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Section 1 How Plants Grow and Develop Section 1 Focus Overview Before beginning this section review with your students the objectives listed in the Student Edition. This section begins by describing seed germination. Then, after defining perennials, annuals, and biennials in the context of plant life spans, the section explains meristems and their role in primary and secondary plant growth. Bellringer Ask students to draw the structure of a seed. (The drawings should show an embryo, a stored food supply, and a protective outer covering.) Ask students to share their drawings so that you can determine their prior knowledge before beginning this section. Allow ELL students to label their drawings in their native language and English. LS Visual Motivate Activity Provide students with bean seeds and corn seeds that you have germinated. (Place the seeds between sheets of wet paper towels, and put the wet towels with seeds in a closed black garbage bag. Place the bag in a warm spot for 3–4 days. Check seeds at days 2 and 3.) Have students slice the germinating seeds longitudinally, or provide pre-cut germinating seeds. Ask students to view the seeds under stereomicroscopes, and identify the structures shown in Figure 1. Bio 10C, 13B Seeds Sprout Objectives A seed contains a plant embryo that is in a state of suspended animation. Some embryos can remain in suspended animation inside a 13B TAKS 3 seed for thousands of years. Seeds sprout with a burst of growth in Contrast annuals, biennials, 10C 13A 13B response to certain changes in the environment. These changes, and perennials. TAKS 3 such as rising temperature and increasing soil moisture, usually sigExplain how primary and nal the start of favorable growing conditions. secondary growth are Many seeds must be exposed to cold or to light before they can produced. 10C 13A 13B TAKS 3 sprout. The seed coats of other seeds must be damaged before they Describe several traits of can sprout. Exposure to fire, passing through the digestive system of bread wheat. 10C 13A 13B an animal, and falling on rocks are several natural ways that seed TAKS 3 Contrast development in coats are damaged. A seed cannot sprout until water and oxygen 5A plants and animals. penetrate the seed coat. When water enters a seed, the tissues in the seed swell, and the seed coat breaks. If enough water and oxygen are Key Terms available after the seed coat breaks, the young plant, or seedling, begins to grow. germination ● Compare seed germination 10C 13A in beans and corn. ● ● ● ● perennial annual biennial primary growth secondary growth apical meristem cork cambium vascular cambium annual ring Germination A plant embryo resumes its growth in a process called germination. The first sign of germination is the emergence of the embryo’s root. What happens next varies somewhat from one type of plant to another, 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 shoot from injury as it grows through the soil. Figure 1 Seed germination Beans and corn show two characteristic patterns of seed germination. 1. The hooked shoot of a germinating bean seed straightens after the cotyledons emerge from the soil. Bean (dicot) Leaves 572 Corn (monocot) First leaf Embryonic shoot Hook Young shoot Cotyledons Embryonic root Seed coat Cotyledon Embryonic root Young shoot 572 Chapter Resource File pp. 572–573 Student Edition TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 13A TEKS Bio 5A, 7B, 10C, 13A, 13B Teacher Edition TAKS Obj 1 Bio/IPC 2A, 2C TAKS Obj 3 Bio 13A TEKS Bio 10C, 13A, 13B 2. The shoot of a germinating corn seed is covered by a sheath. The shoot grows straight up, but the cotyledon stays underground. • Lesson Plan GENERAL • Directed Reading • Active Reading GENERAL • Data Sheet for Skills Practice Lab GENERAL Transparencies TT Seed Germination TT Bellringer Chapter 26 • Plant Growth and Development Planner CD-ROM • Reading Organizers • Reading Strategies • Portfolio Project Plant Focus Worksheet GENERAL Sheath The young shoots of other plants, such as corn, have a protective sheath around their shoots. In some plants, such as beans and marigolds, the cotyledons emerge from the soil and unfold aboveground. In other plants, such as corn and peas, the cotyledons remain underground. After the shoot of a seedling emerges, its roots and shoots continue to grow throughout its life. www.scilinks.org Topic: Texas Perennials Keyword: HXX4020 READING SKILL BUILDER Plant Life Spans Interactive Reading Assign Chapter 26 of the Holt Biology Guided Audio CD Program to help students achieve greater success in reading the chapter. As you have read in a previous chapter, bristlecone pines are the oldest known trees. They are estimated to be about 5,000 years old. In contrast, some plants live for only a few weeks. Depending on how long 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 are perennials. A perennial is a plant that lives for several years. Most perennials reproduce many times during their life span. Others, like the herbaceous perennial shown in Figure 2, reproduce only once before they die. Chrysanthemums, daffodils, and irises are familiar herbaceous perennials. These plants store nutrients for the next season’s growth in fleshy roots or underground stems. The aboveground shoots of herbaceous perennials often die after each season of growth. Trees, shrubs, and many vines are woody perennials. Some woody perennials drop their leaves each year. Plants that drop all of their leaves each year, such as elms, maples, and grapevines, are known as deciduous (dee SIHJ oo uhs) plants. Those that drop a few leaves at a time throughout the year, such as firs, pines, and junipers, are called evergreens. SKILL Figure 2 A herbaceous perennial. Century plants live for many years but reproduce only once. Like the dried-up plant on the left, this flowering century plant will die when its seeds are mature. Annuals Sunflowers, beans, corn, and many weeds are annuals. An annual is a plant that completes its life cycle (grows, flowers, and produces fruits and seeds) and then dies within one growing season. Virtually all annuals are herbaceous plants. Most annuals grow rapidly when conditions are favorable. Individual plants can become quite large if they get enough water and nutrients. two growing seasons to complete its life cycle. During the first growing season, biennials produce roots and shoots. The shoots consist of a short stem and a rosette (circular cluster) of leaves. The roots store nutrients. In the second growing season, a biennial plant uses the stored nutrients to produce a flowering stalk. The plant dies after flowering and producing fruits and seeds. 573 CONNECTION Take students on a walk around the school grounds or a park, and have them keep a log of the plants they see, using general terms such as flower, tree, grass, or shrub. Have students write a paragraph that answers the following questions based on what they observe. What types of plants did you see? Did you see more of one type of plant than another? If so, what might account for the difference? (More annuals tend to be present in spring and summer; only woody perennials may be present in winter.) BUILDER did you know? Plant Collections The Royal Botanic Gardens, Kew, located about 10 km southwest of London, England, is recognized as a global center of excellence in the study of plant diversity. The world’s largest documented living and preserved plant collections are located there. GENERAL Interpreting Visuals Bring students’ attention to Figure 1. Have students compare the structures of the germinating corn seed and bean seed. Ask students how monocot and dicot seedlings differ in the way they emerge from the soil. (Dicot seedlings have a stem that hooks as it emerges to protect the delicate tip, whereas monocots grow straight out of the soil. Monocot seedlings have a protective sheath that guards the tip.) Ask students what other differences they notice. (The cotyledon and seed coat of the corn seed remain underground, while the cotyledons of the bean emerge from English Language Learners the soil.) Bio 13B Group Activity Biennials Carrots, parsley, and onions are biennials. A biennial is a flowering