Section 1 How Plants Grow Focus and Portfolio Project Plant Focus Worksheet GENERAL Planner CD-ROM • Lesson Plan • Directed Reading • Active Reading • Data Sheet for Skills

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section begins bydescribing seed germination. Then,after defining perennials, annuals,and biennials in the context of plantlife spans, the section explainsmeristems and their role in primaryand secondary plant growth.

Ask students to draw the structureof a seed. (The drawings should showan embryo, a stored food supply, anda protective outer covering.) Ask students to share their drawings sothat you can determine their priorknowledge before beginning thissection. Allow ELL students tolabel their drawings in their nativelanguage and English. Visual

Activity Provide students with bean seedsand corn seeds that you have ger-minated. (Place the seeds betweensheets of wet paper towels, and putthe wet towels with seeds in aclosed black garbage bag. Place thebag in a warm spot for 3–4 days.Check seeds at days 2 and 3.) Havestudents slice the germinating seedslongitudinally, or provide pre-cutgerminating seeds. Ask students toview the seeds under stereomicro-scopes, and identify the structuresshown in Figure 1. Bio 10C, 13B

MotivateMotivate

LS

Bellringer

FocusFocus

Section 1

572 Chapter 26 • Plant Growth and Development

Transparencies

TT Seed GerminationTT Bellringer

• Reading Organizers• Reading Strategies• Portfolio Project Plant Focus

Worksheet GENERAL

Planner CD-ROM

• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Skills

Practice Lab GENERAL

GENERAL

GENERAL

Chapter Resource File

1. The hooked shoot of a germi-nating bean seed straightensafter the cotyledons emergefrom the soil.

2. The shoot of a germinating cornseed is covered by a sheath. Theshoot grows straight up, but thecotyledon stays underground.

Cotyledons

Leaves

Seed coat

Hook

Young shootEmbryonic

root

Bean (dicot)

Corn (monocot)

Cotyledon

Sheath

First leaf

Embryonic shoot

YoungshootEmbryonic

root

Section 1 How Plants Grow and Develop

Seeds SproutA seed contains a plant embryo that is in a state of suspended ani-mation. Some embryos can remain in suspended animation inside aseed for thousands of years. Seeds sprout with a burst of growth inresponse to certain changes in the environment. These changes,such as rising temperature and increasing soil moisture, usually sig-nal the start of favorable growing conditions.

Many seeds must be exposed to cold or to light before they cansprout. The seed coats of other seeds must be damaged before theycan sprout. Exposure to fire, passing through the digestive system ofan animal, and falling on rocks are several natural ways that seedcoats are damaged. A seed cannot sprout until water and oxygenpenetrate the seed coat. When water enters a seed, the tissues in theseed swell, and the seed coat breaks. If enough water and oxygen areavailable after the seed coat breaks, the young plant, or seedling,begins to grow.

GerminationA plant embryo resumes its growth in a process called .The first sign of germination is the emergence of the embryo’s root.What happens next varies somewhat from one type of plant toanother, as you can see in Figure 1. The young shoots of some plants,such as beans, form a hook. The hook protects the tip of the shootfrom injury as it grows through the soil.

germination

Objectives● Compare seed germination

in beans and corn.

● Contrast annuals, biennials,and perennials.

● Explain how primary andsecondary growth areproduced.

● Describe several traits ofbread wheat.

● Contrast development inplants and animals.

Key Terms

germinationperennialannualbiennialprimary growthsecondary growthapical meristemcork cambiumvascular cambiumannual ring

Beans and corn show two characteristic patterns of seed germination.

Figure 1 Seed germination

10C 13A 13B

10C 13A 13B

10C 13A 13B

10C 13A 13B

5A

572

TAKS 3

TAKS 3

TAKS 3

TAKS 3

Student Edition TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 13A TEKS Bio 5A, 7B, 10C, 13A, 13B

Teacher EditionTAKS Obj 1 Bio/IPC 2A, 2C TAKS Obj 3 Bio 13ATEKS Bio 10C, 13A, 13B

pp. 572–573

Interactive Reading AssignChapter 26 of the Holt BiologyGuided Audio CD Program to help students achieve greater success in reading the chapter.

Interpreting Visuals Bring stu-dents’ attention to Figure 1. Havestudents compare the structures ofthe germinating corn seed and beanseed. Ask students how monocotand dicot seedlings differ in the waythey emerge from the soil. (Dicotseedlings have a stem that hooks as itemerges to protect the delicate tip,whereas monocots grow straight outof the soil. Monocot seedlings have aprotective sheath that guards the tip.)Ask students what other differencesthey notice. (The cotyledon and seedcoat of the corn seed remain under-ground, while the cotyledons of thebean emerge fromthe soil.)

Group Activity Design a Flower Bed Have stu-dents work in groups of four todesign a flower garden that willprovide color in every season (or inthree seasons, if you live in an areawith a harsh winter climate). Letstudents use nursery catalogs tofind examples of annuals, biennials,and perennials, as well as to deter-mine where each plant will growand when it will bloom. Assigneach group a set of conditions underwhich its garden must grow (e.g.,size, distribution of sun and shade,soil type). Finally, tell them to con-sider aesthetic factors (e.g., colorcombinations, taller plants in back,shorter plants in front). Have eachstudent design a graphic that showsthe group’s garden from the topduring one of the seasons and identifies their plants. Visual

TAKS 3 Bio 13A; Bio 13BTAKS 1 Bio/IPC 2A

LS

GENERAL

Bio 13B

GENERALBUILDERSKILL

SKILLBUILDER

READINGREADING

TeachTeach

Chapter 26 • Plant Growth and Development 573

did you know?Plant Collections The Royal Botanic Gardens,Kew, located about 10 km southwest of London,England, is recognized as a global center ofexcellence in the study of plant diversity. Theworld’s largest documented living and preservedplant collections are located there.

English Language Learners

Take students on a walk around the schoolgrounds or a park, and have them keep a log ofthe plants they see, using general terms such asflower, tree, grass, or shrub. Have studentswrite a paragraph that answers the followingquestions based on what they observe. Whattypes of plants did you see? Did you see moreof one type of plant than another? If so, whatmight account for the difference? (More annualstend to be present in spring and summer; onlywoody perennials may be present in winter.)

Interpersonal TAKS 1 Bio/IPC 2C, Bio 13BLS

REAL WORLDREAL WORLDCONNECTIONCONNECTION

The young shoots of other plants, such as corn, have a protectivesheath around their shoots. In some plants, such as beans andmarigolds, the cotyledons emerge from the soil and unfold above-ground. In other plants, such as corn and peas, the cotyledonsremain underground. After the shoot of a seedling emerges, its rootsand shoots continue to grow throughout its life.

Plant Life SpansAs you have read in a previous chapter, bristlecone pines are the old-est known trees. They are estimated to be about 5,000 years old. Incontrast, some plants live for only a few weeks. Depending on howlong it lives, a plant can be classified as one of three basic types:perennial, annual, or biennial.

Perennials Many herbaceous plants and all woody plants areperennials. A is a plant that lives for several years. Mostperennials reproduce many times during their life span. Others, likethe herbaceous perennial shown in Figure 2, reproduce only oncebefore they die. Chrysanthemums, daffodils, and irises are familiarherbaceous perennials. These plants store nutrients for the next sea-son’s growth in fleshy roots or underground stems. The abovegroundshoots of herbaceous perennials often die after each season ofgrowth. Trees, shrubs, and many vines are woody perennials. Somewoody perennials drop their leaves each year. Plants that drop all oftheir leaves each year, such as elms, maples, and grapevines, areknown as deciduous (dee SIHJ oo uhs) plants.Those that drop a few leaves at a time through-out the year, such as firs, pines, and junipers,are called evergreens.

Annuals Sunflowers, beans, corn, and manyweeds are annuals. An is a plant thatcompletes its life cycle (grows, flowers, andproduces fruits and seeds) and then dies withinone growing season. Virtually all annuals areherbaceous plants. Most annuals grow rapidlywhen conditions are favorable. Individualplants can become quite large if they getenough water and nutrients.

