PlantsWhat You’ll LearnChapter 21

What is a plant?

Chapter 22 The Diversity of Plants

Chapter 23 Plant Structure and Function

Chapter 24 Reproduction in Plants

Unit 7 Review BioDigest and Standardized Test Practice

Why It’s ImportantAlthough plants have different forms, they have commonstructures and functions. Over time, adaptations of thesestructures and functions resulted in the diversity of plantsfound in the land and water biomes on Earth. In thesebiomes, plants are an essential resource for many of theother organisms that live there, including humans. Theseorganisms depend on plants for oxygen and, directly orindirectly, for food.

9000–8001 B.C.Wheat and barleyare the first plantsgrown as foodcrops.

Understanding the PhotoPlant heights vary from a few millimetersto many meters. These conifer trees cangrow to be hundreds of times taller thanthe ferns on the forest floor.

556

300–291 B.C.Theophrastus,often called the“Father of Botany,”describes morethan 500 plants inhis book History ofPlants.

1667Seed plants areclassified as mono-cots or dicotsaccording to thenumber of seedleaves (1 or 2) intheir seeds.

1609–1610Spaniards establish a settlementthat will become present-daySanta Fe, New Mexico.

Carr Clifton/Minden Pictures

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1851It is discovered that alternation of genera-tions is part of the lifecycle of plants, such asmosses.

1986The first field trialsof a geneticallyaltered plant(tobacco) are carried out.

1967Ten thousand-year-oldfrozen lupine seeds arediscovered in the YukonTerritory of Canada.They germinate within48 hours after theythaw.

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1791The Bill of Rightsis ratified.

1930The first packaged, sliced bread is intro-duced in the U.S.

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What You’ll Learn■ You will identify and evaluate

the structural adaptations of plants to their land environments.

■ You will survey and identifythe major divisions of plants.

Why It’s ImportantPlants were the first multicellu-lar organisms to inhabit landover 440 million years ago. Sincethen, plants have developedinto a diverse group of organ-isms that help provide us withfood, oxygen, and shelter.

Visit to • study the entire chapter

online• access Web Links for more

information and activities on plants

• review content with theInteractive Tutor and self-check quizzes

What is a plant?What is a plant?

Because of plant adaptationsover time, different plant speciesgrow in the different biomes onEarth. The flowering plants andothers growing in this mountainmeadow have structural andphysiological adaptations thatensure their long-term survival inthis environment.

Understandingthe Photo

Michelle Westmorland/Earth Scenes

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Adapting to Life on Land

cuticle from theLatin word cutis,meaning “skin”;The cuticle is theoutermost cover-ing of most plants.

21.1 ADAPTING TO LIFE ON LAND 559

SECTION PREVIEWObjectivesCompare and contrastcharacteristics of algae andplants.Identify and evaluatestructural adaptations of plants to their land environments.Describe the alternation of generations in landplants.

Review Vocabularyadaptation: any structure,

behavior, or internalprocess that enables anorganism to respond tostimuli and better survivein an environment (p. 9)

New Vocabularycuticleleafrootstemvascular tissuevascular plantnonvascular plantseed

21.1

Origins of Plants What is a plant? A plant is a multicellular eukaryote. Most plants can

produce their own food in the form of glucose through the process ofphotosynthesis. In addition, plant cells have thick cell walls made of cel-lulose. The stems and leaves of most plants have a waxy waterproofcoating called a cuticle (KYEWT ih kul).

Fossils and other geological evidence suggest that a billion years ago,plants had not yet begun to appear on land. No ferns, mosses, trees,grasses, or wildflowers existed. The land was barren except for some algaeat the edges of inland seas and oceans. However, the shallow waters thatcovered much of Earth’s surface at that time were teeming with bacteria,algae and other protists, as well as simple animals such as corals, sponges,jellyfish, and worms. Evidence indicates that green algae eventuallybecame adapted to life on land.

Scientists hypothesize that all plants probably evolved from filamen-tous green algae that lived in the ancient oceans. Some of the evidencefor their relationship can be found in modern members of both groups. Green algae and plants have cell walls that contain cellulose.Both groups have the same types of chlorophyll used in photosynthe-sis and store food in the form of starch. All other major groups oforganisms store food in the form of glycogen and other complexsugars, and/or lipids.

Gametophyte

Sporophyte

Illustrate and Explain As you read Section 21.1, illustrate and explain eachstage under its tab.

Alternation of Generations Make the following Foldable to help you illustrate and explain how the lives of all plants have two alternating stages.

Draw a mark at the midpoint of a vertical sheet of paper along the side edge.

Fold the outside edges in to touch at the midpoint mark.

Label the tabs as shown.

STEP 1

STEP 3

STEP 2

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The first evidence of plants in thefossil record began to appear over440 million years ago. These earlyplants were simple in structure anddid not have leaves. They were prob-ably instrumental in turning barerock into rich soil. The earliestknown plant fossils are those of psilo-phytes (SI luh fites), such as thoseshown in Figure 21.1.

Explain how earlyland plants contributed to themovement of other plants to land.