plant that takes REAL WORLD Teach GENERAL Design a Flower Bed Have students work in groups of four to design a flower garden that will provide color in every season (or in three seasons, if you live in an area with a harsh winter climate). Let students use nursery catalogs to find examples of annuals, biennials, and perennials, as well as to determine where each plant will grow and when it will bloom. Assign each group a set of conditions under which its garden must grow (e.g., size, distribution of sun and shade, soil type). Finally, tell them to consider aesthetic factors (e.g., color combinations, taller plants in back, shorter plants in front). Have each student design a graphic that shows the group’s garden from the top during one of the seasons and identifies their plants. LS Visual TAKS 1 Bio/IPC 2A TAKS 3 Bio 13A; Bio 13B LS Interpersonal TAKS 1 Bio/IPC 2C, Bio 13B Chapter 26 • Plant Growth and Development 573 Meristems Teach, continued continued Activity GENERAL Apical Meristems Let students observe prepared slides of the apical meristems of the shoots and roots of several plants. Have them draw what they see and label the parts identified in Figure 3. Have students write a brief paragraph describing how the cells in the apical meristems differ from those in the surrounding tissues. (The cells of the apical meristems are small and unspecialized. The surrounding cells tend to be larger and longer and have thicker walls, and some have specialized structures such as chloroplasts or root hairs.) LS Visual Compare and Contrast To compare and contrast primary growth and secondary growth, make a two-column list. In one column write the ways in which the two are alike. In the other column, write the ways in which they are different. www.scilinks.org Topic: Primary Growth in Plants Keyword: HX4148 Bio 5A Teaching Tip GENERAL Removal of the Apical Meristem Ask students what they think would happen if the apical meristem of a stem or root were removed. (Removing or damaging the apical meristems of a plant would stop or limit the vertical growth of the stem or root.) This frequently occurs in nature, as tips of stems are broken off by wind or animals, killed by disease, or eaten by insects or other animals. Lateral buds often begin to grow after the apical meristem is removed. If the plant is a tree, one of these lateral buds will take over as the main trunk, and the tree will take on its normal form again in a few years. If the plant is a shrub or an herbaceous plant, the growth of many lateral buds will make the plant bushier, and it will not grow as tall. TAKS 3 Bio 13A; Bio 5A Transparencies TT Apical Meristems Primary Growth Apical (AP ih kuhl) meristems, which are located at the tips of stems and roots, produce primary growth through cell division. As shown in Figure 3, apical meristems are regions of small, undifferentiated cells. To better understand how primary growth occurs in most plants, 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 apical meristems 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 longer without becoming wider. To learn about primary growth in a monocot, look at Up Close: Bread Wheat later in this section. The tissues that result from primary growth are called primary tissues. The new cells produced by apical meristems differentiate into the primary dermal, ground, and vascular tissues of roots, stems, and leaves. Some of the cells produced by the root apical meristem also become part of the root cap. These cells replace cells that are worn away as the root pushes through the soil. Figure 3 Apical meristems Both shoot tips and root tips contain apical meristems, where cell division occurs. Root tip of a radish plant Shoot tip of a coleus plant Apical meristems 574 MEDICINE CONNECTION Flowering plants and ferns are the original sources 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. pp. 574–575 Student Edition TAKS Obj 3 Bio 7B TEKS Bio 7B Teacher Edition TAKS Obj 3 Bio 13A TEKS Bio 5A, 5B, 5C, 13A 574 Plants grow by producing new cells in regions of active cell division called meristems. Almost all plants grow in length by adding new cells at the tips of their stems and roots. Growth that increases the length or height of a plant is called primary growth. Many plants also become wider as they grow taller. Growth that increases the width of stems and roots is called secondary growth. After new cells are formed by cell division, they grow and undergo differentiation. Recall from your reading that differentiation is the process by which cells become specialized in form and function. Chapter 26 • Plant Growth and Development Cultural Awareness The Asian Art of Bonsai Bonsai is the cultivation of miniature specimens of plants that would normally be much larger. The effect is obtained by frequent, selective pruning of both the shoot and the roots. Bonsai plants are typically grown in small containers. The word bonsai comes from the Japanese characters bon, meaning “tray,” and sai, meaning “plant.” The Chinese practiced bonsai in approximately the third century B.C., but it was the Japanese Buddhist monks who perfected the art. Secondary Growth Secondary growth occurs in parts of many herbaceous plants, such as 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 and roots. One meristem, called the cork cambium (KAM bee uhm), lies within the bark and produces cork cells. The other meristem, called the vascular cambium, lies just under the bark and produces vascular tissues. The tissues that result from secondary growth are called secondary tissues. Figure 4 shows how woody stems develop. Step Demonstration A young woody stem has a ring of vascular bundles between the cortex and the pith. Each vascular bundle contains primary xylem and primary phloem. Vascular cambium develops between the primary xylem and the primary phloem in each vascular bundle. Secondary phloem is produced toward the outside of the stem. Secondary xylem is produced toward the inside of the stem. The cork cambium forms when the epidermis is stretched and broken as the stem grows in diameter. Step Step Eventually, the vascular bundles merge into solid cylinders. No cortex or primary phloem remains. The cork, cork cambium, and secondary phloem make up the bark. The vascular 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 rings are called annual rings. www.scilinks.org Topic: Secondary Growth in Plants Keyword: HX4160 Figure 4 IO B graphic 1 Development of a Woody Stem Bio 5A, 5B, 5C The wood in a woody stem results from secondary growth. Initially, the stem is covered by epidermis and contains cortex, pith, and a ring of vascular bundles with primary xylem and phloem. 2 A vascular cambium forms between the xylem and phloem in each vascular bundle. Cork cambium forms under the epidermis. 3 Teaching Tip In a mature stem, the vascular cambium adds new layers of secondary xylem and phloem each year. Bark Primary phloem Primary xylem Epidermis Pith Cork cambium Cork Secondary phloem Cork cambium Primary phloem Vascular cambium GENERAL Provide students with prepared slides of a cross section of a woody stem. Have them examine the slides under a compound microscope. Point out that vascular cambium is only one layer of cells. It is found just under the bark of a woody stem and can be located in microscope slides of woody stem cross sections by finding the phloem cells and the large, thickened xylem cells. Also point out that both xylem and phloem develop from the vascular cambium cells, so they develop in rows on either side of this “meristematic” tissue. Have students locate the layer between the two types of cells in a woody stem cross section. This is the row of vascular cambium cells. Have students describe how xylem and phloem originate from vascular cambium. (Xylem and phloem originate through cell division and cell differentiation.) LS Visual Secondary phloem Cork GENERAL Summarizing Plant Growth Have students prepare a sequential diagram that summarizes how herbaceous plants grow by primary growth and how woody plants grow by both primary and secondary growth. An example of a completed diagram appears in the Graphic Organizer on this page. LS Visual Bio 5A, 5B Pith Primary xylem Cortex Vascular bundle Secondary Vascular