Biennials Carrots, parsley, and onions are bien-nials. A is a flowering plant that takestwo growing seasons to complete its life cycle.During the first growing season, biennials pro-duce roots and shoots. The shoots consist of ashort stem and a rosette (circular cluster) ofleaves. The roots store nutrients. In the secondgrowing season, a biennial plant uses the storednutrients to produce a flowering stalk. Theplant dies after flowering and producing fruitsand seeds.

biennial

annual

perennial

Figure 2 A herbaceousperennial. Century plants livefor many years but reproduceonly once. Like the dried-upplant on the left, this floweringcentury plant will die when itsseeds are mature.

www.scilinks.orgTopic: Texas PerennialsKeyword: HXX4020

573

ActivityApical Meristems Let studentsobserve prepared slides of the apical meristems of the shoots androots of several plants. Have themdraw what they see and label theparts identified in Figure 3. Havestudents write a brief paragraphdescribing how the cells in the apical meristems differ from thosein the surrounding tissues. (Thecells of the apical meristems are smalland unspecialized. The surroundingcells tend to be larger and longer and have thicker walls, and somehave specialized structures such aschloroplasts or root hairs.) Visual

Teaching TipRemoval of the Apical MeristemAsk students what they think wouldhappen if the apical meristem of a stem or root were removed.(Removing or damaging the apicalmeristems of a plant would stop orlimit the vertical growth of the stemor root.) This frequently occurs innature, as tips of stems are brokenoff by wind or animals, killed bydisease, or eaten by insects or otheranimals. Lateral buds often beginto grow after the apical meristem isremoved. If the plant is a tree, oneof these lateral buds will take overas the main trunk, and the tree willtake on its normal form again in afew years. If the plant is a shrub oran herbaceous plant, the growth ofmany lateral buds will make theplant bushier, and it will not growas tall. TAKS 3 Bio 13A; Bio 5A

GENERAL

Bio 5ALS

GENERAL

Teach, continuedTeach, continued


CulturalAwarenessCulturalAwareness

The Asian Art of Bonsai Bonsai is the cul-tivation of miniature specimens of plants thatwould normally be much larger. The effect isobtained by frequent, selective pruning of boththe shoot and the roots. Bonsai plants aretypically grown in small containers. The wordbonsai comes from the Japanese charactersbon, meaning “tray,” and sai, meaning“plant.” The Chinese practiced bonsai inapproximately the third century B.C., but it was the Japanese Buddhist monks whoperfected the art.

Flowering plants and ferns are the originalsources of approximately 25% of all drugs prescribed each year in North America. In fact, botany was considered a branch of medicine until the early to mid 1800s.

MEDICINEMEDICINECONNECTIONCONNECTION

Transparencies

TT Apical Meristems

www.scilinks.orgTopic: Primary Growth

in PlantsKeyword: HX4148

MeristemsPlants grow by producing new cells in regions of active cell divisioncalled meristems. Almost all plants grow in length by adding newcells at the tips of their stems and roots. Growth that increases thelength or height of a plant is called . Many plantsalso become wider as they grow taller. Growth that increases thewidth of stems and roots is called . After new cellsare formed by cell division, they grow and undergo differentiation.Recall from your reading that differentiation is the process by whichcells become specialized in form and function.

Primary Growth(AP ih kuhl) , which are located at the tips of stems

and roots, produce primary growth through cell division. As shownin Figure 3, apical meristems are regions of small, undifferentiatedcells. To better understand how primary growth occurs in mostplants, imagine a stack of dishes. As you add more dishes to the top,the stack grows taller but not wider. Similarly, the cells in the apicalmeristems of most plants add more cells to the tips of a plant’s body.New cells are added through cell division. The cells then lengthen.Thus, primary growth makes a plant’s stems and roots get longerwithout becoming wider. To learn about primary growth in amonocot, look at Up Close: Bread Wheat later in this section.

The tissues that result from primary growth are called primarytissues. The new cells produced by apical meristems differentiateinto the primary dermal, ground, and vascular tissues of roots,stems, and leaves. Some of the cells produced by the root apicalmeristem also become part of the root cap. These cells replace cellsthat are worn away as the root pushes through the soil.

meristemsApical

secondary growth

primary growth

Compare and ContrastTo compare and contrastprimary growth and sec-ondary growth, make atwo-column list. In onecolumn write the ways inwhich the two are alike. In the other column, write the ways in which they are different.

Both shoot tips and root tips contain apical meristems, where cell division occurs.

Figure 3 Apical meristems

Shoot tip of acoleus plant

Root tip of aradish plant

Apical meristems

574

Student Edition TAKS Obj 3 Bio 7B TEKS Bio 7B

Teacher EditionTAKS Obj 3 Bio 13A TEKS Bio 5A, 5B, 5C, 13A

pp. 574–575

DemonstrationProvide students with preparedslides of a cross section of a woodystem. Have them examine the slidesunder a compound microscope.Point out that vascular cambium isonly one layer of cells. It is foundjust under the bark of a woodystem and can be located in micro-scope slides of woody stem crosssections by finding the phloem cellsand the large, thickened xylemcells. Also point out that bothxylem and phloem develop fromthe vascular cambium cells, so theydevelop in rows on either side ofthis “meristematic” tissue. Havestudents locate the layer betweenthe two types of cells in a woodystem cross section. This is the rowof vascular cambium cells. Havestudents describe how xylem andphloem originate from vascularcambium. (Xylem and phloem originate through cell division andcell differentiation.) Visual

Teaching TipSummarizing Plant GrowthHave students prepare a sequentialdiagram that summarizes howherbaceous plants grow by primarygrowth and how woody plantsgrow by both primary and second-ary growth. An example of a completed diagram appears in theGraphic Organizer on this page.

Visual Bio 5A, 5BLS

GENERAL

Bio 5A, 5B, 5CLS

GENERAL


Transparencies

TT Development of a Wood Stem

Graphic Organizer

Use this graphic organizer with Teaching Tip on this page.

Woodyplant

Secondarytissues

Herbaceousplant

Cell division anddifferentiation

Differentiation

Cork and vascularcambia

Primarytissues

Apicalmeristem

BIOgraphic

Primary phloem

Primary phloem

Cork

Bark

Cork

Primary xylem

Primaryxylem

Secondary xylem

Secondary phloem

Secondary phloemEpidermis

Vascular bundle

Vascular cambium

Vascularcambium

Cortex

Pith

Pith

Corkcambium

Corkcambium

Initially, the stem is covered by epidermis and contains cortex, pith, and a ring of vascular bundles with primary xylem and phloem.

The wood in a woody stem results from secondary growth.

Development of a Woody Stem

1 A vascular cambium forms between the xylem andphloem in each vascular bundle. Cork cambium forms under the epidermis.

2 In a mature stem, the vascular cambium adds new layers of secondary xylem and phloem each year.

3

Secondary GrowthSecondary growth occurs in parts of many herbaceous plants, suchas in carrot roots. However, it is most dramatic in woody plants.Secondary growth is produced by cell division in two meristems,which form thin cylinders near the outside of woody stems androots. One meristem, called the (KAM bee uhm), lieswithin the bark and produces cork cells. The other meristem, calledthe , lies just under the bark and produces vascu-lar tissues. The tissues that result from secondary growth are calledsecondary tissues. Figure 4 shows how woody stems develop.

Step A young woody stem has a ring of vascular bundles betweenthe cortex and the pith. Each vascular bundle contains pri-mary xylem and primary phloem.

Step Vascular cambium develops between the primary xylemand the primary phloem in each vascular bundle.Secondary phloem is produced toward the outside of thestem. Secondary xylem is produced toward the inside of thestem. The cork cambium forms when the epidermis isstretched and broken as the stem grows in diameter.