Adaptations in PlantsLife on land has advantages as well as

challenges. All organisms need water tosurvive. A filamentous green alga float-ing in a pond does not need to conservewater. The alga is completely immersedin a bath of water and dissolved nutri-ents, which it can absorb directly intoits cells. For most land plants, the onlyavailable supply of water and mineralsis in the soil, and only the portion of theplant that penetrates the soil can absorbthese nutrients.

When you studied protists, youlearned that algae reproduce by releas-ing unprotected unicellular gametes

into the water, where fertilization anddevelopment take place. Land plantsevolved structural and physiologicaladaptations that help protect thegametes from drying out. In someplants, the sperm are released near theegg so they only have to travel a shortdistance. Other plants have protectivestructures to ensure the survival of thegametes. Land plants must also with-stand the forces of wind and weatherand be able to grow against the force ofgravity. Over the past 443 million yearsor so, plants have developed a hugevariety of adaptations that reflect boththe challenges and advantages of livingon land.

Preventing water lossIf you run your fingers over the sur-

face of an apple, a maple leaf, or thestem of a houseplant, you’ll probablyfind that it is smooth and slightly slip-pery. Most fruits, leaves, and stems arecovered with a protective, waxy layercalled the cuticle. Waxes and oils arelipids, which are biomolecules that donot dissolve in water. The waxy cuticlecreates a barrier that helps prevent thewater in the plant’s tissues from evap-orating into the atmosphere.

Figure 21.2 There is great diversity in leaf shapes andsizes. Infer What advantage would abroad leaf, like this cottonwood leaf,have over a narrow leaf, like a pineneedle?

560 WHAT IS A PLANT?

AA

BB

Figure 21.1 This fossil of Cooksoniais more than 400 mil-lion years old (A).Cooksonia was proba-bly one of the first vas-cular plants. The planthad leafless stems (B).

(t)Harlan P. Banks, (b)Matt Meadows

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Carrying out photosynthesis

The leaf, like the one in Figure21.2, is a plant organ that growsfrom a stem and usually is wherephotosynthesis occurs. Leaves differgreatly in size and shape and theycan vary on the same plant. Eachplant division has unique leaves orleaflike structures.

Putting down roots

Most plants depend on the soil astheir primary source for water andother nutrients. Plants can take inwater and nutrients from the soil withtheir roots. In most plants, a root is aplant organ that absorbs water andminerals usually from the soil. Rootscontain tissues that transport thosenutrients to the stem. Roots anchor aplant usually in the ground. Someroots, such as those of radishes orsweet potatoes, accumulate starch andfunction as organs of storage. Manypeople use these storage roots as afood source. Find out more about theuses of plants on pages 1076–1079 inthe Focus On.

In the MiniLab on this page, exploreand evaluate some structural adapta-tions of plants that allow them to sur-vive on land. Also, practice your labskills by using a dissecting microscope.

Transporting materials

Water moves from the roots of atree to its leaves, and the sugars pro-duced in the leaves move to the rootsthrough the stem. A stem is a plantorgan that provides support forgrowth, as shown in Figure 21.3. Itcontains tissues for transporting food,water, and other materials from onepart of the plant to another. Stemsalso can serve as organs for food stor-age. In green stems, some cells con-tain chlorophyll and can carry outphotosynthesis.

Figure 21.3 Stems can be soft and flexible like the basil stemshown here (A). Other plants,such as this sugar maple tree,have strong, thick stems thatprovide support and allow the tree to grow to great heights (B).

BB

AA

(t)Bill Beatty/Earth Scenes, (bl)Alan & Linda Detrick/Photo Researchers, (br)Lincoln Nutting/Photo Researchers

Apply ConceptsExamining Land PlantsLiverworts are considered to beone of the simplest of all landplants. They show many of theadaptations that other land plantshave evolved that enable them tosurvive on a land environment.

Procedure! Examine a living or preserved sample of

Marchantia. CAUTION: Wear protective gloves when handling preserved materials.

@ Note and record the following observations. Is the plantunicellular or multicellular? Does it have a top and bot-tom? How do these differ? Is it one cell in thickness ormany cells thick? Does the plant seem to grow upright likea tree or close to the ground?

# Use a dissecting microscope to examine its top and bottomsurfaces. Are tiny holes or pores present? If you answer“yes,” which surface has pores?

Analysis1. Predict How might having a multicellular, thick body be

an advantage to life on land?2. Observe Are rootlike structures present? Evaluate the sig-

nificance of this adaptation to a land environment.3. Infer What might be the role of any pores observed on

the plant? Why is the location of the pores critical to sur-viving on a land environment?

Marchantia

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The stems of most plants containvascular tissues. Vascular tissues (VAS

kyuh lur) are made up of tubelike, elon-gated cells through which water, food,and other materials are transported.Plants that possess vascular tissues areknown as vascular plants. Most of theplants you are familiar with, includingpine and maple trees, ferns, rhododen-drons, rye grasses, English ivy, and sun-flowers, are vascular plants.

Mosses and several other small, less-familiar plants called hornworts and

liverworts are usually classified as non-vascular plants. Nonvascular plantsdo not have vascular tissues. The bod-ies of nonvascular plants are usually nomore than a few cells thick, and waterand nutrients travel from one cell toanother by the processes of osmosisand diffusion.