xylem cambium Transparencies 575 TT Development of a Wood Stem Graphic Organizer Use this graphic organizer with Teaching Tip on this page. Apical meristem Primary tissues Cell division and differentiation Herbaceous plant Differentiation Cork and vascular cambia Secondary tissues Woody plant Chapter 26 • Plant Growth and Development 575 Up Close Up Close Bread Wheat Bread Wheat TAKS 3 Bio 13A; Bio 5A, Scientific name: Triticum aestivum 5B, 5C, 10C, 13B 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 temperate regions of the world. The grains of Triticum aestivum are usually ground into flour that is used to make bread. External Structures ▼ 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 Leaf veins. The leaves are attached blade to the stem by a sheath, which wraps around Leaf sheath the stem. ▼ Teaching Strategies • Show students specimens of living or preserved wheat plants. • Let students dissect grains, or kernels, of wheat and locate the endosperm, bran, and germ of the kernels. Explain that the endosperm serves as a food supply for the embryo when it begins to grow. White wheat flour contains only endosperm and whole wheat flour contains both endosperm and bran. • For interest, have students make bread so that they notice the elasticity of the dough, which is caused by gluten. pp. 576–577 Student Edition TAKS Obj 3 Bio 13A TEKS Bio 5A, 5B, 5C, 13A Teacher Edition TAKS Obj 3 Bio 13A TEKS Bio 5A, 5B, 5C, 10C, 13A, 13B TEKS Bio/IPC 3C 576 Floret Palea Anther Stigma Lemma ▼ Flower spike jointed stems called culms. Given plenty of space, mature plants may develop as many as 100 culms. Each culm in a plant may have from three to six leaves. ▼ Bio/IPC 3C Awn Stems Wheat plants have hollow, Activity The Debate about Food Irradiation Food irradiation is the process of exposing food to radiation—the energy emitted by the unstable nuclei of certain atoms in the form of waves or rays. As it travels through the food, radiation kills organisms such as bacteria and insects. Have students research the history of and the current debate over food irradiation in preparation for a class debate. (Pro: Food irradiation makes the food supply safer, provides a better quality of food, and extends the shelf life of food. Con: irradiation induces chemical changes in food, which may affect the color, odor, and texture of food and lower the nutritional value of food.) TAKS 3 Flowers The flowers, which occur in dense clusters called spikes, develop at the top of each 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 leaves called the palea and the lemma enclose the stamens and pistil of each tiny flower, or floret. The lemmas of some bread-wheat varieties have a long bristle called an awn. Culms Adventitious roots ▼ 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. Fruit A kernel, or grain, of wheat is a one-seeded fruit with a crease on one side and a brush of tiny hairs at one end. The grains are high in gluten, a sticky mixture of proteins that make dough elastic. 576 Wheat Varieties Students may be surprised to learn that more than 200 varieties of wheat are grown in the United States. Hard red wheats, the varieties grown for making bread flour, belong to the species Triticum aestivum. Durum wheats, or macaroni wheats, which are grown for making pasta because they contain less gluten, belong to the species Triticum Chapter 26 • Plant Growth and Development dicoccum. Wheat may be planted in either the fall or the spring. The term winter wheat refers to a crop that is planted in the fall, overwinters as seedlings, and is harvested in late spring or summer. The term spring wheat refers to a crop that is planted in the spring for harvest in the fall. Internal Structures Nucleus Fruit structure A wheat kernel is about 85 percent starchy endosperm. The kernel’s outer layers, called the bran, make up about 12 percent of the kernel. The bran consists of the ovary wall, seed coat, and aleurone layer, which contains protein and oils. The embryo, or wheat germ, makes up less than 3 percent of the kernel. Bread Wheat Bread-wheat karyotype Bread-wheat cell Bran Chromosomes Bread-wheat cells Endosperm Embryo (wheat germ) Kernel (longitudinal section) ▼ Apical meristem have 42 chromosomes. A karyotype reveals that a bread-wheat cell has three sets of 14 chromosomes (7 pairs), shown here in different colors. Thus, bread wheat is not diploid (2n). Instead, it is hexaploid (6n)—a polyploid with six of each kind of chromosome. Polyploidy, having many sets of chromosomes, is common among cultivated plants. Among plants, polyploidy enables hybrids to result from crosses among different species. Such is the case with bread wheat, which is a natural hybrid of three closely related species of wheat. Apical meristems The apical meristems are located within the culms at a point that is usually at or just beneath the surface of the soil. Thus, the apical meristems are protected from being eaten by grazing animals. Each new leaf grows up within a hollow culm and emerges from the sheath of the culm’s uppermost leaf. Up Close Leaf sheath (oldest leaf) Leaf sheath (younger leaf) New leaf Discussion • The chemical 2, 4-D is used to kill dicots. Will it kill wheat plants? Why or why not? (No, wheat is a monocot as it has the typical characteristics of monocots such as parallel leaf veins, fibrous roots, and seeds with a single cotyledon.) • How did our ancestors help produce the bread wheat varieties that exist today? (From wild hybrids, they selected plants with desirable characteristics such as higher yields, larger seeds, and more gluten.) • How would a human karyotype differ from the wheat karyotype? (A human karyotype normally has 23 pairs of chromosomes, while a wheat karyotype has seven sets of six similar chromosomes, in which there are three homologous pairs.) • Is polyploidy beneficial to all living organisms? Why or why not? (No, polyploidy may be beneficial in plants because it causes plants to be larger, have showier flowers, and be more vigorous. In most animals, including humans, polyploidy is usually detrimental.) LS Interpersonal READING 577 Trends in Agriculture Municipal Sewage In recent years, a great deal of research has been conducted to investigate the use of municipal sewage as a fertilizer. Such wastes must receive treatments that remove or kill organisms that might pose a health hazard to humans. One serious concern about these materials is the tendency they have to contain excesses of heavy metals such as lead and cadmium, especially if certain types of industries contribute to the waste. These metals can be harmful to humans even at low levels. Municipal wastes are not recommended for use in the fertilization of food crops for this reason. LS Intrapersonal SKILL BUILDER Paired Summarizing Pair students. Have one student read silently about the external structures of bread wheat and the other about the internal structures. Then have one student summarize his or her section aloud without referring to the text. The partner should listen without interrupting and be prepared to point out any inaccuracies or omissions in the summary. At this point students can refer to the text. Have students switch roles. Co-op Learning Bio 5A, 5B, 5C Chapter 26 • Plant Growth and Development 577 Plant Development Plant Tissue Culture Genes guide the development of both plants and animals, but their patterns of development are very different. As an animal develops, sets of genes that control development are inactivated and may not be used again. Most animals stop developing when they become adults. Plants, in contrast, continuously make new cells in meristems. 