosperm (3n) Embryo

Embryonic root

Bean seedCorn grainPine seed

Embryonicleaves

Cotyledons

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IPC Benchmark Fact

There is a limit on how much protection a tough seedcoat provides for a seed embryo against mechanicalinjury. A mechanical injury to a seed occurs when thekinetic energy of an object that strikes a seedexceeds the intrinsic strength of the seed coat.Remind students that kinetic energy—that is, energyof motion—depends on an object’s mass and itsspeed. Consequently, more massive objects requireless speed in order to damage a seed coat. TAKS 5 IPC 4B

ActivityPlant Propagator Plant propaga-tors work for wholesale and retailnurseries where they grow plantsfor sale. A plant propagator growsplants from seeds and by a varietyof vegetative methods. Have stu-dents use library references oronline databases to find out aboutplant propagation in the nurseryand floral industries. Have studentswrite reports summarizing theirfindings. Verbal Bio 3DLS



Observing theGametophytes ofPinesSkills AcquiredObserving, makingcomparisons, drawingconclusions

Teacher’s Notes Ask students to look for simi-larities between the two typesof cones when they are exam-ined under a microscope.

Answers to Analysis1. Both have whorls of scales, but

male cones are smaller thanfemale cones and containpollen, while female cones con-tain eggs and eventually seeds.

2. The growth rate of pollen tubesin pines is extremely slow.

Bio 10C, 13B

CulturalAwarenessCulturalAwareness

George Washington Carver GeorgeWashington Carver (1864–1943) was ahorticulturist whose agricultural researchrevolutionized the economy of the southernUnited States by encouraging farmers to growmore than just cotton. He urged farmers togrow sweet potatoes, peanuts, pecans, andsoybeans. In 1896, the same year he received

his master’s degree at Iowa State College ofAgriculture and Mechanic Arts, Carver wasasked to head the Department of Agricultureat Tuskegee Institute, in Alabama. There hehelped to develop more than 300 industrialproducts from peanuts, 100 from sweetpotatoes, and 75 from pecans.Bio/IPC 3C; Bio 3F

Transparencies

TT Life Cycle of a Conifer

ConesSeed plants are the most successful of all plants. The success of theseed plants is due in part to the specialized structures in whichseeds develop. In angiosperms, the ovules (immature seeds) arecompletely enclosed by sporophyte tissue at the time of pollination.In gymnosperms, the ovules are not completely enclosed by sporo-phyte tissue until after pollination.

The gametophytes of gymnosperms develop in cones, whichconsist of whorls (circles) of modified leaves called scales.Gymnosperms produce two types of cones. Male cones, or pollencones, produce pollen grains within sacs that develop on the surfaceof their scales. Female cones, or seed cones, produce ovules on thesurface of their scales. Many gymnosperms produce both male andfemale cones on the same plant. As shown in Figure 7, the numeroussmall pollen cones lie to the left of the large seed cone. In some gym-nosperms, male and female cones form on separate plants.

Pollen cones produce large quantities of pollen grains that arecarried by wind to female cones. At the time of pollination, thescales of a female cone are open, exposing the ovules. When a pollengrain lands near an ovule, a slender pollen tube grows out of thepollen grain and into the ovule. The sperm moves through the pollentube and enters the ovule. Thus, the pollen tube delivers a sperm tothe egg inside the ovule. Seed cones close up after pollination andremain closed until the seeds within them are mature. This processcan take up to two years.

Figure 7 Male and femalepine cones. This branch of anAustrian pine has an immatureseed cone and many pollencones.

Observing the Gametophytes of PinesYou can observe the gametophytes of a pine with a microscope.

Materials

prepared slides of the following: male pine cone, femalepine cone, pine ovule; hand lens; compound microscope

Procedure

1. Examine preparedslides of male and

female pine cones first with ahand lens and then under thelow power of a microscope.

2. Make a sketch of each typeof pine cone, and label thestructures that you recognize.

3. Examine a prepared slide of apine ovule under the lowpower of a compound micro-scope. Compare what yousee with the photo above.

4. Draw a pine ovule, and labelthe following structures:scale, ovule, egg, pollen tube(if visible).

Analysis

1. Compare and Contrastthe structure and contents ofmale and female pine cones.

2. Critical ThinkingApplying Information Ittakes 15 months for a pinepollen tube to grow throughthe wall of a pine ovule. Howwould you describe the rate ofpollen-tube growth in pines?

Immature female pine cone

13B

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Teacher Edition TAKS Obj 2 Bio 8C TAKS Obj 5 IPC 4B TEKS Bio 3D, 3F, 6E, 8C, 10C, 13BTEKS Bio/IPC 3CTEKS IPC 4B

pp. 536–537

What is a “Jumping Bean”? Jumping beans,which are grown in Central and SouthAmerica, are the seeds of plants in the spurgefamily. A jumping bean contains a moth larva.The jumping movements occur when the mothlarva inside changes position with a jerk. Thejumping bean is also known as the “broncobean” or “leaper.”

Using the Figure Walk students through thegymnosperm life cycle shown inFigure 8, starting with the zygote.Point out that, as in animals andother multicellular eukaryoticorganisms, repeated mitotic celldivisions of the zygote result in amulticellular diploid organism. Inplants, the multicellular diploidorganism is called the sporophyte.Reproductive cells in the maturesporophyte undergo meiosis.During this process, the chromo-some number is reduced fromdiploid to haploid. Point out thatthere are two kinds of spores pro-duced—male spores (microspores)and female spores (megaspores)—and that these spores grow intotwo different types of gameto-phytes—pollen grains, or malegametophytes (microgameto-phytes), that produce sperm cellsand female gametophytes (megaga-metophytes) that produce egg cells.Both kinds of gametophyte arehaploid. Finally, point out thatwhen fertilization (the uniting of anegg and a sperm) occurs and a newzygote is formed, the diploid chro-mosome number is restored, and anew sporophyte generation begins.