The evolution of vascular tissueswas an important structural adapta-tion for plants that allowed them tosurvive in the many habitats on land.Vascular plants can live farther awayfrom water than nonvascular plants.Also, because vascular tissues includethickened cells called fibers that helpsupport growth, vascular plants cangrow much larger than nonvascularplants.

Reproductive strategiesAdaptations in some land plants

include the evolution of seeds. A seedis a plant organ that contains anembryo, along with a food supply, andis covered by a protective coat, asshown in Figure 21.4. A seed pro-tects the embryo from drying out andalso can aid in its dispersal. Recall thata spore consists only of a haploid cellwith a hard, outer wall. Land plantsreproduce by either spores or seeds.

In non-seed plants, which includemosses and ferns, the sperm require afilm of water on the gametophyteplant to reach the egg. In seed plants,which include all conifers and flower-ing plants, sperm reach the egg with-out using a film of water. Thisdifference is one reason why non-seedplants require wetter habitats thanmost seed plants.

Alternation of generationsAs in algae, the lives of all plants

include two stages, or alternating gen-erations, as shown in Figure 21.5.The gametophyte generation of aplant results in the development of

Seedcoat

Foodsupply

Embryo

Figure 21.4A seed consists of an embryo,a food supply, and a protec-tive seed coat.

GAMETOPHYTE (n)

Spores (n)

Meiosis

SPOROPHYTE (2n)

Mitosis andcell division

Fertilization

Femalegamete (n)

Malegamete (n)

Figure 21.5 The lives of allplants consist oftwo generations.

562 WHAT IS A PLANT?

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Understanding Main Ideas1. Identify three characteristics that plants share

with algae.2. Explain how the development of the cuticle and

the vascular system influenced the evolution ofplants on land.

3. How do seeds and spores differ? What are thebenefits of producing seeds?

4. List the sequence of events involved in the alter-nation of generations in land plants. Do all plantshave alternation of generations?

Thinking Critically5. Explain why vascular plants are more likely to sur-

vive in a dry environment than nonvascular plants.

6. Make and Use Tables Make a table of the differ-ent structural adaptations plants evolved thatallow them to live on land. Include an evaluationof how each specific adaptation helped plants sur-vive on land. For more help, refer to Make and UseTables in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

21.1 ADAPTING TO LIFE ON LAND 563

gametes. All cells of the gametophyte,including the gametes, are haploid (n).The sporophyte generation beginswith fertilization. All cells of thesporophyte are diploid (2n) and areproduced by mitosis and cell division.The spores are produced in the sporo-phyte plant body by meiosis, and aretherefore haploid (n).

In non-seed vascular plants such asferns, spores have hard outer cover-ings. Spores are released into theenvironment where they can growinto haploid gametophyte plants.These plants produce male and femalegametes. Following fertilization, thesporophyte plant develops and growsfrom the gametophyte plant.

In seed plants, such as conifers andflowering plants, spores develop insidethe sporophyte and become the game-tophytes. The gametophytes consist ofonly a few cells. Male and femalegametes are produced by these game-tophytes. After fertilization, a newsporophyte develops within a seed.The seed eventually is released and thenew sporophyte plant grows.

Use the Problem-Solving Lab on thispage to explore further the differ-ences between the gametophyte andsporophyte generations of plants.

Analyze InformationHow do gametophytes and sporophytes compare?A plant has two stages in its life cycle. The stages are calledthe gametophyte generation and the sporophyte generation.

Solve the ProblemDiagram A shows the gametophyte generation of a plant. This plant has a haploid chromosome number of 6. Examinethe diagram carefully and look for errors.Diagram B shows the sporophyte generation of a plant. Thisplant has a diploid chromosome number of 12. Examine thediagram carefully and look for errors.

Thinking Critically1. Observe Analyze diagram A, identify errors, and explain

why they are incorrect.2. Observe Analyze diagram B, identify errors, and explain

why they are incorrect.3. Use Models Illustrate diagrams A and B correctly so that

they connect to one another and form a complete life cyclediagram of a plant.

Gametophyten = 6

Plant stage

Meiosis

Process Male sporen = 12

Female gameten = 12

Sporophyten = 12

Plant stage

Mitosis and cell division

Processes

Sporesn = 12

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21.2SECTION PREVIEWObjectivesDescribe the phylogenicrelationships among divi-sions of plants.Identify the plant king-dom divisions.

Review Vocabularyevolution: gradual change

in an organism throughadaptations over time(p. 10)

New Vocabularyfrondcone

564 WHAT IS A PLANT?

Different Plants in Different PlacesUsing Prior Knowledge Members of theplant kingdom are found worldwide.Plants survive on the coldtundra, in arid deserts, inoceans, in freshwaterlakes, and in your com-munity. If you have evertraveled far from home,you may have seen plantsthat do not grow natu-rally where you live. Evennear your home you mayhave noticed that someplants grow only in sunny locations andothers thrive in shady, damp areas. Infer What structural and physiological adapta-tions do plants, such as the cactus and mosses shownhere, have that would allow them to survive in different biomes on Earth? Compare and then evaluate the significance of these adaptations.