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. Such cells can divide and form masses of undifferentiated cells. In a sense, they can reverse their development. These cells can undergo differentiation and develop into a mature plant. A technique called tissue culture is used to grow new plants from tissue that can reverse its development. A tissue culture is prepared by placing tissue on a sterile nutrient medium. Masses of undifferentiated cells that form grow into plants that are genetically identical to the parent plant. www.scilinks.org Topic: Plant Life Spans Keyword: HX4141 TAKS 2 Bio 4B Teaching Strategies Point out that tissue culture requires sterile conditions and new plants are grown in controlled environmental conditions. Discussion What enables cells from part of a plant to grow into a whole plant? (Undifferentiated plant cells can differentiate into several different types of cells.) Plant Tissue Culture TAKS 2 Magnification: 810⫻ T Close Reteaching Have students work in cooperative groups to summarize the growth of a plant, from a seed to a mature adult. Co-op Learning Quiz GENERAL 1. When you buy seeds in a packet, why have they not germinated? (Water and oxygen must penetrate the seed coat for the seed to sprout.) 2. When you plant perennials, what would you expect to happen after one season of growth? (The plant would live for more than two years.) Alternative Assessment Protoplast Fusion Protoplast fusion has been used to produce hybrid petunias, potatoes, and carrots. A protoplast is a plant cell that has had its cell walls removed by enzymes. Certain chemicals or an electrical shock can cause two protoplasts to fuse, as the photo at right shows. If the protoplasts came from genetically different plants, a hybrid cell results. The hybrid is then placed in a tissue culture and grown into an adult plant. Genetic Engineering Tissue culture is also an essential part of producing genetically engineered plants. First, foreign genes are inserted into a plant’s cells. The genetically altered cells are then grown into adult plants in tissue culture. GENERAL pp. 578–579 Student Edition TAKS Obj 2 Bio 4B TEKS Bio 4B, 5A, 10C, 11A, 11B, 13A, 13B Teacher Edition TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 13A TAKS Obj 4 IPC 7D, 7E TEKS Bio 4B, 5A, 13A, 13B TEKS IPC 7D, 7E www.scilinks.org Topic: Genetic Engineering Keyword: HX4092 Section 1 Review Compare and contrast the germination of bean seeds and corn seeds. 10C 13A 13B Summarize the basic differences between 10C 13B annuals, biennials, and perennials. Provide students with prepared microscope slides of plant tissues, and ask them to identify meristematic and vascular tissues by drawing what they see. LS Visual Bio 5A 578 issue culture is used to propagate orchids, houseplants, and fruit plants. Thousands of cultures can be made from a single plant. Tissue culture can also be used to produce plants with new characteristics. Explain how primary growth and then secondary 13A 13B growth produce a woody stem. Critical Thinking Analyzing Methods In what ways does plant development differ from 5A animal development? TAKS Test Prep Growth that increases the width of a plant’s stems and roots is called 13B A germination. C primary growth. B differentiation. D secondary growth. 578 Answers to Section Review 1. Corn seedlings grow straight up, and the cotyledon stays in the soil. Bean seedlings form a hook as they grow, and the two cotyledons emerge. TAKS 3 Bio 13A; Bio 10C, 13B 2. Annuals live for one growing season, reproduce once, and then die. Biennials live for two growing seasons, reproduce once during the second season, and then die. Perennials live for more than two years and may reproduce many times. Bio 10C; Bio 13B 3. Primary growth lengthens the stem and forms new primary dermal, ground, and vascular tissues. Secondary growth increases the stem’s Chapter 26 • Plant Growth and Development diameter by producing layers of cork and secondary xylem and phloem. TAKS 3 Bio 13A; Bio 13B 4. Plant development is continuous and “reversible,” while animal development is not. Bio 5A 5. A. Incorrect. Germination is the growth of a plant embryo. B. Incorrect. Differentiation is the process by which cells become specialized in form and function. C. Incorrect. Primary growth increases the length or height of a plant. D. Correct. Secondary growth increases the width of stems and roots. Bio 13B Regulating Growth and Development Section 2 Section 2 Focus Overview Nutrients Objectives Like all multicellular organisms, plants grow by adding new cells through cell division. Plants must have a steady supply of the raw materials they use to build new cells in order to grow. Plants need only two raw materials—carbon dioxide and water—to make all the carbohydrates in their tissues. As you learned earlier in this book, carbon dioxide 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 photosynthesis, most of the oxygen used by leaves and stems comes from the air. Roots, which usually do not carry out photosynthesis, get oxygen from the air spaces between soil particles. If the soil around a plant’s roots becomes compacted or saturated with water, it may not provide enough oxygen for the roots, and the plant could die. However, carbon dioxide, water, and oxygen do not satisfy all of a plant’s needs for raw materials. Plants also require small amounts of at least 14 mineral nutrients, which are elements absorbed mainly as inorganic ions. Table 1 lists the six mineral nutrients needed in the greatest amounts for healthy plant growth and describes the importance of each nutrient. Commercial fertilizers may contain most of these mineral nutrients. ● Identify the major nutrients plants need to grow. 10C 13B ● Describe how plant hormones control plant growth. 10C 11B 13B ● Relate environmental factors to plant growth. 11A 11B Bellringer Key Terms Ask students to identify the substances plants need for survival. After taking attendance, write their responses on the board. (Initially, they will probably identify light, water, and carbon dioxide.) Prompt them to identify other needs by asking why people fertilize their yards. Ask students how they think plants might regulate their growth and development without having a nervous system as animals do. (They produce hormones.) mineral nutrient auxin hormone apical dominance tropism photoperiodism dormancy Table 1 Major Mineral Nutrients Required by Plants Nutrient Importance LS Interpersonal TAKS 2 Bio 4B Nitrogen Part of proteins, nucleic acids, chlorophylls, ATP, and coenzymes; promotes growth of green parts Phosphorus Part of ATP, ADP, nucleic acids, phospholipids of cell membranes, and some coenzymes Potassium Needed for active transport, enzyme activation, osmotic balance, and stomatal opening Calcium Part of cell walls; needed for enzyme activity and membrane function Magnesium Part of chlorophyll; needed for photosynthesis and activation of enzymes Sulfur Part of some proteins and coenzyme A; needed for cellular respiration Motivate Discussion/ Question 579 IPC Benchmark Fact Have students find the six mineral nutrients listed in Table 1 on the periodic table. Ask them to compare and contrast the properties of these elements based on their location in the periodic table. Which elements are most alike and most different? Identify whether each mineral nutrient naturally occurs as an element, compound, or both. TAKS 4 IPC 7D (grade 11 only), 7E (grade 10 only) Before beginning this section review with your students the objectives listed in the Student Edition. This section focuses on factors that influence plant growth and development, including nutrients, hormones, and environmental influences such as sunlight, temperature, and the seasons. Chapter Resource File • Chapter Resource File • Lesson Plan GENERAL • Directed Reading • Active Reading GENERAL • Data Sheet for Quick Lab GENERAL • Data Sheet for Data Lab GENERAL • Data Sheet for Math Lab GENERAL Ask students what growth factors soil provides plants, and whether plants can grow without soil. (Usually, soil provides minerals that plants need for growth. Using a practice known as hydroponics, plants are grown with their roots immersed in water through which oxygen is bubbled and to which the minerals needed for plant growth are added.) Consider the possibility of developing a small hydroponic garden in the classroom. LS Verbal TAKS 2 Bio 4B Planner CD-ROM • Reading Organizers • Reading Strategies • Supplemental Reading Guide A Feeling for the Organism The Life and Work of Barbara McClintock Chapter 26 • Plant Growth and Development 579 Hormonal Control of Growth For centuries, people have known that plants bend strongly toward a light source as their shoots elongate. In the 1920s, the Dutch biologist Frits Went showed that a chemical produced in the shoot tip causes