Visual

Group ActivityDiversity of Pollen GrainsProvide students with a variety offlowers with pollen or give thempollen alone (for example, pollenfrom a pine tree). Have studentsmake wet-mount slides of pollensamples to observe the intricatelydetailed coats of pollen grains. Havestudents draw what they observe.You could also provide them withpictures (for example, from a col-lege biology textbook) showingelectron micrographs of somepollen grains.

KinestheticLS

TAKS 2 Bio 8C; Bio 6E, 10C, 13BLS


did you know?

English Language Learners

Life Cycle of a ConiferMost gymnosperms are conifers, a group that includes pines. You cantrace the stages in the life cycle of a pine in Figure 8. In pines, as in allplants, a diploid zygote results from sexual reproduction. The zygotedevelops into an embryo, which then becomes dormant (inactive).The embryo and the surrounding tissues form a seed. When theirseeds are mature, seed cones open, and the seeds fall out. A pine seedhas a wing that causes it to spin like the blade of a helicopter. Thus,pine seeds often travel some distance from their parent tree.

When conditions are favorable for growth, the seeds grow intonew sporophytes. An adult pine tree produces both male and femalecones. Spores form by meiosis, which occurs inside immaturecones. The spores grow into gametophytes, which produce eggs andsperm by mitosis. After pollination, a pollen tube begins to growfrom each pollen grain toward the eggs inside an ovule. Fertilizationoccurs as a sperm fuses with an egg, forming a zygote that will growinto a new sporophyte.

Figure 8 Conifer life cycle. In conifers, a very largesporophyte that producescones alternates with tinygametophytes that form on the scales of cones.

Ovule

Adult sporophyte

Young sporophyte

Gametophytes

Pollencone

Immatureseed cone

Femalespore

Male spore

Pollen(male gametophytes) Sperm

Eggs(within femalegametophyte)

Pollentube

Matureseed cone

Scale

Pine seed(with wing)

Zygote

Scale

An adult pine produces male and female cones.

2

Male and femalespores form onthe scales ofthe cones.

3

Spores develop intomale and femalegametophytes.

4

After pollination, sperm enter the ovule through a pollen tube, andfertilization occurs.

5

The zygote and ovule develop into a seed, which grows intoa new sporophyte.

1

Meiosis

Meiosis

Mitosis

Mitosis


Fertilization

Pollination

537

IPC Benchmark Fact

When a pine seed falls to the ground the force ofgravity causes it to accelerate toward Earth’s surfaceat approximately 9.8 m/s2. However, a pine seed’s wingreduces the rate of acceleration by giving the seedsome upward lift as it spins in the air. Provide the stu-dents with some pine seeds and have them measurethe mass of each seed. Next, have students drop eachfrom various heights and time how long it takes eachseed to reach the ground. Then, have students calcu-late each pine seed’s average acceleration usingNewton’s second law a � F/m and compare thisnumber with the expected acceleration.TAKS 5 IPC 4B



Observing theArrangement ofParts of a Flower

Skills AcquiredObserving, makingcomparisons, drawingconclusions

Teacher’s Notes Provide a variety of monocotand dicot flowers for the classand have each student examineone of each type.Ask students to think abouthow the flowers they examineare pollinated. (Flowers that areopen and have stamens and stig-mas exposed are likely cross-pollinated. Flowers that areclosed and have stamens andstigmas that are not exposed arelikely self-pollinated.)

Answers to Analysis1. Answers may vary. Students

should comment on color, size,and numbers of sepals andpetals.

2. Answers will vary. Studentsshould suggest that large,brightly colored petals mayattract animal pollinators(such as insects) while flowerswith small, inconspicuouspetals are probably wind-pollinated.

3. Answers may vary. Studentsshould note the following:monocots have flower parts inmultiples of three; dicots haveflower parts in multiples oftwo, four, or five.

TAKS 2 Bio 8C;TAKS 3 Bio 13A; Bio 10C, 13B

StrategiesStrategiesINCLUSIONINCLUSION

Using Figure 9 as a guide, ask students tomake a clay model of the basic flower struc-ture. The parts of the flower can be labeledwith straight pins and strips of paper stuckinto the model. The model should be madeto lie flat on a piece of cardboard for easydisplay. Students can show their under-standing of the parts of the flower bydescribing them in a short presentation oftape recording. Bio 13B

• Learning Disability • Attention DeficitDisorder

Transparencies

TT Floral StructureTT Life Cycle of Angiosperms

FlowersIn angiosperms, gametophytes develop within flowers. The basicstructure of a flower is shown in Figure 9. Flower parts arearranged in four concentric whorls. The outermost whorl consistsof one or more (SEE puhlz), which protect a flower fromdamage while it is a bud. The second whorl consists of one ormore , which attract pollinators. The third whorl consists ofone or more (STAY muhnz), which produce pollen. Eachstamen is made of a threadlike filament that is topped by a pollen-

producing sac called an . The fourth andinnermost whorl of a flower consists of one ormore , which produce ovules. Ovulesdevelop in a pistil’s swollen lower portion,which is called the ovary. Usually, a stalk, calledthe style, rises from the . Pollen lands onand sticks to the stigma—the swollen, sticky tipof the style.

Flowers may or may not have all four of thebasic flower parts. A flower that has all fourparts is called a complete flower. Flowers thatlack any one of the four types of parts are calledincomplete flowers. If a flower has both sta-mens and pistils, it is called a perfect flower.Flowers that lack either stamens or pistils arecalled imperfect flowers.

ovary

pistils

anther

stamenspetals

sepals

Petal

Stigma

StyleOvary

AntherFilament Pistil

Sepal

Stamen

Figure 9 Basic flowerstructure. The four basicparts of a flower—sepals,petals, stamens, and pistils—are arranged in concentricwhorls.

Observing the Arrangement of Parts of a FlowerYou can see how the parts of flowers are arrangedby dissecting flowers.

Materials

gloves, monocot flower, dicot flower, paper, tape

Procedure

1. Put on gloves. Examinea monocot flower and

a dicot flower. Locate thesepals, petals, stamens, andpistil of each flower.