Step Eventually, the vascular bundles merge into solid cylinders.No cortex or primary phloem remains. The cork, corkcambium, and secondary phloem make up the bark. Thevascular cambium and secondary xylem lie inside the bark.Thick layers of secondary xylem, or wood, often form rings.Since one new ring is usually formed each year, the ringsare called .annual rings

vascular cambium

cork cambium

www.scilinks.orgTopic: Secondary Growth

in PlantsKeyword: HX4160

Figure 4

575

Activity The Debate about FoodIrradiation Food irradiation is the process of exposing food to radiation—the energy emitted bythe unstable nuclei of certain atomsin the form of waves or rays. As it travels through the food, radiationkills organisms such as bacteria andinsects. Have students research thehistory of and the current debateover food irradiation in prepara-tion for a class debate. (Pro: Foodirradiation makes the food supplysafer, provides a better quality of food,and extends the shelf life of food.Con: irradiation induces chemicalchanges in food, which may affect thecolor, odor, and texture of food andlower the nutritional value of food.)Bio/IPC 3C

Wheat Varieties Students may be surprisedto learn that more than 200 varieties of wheatare grown in the United States. Hard redwheats, the varieties grown for making breadflour, belong to the species Triticum aestivum.Durum wheats, or macaroni wheats, whichare grown for making pasta because they con-tain less gluten, belong to the species Triticum

dicoccum. Wheat may be planted in either thefall or the spring. The term winter wheatrefers to a crop that is planted in the fall, overwinters as seedlings, and is harvested inlate spring or summer. The term spring wheatrefers to a crop that is planted in the springfor harvest in the fall.


Bread Wheat Teaching Strategies• Show students specimens of

living or preserved wheatplants.

• Let students dissect grains, orkernels, of wheat and locatethe endosperm, bran, andgerm of the kernels. Explainthat the endosperm serves asa food supply for the embryowhen it begins to grow.White wheat flour containsonly endosperm and wholewheat flour contains bothendosperm and bran.

• For interest, have studentsmake bread so that theynotice the elasticity of thedough, which is caused by gluten.

Up Close

External Structures

Up CloseBread Wheat

Scientific name: Triticum aestivum

Size: 0.3 to 0.8 m (1 to 2.5 ft) tall

Range: Agricultural regions worldwide

Habitat: Cultivated fields in temperate and subtropical grasslands

Importance: Wheat is the principal staple food in temperateregions of the world. The grains of Triticum aestivum are usually ground into flour that is used to make bread.

Stems Wheat plants have hollow,jointed stems called culms. Givenplenty of space, mature plants may develop as many as 100 culms. Each culm in a plant may have from three to six leaves.

Leaves Wheat, a member of the grass family, is a monocot. Its leaves are long but only about 2 cm (0.8 in.) wide, with parallel veins. The leaves are attached to the stem by a sheath, which wraps around the stem.

Leafsheath

▼

Leafblade

▼

Culms

▼

Fruit A kernel, or grain, of wheatis a one-seeded fruit with a creaseon one side and a brush of tinyhairs at one end. The grainsare high in gluten, a stickymixture of proteins thatmake dough elastic.

Adventitiousroots▼

Roots Wheat plants have a fibrous root system composed of adventitious roots, as do most grasses. The extensive root system may be more than 2.2 m (7 ft) deep.

AntherStigmaLemma

Palea

Floret

Flowers The flowers, whichoccur in dense clusters calledspikes, develop at the top ofeach culm. Spikes range from 5 to 13 cm (2 to 5 in.) in length.Like all grass flowers, wheat flowers lack petals and sepals.Instead, two modified leavescalled the palea and the lemmaenclose the stamens and pistil of each tiny flower, or floret. Thelemmas of some bread-wheatvarieties have a long bristle called an awn.

Awn

▼ Flower spike

576

TAKS 3 Bio 13A; Bio 5A,5B, 5C, 10C, 13B

Student EditionTAKS Obj 3 Bio 13ATEKS Bio 5A, 5B, 5C, 13A

Teacher EditionTAKS Obj 3 Bio 13ATEKS Bio 5A, 5B, 5C, 10C, 13A, 13BTEKS Bio/IPC 3C

pp. 576–577

TAKS 3

Trends in AgricultureMunicipal Sewage In recent years, a greatdeal of research has been conducted to investi-gate the use of municipal sewage as a fertilizer.Such wastes must receive treatments thatremove or kill organisms that might pose ahealth hazard to humans. One serious concernabout these materials is the tendency they

have to contain excesses of heavy metals suchas lead and cadmium, especially if certain typesof industries contribute to the waste. Thesemetals can be harmful to humans even at lowlevels. Municipal wastes are not recommendedfor use in the fertilization of food crops forthis reason. IntrapersonalLS

Paired Summarizing Pair students.Have one student read silently aboutthe external structures of breadwheat and the other about theinternal structures. Then have onestudent summarize his or her sectionaloud without referring to the text.The partner should listen withoutinterrupting and be prepared topoint out any inaccuracies or omis-sions in the summary. At this pointstudents can refer to the text. Havestudents switch roles.

Bio 5A, 5B, 5CCo-op Learning

SKILLBUILDER

READINGREADING


Bread Wheat Discussion• The chemical 2, 4-D is used to

kill dicots. Will it kill wheatplants? Why or why not? (No,wheat is a monocot as it has thetypical characteristics of mono-cots such as parallel leaf veins,fibrous roots, and seeds with asingle cotyledon.)

• How did our ancestors helpproduce the bread wheat vari-eties that exist today? (Fromwild hybrids, they selectedplants with desirable character-istics such as higher yields,larger seeds, and more gluten.)

• How would a human kary-otype differ from the wheatkaryotype? (A human kary-otype normally has 23 pairs ofchromosomes, while a wheatkaryotype has seven sets of sixsimilar chromosomes, in whichthere are three homologouspairs.)

• Is polyploidy beneficial to allliving organisms? Why orwhy not? (No, polyploidymay be beneficial in plantsbecause it causes plants to be larger, have showierflowers, and be more vigorous.In most animals, includinghumans, polyploidy is usuallydetrimental.) InterpersonalLS

Up CloseInternal Structures

Bread-wheatcell

Nucleus

Bread-wheatkaryotype

Bran

Endosperm

Embryo(wheat germ)

Kernel(longitudinal section)

Fruit structure A wheat kernelis about 85 percent starchy endo-sperm. The kernel’s outer layers,called the bran, make up about 12 percent of the kernel. The branconsists of the ovary wall, seedcoat, and aleurone layer, whichcontains protein and oils. Theembryo, or wheatgerm, makes upless than 3 percentof the kernel.

Apical meristems The apicalmeristems are located within theculms at a point that is usually ator just beneath the surface of thesoil. Thus, the apical meristemsare protected from being eaten bygrazing animals. Each new leafgrows up within a hollow culmand emerges from thesheath of the culm’suppermost leaf.

Chromosomes Bread-wheat cells have 42 chromosomes. A karyotype revealsthat a bread-wheat cell has three sets of 14chromosomes (7 pairs), shown here in differentcolors. Thus, bread wheat is not diploid (2n).Instead, it is hexaploid (6n)—a polyploid withsix of each kind of chromosome. Polyploidy,having many sets of chromosomes, iscommon among cultivated plants. Amongplants, polyploidy enables hybrids to resultfrom crosses among different species. Such isthe case with bread wheat, which is a naturalhybrid of three closely related species of wheat.▼ Apical meristem

Leaf sheath(younger leaf)

Leaf sheath(oldest leaf)

New leaf

577

ReteachingHave students work in cooperativegroups to summarize the growth ofa plant, from a seed to a matureadult.

Quiz1. When you buy seeds in a packet,

why have they not germinated?(Water and oxygen must penetratethe seed coat for the seed to sprout.)

2. When you plant perennials, whatwould you expect to happenafter one season of growth? (The plant would live for morethan two years.)

AlternativeAssessmentProvide students with preparedmicroscope slides of plant tissues,and ask them to identify meristem-atic and vascular tissues by drawingwhat they see. Visual Bio 5ALS

GENERAL

GENERAL

Co-op Learning

CloseClose

Answers to Section Review

1. Corn seedlings grow straight up, and the cotyle-don stays in the soil. Bean seedlings form a hookas they grow, and the two cotyledons emerge.

2. Annuals live for one growing season, reproduceonce, and then die. Biennials live for two grow-ing seasons, reproduce once during the secondseason, and then die. Perennials live for morethan two years and may reproduce many times.