this bending response. Went named the growth-promoting chemical that causes stems to bend auxin (AWK sin). The steps in Went’s experiment are summarized in Figure 5. Real Life Teach Real Life Answer Bio 11C The chemicals found in Agent Orange are 2,4-D (2,4-dichlorophenoxyacetic acid), 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), and trace amounts of dioxin. Exposure to Agent Orange has been blamed for miscarriages, skin diseases, cancers, and birth defects. The herbicide Agent Orange contains two synthetic auxins. This herbicide was used to defoliate plants in the jungles of Vietnam during the Vietnam War. One ingredient of Agent Orange is still commonly used as a herbicide. Finding Information Find out the names of the chemicals in Agent Orange, and identify the health problems to which 11C it has been linked. Step Went removed the tip of an oat shoot and placed the tip on an agar block. Auxin diffused from the tip into the block. Step Went then transferred the agar block to the cut end of a shoot, which caused the shoot to grow. Step When Went placed an agar block with auxin on either side of cut shoots, the shoots grew in the opposite direction. Step As a control, Went placed an agar block without auxin on the cut end of other shoots. These shoots did not grow. Auxin Auxin is one of many plant hormones. The word hormone comes from the Greek word horman, meaning “to set in motion.” A hormone is a chemical that is produced in one part of an organism and transported to another part, where it causes a response. Auxin causes plant cell walls to become more flexible, which allows the cells READING SKILL BUILDER Reading Hint Tell students that this textbook uses typographic aids, such as boldfaced words and in-text pronunciation guides, to help them learn new terms. Tell students that before they read a section of the book, to find the boldfaced terms and determine their meanings by reading the sentence in which each term appears. Figure 5 IO B graphic 1 Using the Figure The Steps in Went’s Experiment Auxin causes oat seedlings to elongate and bend toward light. Auxin diffused from the cut tip of an oat shoot into an agar block. 2 Application of the agar block with the auxin to a second shoot resulted in growth. 3 Cut shoots grew away from contact with agar with auxin. 4 Agar without auxin did not cause a cut oat shoot to grow. Shoot tip Walk students through Figure 5, which summarizes the steps of Fritz Went’s classic experiment on the effects of auxin. Help students to understand that when the agar is purple, it contains auxin. Ask students to state the significance of step 4. (It is a control designed to show that agar is not the cause of the effect.) Bio 3F Agar block Agar block with auxin Auxin 580 did you know? pp. 580–581 Student Edition TAKS Obj 1 Bio/IPC 2B, 2C TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 13A TEKS Bio 4B, 10C, 11C, 13A, 13B TEKS Bio/IPC 2B, 2C Teacher Edition TAKS Obj 1 1 Bio/IPC 2B, 2C TAKS Obj 1 IPC 3A, 3B TAKS Obj 4 IPC 8A TEKS Bio 3F, 11B, 11C, 13B TEKS Bio/IPC 2B, 2C TEKS IPC 3A, 3B, 8A 580 Darwin’s Plant Research Charles Darwin did many experiments with plants. In the mid-1800s, Darwin and his son Francis did the earliest experiments on phototropism. They discovered that a grass seedling responds to light coming from one direction with growth on the opposite (shaded) side, resulting in the seedling bending toward the light source. Bio 3F, 11B Chapter 26 • Plant Growth and Development IPC Benchmark Fact Have students review Went’s experiment on the hormone auxin. Ask them to determine if his experimental results demonstrate a physical or chemical change in the plant. Have them defend their answers. In addition, instruct students to analyze and critique Went’s experiment as to its strengths and weaknesses using the information provided. TAKS 1 IPC 3A TAKS 4 IPC 8A to elongate as they grow. Auxin accumulates on the dark side of a stem. As a result, the cells on the dark side of a stem elongate more than the cells on the light side. The difference in elongation causes the stem to grow toward the light. Auxin also inhibits the growth of the buds along a stem. This inhibition is called apical dominance. Cutting off the tip of a stem removes the source of auxin and enables the other buds to grow. That is why pruning the stems of a plant makes the plant become bushier. Investigating the Effects of Ethylene on a Plant TAKS 1 Bio 2B, 2C; Bio 13B Skills Acquired Observing, making comparisons, drawing conclusions Hormones in Agriculture More than a century ago, citrus farmers discovered that they could cause citrus fruits to ripen by storing them in a room heated by a kerosene stove. The ripening was caused by ethylene, which is a gaseous organic compound produced when kerosene is incompletely burned. Most plant tissues produce ethylene. Today, ethylene is used to promote the ripening of tomatoes, bananas, and other fruits that are harvested before they ripen. Ethylene also loosens the fruit of cherries, blackberries, and blueberries, making it easier to harvest these crops mechanically. Gibberellins (jihb uhr EHL ihnz) are produced in developing shoots and seeds. They stimulate stem elongation, fruit development, and seed germination. Gibberellins are used to enlarge Thompson seedless grapes. Other seedless fruits treated with gibberellins include 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 on fruits and vegetables to extend their shelf life. Cytokinins are added to tissue-culture media to cause undifferentiated cells to form shoots. Investigating the Effects of Ethylene on a Plant Teacher’s Notes Tell students that ethylene affects plants in many ways. For example, when some plants are exposed to ethylene gas, they do not elongate normally. Ethylene also promotes the production of male flowers in plants such as squash and cucumbers. Ethylene is used by citrus-fruit growers to ripen fruits that are picked while they are still green. www.scilinks.org Topic: Plant Hormones Keyword: HX4140 Answers to Analysis 1. Answers will vary. Plants in jars containing an apple should begin to lose their leaves after a few days. 2. Answers will vary. From the results of this experiment, students should conclude that ethylene promotes plant aging and leaf drop. 2B 2C 13B TAKS 1 You can use a ripe apple to see one of the effects of ethylene on plants. Materials 4 L glass jars with lids (2), 2 plants in 5 cm pots, small ripe apple IPC Benchmark Mini-Lesson Procedure 1. Place a plant inside one of the jars. Tightly secure the lid. 3. Observe both jars for several days. Record what you see. 2. Place the other plant and the apple inside the other jar. Tightly secure the lid. Analysis 1. Describe any changes in the plant in each jar. 2. Critical Thinking Drawing Conclusions A ripe apple gives off ethylene gas. Based on your observations, how does ethylene affect a plant? 581 MISCONCEPTION ALERT Anthropomorphizing Plants It is common for students to attribute human characteristics to nonhuman organisms, such as plants and animals. Thus, students might think that a plant’s response to light, for example, is somehow conscious, or that plants bend toward the light because they see it. Emphasize that a plant’s response to light, gravity, or other environmental stimuli is simply a hormonal stimulus-response. Plants do not perceive environmental stimuli in the same way that humans and animals do. Bio 11B Rotten Apples The expression “One rotten apple spoils the whole barrel” is commonly used to refer to people whose unacceptable behavior may influence others to behave unacceptably. This expression comes from the observation by food growers and handlers that a rotten apple in a barrel of apples results in all the apples rotting. The explanation is that rotting fruit give off ethylene, which promotes the ripening of other nearby fruits. The rotting fruit is infected with a fungus, which easily infects other fruit after they ripen. Bio 11B IPC Skills TAKS 1 IPC 3B Draw inferences based on data related to promotional materials for products and services. Activity Bring in advertisements, packages or containers for products that claim they can cause muscle growth and increased strength. Have the students research the