2. Separate the parts of eachflower, and tape them to apiece of paper. Label eachset of parts.

3. Count the number of petals,sepals, and stamens in eachflower. Record this informa-tion below each flower.

Analysis

1. Compare and Contrastthe appearance of the sepalsand petals of each flower.

2. Critical ThinkingForming a HypothesisFor each flower, suggest afunction for the petals basedon their appearance.

3. Critical ThinkingJustifying ConclusionsExplain why each flower is fromeither a monocot or a dicot.

13A 13B

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Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 12B TAKS Obj 3 Bio 13A TEKS Bio 7B, 8C, 12B, 13A, 13B

Teacher Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B, 13A TEKS Bio 7B, 8C, 10C, 13A, 13B

pp. 538–539

TAKS 2, TAKS 3

Teaching TipDouble Fertilization inAngiosperms Have studentsmake a Graphic Organizer similarto the one at the bottom of thispage to illustrate the process ofdouble fertilization in angiosperms,discussed on the following page.Ask students to use the applicablevocabulary words for this section,plus any other words that they wishto include. Visual Bio 10C, 13B LS

GENERAL


Use this graphic organizer with Teaching Tip on this page.

Pollination

Fertilization

Fertilization

Ovules with 1 egg

Flowers

Pollen grainswith 2 sperm

Sperm (n) +

egg (n)

Sperm (n) +

2 nuclei (n)Endosperm

3n

Zygote2n

Graphic Organizer

Protecting HoneybeesTeaching Strategies • Tell students that in addition

to food plants, many rare andendangered plants are alsopollinated by honeybees.Scientists are worried thathoneybee losses could causedeclines in rare and endan-gered plant populations.

• Have students research croppollination using the Web sitein the Internet Connect box onthis page and write a reportsummarizing their findings.

Discussion• In what ways are bees impor-

tant in food production? (They produce honey, and theypollinate the flowers of manyfood crops.)

• Why have European honey-bee populations declined inthe United States in the lastdecade? (Many Europeanhoneybees have been killedby diseases, parasites, andpesticides.)

TAKS 3 Bio7B; Bio 13B

Flowers and Their PollinatorsMany flowers have brightly colored petals, sugarynectar, strong odors, and shapes that attract animalpollinators. Flowers are a source of food for pollina-tors such as insects, birds, and bats. For example, beeseat nectar and collect pollen, which is a rich source ofprotein they feed to their larvae. A bee gets coatedwith pollen as it visits a flower and then carries thatpollen to other flowers.

Bees locate flowers by scent first and then by colorand shape. Bee-pollinated flowers are usually blue oryellow and often have markings that show the loca-tion of nectar. Moths, which feed at night, tend to visit heavilyscented white flowers, which are easy to find in dim light. Flies maypollinate flowers that smell like rotten meat.

Many flowers are not pollinated primarily by insects. Red flowers,for instance, may be pollinated by hummingbirds. Some large whiteflowers that open at night are pollinated by nighttime visitors—bats,as seen in Figure 10. Many flowers, such as those of grasses andoaks, are pollinated by wind. Wind-pollinated flowers are usuallysmall and lack bright colors, strong odors, and nectar.

Figure 10 Bat pollination.This lesser long-nosed bat pol-linates an organ pipe cactus asit feeds on the pollen of theplant’s flowers.

Protecting Honeybees

Bees pollinate more species ofplants than any other animal.

The most familiar of the more than20,000 species of bees is theEuropean honeybee, Apis mellif-era, which was imported to theUnited States in the 1600s.Beekeepers raise honeybeesmainly for the honey they pro-duce. However, the bees alsobenefit farmers by pollinatingmore than 90 kinds of crop plants,which are worth $10 billion a year.

Threats to HoneybeesSince 1990, the population ofbeekeeper-raised honeybees hasdecreased by 25 percent in theUnited States. Some of thisdecline is due to pesticide useand loss of food sources, but themajor culprits are parasites,pests, and diseases. The most

serious problem currently facingU.S. honeybees is the varroamite. This tiny, blood-suckingparasite probably entered theUnited States in the 1980s. Itnow infests beehives throughoutmost of North America, causingapproximately $160 million worthof damage each year.

The small hive beetle is a pestthat was introduced to the south-ern United States from Africa in1998. The immature beetles tun-nel through hives in search ofhoney and pollen, killing the devel-oping bees and forcing entirecolonies to abandon their hives.

American foulbrood is a bacte-rial disease that attacks develop-ing honeybees. Highly contagious,the disease has the potential tospread rapidly throughout theUnited States.

Research to the RescueScientists at the Kika De LaGarza Subtropical AgriculturalResearch Center in Weslaco,Texas are studying ways to defeatthe biological threats to honey-bees. The scientists test naturaland synthetic chemicals for use incontrolling varroa mites and smallhive beetles. They are also work-ing to develop new antibiotics thatwill be effective against the bacte-ria that cause American foulbrood.

www.scilinks.orgTopic: Crop PollinationKeyword: HX4053

539

TAKS 3

ReteachingHave students construct a cross-word puzzle using the termspresented in this section and thedefinitions they wrote as directed in the lesson opener Activity.

Verbal

Quiz1. What do male and female game-

tophytes produce, respectively?(sperm and eggs)

2.What are the three main compo-nents of a seed? (embryo,endosperm, seed coat)

3. Which is larger in a conifer, thesporophyte or the gametophyte?(sporophyte)

4. Which structure in a flower isthe male equivalent of the pistil?(the stamen)

AlternativeAssessmentProvide students with a variety ofcones and fruits. Try to includepine, spruce, and fir cones. Try toinclude peaches; tomatoes, grapes,or blueberries; apples; beans; nuts;strawberries; pineapple or figs; andelm or maple fruits. Provide abotany textbook or field guide that students can use to classify the fruits. VisualTAKS 2 Bio 8C; Bio 8A, 8B, 10C, 13B

LS

GENERAL

LS

CloseClose


1. A pollen grain is a male gametophyte that con-tains cells that form sperm cells and a pollentube. An ovule is a sporophyte structure thatcontains a female gametophyte, in which anegg cell forms.