Phylogeny of Plants Many geological and climate changes have taken place since the first

plants became adapted to life on land. Landmasses have moved fromplace to place over Earth’s surface, climates have changed, and bodies ofwater have formed and disappeared. Hundreds of thousands of plantspecies evolved, and countless numbers of these became extinct as condi-tions continually changed. These processes of evolution and extinctioncontinue to be affected by local and global changes. As plant speciesevolved in this changing landscape, they retained many of their old char-acteristics and also developed new ones. These processes of evolution andextinction continue today.

Some botanists use plant characteristics to classify plants into divi-sions. Recall that a plant division is similar to a phylum in other king-doms. The highlights of plant evolution include origins of plants fromgreen algae, the production of a waxy cuticle, the development of vascu-lar tissue and roots, and the production of seeds. The production ofseeds can be used as a basis to separate the divisions into two groups—non-seed plants and seed plants.

Survey of the Plant Kingdom

A Saguaro cactus (right)and mosses (left)

Movement oflandmassesLandmassescontinually moveover Earth’ssurface. Earth’souter layer isbroken into hugesections calledplates. Theseplates move slowlyover the materialunderneath. Manyscientists thinkthat the motion ofhot material deepwithin Earthgenerates theforces that causeplates to move.

(l)Paul Wakefield/Tony Stone Images, (r)David Wrobel/Visuals Unlimited

PhysicalScience

Connection

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Non-seed PlantsThe divisions of non-seed plants are

shown in Figure 21.6. These plantsproduce hard-walled reproductive cellscalled spores. Non-seed plants includevascular and nonvascular organisms.

Hepaticophyta Hepaticophytes (heh PAH tih koh

fites) include small plants commonlycalled liverworts. Their flattenedbodies resemble the lobes of an ani-mal’s liver. Liverworts are nonvascu-lar plants that grow only in moistenvironments. Water and nutrients

move throughout a liverwort byosmosis and diffusion. Studies com-paring the biochemistry of differentplant divisions suggest that liverwortsmay be the ancestors of all plants.

There are two kinds of liverworts:thallose liverworts and leafy liver-worts. Thallose liverworts have abroad body that looks like a lobedleaf. Leafy liverworts are creepingplants with three rows of thin leavesattached to a stem.

Anthocerophyta Anthocerophytes (an THOH ser

oh fites) are also small thallose plants.

21.2 SURVEY OF THE PLANT KINGDOM 565

hepato- from theGreek word hepar,meaning “liver”;Hepaticophyteshave liver-shapedgametophytes.

Figure 21.6The plant kingdom includes severaldivisions of non-seed plants.

Selaginella, a spike moss, is a lycophyte. Lycophytesare vascular plants adaptedto moist environments.

A

Sphagnum is a bryophyte.It grows in peat bogs.

D

Psilotum sporophyteshave simple stemsbut no leaves or roots.

G

Equisetum is an arthrophyte.It has roots, stems, andleaves, but the stems arehollow and appear jointed.

C

Anthoceros, ahornwort, is ananthocerophyte.It is found inmoist, shadyhabitats.

F

Marchantia is ahepaticophyte. It isfound on damp rocks.

E

All ferns are pterophytes.The cinnamon fern,Osmunda cinnamomea,grows in swampy habitatsthroughout the UnitedStates.

B

(tl)David T. Roberts/Nature’s Images/Photo Researchers, (tc)Jim Strawser/Grant Heilman, Inc., (tr)James H. Robinson/Earth Scenes, (bl)Patti Murray/Earth Scenes, (bcl)Gregory K. Scott/Photo Researchers, (bcr)Runk-Schoenberger/Grant Heilman, Inc., (br)Doug Wechsler/Earth Scenes

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The sporophytes of these plants,which resemble the horns of an ani-mal, give the plants their commonname—hornworts. These nonvascu-lar plants grow in damp, shady habi-tats and rely on osmosis and diffusionto transport nutrients.

Bryophyta Bryophytes (BRI uh fites), the

mosses, are nonvascular plants thatrely on osmosis and diffusion totransport materials. However, somemosses have elongated cells that con-duct water and sugars. Moss plantsare usually less than 5 cm tall andhave leaflike structures that are usu-ally only one to two cells thick. Theirspores are formed in capsules.

Psilophyta Psilophytes, known as whisk ferns,

consist of thin, green stems. Thepsilophytes are unique vascular plantsbecause they have neither roots norleaves. Small scales that are flat, rigid,overlapping structures cover eachstem. The two known genera ofpsilophytes are tropical or subtropi-cal. Only one genus is found in thesouthern United States.

Describe the maindifference between bryophytes andpsilophytes.

Lycophyta Lycophytes (LI koh fites), the club

mosses, are vascular plants adaptedprimarily to moist environments.Lycophytes have stems, roots, andleaves. Their leaves, although verysmall, contain vascular tissue. Speciesexisting today are usually less than 25 cm high, but their ancestors grewas tall as 30 m and formed a large partof the vegetation of Paleozoic forests.The plants of these ancient forestshave become part of the coal that is now used by people for fuel.