3. Primary growth lengthens the stem and formsnew primary dermal, ground, and vascular tissues. Secondary growth increases the stem’s

Bio 10C; Bio 13B

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

diameter by producing layers of cork and secondary xylem and phloem.

4. Plant development is continuous and“reversible,” while animal development is not.

5. A. Incorrect. Germination is the growth of aplant embryo. B. Incorrect. Differentiation isthe process by which cells become specializedin form and function. C. Incorrect. Primarygrowth increases the length or height of aplant. D. Correct. Secondary growth increasesthe width of stems and roots. Bio 13B

Bio 5A

TAKS 3 Bio 13A; Bio 13B


Plant Tissue Culture

Teaching StrategiesPoint out that tissue culturerequires sterile conditions and new plants are grown incontrolled environmentalconditions.

DiscussionWhat enables cells from part ofa plant to grow into a wholeplant? (Undifferentiated plantcells can differentiate into severaldifferent types of cells.)

TAKS 2 Bio 4B

www.scilinks.orgTopic: Plant Life SpansKeyword: HX4141

Compare and contrast the germination of beanseeds and corn seeds. 10C 13A 13B

Summarize the basic differences betweenannuals, biennials, and perennials. 10C 13B

Explain how primary growth and then secondarygrowth produce a woody stem. 13A 13B

Critical Thinking Analyzing Methods Inwhat ways does plant development differ fromanimal development?

Growth that increases thewidth of a plant’s stems and roots is called A germination. C primary growth.B differentiation. D secondary growth.

TAKS Test PrepTAKS Test Prep

Section 1 Review

13B

Plant Development Genes guide the development of both plants and animals, but theirpatterns of development are very different. As an animal develops,sets of genes that control development are inactivated and may notbe used again. Most animals stop developing when they becomeadults. Plants, in contrast, continuously make new cells in meri-stems. These cells differentiate and replace or add to existing tissues.Thus, a plant continues to develop throughout its life.

Many cells in a mature plant can activate all of their genes. Suchcells can divide and form masses of undifferentiated cells. In asense, they can reverse their development. These cells can undergodifferentiation and develop into a mature plant. A technique calledtissue culture is used to grow new plants from tissue that can reverseits development. A tissue culture is prepared by placing tissue on asterile nutrient medium. Masses of undifferentiated cells that formgrow into plants that are genetically identical to the parent plant.

Plant Tissue Culture

T issue culture is used to propa-gate orchids, houseplants,

and fruit plants. Thousands ofcultures can be made from a singleplant. Tissue culture can also beused to produce plants with newcharacteristics.

Protoplast FusionProtoplast fusion has been usedto produce hybrid petunias, pota-toes, and carrots. A protoplast isa plant cell that has had its cellwalls removed by enzymes. Cer-tain chemicals or an electricalshock can cause two protoplasts

to fuse, as the photo at rightshows. If the protoplasts camefrom genetically different plants, ahybrid cell results. The hybrid isthen placed in a tissue cultureand grown into an adult plant.

Genetic EngineeringTissue culture is also an essentialpart of producing geneticallyengineered plants. First, foreigngenes are inserted into a plant’scells. The genetically altered cellsare then grown into adult plantsin tissue culture.

www.scilinks.orgTopic: Genetic EngineeringKeyword: HX4092

Magnification: 810�

5A

578

TAKS 2

Student EditionTAKS Obj 2 Bio 4B TEKS Bio 4B, 5A, 10C, 11A, 11B,13A, 13B

Teacher EditionTAKS Obj 2 Bio 4BTAKS Obj 3 Bio 13ATAKS Obj 4 IPC 7D, 7E TEKS Bio 4B, 5A, 13A, 13BTEKS IPC 7D, 7E

pp. 578–579

Section 2

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section focuses on fac-tors that influence plant growth anddevelopment, including nutrients,hormones, and environmental influ-ences such as sunlight, temperature,and the seasons.

Ask students to identify the sub-stances plants need for survival.After taking attendance, write theirresponses on the board. (Initially,they will probably identify light,water, and carbon dioxide.) Promptthem to identify other needs byasking why people fertilize theiryards. Ask students how they thinkplants might regulate their growthand development without having a nervous system as animals do.(They produce hormones.)

Interpersonal

Discussion/QuestionAsk students what growth factorssoil provides plants, and whetherplants can grow without soil.(Usually, soil provides minerals thatplants need for growth. Using a prac-tice known as hydroponics, plantsare grown with their roots immersedin water through which oxygen isbubbled and to which the mineralsneeded for plant growth are added.)Consider the possibility of develop-ing a small hydroponic garden in theclassroom. Verbal TAKS 2 Bio 4BLS

MotivateMotivate

TAKS 2 Bio 4BLS

Bellringer

FocusFocus


• Chapter Resource File• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Quick Lab• Data Sheet for Data Lab• Data Sheet for Math Lab GENERAL

GENERAL

GENERAL

GENERAL

GENERAL


• Reading Organizers• Reading Strategies • Supplemental Reading Guide

A Feeling for the Organism The Life and Work of Barbara McClintock

Planner CD-ROM

NutrientsLike all multicellular organisms, plants grow by adding new cellsthrough cell division. Plants must have a steady supply of the rawmaterials they use to build new cells in order to grow. Plants need onlytwo raw materials—carbon dioxide and water—to make all the carbo-hydrates in their tissues. As you learned earlier in this book, carbondioxide and water are needed for photosynthesis.

Like animals, plants also need oxygen for cellular respiration.Although the green parts of a plant produce oxygen during photo-synthesis, most of the oxygen used by leaves and stems comes fromthe air. Roots, which usually do not carry out photosynthesis, getoxygen from the air spaces between soil particles. If the soil arounda plant’s roots becomes compacted or saturated with water, it maynot provide enough oxygen for the roots, and the plant could die.

However, carbon dioxide, water, and oxygen do not satisfy all of aplant’s needs for raw materials. Plants also require small amounts ofat least 14 , which are elements absorbed mainlyas inorganic ions. Table 1 lists the six mineral nutrients needed inthe greatest amounts for healthy plant growth and describes theimportance of each nutrient. Commercial fertilizers may containmost of these mineral nutrients.

mineral nutrients

Regulating Growthand Development

Section 2

Objectives● Identify the major

nutrients plants need togrow.

● Describe how planthormones control plantgrowth.

● Relate environmentalfactors to plant growth.

Key Terms

mineral nutrientauxinhormoneapical dominancetropismphotoperiodismdormancy

10C 13B

10C 11B 13B

11A 11B

Table 1 Major Mineral Nutrients Required by Plants

Nutrient Importance

NitrogenPart of proteins, nucleic acids, chlorophylls, ATP, and coenzymes; promotes growth of green parts

PhosphorusPart of ATP, ADP, nucleic acids, phospholipids of cell membranes, and some coenzymes

PotassiumNeeded for active transport, enzyme activation, osmotic balance, and stomatal opening

CalciumPart of cell walls; needed for enzyme activity and membrane function

MagnesiumPart of chlorophyll; needed for photosynthesisand activation of enzymes

SulfurPart of some proteins and coenzyme A; needed for cellular respiration

579

IPC Benchmark Fact

Have students find the six mineral nutrients listed inTable 1 on the periodic table. Ask them to compareand contrast the properties of these elements basedon their location in the periodic table. Which elementsare most alike and most different? Identify whethereach mineral nutrient naturally occurs as an element,compound, or both.7E (grade 10 only)

TAKS 4 IPC 7D (grade 11 only),


did you know?Darwin’s Plant Research Charles Darwindid many experiments with plants. In the mid-1800s, Darwin and his son Francis did theearliest experiments on phototropism. Theydiscovered that a grass seedling responds tolight coming from one direction with growthon the opposite (shaded) side, resulting in theseedling bending toward the light source.Bio 3F, 11B

Answer

The chemicals found in Agent Orange are 2,4-D (2,4-dichlorophenoxyacetic acid),2,4,5-T (2,4,5-trichloro-phenoxyacetic acid), and traceamounts of dioxin. Exposure toAgent Orange has been blamedfor miscarriages, skin diseases,cancers, and birth defects.

