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Home , Double fertilization, Flowering plant, Petal, Plant hormone, Root, Sepal

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Q How does a mothlike appearance help this plant? Some are attracted to flowers that mimic . This orchid belongs to a com- monly called “ orchids.” may be drawn to this and be dusted with grains. The pollen then has a free ride to the next flower on the moth’s route. When pollen comes into contact with the female parts of another flower, the reproductive cycle begins.

READING Toolbox This reading tool can help you learn the material in the following pages.

USING LANGUAGE Your Turn Describing Space Understanding plant processes Use spatial language to describe the following processes. involves understanding what’s happening inside the plant. 1. A train follows a path over the mountains. When you read about transport within the plant, look for 2. are transported through a plant. words such as up and down that indicate where things are moving. This kind of language is called spatial language because it describes how things are moving through space.

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22.1 Plant Life Cycles

6G, 10B Key Concept All plants alternate between two phases in their life cycles. VOCABULARY MAIN IDEAS alternation of generations Plant life cycles alternate between producing and . Life cycle phases look different among various plant groups.

Connect to Your World 6G recognize the significance of to sexual The moth orchid flower mimics the shape of its pollinators, which are attracted to reproduction and 10B describe the what they think is a potential mate. is a part of sexual reproduction in interactions that occur among systems that perform the functions seed plants. But how do seedless plants, such as , reproduce? And what are the of transport, reproduction, and common features of all plant life cycles? response in plants

MAIN IDEA 6G, 10B Plant life cycles alternate between producing spores and gametes. Recall that produce gametes— and eggs—through meiosis. When a sperm fertilizes an egg, a new diploid is produced. Plants also produce gametes, but their reproductive cycle includes a few extra steps. Plants complete their life cycle by alternating between two phases. Together, these phases allow plants to reproduce sexually and disperse to new areas. One phase involves a diploid plant body that produces spores. Remember, diploid cells have two copies of each chromosome (2n). The other Figure 1.1 ALTERNATION OF GENERATIONS phase involves a haploid plant body that produces gametes. Haploid cells have one copy of each chromosome (1n). Plant life cycles alternate between a sporophyte phase, which produces spores, and a gametophyte stage, which This type of life cycle, which alternates between diploid produces gametes. and haploid phases, is called alternation of generations. sporophyte As shown in FIGURE 1.1, the diploid phase of a plant life (2n) cycle begins with a fertilized egg, called a . A zygote divides by and grows into a mature sporophyte zygote (SPAWR-uh-fyt), or -producing plant. A mature (2n) sporophyte has specialized cells that divide by meiosis to SPOROPHYTE produce haploid spores. Recall that by meiosis fertilization PHASE reduces the number of chromosomes in a cell by one-half. GAMETOPHYTE meiosis A spore marks the beginning of the haploid phase of PHASE the plant life cycle. A spore divides by mitosis and grows gametes into a mature gametophyte (guh-mee-tuh-fyt), or (1n) spores (1n) -producing plant. Specialized parts of a mature gametophyte produce gametes—sperm and eggs—through mitosis. When a sperm meets an egg, fertilization takes gametophyte (1n) place, and the cycle continues with a new sporophyte. Analyze Why must gametophyte cells divide by mitosis?

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MAIN IDEA 6G, 10B Life cycle phases look different among various plant groups.

Different plant groups each have their own version of alternation of genera- R E ADI N G TO OLB ox tions. The sporophyte and gametophyte generations look different for non- vascular plants, seedless vascular plants, and seed plants. TAKING NOTES Use combination notes to summarize the life cycles of Life Cycle of Nonvascular Plants: Moss nonvascular, seedless vascular, Nonvascular plants are the only plants in which the gametophyte phase is and seed plants. dominant. In other words, the green, carpetlike plants that you might recog- type of plant life cycle nize as moss are . If you look very closely, sometimes you can see the moss . Moss sporophytes are stalklike structures that grow up from the gametophyte. As you can see in FIGURE 1.2, the moss sporophyte looks like a brown stem topped with a tiny cup called a . The capsule at the tip of the moss sporophyte contains spore-producing sacs called sporangia. When the spores are mature, the capsule opens and releases them. Spores allow seedless plants to disperse to new areas. If a spore lands in a favorable spot for growing, it can grow into a gametophyte. R E ADI N G TO OLB ox A moss gametophyte produces gametes in special reproductive structures. Each male structure produces hundreds of sperm with whiplike flagella, and VOCABULARY each female structure produces a single egg. When is present, sperm The suffix –phyte comes from the Greek word phuton, swim toward an egg. Once a sperm fertilizes an egg, the sporophyte phase meaning “plant.” begins once again.