2. The embryo is the young sporophyte, the foodreserves (endosperm) nourish the young sporo-phyte when the seed germinates, and the seedcoat protects the embryo from harsh environ-mental conditions.

3. First, a zygote grows into a sporophyte bymitotic cell division. Next, the sporophyte formsmale and female spores in cones following mei-otic cell division. Then, the spores grow into

TAKS 3 Bio 13A

Bio 5A, 13B

male and female gametophytes by mitotic celldivision. After the gametophytes form eggs andsperm by mitotic cell division, eggs are fertilizedby sperm and a new zygote forms. The zygote andsurrounding tissue develop into a seed.

4. Answers should summarize the information inFigure 11.

5. Answers may vary.6. A. Incorrect. The sepals protect

a flower from damage while it is a bud. B. Correct. C. Incorrect. The pistils produceovules. D. Incorrect. The ovules producefemale gametophytes. TAKS 3 Bio 13A; Bio 13B

Bio 13BTAKS 3 Bio 13A

Bio 13B


Life Cycle of an AngiospermFigure 11 summarizes the life cycle of an angiosperm. Following fer-tilization, the zygote and the tissues of the ovule develop into a seed,which grows into a new sporophyte. The adult sporophytes ofangiosperms produce spores by meiosis. These spores grow intogametophytes. The female gametophytes grow inside the ovules,which develop within the ovary of a pistil. The male gametophytes,or pollen grains, are produced in the anther of a stamen. A pollengrain contains two sperm cells. One sperm fuses with the egg, form-ing the zygote. The other sperm fuses with the haploid nuclei of twoother cells produced by meiosis. The fusing of three haploid (n) cellsforms a triploid (3n) cell that develops into endosperm. This is aprocess called .double fertilization

Stamen

Pistil

Adult sporophyte

Flower

Gametophytes

Ovule

Ovule

Pollentube

Egg

Male spores

Pollen grains(male gametophytes)

Sperm

Mature female spore(female gametophyte)

Pollentube

3n nucleus

Zygote

Seedcoat

Seed

Sporophyteembryo

Endosperm(3n)

AntherA flower produces male spores inside its anthers and female spores inside its pistil.

2 Spores develop into male and femalegametophytes.

3

4 Pollination occurswhen a pollen grainlands on the stigmaof a pistil.

Sperm enter an ovule through a pollen tube, and fertilization occurs.

5The zygote and ovule develop into a seed, which grows into a new sporophyte.

1

Meiosis

Mitosis

Mitosis

Meiosis


Doublefertilization

Pollination

Distinguish pollen grains from ovules. 5A 13B

Describe the function of each part of a seed.

Summarize the life cycle of a conifer. 13B

Critical Thinking Relating Concepts How iseach part of a flower suited to its function?

Critical Thinking Summarizing InformationWhat are the main events in the life cycle of anangiosperm?

In angiosperms, pollen isproduced in sacs called A sepals. C pistils.B anthers. D ovules.


Section 2 Review

13A 13B

13B

13A

Figure 11 Angiospermlife cycle. In angiosperms, a large sporophyte alternateswith tiny gametophytes.

540

Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 13A TEKS Bio 5A, 7B, 8C, 13A, 13B

Teacher Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 13ATEKS Bio 8A, 8B, 8C, 10C, 13A, 13B

pp. 540–541

TAKS 3 Bio 13A

Section 3

Overview Before beginning this sectionreview with your students theobjectives listed in the StudentEdition. The purpose of this lessonis to introduce the different waysthat plants reproduce withoutforming seeds. The lesson describesasexual reproduction in one plantspecies in detail. It concludes with a discussion of how plants can bepropagated vegetatively.

Ask students to think of examplesof how flowering plants reproducewithout making seeds. Help themby asking about gardening, hiking,or other nature experiences theymay have had. Students may haveseen clumps of plants of the sametype, strawberry runners, or clus-ters of bulbs. Ask students why allthe plants in a lawn might look thesame. (They are all clones from oneplant.) Interpersonal

DemonstrationShow students example of bulbs(lily, onion, tulip); corms (crocus,gladiolus); rhizomes (iris); runners(airplane plant, strawberry); andtubers (potato). Point out that allof these are modified stems andtherefore have buds that can growinto new plants. Demonstrate vege-tative propagation by rooting anairplane plant or a potato. Be sureto include a bud in the section you set up for rooting. VisualTAKS 3 Bio 13A; Bio 10C, 13A

LS

MotivateMotivate

TAKS 3 Bio 13A; Bio 13BLS

Bellringer

FocusFocus


• Lesson Plans• Directed Reading• Active Reading• Data Sheet for

Exploration Lab GENERAL

GENERAL

GENERAL

Chapter Resource File English Language Learners

• Reading Organizers• Reading Strategies• Supplemental Reading Guide

A Feeling for the Organism: The Life andWork of Barbara McClintock

Planner CD-ROM

Transparencies

TT BellringerTT Stems Modified for Vegetative

Reproduction

Vegetative ReproductionMost plants are able to reproduce asexually. The new individualsthat result from asexual reproduction are genetically the same as the parent plant. Plants reproduce asexually in a variety of ways that involve nonreproductive parts, such as stems, roots, andleaves. The reproduction of plants from these parts is called

. Many of the structures by which plantsreproduce vegetatively are modified stems, such as runners, bulbs,corms, rhizomes, and tubers. Table 1 describes these structures.

Vegetative reproduction is faster than sexual reproduction inmost plants. A single plant can spread rapidly in a habitat that isideal for its growth by reproducing vegetatively. Therefore, a mass ofhundreds or even thousands of individuals, such as a stand ofgrasses or ferns, may have come from one individual. To learn aboutone unique method of vegetative reproduction in one plant, look atUp Close: Kalanchoë, on the next two pages.

vegetative reproduction

Asexual Reproduction Section 3

Objectives● Describe several types of

vegetative reproduction inplants.

● Distinguish sexual repro-duction in kalanchoës fromasexual reproduction inkalanchoës.

● Recommend several ways to propagate plants.