566 WHAT IS A PLANT?

AA

BB

Compare and ContrastLooking at Modern and Fossil Plants Many modern plantshave relatives that are known only from the fossil record. Aremodern plants similar to their fossil relatives? Are there anydifferences?

Procedure! Examine a preserved or living sample of Lycopodium, a

club moss. CAUTION: Wear protective gloves when han-dling preserved material.

@ Note and record the following observations:a. Does the plant grow flat or upright like a tree? b. Describe the appearance of its leaves and its stem.c. Measure the plant’s height and diameter in centimeters.

# Repeat step 2 for diagram A, a fossil relative.$ Repeat steps 1–3 using a preserved or living sample of

Equisetum, a horsetail and diagram B, a fossil relative.

Analysis1. Compare and Contrast Describe the similarities and dif-

ferences between Lycopodium and Lepidodendron. Do yourobservations justify their closeness as relatives? Explain.

2. Compare and Contrast Describe the similarities and dif-ferences between Equisetum and Calamites. Do yourobservations justify their closeness as relatives? Explain.

2 meters1 meter

20 meters

30 meters

Representation ofLepidodendron

Representationof Calamites

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21.2 SURVEY OF THE PLANT KINGDOM 567

Try MiniLab 21.2 to explore the simi-larities and differences between mod-ern and fossil lycophytes.

ArthrophytaArthrophytes (AR throh fites), the

horsetails, are vascular plants. Theyhave hollow, jointed stems sur-rounded by whorls of scalelike leaves.The cells covering the stems of somearthrophytes contain large deposits ofsilica. Although primarily a fossilgroup, about 15 species of arthro-phytes exist today. All modern horse-tails are small, but their fossil relativeswere the size of trees.

Pterophyta Pterophytes (TER oh fites), ferns, are

the most well-known and diversegroup of non-seed vascular plants.Ferns were abundant in Paleozoic andMesozoic forests. They have leavescalled fronds that vary in length from1 cm to 500 cm. The large size andcomplexity of fronds is one differencebetween pterophytes and other groupsof seedless vascular plants. Althoughferns are found nearly everywhere,most grow in the tropics.

Seed Plants Seed plants produce seeds, which

in a dry environment are a moreeffective means of reproduction thanspores. A seed consists of an embry-onic plant and a food supply coveredby a hard protective seed coat. Allseed plants have vascular tissues. InProblem-Solving Lab 21.2, you cancompare a characteristic common toseed plants and non-seed plants.

CycadophytaCycads (SI kuds) were abundant

during the Mesozoic Era. Today,there are about 100 species of cycads.They are palmlike trees with scaly

trunks and can be short or more than20 m in height. Cycads produce maleand female cones on separate trees.Cones are scaly structures that sup-port male or female reproductivestructures. Cycad cones can be aslong as 1 m. Seeds are produced infemale cones. Male cones produceclouds of pollen.

Apply ConceptsWhat trend in size is seen with gametophyte and sporo-phyte generations? All plants undergo alternation of gener-ations. There is a specific trend, however, that occurs in size asone goes from one plant division to the next.

Solve the Problem The following graph shows the trend that occurs within theplant kingdom as one compares the size of sporophyte andgametophyte generations in three major divisions.

Thinking Critically1. Analyze Describe the trend that occurs to the size of the

gametophyte generation as one moves from bryophytes toanthophytes.

2. Analyze Describe the trend that occurs to the size of thesporophyte generation as one moves from bryophytes toanthophytes.

3. Predict Estimate the size of the gametophyte generationcompared with the sporophyte generation in:a. Coniferophyta. Explain.b. Lycophyta. Explain.

4. Infer You are looking at a giant redwood tree. Whichgeneration is it and how do you know?

Gam

etop

hyte

gen

erat

ion

Spor

ophy

te g

ener

atio

n

Increasing sporophyte size

BRY

OPH

YTA

PTER

OPH

YTA

AN

THO

PHY

TA

Decreasing gametophyte size

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GnetophytaThere are three genera of gneto-

phytes (NEE toh fites) and each has dis-tinct characteristics. Gnetum (NEE tum)includes about 30 species of tropicaltrees and climbing vines. There areabout 35 Ephedra (eh FEH dra) species

that grow as shrubby plants in desertand arid regions. Welwitschia (welWITCH ee uh) has only one species,which is found in the deserts of south-west Africa. Its leaves grow from thebase of a short stem that resembles alarge, shallow cap.

568 WHAT IS A PLANT?

Table 21.1 Seed Plant Divisions

Division Example Common Names Characteristics

Cycadophyta Sago palm, cycad, Cycads grow in tropical or subtropical zamia, dioon environments. These plants are slow-growing

trees with unbranched trunks. Their leaves are palmlike. Seeds are produced in cones onfemale plants.

Gnetophyta Joint fir, Gnetum, Gnetophytes are usually found in desert or Welwitschia arid environments, but some are tropical.

They exhibit diverse growth habits from vines to low-growing forms. These plants produce seeds in conelike structures.