Figure 1.2 moss life cycle

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CONNECT TO The gametophyte of is the carpet- Spores form inside the capsule. When the like plant that may be familiar to you. The spores are mature, the capsule opens and Life Cycles sporophyte grows up from the gametophyte. releases them. Spores can grow into new Refer to Appendix B for A tiny cup called a capsule forms at the tip gametophytes when the environmental a detailed view of the moss of each moss sporophyte. conditions are favorable. life cycle. (bl) ©Ed Reschke/Peter Arnold, (bl) Inc.; Arnold, ©Ed (br) Reschke/Peter ©Dwight Kuhn R.

Chapter 22: Plant Growth, Reproduction, and Response 641 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 642 cycles. views offern andconifer life Refer to AppendixBfor detailed L if Figure 1.3 Figure , orfrond. sacs called sori grow ontheundersideofeach may befamiliar with.Clusters ofspore-holding The fern sporophyte istheleafy plant that you bottom oftheprothallus. produce spermandeggs are located onthe size ofyour fingernail. little Structures that called aprothallus. Theprothallus isaboutthe A fern spore can grow into afern gametophyte, CO sporophyte (2 e C gametophyte (1 sori

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the pollen tothe reach which is just egg, the millimeters away. to grow from grain toward pollen the In an egg. it , takesayear for After pollination, are eggs produced inside the and tube apollen begins cone-bearing plant grain reaches apollen when opening small the of an ovule. When grain lands apollen on afemale cone, it sticks. Pollination ina occurs gametophytes plants. of seed weeks. die. will in each ovule can develop into amicroscopic female gametophyte, and rest the E larger and more than cones. male scaly live They and grow for . several cone-bearing plants have and male female cones. Female cones are usually a pine , you may notice two different of types cones. This is because ach s A pine t As sh cale ofcale afemale pinecone has two that produce spores. One spore M M own inF ale s ale ale s ale ree is atypical sporophyte. If you closely look at abranch of pores develop into grains, pollen which aretiny male very the underside of each frond, and again. begins cycle the grow.they forming fronds areand slowly , they called uncurl as away. The mature sporophyte is familiar the fern plant. Newly The zygote grows above prothallus, the which eventually rots that zygote the of is beginning the sporophyte the generation. azygote an egg, fertilizes forms on prothallus. the Remember toward swim Spermthen sperm. When an egg. asperm reproductivespecial structures that produce and sperm eggs. rhizoids.threadlike structures called The prothallus contains your little fingernail. It anchors itself to with the tiny inF see develop into a gametophyte. mature. If aspore lands inafavorable spot for growing, it can frond. Spores are released from sporangia the are they when As shown inF areSori clusters of sporangia, which are spore-producing sacs. undersidethe of afrond, afern leaf, called you might sori. see plantsthe you recognize as are sporophytes. If you at look including plants vascular seedless such as ferns. This means that The sporophyte is dominant the phase forplants, vascular all Life Cycle Vascular Seedless of Plants: Ferns that gametophytes the plants of seed are microscopic. difference plants most between seedless plants and seed is that develop into and male female gametophytes. Another plants,most plants seedless seed produce of two types spores The sporophyte is familiar the form plants. for seed all Unlike Life Cycle Plants: Seed of pores are produced inside cones, male which live only for afew IGURE Whe A fer IGURE n freestanding water is present, structures male release n gametophyte aprothallus. is often called As you can 1.4, E male conesmale release clouds of spring. inthe pollen ven 1.3, IGURE aprothallus is aplant about body sizeof the tually, sporophyte the produce will spores on the 1.3, sori look like look sori brown dots on fern the

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FIGURE 1.4 Conifer Life Cycle The pine tree is a typical conifer sporophyte. Male and female gametophytes are produced on separate male and female pine cones. sporophyte (2n) male cone

A fertilized egg grows into an while the ovule meiosis develops into a pine seed. pine seed female cone Male spores interior of meiosis are produced female scale pollen grain through Female spores meiosis. eggs sperm are produced through meiosis. ovule ovule

fertilization gametophyte (1n) When a pollen grain female scale reaches the end of a Female spores develop female scale, a pollen into female gameto- pollen grains tube grows. Sperm phytes, which produce Male spores develop into travel through this eggs in the ovules. male gametophytes, tube toward an egg. called pollen grains.