substances in the products to determine if the products are truly effective. Transparencies TT Major Mineral Nutrients Required by Plants TT Bread Wheat TT Went’s Experiment Chapter 26 • Plant Growth and Development 581 Environmental Influences on Growth Teach, continued continued READING SKILL BUILDER Reading Organizer Before students finish reading this section, have them make a list of the following terms: auxin, tropism, phototropism, gravitropism, and thigmotropism. As they learn about the terms, have them write a brief definition of each term. Have them save their list of terms and definitions for use later in the Reteaching exercise at the end of this section. LS Verbal Teaching Tip The word thigmotropism comes from the Greek words thigma, meaning “touch,” and tropos, meaning “turn.” Tropisms A tropism (TROH piz uhm) is a response in which a plant grows either toward or away from a stimulus. Auxin is responsible for producing tropisms. Figure 6 shows examples of three common types of tropisms. Phototropisms are responses to light. Responses to gravity are called gravitropisms. A thigmotropism is a response to touch. If a plant grows toward a stimulus, the response is called a positive tropism. If a plant grows away from the direction of the stimulus, the response is called a negative tropism. Thus, a shoot that grows up out of the ground shows both positive phototropism (growing toward the light) and negative gravitropism (growing away from the pull of gravity). GENERAL Tissue Culture Tell students that the growth of whole plants from pieces of plants in tissue culture requires the addition of plant hormones in order for them to differentiate properly. The relative amounts of the hormones affect the process of differentiation. Typically, auxins and cytokinins are first added to the culture medium to promote the formation of a mass of undifferentiated cells. Next a high level of auxins and a low level of cytokinins are added to the culture medium. This promotes root formation. Then a low level of auxins and a high level of cytokinins are added to the culture medium. This promotes shoot formation. Because most plants are anchored in one spot, they cannot move from an unfavorable environment to a more favorable one as animals do. Instead, plants respond to their environment by adjusting the rate and pattern of their growth. For example, a plant that receives plenty of water and mineral nutrients may grow much faster and larger than it would if it received very little water and mineral nutrients. Also, a plant grown in full sun may grow much faster and larger than it would if it were grown in the shade or indoors. So the availability of light and nutrients affect the rate of plant growth. Many of a plant’s responses to environmental stimuli, however, are triggered by the hormones that regulate plant growth. Figure 6 Tropisms Tropisms are growth responses that occur either toward or away from a stimulus. TAKS 2 Bio 4B; Bio 5B, 5C The bending of an amaryllis toward the light is a positive phototropism. The upward growth of shoots is a negative gravitropism; the downward growth of roots is a positive gravitropism. The coiling of grapevine tendrils around a wire is a thigmotropism. 582 Career pp. 582–583 Student Edition TAKS Obj 3 Bio 13A TEKS Bio 13A, 13B Teacher Edition TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 7B, 13A TEKS Bio 3D, 4B, 5B, 5C, 7B, 11B, 13A, 13B 582 Horticulturist Horticulturists study fruits, vegetables, and ornamental plants. These plant scientists are interested in producing better fruit, vegetable, and ornamental crops with less pesticides, fertilizers, and water. Have students work 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 research projects in horticulture, and have them report their findings to their classmates. Bio 3D Chapter 26 • Plant Growth and Development Trends in Plant Genetics Genetic Diversity The National Plant Germplasm System (NPGS) is a cooperative effort to preserve the genetic diversity of plants. When plants lose their genetic diversity, which happens when only a few varieties of a species are cultivated, these species can be wiped out easily by a single disease or environmental condition to which they are sensitive. However, when many varieties of a species are cultivated, some varieties will have genes that confer resistance to various pests and diseases, or allow the plant to survive certain adverse conditions. TAKS 3 Bio 7B, 13A 0100010110 011101010 0010010001001 1100100100010 0000101001001 1101010100100 0101010010010 Interpreting Annual Rings 13A 13B Background TAKS 3 The annual rings of a woody stem provide important clues to annual variations in the rainfall an area receives over time. Thick rings form in years with heavy rainfall. Relatively thin rings form in dry years. Use the photo at right to answer the following questions. TAKS 3 Bio 13A; 13B 0100010110 011101010 0010010001001 1100100100010 0000101001001 1101010100100 0101010010010 A B Analysis 1. Critical Thinking Interpreting Data What do the annual rings indicate about the climate where this plant grew? Interpreting Annual Rings 2. Critical Thinking Drawing Conclusions Which ring, A or B, indicates a year when this plant received more rainfall? 3. Critical Thinking Making Predictions How will the annual rings of a nearby tree of the same age and species compare with those of this tree? Photoperiodism Certain plants bloom in the spring and others bloom in the summer or fall. Some plants bloom as soon as they reach a mature size. In many plants, seasonal patterns of flowering and other aspects of growth and development are caused by changes in the length of Figure 7 Flowering and days and nights. The response of a plant to the length of days and photoperiodism. Long-day plants flower when nights are nights is called photoperiodism. short. Short-day plants flower Most plants can be categorized as one of three types in reference when nights are long. If a flash to photoperiodism. A plant that responds when days become shorter of light interrupts a long night, than a certain number of hours is said to be a short-day plant. A long-day plants flower and plant that responds when days become longer than a certain numshort-day plants do not. ber of hours is called a long-day Early summer Late fall Night interrupted plant. Plants whose growth and Midnight Midnight Midnight development are not affected by day 6 A.M. 6 A.M. 6 A.M. 6 P.M. 6 P.M. 6 P.M. length are known as day-neutral plants. It is really the length of the Noon Noon Noon nights, however, rather than the length of the days that controls photoperiodism, as Figure 7 shows. Long-day plant: Bearded iris Knowledge of photoperiodism is very important to the nursery and floral industries. The length of days and nights is controlled artificially in greenhouses where plants such as poinsettias and chrysanthemums are grown. Thus, commercial growers Short-day plant: Poinsettia force the plants to produce flowers at times of the year when they ordinarily would not. This makes it possible for poinsettias to be available for Christmas and chrysanthemums to be available year round. 