Key Terms

vegetativereproduction

plant propagationtissue culture

Table 1 Stems Modified for Vegetative Reproduction

Name Description Examples

TuberSwollen, fleshy, Potato, underground stem caladium

RhizomeHorizontal underground stem

Iris, fern, sugar cane

Very short, thickened, Corm underground stem with

Gladiolus,

thin, scaly leavescrocus

Very short, stem with Bulb thick, fleshy leaves;

only in monocots

Onion, daffodil, tulip

RunnerHorizontal, above- Airplane plant,ground stem Bermuda grass

13B

13B

13A 13B

541

TAKS 3


StrategiesStrategiesINCLUSIONINCLUSION

Bring a variety of vegetation, such as thoselisted in Table 1, for students to observe,touch, and sketch during class. Placing themin dirt, water, or in a cool dark place overtime will allow roots and stems to sproutand begin to grow. The changes observedeach day should be discussed, recorded, anddrawn. Student understanding of the differ-ent stems used for vegetative reproductionwould be greater for having observed theprocess in person. Bio 13B

• Developmental Delay

Kalanchoë

Teaching Strategies Bringspecimens of Kalanchoë dai-gremontiana to class. Letstudents propagate the plantby planting stem cuttings, leafcuttings, or plantlets.• Point out to students that the

formation of plantlets alongthe leaf margin that occurs inkalanchoës is a very unusualform of asexual reproductionthat occurs in only a fewspecies. Tell students thatthese plants are often growncommercially because oftheir unusual appearance andmethod of asexual reproduc-tion. Also tell students thatbecause kalanchoës are easyto grow, they often becomeserious greenhouse weeds.

• For interest, take students toa greenhouse where succu-lents are grown, or have ahorticulturist talk to studentsabout the characteristics andpropagation of kalanchoësand other succulents.

• CAM photosynthesis maybe difficult for students tocomprehend. Help studentsunderstand CAM photo-synthesis by having themillustrate the process.

VisualLS

TAKS 3 Bio 13A; Bio 10C, 13B

Up Close

Transparencies

TT External Structure of KalanchoëTT Internal Structures of Kalanchoë

Many commercial fruit trees are composed oftwo different plants. Fruit trees, such as thosethat produce apples and citrus fruits, are typi-cally composed of one variety (genotype) of aspecies grafted onto another variety. The rootstock is often that of a hardy variety that canwithstand harsh environmental conditions and isresistant to diseases common for that crop. Thescion (SEYE on), or the part that is grafted ontothe root stock, is a variety that has desirablecharacteristics (such as flavor, color, early fruitset), but it is not always well adapted to the envi-ronmental conditions under which it is grown.

Up Close

External Structures

KalanchoëScientific name: Kalanchoë daigremontiana

Size: Grows from 30 cm (1 ft) to 1 m (3 ft) tall

Range: Native to southwestern Madagascar; cultivated worldwide

Habitat: Semiarid tropical grassland with moist summers andwell-drained, fertile soil

Importance: Kalanchoës (kal an KOH eez) are grown as indoorpotted plants and as outdoor perennials in warm climates.

Flowers A cluster of flowersforms on a flowering stalk thatgrows from the end of a stem.The flowers are bell-shaped andabout 2.5 cm (1 in.) long. Flower

parts occur in fours. Each flower producesmany tiny seeds.

Leaves The fleshy leaves arebluish green, with purple markingsand saw-toothed margins. Leafblades range from 12 to 25 cm (4 to 10 in.) long. Leaves arearranged in pairs that are opposite one another.

Plantlets Tiny newplants develop along leafmargins. These plantletsare a means of vegetativereproduction. When aplantlet falls to the ground,it grows into a new plant.

Stem and leaf cuttingsKalanchoës are often propagatedvegetatively by planting stem and leaf cuttings.

▼ Leaf cutting

▲ Flower

Air roots The roots that growfrom the stems and fromplantlets originate from stem tissue.

▼ Air roots

▼ Plantlet

542

Student EditionTAKS Obj 2 Bio 6DTAKS Obj 3 Bio 13ATEKS Bio 6D, 10C, 13A, 13B

Teacher EditionTAKS Obj 2 Bio 6D, 8C TAKS Obj 3 Bio 13ATEKS Bio 6D, 8C, 10C, 13A, 13B

pp. 542–543

TAKS 2, TAKS 3


Like Kalanchoë daigremontiana, many otherhorticulturally important plants are natives ofMadagascar, which is an island off the south-east coat of Africa. One such plant is the rosyperiwinkle, Catharanthus roseus, which is apopular bedding plant in the United Statesand the original source of two cancer treat-ment drugs. Have students use the Internet toresearch other economically important plantsto find out where they are grown and howmuch income they bring to the countrieswhere they are grown. InterpersonalLS

SOCIAL STUDIESSOCIAL STUDIESCONNECTIONCONNECTION

Internal Structures

CAM photosynthesis Kalanchoës belong to theCrassulaceae family, a group of succulent plants that areadapted to hot climates. Photosynthesis in kalanchoës involves a process called crassulacean acid metabolism (CAM).

The stomata of CAM plants open only at night, unlike thoseof other plants. At night, the plants fix carbon dioxide by using itto make malic acid. The malic acid is stored in the large centralvacuoles of the mesophyll cells. In daytime, the stomata remainclosed, which prevents water loss. Carbon dioxide is releasedfrom malic acid during the day and used by the Calvin cycle tomake sugar.

Large central vacuole The cells insidea leaf, called the mesophyll cells, have alarge central vacuole that can hold a greatdeal of water.

▼ Central vacuole

Mesophyll

Cuticle

Epidermis

Epidermis

Leaf structure Kalanchoës are succulents, which means they have fleshy leaves and stems that store water. A kalanchoë leaf shows how some succulents are adapted for conserving water. A thick cuticle covers the leaf, and the epidermis (outer layer of cells) consists of several layers of cells. Relatively few, very small stomata dot the leaf surfaces.