Ginkgophyta Ginkgo, maiden- Ginkgoes are tolerant of a wide range of hair tree habitats from urban to open environments.

These trees drop their leaves in the fall. Their seeds are surrounded by soft, fruitlike structures.

Coniferophyta Pine, spruce, Conifers grow in a wide range of habitats. juniper, redwood, Depending on the species, conifers can be tall fir, yew, hemlock, trees or ground-covering shrubs. The leaves arborvitae, cedar of conifers are needlelike or scalelike. Seeds

develop in cones or berrylike structures.

Anthophyta Rice, tomato, rose, Anthophytes are found worldwide. The divisioncorn, basil, apple, includes a great diversity of growth habits, oak, grass, cattail, forms, and sizes. All anthophytes produce grape, bluebell flowers from which dry or fleshy fruits with

one or more seeds develop.

(1)W.H. Hodge/Peter Arnold, Inc., (2)Gunter Ziesler/Peter Arnold, Inc., (3)Jim Strawser/Grant Heilman, Inc., (4)Runk-Schoenberger/Grant Heilman, Inc., (5)Jeff Lepore/Photo Researchers

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GinkgophytaThis division has only one living

species, Ginkgo biloba, a distinctivetree with small, fan-shaped leaves.Like cycads, ginkgoes (GING kohs)have male and female reproductivestructures on separate trees. Theseeds produced on female trees havean unpleasant smell, so ginkgoesplanted in city parks are usually maletrees. Ginkgoes are hardy and resist-ant to insects and to air pollution.

ConiferophytaThese are the conifers (KAH nuh

furz), cone-bearing trees such as pine,fir, cypress, and redwood. Conifersare vascular seed plants that produceseeds in cones. Species of conifers canbe identified by the characteristics oftheir cones or leaves that are needle-like or scaly. You can learn moreabout how to identify conifers in theBioLab at the end of the chapter.

Bristlecone pines, the oldestknown living trees in the world, aremembers of this plant division.Another type of conifer, the Pacificyew, is a source of cancer-fightingdrugs. Read more about medicinalplants in the Connection to Health atthe end of this chapter.

AnthophytaAnthophytes (AN thoh fites), com-

monly called the flowering plants,

are the largest, most diverse group of seed plants living on Earth. Thereare approximately 250 000 species of anthophytes. Fossils of theAnthophyta date to early in theCretaceous Period. Unlike conifers,anthophytes produce flowers fromwhich fruits develop, like those inFigure 21.7. A fruit usually containsone or more seeds. This division hastwo classes: the monocotyledons (mahnuh kah tul EE dunz) and dicotyledons(di kah tul EE dunz). You will learnmore about the distinctions betweenmonocots and dicots when you readabout anthophyte tissues in Chapter 23.

Table 21.1 lists some informationabout the divisions of seed plants. Doyou recognize any of the commonnames of the plants? Can you add tothe list of common names?

Understanding Main Ideas1. What is the primary difference between the seeds

of conifers and anthophytes?2. Why are seeds an important structural adapta-

tion? What plant divisions produce seeds? Whichplant divisions do not produce seeds?

3. What structural adaptation allows pterophytes togrow larger than bryophytes?

4. Compare and contrast anthophytes and anthocerophytes.

Thinking Critically5. In which division would you expect to find apple

trees? Why?

6. Get the Big Picture Make a table of the plantdivisions. Label columns: Division, Seed Plants,Non-seed Plants, Vascular Plants, NonvascularPlants, and Seeds in Fruits. For more help, refer toGet the Big Picture in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

21.2 SURVEY OF THE PLANT KINGDOM 569

conifero- from theLatin word conifer,meaning “conebearing”; Manyplants in the divi-sion Coniferophyta produce theirseeds on cones.

Figure 21.7These fruits and seedsdeveloped from flowers.List Can you namethree vegetables thatare really fruits?

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Before YouBegin

Each conifer species has aunique cone. The leaves ofconifer species also havedifferent characteristics.How would you identify aconifer? You would proba-bly use a dichotomous key.Dichotomous keys list fea-tures of related organismsin a way that allows youto determine each organ-ism’s scientific name.Below is an example froma dichotomous key thatmight be used to identifytrees.

Needles grouped in bundlesNeedles not grouped in

bundlesNeedlelike leavesFlat, thin leavesLeaves composed of three

or more leafletsLeaves not made up of

leaflets

Arborvitae

Hemlock

570 WHAT IS A PLANT?

Pine needles

How can you make a keyfor identifying conifers?

ProblemWhat characteristics can be used to create a dichotomous key for identifying different kinds of conifers?

HypothesesState your hypothesis according to the kinds of characteristics you predict will best serve to distinguish among several conifer groups. Explain your reasoning.

ObjectivesIn this BioLab, you will:■ Compare structures of several different

conifer specimens.■ Identify which characteristics can be used

to distinguish one conifer from another.■ Develop a model of a hierarchical classification system

(division, genus, species) based on similarities and differ-ences using taxonomic nomenclature.