583 MISCONCEPTION ALERT GENERAL Plant ”Food“ Fertilizers are often referred to as plant “food.” However, the term food is usually reserved for organic substances that provide a source of energy and organic molecules for living things when they are broken down. Because minerals do not contain usable energy and are not broken down in plants, they should not be referred to as food. Plants do not eat food; rather, they produce their own organic molecules during photosynthesis. Skills Acquired Making observations, analyzing data, making conclusions Teacher’s Notes Point out to students that it is the number of rings in a tree trunk that indicates its age, not the diameter of the trunk. A number of environmental factors can influence the width of an annual ring. Answers to Analysis 1. Answers will vary. The rings indicate that the tree grew in a temperate climate and that the amount of rainfall varied from year to year. 2. A 3. They should be very similar. Using the Figure GENERAL Walk students through Figure 7 by first following what happens to long-day (short-night) and shortday (long-night) plants when the days are long and the nights are short. Then follow what happens to long-day (short-night) and shortday (long-night) plants when the days are short and the nights are long. Finally, follow what happens to long-day (short-night) and shortday (long-night) plants when they are grown under long nights that are interrupted by a flash of light in the middle of the night. Tell students that poinsettias are short-day (long-night) plants that are desirable ornamentals for the Christmas holidays. Ask students if these plants would normally produce flowers in late December. (yes) Ask students what would happen if lights were turned on during the night in a greenhouse where poinsettias are grown? (The plants would not bloom.) Bio 11B Transparencies TT Flowering and Photoperiodism Chapter 26 • Plant Growth and Development 583 6C Responses to Temperature Temperature affects growth and development in many plants. For example, most tomato plants will not produce fruit if the nighttime temperatures are too high. Many plants that flower in early spring will not produce flowers until they have been exposed to cold temperatures for a certain number of hours. Most deciduous woody plants drop their leaves in the fall in response to shorter periods of daylight. Thick, protective scales develop around their buds, as Figure 8 shows. After a period of low temperatures, the buds begin growing into new leaves or sections of woody stem. Dormancy is the condition in which a plant or a seed remains inactive, even when conditions are suitable for growth. Many plants and seeds remain dormant until they have been exposed to low temperatures for several weeks. Dormancy helps plants to survive by keeping buds from growing and seeds from germinating during warm spells before winter has ended. Teach, continued continued 76 0 2 x 2+ 6x 5 -7-0 < 493 Analyzing the Effect of Cold on Seed Germination Bio 10C, 11B, 13B Figure 8 Bud dormancy. Thick scales cover the dormant buds on this twig from an apple tree. Skills Acquired Interpreting graphs, analyzing data 8 493 x 2+ 6x 0 2 5 -7-0 < Teacher’s Notes Seeds with true dormancy cannot germinate until the plant hormone abscisic acid is either washed away or broken down. Answers to Analysis 1. Cold temperatures promote the germination of apple seeds. 2. 45 days ⫼ 7 days/week ⫽ 6.43 weeks 3. 30 percent 4. 100 percent TAKS 9 TAKS 10 Background In some plants, a period of low temperatures is needed to break seed dormancy. The graph at right shows how being stored at a low temperature (4ºC) affected the ability of apple seeds to germinate. Use the graph to answer the following questions. Reteaching Have students list the boldfaced terms in this section with their definitions. Have them create a crossword puzzle using the definitions as clues and the terms as words in the puzzle. LS Logical GENERAL True or False: 1. Minerals and water satisfy all of a plant’s raw materials needs. (false) 2. Auxin is a type of plant hormone. (true) Effect of Cold Storage 100 80 60 40 20 0 10 20 30 40 50 60 70 Number of days at 4ºC Analysis 1. Summarize the overall effect of cold temperatures on the germination of apple seeds. Close Quiz Analyzing the Effect of Cold on Seed Germination 10C 11B 13B Percent germination 18 2. Calculate the number of weeks that apple seeds must be stored at 4ºC for at least 80 percent of the seeds to germinate. 3. Critical Thinking Interpreting Graphs What percentage of apple seeds germinate after storage at 4ºC for 20 days? 4. Critical Thinking Predicting Patterns What percentage of apple seeds will germinate after being stored at 4ºC for 80 days? Math TAKS Obj. 10, 8.14C; Obj 9, 8.3B Section 2 Review List the six mineral nutrients that plants require Critical Thinking Predicting Outcomes Why in the greatest amounts. is it an advantage for plant growth and development to be regulated by environmental stimuli? Explain how auxin causes a stem to grow toward a light source. 11B Describe an example of a negative gravitropism. 11B 11A TAKS Test Prep When a vine responds to the touch of a fence wire by growing a tendril around 11B the wire, the vine is exhibiting A gravitropism. C phototropism. B thigmotropism. D photoperiodism. 584 Alternative Assessment GENERAL Ask students to summarize the roles of the plant hormones discussed in this section. pp. 584–585 Student Edition TAKS Obj 3 Bio 13A Math TAKS Obj 9 Math 8.3B Math TAKS Obj 10 Math 8.14C TEKS Bio 10C, 11B, 13A, 13B Teacher Edition TEKS Bio 10C, 11A, 11B, 13B 584 Answers to Section Review 1. nitrogen, phosphorus, potassium, calcium, magnesium, sulfur 2. Auxin diffuses to the side of a stem away from a light source. There, it stimulates cells to grow longer than they do on the side of the stem facing the light source. This results in the stem bending toward the light source. Bio 11B 3. An example of a negative gravitropism is a shoot growing upward from the soil after a seed germinates. Bio 11B Chapter 26 • Plant Growth and Development 4. It is an advantage for plant growth to be regulated by environmental stimuli because plants are unable to move to a new environment when conditions become unfavorable. Bio 11A 5. A. Incorrect. Gravitropism is the response of a plant to gravity. B. Correct. Thigmotropism is the response of a plant to touch. C. Incorrect. Phototropism is the response of a plant to light. D. Incorrect. Photoperiodism is the response of a plant to the length of days and nights. Bio 11B Study CHAPTER HIGHLIGHTS ZONE Alternative Assessment Key Concepts Key Terms Organize students into groups. Have each group use the information in Chapter 26 to prepare a multimedia presentation on plant growth and development that they could give to a middle-school science class or to the general public. Section 1 1 How Plants Grow and Develop ● Germination is the resumption of growth by the embryo in a seed. Water and oxygen must penetrate the seed coat before germination 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 roots produce primary growth. The tissues that result from primary 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 cork cambium and vascular cambium, two meristems near the outside 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 form masses of undifferentiated cells, which can develop into a new plant. germination (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) Chapter Resource File • Science Skills Worksheet • Critical Thinking Worksheet • Test Prep Pretest GENERAL • Chapter Test GENERAL GENERAL Section 2 2 Regulating Plant Growth and Development ● Plants need at least 14 mineral nutrients for growth. They also need carbon dioxide and water for photosynthesis and oxygen for cellular respiration. ● Hormones regulate plant growth and development. Auxin is a hormone that causes shoots to elongate and inhibits the growth 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 unfavorable environmental conditions by becoming dormant. ● In many plants, seasonal patterns of flowering and other aspects of growth and development are caused by changes in the length of days and nights. mineral nutrient (579) auxin (580) hormone (580) apical dominance (581) tropism (582) photoperiodism (583) dormancy (584) 585 Answer to Concept Map The following is one of several possible answers to Performance Zone item 15. apical meristem which produces primary tissues Meristems include vascular cambium cork cambium which produces which produces secondary xylem secondary phloem by by in bark primary growth secondary growth which increases the which increases the length width of of stems cork roots stems roots Chapter 26 • Plant Growth and Development 585 Performance CHAPTER REVIEW ZONE CHAPTER 26 ANSWERS Using Key Terms Using Key Terms 1. The first sign of germination of a bean seed 1. a Bio 13B 2. c Bio 13B 3. c Bio 13B 4. d Bio 5A TAKS 3 Bio 13A 5. a. Germination is the term for the resumption of growth by the embryo in a seed. b. A perennial is a plant that lives for more than two years and may reproduce many times. c. Apical dominance is the inhibition of the growth of side buds that is caused by auxin produced in the tip of a shoot. d. Dormancy is the condition in which seeds or buds do not grow even when environmental conditions are favorable for growth to occur. Bio 11B 6. a Bio 5B, 10C 7. d 8. b 9. b Bio 10C, 11B 10. d Bio 11B, 13B 11. b TAKS 3, Bio 11A, 11B, 13A, 13B 12. Cytokinins stimulate cell division and slow aging. They are used in agriculture to prolong freshness of cut flowers, fruits, and vegetables and to stimulate shoot growth in tissue cultures. Gibberellins stimulate stem elongation, fruit development, and seed germination. They are used in agriculture to induce fruit formation without seeds and to enlarge seedless fruits. Bio 11B is the emergence of the embryo’s 13B a. root. c. sheathed shoot. b. hooked shoot. d. cotyledons. 