Vascularbundle

Stoma

CO2

CO2

Night Day

Malicacid

Calvincycle

Sugar

Organelles

Mesophyll cells

Mesophyll cell

Centralvacuole

Cellwall

Cellmembrane

Cytoplasm

543

KalanchoëDiscussion• Ask students to describe sex-

ual and asexual reproductionin kalanchoës. (Kalanchoësare flowering plants thatreproduce sexually by formingseeds following pollinationand fertilization. They repro-duce asexually by formingplantlets containing roots,stems, and leaves on the mar-gins of the mother plant’sleaves. They can also producenew plants from pieces ofstems and leaves.)

• Ask students how the geneticcomposition of a plantletcompares with that of themother plant. (The two areidentical because the plantletsare clones of the mother plant.)

• Ask students to name someadaptations found in kalan-choës that enable them tosurvive in dry environments.(Kalanchoës have thick, fleshyleaves and stems that storewater; the leaves have a thickcuticle, several layers of epider-mal cells, and few stomata; theplants photosynthesize using theCAM process, which enablesthem to have their stomata openat night and capture energyfrom the sun during the day.)

InterpersonalTAKS 2 Bio 6D (grade 10 only);TAKS 3 Bio 13A

LS

Up Close

did you know?Asexual reproduction is energy efficient.Asexual reproduction enables plants toproduce many offspring by using less energythan is required for sexual reproduction.However, because offspring produced asexuallyare genetically identical to their parent, theyare all equally susceptible to any environmentalcondition or disease to which the parent wassusceptible. Sexual reproduction results ingenetic variation among the offspring, which isparticularly advantageous when the environmentis very changeable or when new disease-causingagents enter the environment.TAKS 2 Bio 8C; TAKS 3 Bio 13A; Bio 13B

ReteachingAsk students to describe character-istics of plants that would indicatethat they have been asexually prop-agated. (uniformity of appearance, asin flower color, fruit color and size,plant size, etc.)

Quiz1. What is the most common part

of a plant that is involved inasexual reproduction? (stems)

2.Can plants that reproduce asexu-ally also reproduce sexually?(yes)

3. How do CAM plants comparewith most other plants in theway in which they undergo pho-tosynthesis? (CAM plants havetheir stomata open at night, whenthe stomata of most other plantsare closed. Carbon dioxide is fixedduring the night, stored, and thenused in the Calvin cycle to makesugar during the day.) Verbal

AlternativeAssessmentGarden Design Have students useposter board to design a gardenthat includes both sexually andasexually reproducing plants. Havestudents include the name of eachplant and how it reproduces in table format.

TAKS 1 Bio/IPC 2C; TAKS 2 Bio 8C, 13B

GENERAL

TAKS 3Bio 13ALS

Bio 13B

Bio 13B

GENERAL

Bio 13B

CloseClose


1. Bulbs are short stems with thick, fleshy leaves(daffodil, onion, tulip); corms are short, thick-ened underground stems with thin, scaly leaves(crocus, gladiolus); rhizomes are horizontalunderground stems (fern, iris, sugar cane);tubers are swollen, fleshy, underground stems(potato, caladium); runners are aerial stemsthat form roots (airplane plant, kalanchoë);plantlets form on leaves (kalanchoë)

2. Formation of seeds is sexual reproduction.Formation of plantlets on the leaf margins orgrowth of new plants from pieces of stems orleaves is asexual reproduction. Bio 13B

Bio 13B

3. planting seeds; planting vegetative reproductivestructures such as bulbs, corms, tubers, rhi-zomes, or plantlets; budding or grafting; takingstem or leaf cuttings; tissue culture

4. Someone might choose to propagate a plantcommercially using vegetative structures toproduce a new crop rapidly and/or to producea crop of identical plants.

5. A. Incorrect. Corms are short,underground stems. B. Incorrect. Rhizomes arehorizontal, underground stems. C. Incorrect.Tubers are swollen, fleshy, underground stems.D. Correct. TAKS 2 Bio 13A; Bio 13B

Bio 13B

Bio 13B


English Language Learners

Transparencies

TT Methods of Vegetative PlantPropagation

Plant PropagationPeople grow plants for many purposes, such as for food, to beautifyhomes, or to sell. Most field crops, such as cereal grains, vegetables,and cotton, are grown from seed. Many other plants are grown fromvegetative parts. Growing new plants from seed or from vegetativeparts is called .

Plants are often propagated using the structures the plants producefor vegetative reproduction. Bulbs and corms divide as they grow,

forming many pieces that can each grow into a newplant. Rhizomes, roots, and tubers can be cut orbroken into pieces with one or more buds that cangrow into new shoots. But people also grow plantsfrom vegetative parts that are not specialized forvegetative reproduction. For example, pieces ofplants, such as the stems of ivys and the leaves ofAfrican violets, are cut from the parent plant. Thecuttings are then used to grow new plants. Figure 12shows a method of propagating trees called bud-ding. In another technique called ,pieces of plant tissue are placed on a sterile mediumand used to grow new plants. Table 2 summarizessome of the methods of vegetative plant propagationthat are widely used to grow plants.

tissue culture

plant propagation

Figure 12 Budding pears.A bud from a desirable varietyof pears is attached to a stemof another pear species. Thebud will grow into a branchthat produces the desirablevariety of pears.

Table 2 Methods of Vegetative Plant Propagation

Method Description Examples

Budding Small stems from one plant are attached to Grape vines, hybrid roses, fruit and and grafting larger stems or roots of another plant. nut trees

Taking Leaves or pieces of stems or roots are cut from African violets, ornamental trees and cuttings one plant and used to grow new individuals. shrubs, figs

Tissue Pieces of tissue from one plant are placed on a Orchids, potatoes, many houseplants

culture sterile medium and used to grow new individuals.

Describe four types of vegetative reproductionin plants, and give an example of each. 13B

Classify methods of reproduction in kalanchoësas sexual or asexual. 13B

Recommend five ways to propagate plants.

Critical Thinking Justifying ConclusionsWhy would someone choose to propagate aparticular plant for commercial purposes byusing vegetative structures instead of seed?