Bio 11C

Real Life

TeachTeach

Reading Hint Tell students thatthis textbook uses typographicaids, such as boldfaced words andin-text pronunciation guides, tohelp them learn new terms. Tell students that before they read asection of the book, to find theboldfaced terms and determinetheir meanings by reading the sen-tence in which each term appears.

Using the FigureWalk students through Figure 5,which summarizes the steps of FritzWent’s classic experiment on theeffects of auxin. Help students tounderstand that when the agar ispurple, it contains auxin. Ask stu-dents to state the significance ofstep 4. (It is a control designed toshow that agar is not the cause of the effect.) Bio 3F

SKILLBUILDER

READINGREADING

Hormonal Control of GrowthFor centuries, people have known that plants bend strongly toward alight source as their shoots elongate. In the 1920s, the Dutch biologistFrits Went showed that a chemical produced in the shoot tip causesthis bending response. Went named the growth-promoting chemicalthat causes stems to bend (AWK sin). The steps in Went’sexperiment are summarized in Figure 5.

Step Went removed the tip of an oat shoot and placed the tip onan agar block. Auxin diffused from the tip into the block.

Step Went then transferred the agar block to the cut end of ashoot, which caused the shoot to grow.

Step When Went placed an agar block with auxin on either sideof cut shoots, the shoots grew in the opposite direction.

Step As a control, Went placed an agar block without auxin onthe cut end of other shoots. These shoots did not grow.

Auxin Auxin is one of many plant hormones. The word hormone comesfrom the Greek word horman, meaning “to set in motion.” A

is a chemical that is produced in one part of an organismand transported to another part, where it causes a response. Auxincauses plant cell walls to become more flexible, which allows the cells

hormone

auxin

BIOgraphic

Auxin diffused from the cut tip of an oat shoot into an agar block.

Auxin causes oat seedlings to elongate and bend toward light.

The Steps in Went’s Experiment

1 Application of the agar block with the auxin to a second shoot resulted in growth.

2 Cut shoots grew away from contact with agar with auxin.

3 Agar without auxin did not cause a cut oat shoot to grow.

4

Shoottip

Agarblock

Agarblockwithauxin

Auxin

Figure 5

Real LifeThe herbicide AgentOrange contains twosynthetic auxins. This herbicide was used to defoliate plants in thejungles of Vietnam duringthe Vietnam War. Oneingredient of Agent Orangeis still commonly used as a herbicide.Finding Information Find out the names of the chemicals in AgentOrange, and identify thehealth problems to whichit has been linked. 11C

580

Student EditionTAKS Obj 1 Bio/IPC 2B, 2CTAKS Obj 2 Bio 4B TAKS Obj 3 Bio 13A TEKS Bio 4B, 10C, 11C, 13A, 13BTEKS Bio/IPC 2B, 2C

Teacher EditionTAKS Obj 1 1 Bio/IPC 2B, 2CTAKS Obj 1 IPC 3A, 3BTAKS Obj 4 IPC 8ATEKS Bio 3F, 11B, 11C, 13BTEKS Bio/IPC 2B, 2CTEKS IPC 3A, 3B, 8A

pp. 580–581

IPC Benchmark Fact

Have students review Went’s experiment on the hor-mone auxin. Ask them to determine if his experimentalresults demonstrate a physical or chemical change inthe plant. Have them defend their answers. In addi-tion, instruct students to analyze and critique Went’sexperiment as to its strengths and weaknesses usingthe information provided.TAKS 4 IPC 8A

TAKS 1 IPC 3A

Rotten Apples The expression “One rottenapple spoils the whole barrel” is commonlyused to refer to people whose unacceptablebehavior may influence others to behave unac-ceptably. This expression comes from theobservation by food growers and handlers thata rotten apple in a barrel of apples results in allthe apples rotting. The explanation is that rot-ting fruit give off ethylene, which promotes theripening of other nearby fruits. The rottingfruit is infected with a fungus, which easilyinfects other fruit after they ripen. Bio 11B


MISCONCEPTION ALERT

Anthropomorphizing Plants It is commonfor students to attribute human characteris-tics to nonhuman organisms, such as plantsand animals. Thus, students might think thata plant’s response to light, for example, issomehow conscious, or that plants bendtoward the light because they see it.Emphasize that a plant’s response to light,gravity, or other environmental stimuli issimply a hormonal stimulus-response. Plantsdo not perceive environmental stimuli in thesame way that humans and animals do.

Investigating theEffects of Ethyleneon a Plant

Skills AcquiredObserving, makingcomparisons, drawingconclusions

Teacher’s NotesTell students that ethyleneaffects plants in many ways.For example, when some plantsare exposed to ethylene gas,they do not elongate normally.Ethylene also promotes the pro-duction of male flowers in plantssuch as squash and cucumbers.Ethylene is used by citrus-fruitgrowers to ripen fruits that arepicked while they are still green.

Answers to Analysis1. Answers will vary. Plants in

jars containing an apple shouldbegin to lose their leaves aftera few days.

2. Answers will vary. From theresults of this experiment, students should conclude thatethylene promotes plant agingand leaf drop.

TAKS 1 Bio 2B, 2C; Bio 13B

to elongate as they grow. Auxin accumulates on the dark side of astem. As a result, the cells on the dark side of a stem elongate morethan the cells on the light side. The difference in elongation causes thestem to grow toward the light. Auxin also inhibits the growth of thebuds along a stem. This inhibition is called .Cutting off the tip of a stem removes the source of auxin and enablesthe other buds to grow. That is why pruning the stems of a plantmakes the plant become bushier.

Hormones in AgricultureMore than a century ago, citrus farmers discovered that they couldcause citrus fruits to ripen by storing them in a room heated by akerosene stove. The ripening was caused by ethylene, which is agaseous organic compound produced when kerosene is incom-pletely burned. Most plant tissues produce ethylene. Today, ethyleneis used to promote the ripening of tomatoes, bananas, and otherfruits that are harvested before they ripen. Ethylene also loosens thefruit of cherries, blackberries, and blueberries, making it easier toharvest these crops mechanically.

Gibberellins (jihb uhr EHL ihnz) are produced in developingshoots and seeds. They stimulate stem elongation, fruit development,and seed germination. Gibberellins are used to enlarge Thompsonseedless grapes. Other seedless fruits treated with gibberellinsinclude apples, cucumbers, mandarin oranges, and peaches.

Cytokinins (sie toh KIE nihnz), which are produced in root tips,stimulate cell division and slow the aging of some plant organs.Cytokinins are sprayed on cut flowers to keep them fresh and onfruits and vegetables to extend their shelf life. Cytokinins areadded to tissue-culture media to cause undifferentiated cells toform shoots.

apical dominance

Investigating the Effects of Ethylene on a PlantYou can use a ripe apple to see one of theeffects of ethylene on plants.

Materials

4 L glass jars with lids (2), 2 plants in 5 cm pots,small ripe apple

Procedure

1. Place a plant inside one ofthe jars. Tightly secure the lid.

2. Place the other plant andthe apple inside the other jar.Tightly secure the lid.

3. Observe both jars for severaldays. Record what you see.

Analysis

1. Describe any changes inthe plant in each jar.

2. Critical ThinkingDrawing ConclusionsA ripe apple gives off ethylenegas. Based on your observa-tions, how does ethyleneaffect a plant?

www.scilinks.orgTopic: Plant HormonesKeyword: HX4140

2B 2C 13B

581

TAKS 1

Bio 11B

IPC BenchmarkMini-Lesson

IPC Skills TAKS 1 IPC 3BDraw inferences based on data relatedto promotional materials for productsand services.Activity Bring in advertisements, pack-ages or containers for products thatclaim they can cause muscle growthand increased strength. Have the stu-dents research the substances in theproducts to determine if the productsare truly effective.