Possible Materialstwigs, branches, and cones from several different conifersthat have been identified for you

Safety PrecautionsCAUTION: Always wash your hands after handling biologicalmaterials. Always wear goggles in the lab.

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

PREPARATIONPREPARATION

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21.2 SURVEY OF THE PLANT KINGDOM 571

1. Make a list of characteristics that could be included inyour key. You might consider using shape, color, size,habitat, or other factors.

2. Determine which of those characteristics would be mosthelpful in classifying your conifers.

3. Determine in what order the characteristicsshould appear in your key.

4. Decide how to describe each characteristic.

Check the Plan1. The traits described at each step in a key

are often pairs of contrasting characteris-tics. For example, the first step in a keyto conifers might compare “needlesgrouped in bundles” with “needlesattached singly.”

2. Someone who is not familiar with conifer identification should be able to use your keyto correctly identify any conifer it includes.

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

4. Carry out your plan by creating your key.5. Return all conifer specimens to

the location specified by your teacher for reuse by otherstudents. Wash your hands thoroughly.

CLEANUP AND DISPOSAL

PLAN THE EXPERIMENTPLAN THE EXPERIMENT

Spruce

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

1. Check Your Hypothesis Have someoneoutside your lab group use your key to iden-tify a conifer specimen. If he or she cannotidentify it, try to determine what the prob-lem is and make improvements to your key.

2. Relate Concepts Give one or more exam-ples of situations in which a dichotomouskey would be a useful tool.

3. Is there only one correctway to design a dichotomous key for yourspecimens? Explain why or why not.

ERROR ANALYSIS

Project Design a different dichotomous keythat would also work to identify your speci-mens. You may expand your key to includeadditional conifers.

Web Links To find out more about conifers, visit

(l)Scott Nielsen/DRK Photo, (r)Michel Viard/Peter Arnold, Inc.

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572 WHAT IS A PLANT?

Medicines fromPlants

What comes to mind when you hear theword plant? A vase full of flowers? A fruit

and vegetable garden? An evergreen forest?Although these examples are what most peoplethink of when they hear the word plant, plantsprovide us with much more than bouquets, food,and lumber. Nearly 80 percent of the world’spopulation relies on medications derived fromplants. In fact, just fewer than 100 plants providethe active ingredients used in the ten dozen or soplant-derived medicines currently on the market.

For thousands of years, the words plants andmedicines were used synonymously. In the fifthcentury A.D., doctors of the Byzantine Empireused the autumn crocus to effectively treatrheumatism and arthritis. Hundreds of yearsago, certain groups of Native North Americansused the rhizomes of the mayapple as a laxative,a remedy for intestinal worms, and as a topicaltreatment for warts and other skin growths. Theoils from peppermint leaves have long been usedto settle an upset stomach. Lotions containingthe liquid from the plant Aloe vera are often usedto relieve the pain associated with minor burns,including sunburn. “Herbal” medicines haveagain begun to play an important role in so-called modern medicine.

Aspirin—The wonder drug Evidence sug-gests that almost 2500 years ago, a Greek physi-cian named Hippocrates used a substance fromthe bark of a white willow tree to treat minorpains and fever. The substance, which is calledsalicin, unfortunately upset the stomach. Researchin the late 1800s led to the discovery of acetylsali-cylic acid (ah SEE till sa lih SIH lick • A sid), oraspirin. Aspirin originally was developed bychemist Felix Hoffmann to relieve the joint discomfort associated with rheumatism. Salicylic

acid—a major component of aspirin—was finallysynthesized in the laboratory in the early 1900s.Since then, aspirin’s use has become widespread.

New drugs for cancer Drugs that fight two types of cancer—Hodgkin’s disease and leukemia—have been derived from theMadagascar rosy periwinkle. Drugs producedfrom the needles and bark of the Pacific yewhave been used to treat breast, ovarian, lung, andother cancers. Although the interest in medicinalplants by consumers, medical experts, and phar-maceutical companies is growing, it is estimatedthat less than five percent of the 250 000 differ-ent flowering plant species have been studied fortheir potential use in the field of medicine.

Madagascar rosy periwinkle

Project Identify a plant not mentioned in thisfeature that is known to have medicinal proper-ties. Research the plant’s geographic distributionon Earth, its use(s), the active ingredient derivedfrom the plant, and whether or not a syntheticform of the active ingredient is available for use.As a class, compile all findings and create a class-room display.

To find out more about medicines derivedfrom plants, visit

Richard Shiell/Earth Scenes

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Section 21.1

Section 21.2

Key Concepts■ Plants are multicellular eukaryotes with

cells that have cell walls containing cellu-lose. A waterproof cuticle covers the outer surface of most plants. Most plantsundergo photosynthesis, which producesglucose, a form of food.

■ All plants on Earth probably evolved from filamentous green algae that lived inancient oceans. The first plants to eventu-ally move from water to land probablywere leafless forms.

■ Adaptations for life on land include a cuticle; the development of leaves, roots,stems, and vascular tissues; alternation ofgenerations; and the evolution of the seed.