Bermuda grass reproducesasexually by means of horizontal, abovegroundstems called 13B

A corms. C tubers.B rhizomes. D runners.


Section 3 Review

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13B

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13A TAKS 2

Student Edition TAKS Obj 3 Bio 13A TEKS Bio 7B, 8C, 13A, 13B

Teacher Edition TAKS Obj 1 Bio/IPC 2C TAKS Obj 2 Bio 8C TAKS 3 Bio 13A TEKS Bio 8C, 13A, 13BTEKS Bio/IPC 2C

pp. 544–545

AlternativeAssessmentAssign students to four cooperativegroups. Have each group draw andlabel a life cycle diagram of a dif-ferent type of plant (moss, fern,gymnosperm, angiosperm). Collectthe diagrams, and then redistributethem to the groups for evaluation,making sure that none of thegroups gets its own diagram back.Discuss each life cycle diagram,making corrections as necessary.

GENERAL

Answer to Concept Map

The following is one of several possible answers to Performance Zone item 15.


• Science Skills Worksheet• Critical Thinking

Worksheet• Test Prep Pretest• Chapter Test GENERAL

GENERAL

GENERAL


of

in

flowering plants

in

flowering plants

male cones

club mossesgymnosperms

of

club mossesgymnosperms

female cones

by which involves

that fuse during

Plants reproduce

to produce a

sexual reproduction

eggs

fertilization

that are part of

zygote

sperm

ovules in

antheridia

seedless plants

in

seedless plants

of

stamens

antherswhich are produced in

within

pistils

ovaries

archegonia

which are produced in

which involves

with

asexual reproduction

roots stems leaves

spores vegetativereproduction

Key Concepts

Study CHAPTER HIGHLIGHTS

ZONEKey Terms

Section 1archegonium (530)antheridium (530)sorus (532)

Section 2pollen grain (534)ovule (534)pollination (534)pollen tube (534)seed coat (535)cotyledon (535)sepal (538)petal (538)stamen (538)anther (538)pistil (538)ovary (538)double fertilization (540)

Section 3vegetative reproduction (541)plant propagation (544)tissue culture (544)

Sexual Reproduction in Seedless Plants

● In mosses, the “leafy” green gametophytes are larger than thesporophytes, which consist of a bare stalk and a spore capsule.

● In the life cycle of a fern, the sporophytes are much largerthan the gametophytes. The thin, green, heart-shapedgametophytes produce both sperm and eggs.

● Nonvascular plants and seedless vascular plants need waterfor fertilization because sperm must swim to eggs.

Sexual Reproduction in Seed Plants

● The tiny gametophytes of seed plants develop from sporesthat remain within sporophyte tissues. Male gametophytesdevelop into pollen grains. Female gametophytes developinside ovules.

● A seed contains an embryo, which is a new sporophyte, and a supply of nutrients for the embryo. The cotyledons of anembryo help transfer nutrients to the embryo. A seed coatcovers and protects a seed.

● In gymnosperms, male and female gametophytes develop inseparate cones on the sporophytes. After fertilization, ovulesdevelop into seeds, which grow into new sporophytes.

● Flowers have four types of parts—petals, sepals, stamens, and pistils. Petals attract pollinators. Sepals protect buds andmay also attract pollinators. Pollen forms in the anthers ofstamens. Seeds develop in the ovary of a pistil.

● In angiosperms, male and female gametophytes develop in the flowers of the sporophytes. After fertilization, ovulesdevelop into seeds, which grow into new sporophytes.

Asexual Reproduction

● Vegetative reproduction is the growth of new plants fromnonreproductive plant parts, such as stems, roots, and leaves.

● Kalanchoës are succulents that are often grown as pottedplants and readily reproduce either vegetatively or by seeds.

● People often grow plants from their vegetative structures.This is called vegetative propagation.

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ANSWERS

Using Key Terms

1. a2. d3. b4. a5. a. Pollen grains are mature male

gametophytes that consist ofonly two or three cells andproduce sperm cells. An ovuleis a multicellular structure thatdevelops in a female cone or inthe ovary of a flower and inwhich a female gametophytethat contains an egg celldevelops.

b. A sepal encloses and protects aflower bud, while a petal usu-ally attracts animalpollinators.

c. A cotyledon is a structure of aplant embryo in all seeds, andendosperm is a triploid foodsupply that is not part of theembryo and is found only inangiosperm seeds.

d. Reproduction is the process bywhich organisms produce off-spring. Propagation is theprocess of producing plants(or other organisms) from aseed or from vegetativestructures.

Understanding Key Ideas

6. c

7. c8. d9. d

10. b11. c Bio 13B

Bio 13BBio 5A, 13BBio 5A, 13BBio 13BBio 13BTAKS 3 Bio 7B, TAKS 2 Bio 8C,

Bio 5A, 13BBio 13BBio 5A, 13BBio 5A, 13B

Section Questions1 1, 6, 7, 15, 16, 222 2, 3, 4, 5, 8, 12, 13, 14, 15, 17, 18,

19, 223 5, 9, 10, 11, 19, 20, 21, 22

Assignment Guide


CHAPTER 24

12. Students should recognize that this flower isprobably bee pollinated because it is yellow,has a landing platform, and has pollen guidesshowing the location of nectar.

13. Scientists are testing chemicals that can beused against varroa mites and small hive bee-tles and developing new antibiotics that willbe effective against bacteria that causeAmerican foulbrood.

14. The dispersal of seeds is the main function offruits. TAKS 3 Bio 7B, Bio 13B

TAKS 3 Bio 12B, Bio 13B

Using Key Terms1. A structure that produces eggs in mosses

and ferns is called a(n) a. archegonium. c. ovule.b. sporangium. d. antheridium.