Transparencies

TT Major Mineral Nutrients Requiredby Plants

TT Bread WheatTT Went’s Experiment

Reading Organizer Before studentsfinish reading this section, have themmake a list of the following terms:auxin, tropism, phototropism,gravitropism, and thigmotropism.As they learn about the terms, havethem write a brief definition ofeach term. Have them save their list of terms and definitions for uselater in the Reteaching exercise atthe end of this section. Verbal

Teaching TipTissue Culture Tell students thatthe growth of whole plants frompieces of plants in tissue culturerequires the addition of plant hormones in order for them to differentiate properly. The relativeamounts of the hormones affect theprocess of differentiation. Typically,auxins and cytokinins are firstadded to the culture medium topromote the formation of a mass ofundifferentiated cells. Next a highlevel of auxins and a low level ofcytokinins are added to the culturemedium. This promotes root for-mation. Then a low level of auxinsand a high level of cytokinins areadded to the culture medium. Thispromotes shoot formation.TAKS 2 Bio 4B; Bio 5B, 5C

GENERAL

LS

SKILLBUILDER

READINGREADING


Trends in Plant GeneticsGenetic Diversity The National PlantGermplasm System (NPGS) is a cooperativeeffort to preserve the genetic diversity ofplants. When plants lose their genetic diversity,which happens when only a few varieties of aspecies are cultivated, these species can bewiped out easily by a single disease or environ-mental condition to which they are sensitive.However, when many varieties of a species arecultivated, some varieties will have genes thatconfer resistance to various pests and diseases,or allow the plant to survive certain adverseconditions. TAKS 3 Bio 7B, 13A


CareerCareerHorticulturist Horticulturists study fruits,vegetables, and ornamental plants. These plantscientists are interested in producing betterfruit, vegetable, and ornamental crops with lesspesticides, fertilizers, and water. Have studentswork in teams to use library references or on-line databases to find information about the role of horticulturists in food production.Have students investigate current researchprojects in horticulture, and have them reporttheir findings to their classmates. Bio 3D

Environmental Influences on GrowthBecause most plants are anchored in one spot, they cannot movefrom an unfavorable environment to a more favorable one asanimals do. Instead, plants respond to their environment byadjusting the rate and pattern of their growth. For example, a plantthat receives plenty of water and mineral nutrients may growmuch faster and larger than it would if it received very little waterand mineral nutrients. Also, a plant grown in full sun may growmuch faster and larger than it would if it were grown in the shadeor indoors. So the availability of light and nutrients affect the rateof plant growth. Many of a plant’s responses to environmentalstimuli, however, are triggered by the hormones that regulate plant growth.

Tropisms A (TROH piz uhm) is a response in which a plant growseither toward or away from a stimulus. Auxin is responsible for pro-ducing tropisms. Figure 6 shows examples of three common types oftropisms. Phototropisms are responses to light. Responses to gravityare called gravitropisms. A thigmotropism is a response to touch. Ifa plant grows toward a stimulus, the response is called a positivetropism. If a plant grows away from the direction of the stimulus,the response is called a negative tropism. Thus, a shoot that growsup out of the ground shows both positive phototropism (growingtoward the light) and negative gravitropism (growing away from thepull of gravity).

tropism

The bending of an amaryllis towardthe light is a positive phototropism.

The upward growth of shoots is a nega-tive gravitropism; the downward growthof roots is a positive gravitropism.

The coiling of grapevine tendrilsaround a wire is a thigmotropism.

Tropisms are growth responses that occur either toward or away from a stimulus.

Figure 6 Tropisms

The word thigmotropismcomes from the Greekwords thigma, meaning“touch,” and tropos,meaning “turn.”

582

Student EditionTAKS Obj 3 Bio 13ATEKS Bio 13A, 13B

Teacher EditionTAKS Obj 2 Bio 4BTAKS Obj 3 Bio 7B, 13ATEKS Bio 3D, 4B, 5B, 5C, 7B, 11B,13A, 13B

pp. 582–583


Using the Figure Walk students through Figure 7by first following what happens tolong-day (short-night) and short-day (long-night) plants when thedays are long and the nights areshort. Then follow what happensto long-day (short-night) and short-day (long-night) plants when thedays are short and the nights arelong. Finally, follow what happensto long-day (short-night) and short-day (long-night) plants when theyare grown under long nights thatare interrupted by a flash of light in the middle of the night. Tell stu-dents that poinsettias are short-day(long-night) plants that are desir-able ornamentals for the Christmasholidays. Ask students if these plantswould normally produce flowers inlate December. (yes) Ask studentswhat would happen if lights wereturned on during the night in agreenhouse where poinsettias aregrown? (The plants would not bloom.)Bio 11B

GENERAL

Transparencies

TT Flowering and Photoperiodism

MISCONCEPTION ALERT

Plant ”Food“ Fertilizers are often referredto as plant “food.” However, the term foodis usually reserved for organic substancesthat provide a source of energy and organicmolecules for living things when they arebroken down. Because minerals do not con-tain usable energy and are not broken downin plants, they should not be referred to asfood. Plants do not eat food; rather, theyproduce their own organic molecules duringphotosynthesis.

GENERAL

InterpretingAnnual RingsSkills AcquiredMaking observations,analyzing data, makingconclusions

Teacher’s NotesPoint out to students that it isthe number of rings in a treetrunk that indicates its age, not the diameter of the trunk. A number of environmental factors can influence the widthof an annual ring.

Answers to Analysis1. Answers will vary. The rings

indicate that the tree grew in atemperate climate and that theamount of rainfall varied fromyear to year.

2. A3. They should be very similar.

Photoperiodism Certain plants bloom in the spring and others bloom in the summeror fall. Some plants bloom as soon as they reach a mature size. Inmany plants, seasonal patterns of flowering and other aspects ofgrowth and development are caused by changes in the length ofdays and nights. The response of a plant to the length of days andnights is called .

Most plants can be categorized as one of three types in referenceto photoperiodism. A plant that responds when days become shorterthan a certain number of hours is said to be a short-day plant. Aplant that responds when days become longer than a certain num-ber of hours is called a long-dayplant. Plants whose growth anddevelopment are not affected by daylength are known as day-neutralplants. It is really the length of thenights, however, rather than thelength of the days that controlsphotoperiodism, as Figure 7 shows.Knowledge of photoperiodism isvery important to the nursery andfloral industries. The length of daysand nights is controlled artificially ingreenhouses where plants such aspoinsettias and chrysanthemums aregrown. Thus, commercial growersforce the plants to produce flowersat times of the year when they ordi-narily would not. This makes itpossible for poinsettias to be availablefor Christmas and chrysanthemumsto be available year round.

photoperiodism

Analysis

1. Critical ThinkingInterpreting Data What dothe annual rings indicateabout the climate where thisplant grew?

2. Critical ThinkingDrawing ConclusionsWhich ring, A or B, indicates ayear when this plant receivedmore rainfall?

3. Critical ThinkingMaking Predictions Howwill the annual rings of anearby tree of the same ageand species compare withthose of this tree?

Interpreting Annual RingsBackground

The annual rings of a woody stem provide importantclues to annual variations in the rainfall an area receivesover time. Thick rings form in years with heavy rainfall.Relatively thin rings form in dry years. Use the photo atright to answer the following questions.

010001011001110101000100100010011100100100010000010100100111010101001000101010010010 A

B

Early summer Late fall Night interruptedMidnight

Noon

6 A.M.6 P.M.

Midnight

Noon

6 A.M.6 P.M.

Midnight

Noon

6 A.M.6 P.M.

Short-day plant: Poinsettia

Long-day plant: Bearded iris

Figure 7 Flowering andphotoperiodism. Long-dayplants flower when nights areshort. Short-day plants flowerwhen nights are long. If a flashof light interrupts a long night,long-day plants flower andshort-day plants do not.

13A 13B

583

010001011001110101000100100010011100100100010000010100100111010101001000101010010010

TAKS 3

TAKS 3 Bio 13A; 13B

ReteachingHave students list the boldfacedterms in this section with theirdefinitions. Have them create acrossword puzzle using the defini-tions as clues and the terms aswords in the puzzle. Logical

QuizTrue or False:

1. Minerals and water satisfy all of aplant’s raw materials needs. (false)

2. Auxin is a type of planthormone. (true)

AlternativeAssessmentAsk students to summarize the rolesof the plant hormones discussed inthis section.