Vocabularycuticle (p. 559)leaf (p. 561)nonvascular plant

(p. 562)root (p. 561)seed (p. 562)stem (p. 561)vascular plant (p. 562)vascular tissue (p. 562)

Key Concepts■ The plant kingdom is grouped into major

categories called divisions.■ Nonvascular plants are in the divisions

Anthocerophyta, Hepaticophyta, andBryophyta. They reproduce mainly byusing spores. Nonvascular plants do notproduce seeds.

■ Non-seed vascular plants are in the divi-sions Psilophyta, Lycophyta, Arthrophyta,and Pterophyta. These plants have tissuesthat conduct water and other materials and reproduce mainly by spores.

■ Vascular seed plants in the divisionsCycadophyta, Gnetophyta, Ginkgophyta,and Coniferophyta produce seeds on cones.Male cones and female cones can be onseparate plants or the same plant.

■ The division Anthophyta includes vascular,seed-producing plants that flower. Fruitswith seeds develop from flowers. Antho-phytes are divided into two groups—monocotyledons and dicotyledons.

Vocabularycone (p. 567)frond (p. 567)Survey of the

Plant Kingdom

CHAPTER 21 ASSESSMENT 573

Adapting toLife on Land

To help you review plant adaptations to land, use theOrganizational Study Fold on page 559.

STUDY GUIDESTUDY GUIDE

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Review the Chapter 21 vocabulary words listed inthe Study Guide on page 573. Match the wordswith the definitions below.

1. plants in which the transport of water andother substances is mainly by osmosis anddiffusion from cell to cell

2. the organ that anchors a plant and absorbsmost of the water and minerals used by aplant

3. for plants such as pines and spruces, it is theorgan that contains reproductive structures

4. the plant organ that is usually the site ofphotosynthesis

5. a group of tubelike, elongated cells throughwhich water and other materials are trans-ported throughout a plant

6. Which of these traits is NOT common toplants and green algae?A. reproduce by fissionB. contain cellulose in cell wallsC. store food as starchD. contain the same kind of chlorophyll

7. Vascular tissues are found in ________.A. bacteria C. fernsB. algae D. hornworts

8. Which of the following characteristics isNOT found in plants?A. eukaryotic cells C. prokaryotic cellsB. cellulose cell walls D. waxy cuticle

9. The plant organ in the photo to the right is from a plant in division ________.A. AnthocerophytaB. ConiferophytaC. LycophytaD. Anthophyta

10. Which group of organisms is probably theancestor of land plants?A. cyanobacteria C. bryophytesB. archaebacteria D. green algae

11. Seeds enclosed in a fruit is a structural adap-tation of ________.A. Anthophytes C. ConiferophytesB. Bryophytes D. Pterophytes

12. The fern structure to the right is called a________.A. rhizomeB. rootC. gametophyteD. frond

13. Open Ended Explain why biologistshypothesize that the first plants to adapt to life on land may have been similar to liverworts.

14. Open Ended Anthophytes are found world-wide and include the greatest number ofknown plant species. Identify, describe, andevaluate characteristics of this division thatwere important to its success. Explain yourchoices.

15. Open Ended Observe the plants in Figure 21.6 D and E. Describe the struc-tural adaptations that contribute to theirlong-term survival in moist environments.

16. Concept Map Copy the concept map belowthen complete it the using the followingterms: leaves, roots, stems, vascular tissue,vascular plant.

contains

1.

which is found in

2.

4.

3. 5.

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17. You areappointed to a committee at school that is toplan and plant a flower garden. What factorsmust be considered when selecting plants for

this garden? Visit toresearch plants and plan the garden. Sketch a plan and list your plant selections. Explainwhy each plant was chosen.

REAL WORLD BIOCHALLENGE

Constructed Response/Grid InRecord your answers or fill in the bubbles on your answer document using the correct place value.

23. Grid In The sporophyte of corn has 20 chromosomes. How many chromosomes would youexpect to find in corn gametes?

24. Open Ended Describe the differences between seed and non-seed plants. Considering structuraland physiological adaptations of these two plant types, infer why seed plants are found in morediverse environments than non-seed plants.

Seed plants

Conifers

Gnetophytes

Amborella

Water liliesMagnolias Modern

monocotsModerndicots

Flowering plants

CHAPTER 21 ASSESSMENT 575

Multiple ChoiceStudy the cladogram below and answer questions18–20.

18. The cladogram shows the evolution of someflowering plants. According to the clado-gram, modern monocots developed________ Amborella.A. at the same time as C. afterB. before D. none of these

19. Amborella is most closely related to________.A. modern monocots C. water liliesB. modern dicots D. magnolias

20. Which of the following plant types evolvedbefore Amborella?A. gnetophytes C. magnoliasB. modern dicots D. water lilies

Use the diagram below to answer questions 21and 22.

21. The sporophyte produces spores by theprocess of ________.A. mitosis C. fissionB. meiosis D. fertilization

22. Which of the following would NOT have ahaploid or n number of chromosomes?A. gametophyte C. sporophyteB. spore D. gamete

GAMETOPHYTE (n)Spores (n)

Meiosis

SPOROPHYTE (2n) Mitosis andcell division

Fertilization

Femalegamete (n)

Malegamete (n)

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