2. In seed plants, the ____ transfers spermfrom a pollen grain directly to an egg in an ovule.a. pollinator c. endospermb. seed coat d. pollen tube

3. In conifers, the sporophyte produces sporesand gametophytes in a. flowers. c. sori.b. cones. d. sporangia.

4. Which part of a flower produces eggs?a. pistil c. stamenb. petal d. sepal

5. For each pair of terms, explain thedifference in their meanings.a. pollen grain, ovuleb. sepal, petalc. cotyledon, endospermd. reproduction, propagation

Understanding Key Ideas6. Mosses and liverworts thrive in a moist

environment because they need _____ forreproduction. a. bees c. waterb. birds d. wind

7. The life cycle of a moss differs from the lifecycle of a fern in that a. the gametophyte is absent in ferns.b. the sporophyte is absent in mosses.c. moss spores do not form on leaves.d. the gametophytes of mosses are green.

8. In angiosperms, the zygote and the first cellof the endosperm form by a. mitosis.b. meiosis.c. pollination. d. double fertilization.

9. Vegetative reproduction has not occurredwhen a new plant grows from a a. leaf. c. stem.b. root. d. seed.

10. Which of the following structures do kalanchoës produce for vegetative reproduction?a. seeds c. flowersb. plantlets d. bulbs

11. Which of the following structures is not usedto propagate dicots vegetatively?a. tubers c. bulbsb. rhizomes d. stem cuttings

12. Look at the flower in the photographbelow. It is the flower of the unicorn plant.How is this flower probably pollinated?Justify your answer.

13. What is being done tocounter biological threats to honeybees in Texas?

14. What is the function of the fruits in whichseeds mature? (Hint: See Chapter 23,Section 1.)

15. Concept Mapping Make a conceptmap that explains how plants reproduce.Try to include the following terms in your map: archegonium, antheridium, egg,sperm, ovule, zygote, stamen, anther, pistil,ovary, fertilization, spore, and vegetativereproduction.

PerformanceZONE

CHAPTER REVIEW

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3E

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Review and AssessTAKS Obj 2 Bio 8CTAKS Obj 3 Bio 7B, 12BTEKS Bio 3B, 5A, 7B, 8C, 13A, 13B

pp. 546–547

Critical Thinking

16. Answers will vary. Studentsshould offer evidence to supporttheir conclusion. Some studentsmay recognize that this conclu-sion is not valid because nonvas-cular plants are found in dryclimates. These plants survive inshady spots under trees androcks, where moisture accumu-lates occasionally, and nearsprings, creeks, and rivers.

17. The primary role of petals is to attract animal pollinators.Therefore, the absence of petals isa strong indication that the plantis wind-pollinated.

18. Pesticides can kill insect pollina-tors such as bees and flies.Reducing the number of insectpollinators in an area can resultin a reduced number of floweringplants which depend on insectpollination.

19. Answers will vary, but studentsshould recommend a type ofvegetative propagation, such ascuttings or tissue culture sincethese methods produce plants thatare genetically identical to eachother and to their parent plant.

Alternative Assessment

20. Answers will vary.21. Answers will vary.22. Plant breeders are scientists who

work to improve plants that havecommercial value. Plant breedersmake crosses between plants thathave desirable characteristics andselect plants with the most desir-able combination of traits. Someplant breeders use genetic engi-neering in their work. Plantbreeders work for universities,federal agencies, and privateindustries. To become a plantbreeder, you must obtain amaster’s degree or a Ph.D. inagronomy, horticulture, or plantbreeding. Starting salary will varyby region. Bio 3D

Bio 13BBio 13B

Bio 13B

Bio 13B

TAKS 2 Bio 8C, TAKS 3 Bio 13A

Standardized Test Prep

1. A. Incorrect. A shows the endosperm. B. Correct. C. Incorrect. C shows the cotyle-don. D. Incorrect. D shows the seed coat.

2. F. Correct. G. Incorrect. The embryonic root gives rise to the mature plant root. H. Incorrect. The cotyledon transfers nutrientsto the embryo. J. Incorrect. The seed coatprotects the plant embryo.

3. A. Incorrect. Nonvascular plants reproduce byspores. B. Incorrect. Gymnosperms do nothave cotyledons. C. Incorrect. Dicots have twocotyledons. D. Correct. Bio 13B

Bio 13B

Bio 13B


Test

Critical Thinking16. Evaluating Conclusions All nonvascular

plants require a film of water for sperm toswim through and fertilize eggs. Therefore,many people conclude that nonvascularplants are not able to survive in very dryclimates, such as deserts. Is this a validconclusion? Justify your answer.

17. Justifying Conclusions A classmate hasfound a plant whose flowers lack petals and have many stamens. Your classmatetells you that the plant is wind-pollinated.Justify this conclusion.

18. Applying Information Explain how pesti-cide use could reduce the number of plantsin a geographic area.

19. Evaluating Methods You are asked to growa large number of identical potted plantsfor a florist. The plants can be grown fromeither seeds or cuttings. Which method ofplant propagation would you use? Justify your choice.

Alternative Assessment20. Finding Information Use the media center

or Internet sources to find out how theplants commonly sold in your local gardencenters and plant nurseries are propagated.Write a report summarizing the most com-mon method used to propagate each of theplants you researched. Explain why eachplant is usually propagated by this methodinstead of another method.

21. Working Cooperatively Go with two or threeof your classmates to visit a wholesale plantgrower. Orchid growers would be an excel-lent choice if one is in your area. Find outhow tissue culture is used to propagatedifferent kinds of plants. Try to find outinformation on two methods of vegetativepropagation that are not described in thischapter. Prepare an illustrated report of yourfindings to share with the class.

22. Career Connection Plant Breeder Use themedia center or Internet to find out aboutthe field of plant breeding. Write a report onyour findings. Your report should include ajob description, the training required, namesof employers, growth prospects, and anaverage starting salary.


Choose the best possible answer for each question,even if you think there is another possible answerthat is not given.

Use the drawing of a plant seed below and yourknowledge of science to answer questions 1–3.

1. Which structure is the embryonic root? A A C CB B D D

2. Which structure is the source of nutrientsfor the embryo? F A H CG B J D

3. What type of plant produced this seed?A nonvascular C dicot

plant D monocotB gymnosperm

13B

13A

13B

13B

3D

13B

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13B

D

A

B

C

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