GENERAL

GENERAL

LS

CloseClose

Answers to Section Review

1. nitrogen, phosphorus, potassium, calcium,magnesium, sulfur

2. Auxin diffuses to the side of a stem away froma light source. There, it stimulates cells to growlonger than they do on the side of the stem facing the light source. This results in the stembending toward the light source.

3. An example of a negative gravitropism is ashoot growing upward from the soil after aseed germinates. Bio 11B

Bio 11B

4. It is an advantage for plant growth to be regu-lated by environmental stimuli because plantsare unable to move to a new environmentwhen conditions become unfavorable.

5. A. Incorrect. Gravitropism is the response of a plant to gravity. B. Correct. Thigmotropism isthe response of a plant to touch. C. Incorrect.Phototropism is the response of a plant to light.D. Incorrect. Photoperiodism is the response ofa plant to the length of days and nights. Bio 11B

Bio 11A


Analyzing theEffect of Cold onSeed GerminationSkills AcquiredInterpreting graphs,analyzing data

Teacher’s NotesSeeds with true dormancy can-not germinate until the planthormone abscisic acid is eitherwashed away or broken down.

Answers to Analysis1. Cold temperatures promote

the germination of apple seeds.2. 45 days � 7 days/week �

6.43 weeks3. 30 percent4. 100 percent

<x + 6x - 7 - 02

18

49376

0

52

List the six mineral nutrients that plants requirein the greatest amounts.

Explain how auxin causes a stem to growtoward a light source. 11B

Describe an example of a negative gravitropism. 11B

Critical Thinking Predicting Outcomes Whyis it an advantage for plant growth and develop-ment to be regulated by environmental stimuli?

When a vine responds to thetouch of a fence wire by growing a tendril aroundthe wire, the vine is exhibiting 11B

A gravitropism. C phototropism.B thigmotropism. D photoperiodism.


Section 2 Review

11A

Responses to Temperature Temperature affects growth and development in many plants. Forexample, most tomato plants will not produce fruit if the nighttimetemperatures are too high. Many plants that flower in early springwill not produce flowers until they have been exposed to cold tem-peratures for a certain number of hours. Most deciduous woodyplants drop their leaves in the fall in response to shorter periods ofdaylight. Thick, protective scales develop around their buds, asFigure 8 shows. After a period of low temperatures, the buds begingrowing into new leaves or sections of woody stem.

is the condition in which a plant or a seed remainsinactive, even when conditions are suitable for growth. Many plantsand seeds remain dormant until they have been exposed to low tem-peratures for several weeks. Dormancy helps plants to survive bykeeping buds from growing and seeds from germinating duringwarm spells before winter has ended.

DormancyFigure 8 Bud dormancy.Thick scales cover thedormant buds on this twigfrom an apple tree.

Analysis

1. Summarize the overall effectof cold temperatures on thegermination of apple seeds.

2. Calculate the number ofweeks that apple seeds mustbe stored at 4ºC for at least

80 percent of the seeds togerminate.

3. Critical ThinkingInterpreting Graphs Whatpercentage of apple seedsgerminate after storage at 4ºCfor 20 days?

4. Critical ThinkingPredicting Patterns Whatpercentage of apple seeds willgerminate after being stored at4ºC for 80 days?

Analyzing the Effect of Cold on Seed GerminationBackground

In some plants, a period of low temperatures is neededto break seed dormancy. The graph at right shows howbeing stored at a low temperature (4ºC) affected theability of apple seeds to germinate. Use the graph toanswer the following questions.

<x + 6x - 7 - 02

8

493 0

52

Perc

ent

germ

inati

on 100

80

60

40

20

Number of days at 4ºC

706050403020100

Effect of Cold Storage

10C 11B 13B

584

Bio 10C, 11B, 13B

6C

TAKS 9 TAKS 10


Student EditionTAKS Obj 3 Bio 13A Math TAKS Obj 9 Math 8.3BMath TAKS Obj 10 Math 8.14CTEKS Bio 10C, 11B, 13A, 13B

Teacher EditionTEKS Bio 10C, 11A, 11B, 13B

pp. 584–585

Math TAKS Obj. 10, 8.14C; Obj 9, 8.3B

Alternative Assessment Organize students into groups. Haveeach group use the information inChapter 26 to prepare a multimediapresentation on plant growth anddevelopment that they could give to a middle-school science class orto the general public.

Answer to Concept Map

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


• Science Skills Worksheet• Critical Thinking

Worksheet • Test Prep Pretest• Chapter Test GENERAL

GENERAL

GENERAL


include

which produces which produces

Meristems

apical meristem vascular cambium cork cambium

primary tissues cork

stems roots stems roots

primary growth secondary growth

which produces

length width

barkwhich increases the

of

which increases the

of

by by in

secondary xylem secondary phloem

Key Concepts

Study CHAPTER HIGHLIGHTS

ZONEKey Terms

Section 1germination (572)perennial (573)annual (573)biennial (573)primary growth (574)secondary growth (574)apical meristem (574)cork cambium (575)vascular cambium (575)annual ring (575)

Section 2mineral nutrient (579)auxin (580)hormone (580)apical dominance (581)tropism (582)photoperiodism (583)dormancy (584)

How Plants Grow and Develop

● Germination is the resumption of growth by the embryo in aseed. Water and oxygen must penetrate the seed coat beforegermination can occur.

● Annuals complete their life cycle in one growing season.Biennials complete their life cycle in two growing seasons.Perennials live several years and may reproduce many times.

● Apical meristems located at the tips of shoots and rootsproduce primary growth. The tissues that result fromprimary growth are known as primary tissues.

● Secondary growth increases a plant’s stem and root width. In woody stems, secondary growth is produced by the corkcambium and vascular cambium, two meristems near theoutside of the stem.

● Bread wheat is a cereal grass with long leaves, hollow stems, and clusters of tiny flowers. The fruits, or grains, are usually ground into flour that is used to make bread.

● Plants develop throughout their lives. Plant development is reversible. Many mature plant cells can divide to formmasses of undifferentiated cells, which can develop into a new plant.

Regulating Plant Growth and Development

● Plants need at least 14 mineral nutrients for growth. Theyalso need carbon dioxide and water for photosynthesis andoxygen for cellular respiration.

● Hormones regulate plant growth and development. Auxin is a hormone that causes shoots to elongate and inhibits thegrowth of lateral buds.

● Plants modify their growth in response to the direction of light, gravity, and touch. Such growth responses are called tropisms.

● Seeds and many mature plants survive periods of unfavorableenvironmental conditions by becoming dormant.

● In many plants, seasonal patterns of flowering and otheraspects of growth and development are caused by changes inthe length of days and nights.

2

1

585

ANSWERS

Using Key Terms

1. a2. c3. c4. d5. a. Germination is the term for

the resumption of growth bythe embryo in a seed.

b. A perennial is a plant that livesfor more than two years andmay reproduce many times.

c. Apical dominance is the inhi-bition of the growth of sidebuds that is caused by auxinproduced in the tip of a shoot.

d. Dormancy is the condition inwhich seeds or buds do notgrow even when environmentalconditions are favorable forgrowth to occur.

6. a7. d 8. b9. b

10. d11. b12. Cytokinins stimulate cell division

and slow aging. They are used inagriculture to prolong freshness ofcut flowers, fruits, and vegetablesand to stimulate shoot growth in tissue cultures. Gibberellinsstimulate stem elongation, fruitdevelopment, and seed germina-tion. They are used in agricultureto induce fruit formation withoutseeds and to enlarge seedless fruits.Bio 11B

TAKS 3, Bio 11A, 11B, 13A, 13BBio 11B, 13BBio 10C, 11B

Bio 5B, 10CBio 11B

Bio 5A TAKS 3 Bio 13ABio 13BBio 13BBio 13B

13. Wheat cells have six of each kind of chromo-some rather than two of each kind as indiploid organisms.

14. Hybrid cells, made from the fusion of two cellsfrom two different types of plants, are growninto new, hybrid plants in tissue culture.