2. Plants that live several years or more are known as 13B a. annuals. b. biennials. 10. Which of the following caused the growth patterns of the mums shown below? a. apical meristem b. auxin c. apical dominance d. all of the above c. perennials. d. terminals. 3. Providing cells for growth at the tips of a plant 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 of a woody stem occurs in the a. pith. b. primary tissues. c. apical meristems. d. vascular cambium. 5A 5. Write a sentence that shows your under- 11. The response of a plant to the length of standing of each of the following terms. a. germination b. perennial c. apical dominance d. dormancy 11B 6. Plant and animal development differ in that plant development 5B 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 raw material needed for plant growth? a. carbon dioxide b. water c. oxygen d. vitamins 8. Major mineral nutrients required by plants include all of the following except a. nitrogen. c. phosphorus. b. lead. d. potassium. days and nights is a. gravitropism. b. photoperiodism. c. phototropism. d. thigmotropism. 11A 11B 12. How do cytokinins and gibberellins affect plant growth, and how are these hormones 11B used in agriculture? 13. Up Close How does the chromosome number of bread wheat differ from that of 6A 6D diploid organisms? 14. How is tissue culture used to produce hybrid varieties of plants? 6D 15. Concept Mapping Construct a concept map that describes growth in vascular plants. Try to include the following terms in your map: meristems, apical meristem, primary growth, primary tissues, cork cambium, secondary growth, cork, secondary phloem, secondary xylem, and vascular cambium. 2C 586 10 only) 14. Hybrid cells, made from the fusion of two cells from two different types of plants, are grown into new, hybrid plants in tissue culture. TAKS 2 Bio 6D (grade 10 only) pp. 586–587 Review and Assess TAKS Obj 1 Bio/IPC 2B, 2C, 2D TAKS Obj 2 Bio 6A, 6D TAKS Obj 3 Bio 13A TEKS Bio 3D, 5A, 5B, 6A, 6B, 10C, 11A, 11B, 13A, 13B 11B 13B 13. Wheat cells have six of each kind of chromosome rather than two of each kind as in diploid organisms. TAKS 2 Bio 6A, 6D (grade 586 9. Auxin causes cells to 11B a. have less flexible cell walls. b. elongate more as they grow. c. bend toward light. d. develop lateral buds. 15. One possible answer to the concept map is found at the bottom of the Study Zone page. TAKS 1 Bio/IPC 2C Chapter 26 • Plant Growth and Development Assignment Guide Section 1 2 Questions 1–5b, 13–16, 18, 19, 21 5c–d, 6–12, 17, 20 Critical Thinking Alternative Assessment Critical Thinking 16. Analyzing Methods Some seeds are soaked 20. Finding and Communicating Information 16. Answers will vary. Students should realize that acid would probably damage the seed coat. Water can then penetrate the seed, and the seed will sprout. Seeds treated with acid germinate more quickly and more uniformly than do untreated seeds. 17. The energy for a carrot plant’s second year of growth comes from compounds that are stored in the root. Bio 13B 18. The cells in these plant parts are able to reverse their development. These cells can produce cells that are undifferentiated, which can then undergo differentiation to form all of the tissues necessary to grow an entire new plant. in acid before they are packaged and sold to farmers and home gardeners. What is the purpose of this treatment? 17. Applying Information Carrots are biennials. What role does the root of a carrot plant play in the plant’s second year of growth? 13B 18. Forming Reasoned Opinions Why is it possible for people to grow new plants from pieces of leaf, stem, or root tissue in which the cells have already undergone differentiation? 5A 19. Evaluating Results A student placed a green banana in each of 10 plastic bags. The student also placed a ripe pear in five of the bags and then sealed all of the bags. The bananas in the bags without pears took longer to ripen than the bananas in the bags with pears. Evaluate these experimental results. 2C Use the media center or Internet resources to learn how commercial growers produce plants such as poinsettias and chrysanthemums that flower at times when they would not flower in nature. Summarize your findings in a written report. 2B 2D 21. Organizing Information Research bonsai— the Asian art of growing miniature plants. Relate your findings in a report that explains plant growth and development in bonsai. 22. Career Connection Agronomist Agrono- mists study soil management and crop production. Write a report that includes a job description, training required, kinds of employers, growth prospects, and starting salary. 3D Bio 5A TAKS Test Prep The diagram below summarizes an experiment investigating the hormonal control of growth in an oat shoot. Use the diagram and your knowledge of science to answer questions 1–3. Shoot tip 1 Agar block Agar block with auxin 2 3 Auxin Oat shoot 13B 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 opposite direction. H The agar block shielded one side of the shoot from light, causing the shoot to grow in the opposite direction. J Auxin from the agar block caused the shoot to exhibit positive gravitropism. 3. What would likely happen if an agar block 1. What happened in step 2? 13B 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. 1. A. Correct. Auxin is a growth-promoting chemical. It diffused from the agar block into the shoot, causing it to grow. B. Incorrect. Agar does not stimulate plants to produce auxin. C. Incorrect. Agar does not stop the growth. D. Incorrect. Agar does not stimulate shoots. Bio 13B 2. F. Incorrect. If the weight of the agar block were to cause the shoot to bend, it would bend in the direction of the block, where the weight is applied. G. Correct. The auxin diffused from the agar block into the side of the shoot. Growth on this side of the shoot resulted in without auxin were placed on the cut end of an oat shoot? 13B 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. Test Carefully study all of the details of a diagram before answering the question or questions that refer to it. 587 bending in the opposite direction. H. Incorrect. Light is not the direct cause of plant growth. J. Incorrect. Gravitropism is a response to gravity, not to auxin. Bio 13B 3. A. Incorrect. An agar block without auxin would not stimulate the shoot to grow. B. Incorrect. The shoot cannot grow straight down. C. Incorrect. An agar block without auxin would not stimulate the shoot to grow. D. Correct. An agar block without auxin would not stimulate the shoot to grow. Bio 13B 19. Ripe pears give off ethylene, which promoted ripening in the bananas. TAKS 1 Bio/IPC 2C Alternative Assessment 20. Answers will vary. TAKS 1 Bio/IPC 2B, 2D 21. In the practice of bonsai, plants are shaped by selective pruning and training and are kept small by pruning their roots and shoots, potting them in small containers, and watering and fertilizing them sparingly. 22. Agronomists are plant scientists who traditionally study crops and soils. Many agronomists work in the field, in government and at universities. Others work for private industry or state agricultural extension services. Positions are available for individuals with bachelor’s degrees, master’s degrees, and PhD’s in agronomy or soil science. Starting salary will vary by region. Bio 3D TAKS Test Prep • The Science TAKS Prep Appendix in this book provides integrated biology and IPC TAKS practice. • The Holt Science TAKS Practice Workbook provides a review of biology, chemistry, and physics concepts tested on the grades 10 and 11 science TAKS. Chapter 26 • Plant Growth and Development 587