15. One possible answer to the concept map isfound at the bottom of the Study Zone page.TAKS 1 Bio/IPC 2C

TAKS 2 Bio 6D (grade 10 only)

10 only)TAKS 2 Bio 6A, 6D (grade Section Questions

1 1–5b, 13–16, 18, 19, 212 5c–d, 6–12, 17, 20

Assignment Guide


CHAPTER 26

Using Key Terms1. The first sign of germination of a bean seed

is the emergence of the embryo’s a. root. c. sheathed shoot.b. hooked shoot. d. cotyledons.

2. Plants that live several years or more areknown as a. annuals. c. perennials.b. biennials. d. terminals.

3. Providing cells for growth at the tips of aplant is the main function of the a. cork cambium.b. root cap.c. apical meristems.d. lateral meristems.

4. Cell division that increases the diameter ofa woody stem occurs in the a. pith.b. primary tissues.c. apical meristems.d. vascular cambium.

5. Write a sentence that shows your under-standing of each of the following terms.a. germinationb. perennialc. apical dominanced. dormancy

6. Plant and animal development differ inthat plant development a. is continuous and reversible.b. stops after a plant reaches maturity.c. is not affected by environment.d. is controlled by genes that cannot be

reactivated.

7. Which of the following is not a rawmaterial needed for plant growth?a. carbon dioxideb. waterc. oxygend. vitamins

8. Major mineral nutrients required by plantsinclude all of the following excepta. nitrogen. c. phosphorus.b. lead. d. potassium.

9. Auxin causes cells to a. have less flexible cell walls.b. elongate more as they grow.c. bend toward light.d. develop lateral buds.

10. Which of the following caused the growthpatterns of the mums shown below? a. apical meristemb. auxinc. apical dominanced. all of the above

11. The response of a plant to the length ofdays and nights is a. gravitropism.b. photoperiodism.c. phototropism.d. thigmotropism.

12. How do cytokinins and gibberellins affectplant growth, and how are these hormonesused in agriculture?

13. Up Close How does the chromosomenumber of bread wheat differ from that ofdiploid organisms?

14. How is tissue culture used toproduce hybrid varieties of plants?

15. Concept Mapping Construct aconcept map that describes growth invascular plants. Try to include the follow-ing terms in your map: meristems, apicalmeristem, primary growth, primary tissues,cork cambium, secondary growth, cork,secondary phloem, secondary xylem, andvascular cambium.

PerformanceZONE

CHAPTER REVIEW

13B

11B

11B

11A 11B

11B

6A 6D

6D

2C

13B

13B

5A

5B

11B

586

Review and AssessTAKS Obj 1 Bio/IPC 2B, 2C, 2DTAKS Obj 2 Bio 6A, 6DTAKS Obj 3 Bio 13ATEKS Bio 3D, 5A, 5B, 6A, 6B, 10C,11A, 11B, 13A, 13B

pp. 586–587

Critical Thinking

16. Answers will vary. Students shouldrealize that acid would probablydamage the seed coat. Water canthen penetrate the seed, and theseed will sprout. Seeds treatedwith acid germinate more quicklyand more uniformly than dountreated seeds.

17. The energy for a carrot plant’ssecond year of growth comesfrom compounds that are storedin the root.

18. The cells in these plant parts areable to reverse their development.These cells can produce cells thatare undifferentiated, which canthen undergo differentiation toform all of the tissues necessaryto grow an entire new plant.

19. Ripe pears give off ethylene, whichpromoted ripening in the bananas.

Alternative Assessment

20. Answers will vary.

21. In the practice of bonsai, plantsare shaped by selective pruningand training and are kept smallby pruning their roots and shoots,potting them in small containers,and watering and fertilizing themsparingly.

22. Agronomists are plant scientistswho traditionally study crops andsoils. Many agronomists work inthe field, in government and atuniversities. Others work for pri-vate industry or state agriculturalextension services. Positions areavailable for individuals withbachelor’s degrees, master’sdegrees, and PhD’s in agronomyor soil science. Starting salary willvary by region. Bio 3D

TAKS 1 Bio/IPC 2B, 2D

TAKS 1 Bio/IPC 2C

Bio 5A

Bio 13B

1. A. Correct. Auxin is a growth-promotingchemical. It diffused from the agar block intothe shoot, causing it to grow. B. Incorrect. Agardoes not stimulate plants to produce auxin.C. Incorrect. Agar does not stop the growth.D. Incorrect. Agar does not stimulate shoots.

2. F. Incorrect. If the weight of the agar blockwere to cause the shoot to bend, it would bendin the direction of the block, where the weightis applied. G. Correct. The auxin diffused fromthe agar block into the side of the shoot.Growth on this side of the shoot resulted in

Bio 13B

bending in the opposite direction. H. Incorrect.Light is not the direct cause of plant growth. J. Incorrect. Gravitropism is a response togravity, not to auxin.

3. A. Incorrect. An agar block without auxinwould not stimulate the shoot to grow.B. Incorrect. The shoot cannot grow straightdown. C. Incorrect. An agar block withoutauxin would not stimulate the shoot to grow.D. Correct. An agar block without auxinwould not stimulate the shoot to grow.Bio 13B

Bio 13B


• The Science TAKS Prep Appendixin this book provides integrated biology and IPC TAKS practice.

• The Holt Science TAKS PracticeWorkbook provides a review of biology, chemistry, and physics concepts tested on the grades 10and 11 science TAKS.


Test

Critical Thinking16. Analyzing Methods Some seeds are soaked

in acid before they are packaged and soldto farmers and home gardeners. What isthe purpose of this treatment?

17. Applying Information Carrots are biennials.What role does the root of a carrot plant playin the plant’s second year of growth?

18. Forming Reasoned Opinions Why is itpossible for people to grow new plantsfrom pieces of leaf, stem, or root tissue inwhich the cells have already undergonedifferentiation?

19. Evaluating Results A student placed agreen banana in each of 10 plastic bags.The student also placed a ripe pear in fiveof the bags and then sealed all of the bags.The bananas in the bags without pears tooklonger to ripen than the bananas in thebags with pears. Evaluate theseexperimental results.

Alternative Assessment20. Finding and Communicating Information

Use the media center or Internet resourcesto learn how commercial growers produceplants such as poinsettias and chrysanthe-mums that flower at times when theywould not flower in nature. Summarizeyour findings in a written report.

21. Organizing Information Research bonsai—the Asian art of growing miniature plants.Relate your findings in a report that explainsplant growth and development in bonsai.

22. Career Connection Agronomist Agrono-mists study soil management and cropproduction. Write a report that includes a job description, training required, kindsof employers, growth prospects, andstarting salary.


The diagram below summarizes an experimentinvestigating the hormonal control of growth inan oat shoot. Use the diagram and your knowl-edge of science to answer questions 1–3.

1. What happened in step 2?A Auxin from the agar block stimulated the

shoot to grow. B The shoot produced auxin in response to

the agar block.C The agar block stopped further growth of

the shoot.D The shoot grew straight up in response to

an agar block.

2. What happened in step 3?F The weight of the agar block caused the

shoot to bend.G Exposing one side of the shoot to auxin

caused the shoot to grow in the oppositedirection.

H The agar block shielded one side of theshoot from light, causing the shoot togrow in the opposite direction.

J Auxin from the agar block caused theshoot to exhibit positive gravitropism.

3. What would likely happen if an agar blockwithout auxin were placed on the cut end ofan oat shoot? A The shoot would grow straight up.B The shoot would grow straight down.C The shoot would bend and grow around

the agar block.D The shoot would not grow.

1 23

Shoottip

Agarblock

Agar blockwith auxin Auxin

Oat shoot

Carefully study all of the details of a diagram beforeanswering the question or questions that refer to it.

13B2B 2D

3D

5A

2C

13B

13B

13B

587

Documents

Section 1 How Plants Grow Focus and Portfolio Project Plant Focus Worksheet GENERAL Planner CD-ROM • Lesson Plan • Directed Reading • Active Reading • Data Sheet for Skills