Two sperm also develop inside the pollen grain during this time. Eventu- ally, these sperm travel down the pollen tube toward the egg. The sperm of seed plants do not have flagella, because they do not need to swim through water to reach an egg. One sperm may fertilize an egg, forming a zygote, which will develop into an embryo. Meanwhile, the ovule develops into a protective pine seed. Each scale of a female pinecone can be home to two developing pine seeds. Once the seeds are mature, the scales open up and release them. The life cycle then begins again with a new sporophyte—a pine tree . Contrast What is the difference between how seedless plants and seed plants disperse to new areas? 10B (tr) ©Darrell Gulin/Corbis; (r) ©Dr. (tr) Jeremy ©Darrell Burgess/Photo Inc; Gulin/Corbis; Researchers, (br) (r) ©Noah ©Dr. Berger/AP Images Self-check Online HMDScience.com 22.1 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What is the main difference between 3. Apply Why do seedless plants Genetics the two types of plant bodies require freestanding water for 5. Draw a diagram to show how involved in the alternation of sexual reproduction, while seed cellular division through mei- generations? plants do not? 10B osis results in the haploid 2. What is the main difference between 4. Infer The scales of female pine- spores of plants. 6G the gametophytes of nonvascular cones produce a sticky substance. plants and those of seed plants? Describe the this might serve. 10B

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22.2 Reproduction in Flowering Plants

6G, 10B Key Concept Reproduction of flowering plants takes place within flowers. VOCABULARY MAIN IDEAS Flowers contain reproductive organs protected by specialized . Flowering plants can be pollinated by wind or animals. Fertilization takes place within the flower. carpel Connect to Your World When planning a garden, you might choose plants with sweet-smelling flowers that will add splashes of color to the space. But did you know that these same qualities 6G recognize the signif- can attract and guide pollinators? So don’t be surprised if you and the insects icance of meiosis to sexual in your garden have a similar taste in flowers. reproduction and 10B describe the interactions that occur among systems that perform the functions of transport, reproduction, and response in plants

MAIN IDEA 10B Flowers contain reproductive organs protected by specialized leaves. Look at a bouquet of flowers in various stages of bloom, and you will likely notice that different flower parts are arranged in layers. The outermost layer of a flower is made up of . Sepals are modified leaves that protect the developing flower. They are often green but can also be brightly colored. The FIGURE 2.1 This lily has both male layer just inside the sepals is made up of , which are also modified and female structures. In lilies and leaves. Their bright colors often help attract animal pollinators. Monocot other monocots, sepals and petals look similar and are often called flowers, such as lilies, have sepals and petals that look the same. These struc- . tures are often called tepals. Flowering plants that are not pollinated by stamen animals usually have very small sepals and petals, or they have none at all. Some species have flowers with only male or only female structures, but filament anther the flowers of most species have both. A typical monocot flower is illustrated in Figure 2.1. A stamen is the male structure of a flower. Each stamen has a stalk called a filament that supports an anther. Anthers produce pollen grains, the male gametophytes. The innermost layer of a flower is made up of the female structure, called a carpel. Most flowers have several carpels fused together, forming a structure called a pistil. Each carpel is made of three parts. The tip, called the style carpel stigma, is often covered with a sticky substance that holds ovary pollen grains when they land there. The style is a tube that leads from the stigma to the ovary. Female gametophytes are pro- duced inside the ovary, which is found at the base of a flower. Compare What parts of conifers have functions similar petal sepal to ?

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(tl) ©Susumu Nishinaga/Photo Researchers, Inc.; (tr) ©Darwin Dale/Photo Researchers, Inc.; (br) ©Archie Young/Photo Researchers, Inc. wind or animals. or wind Flowering canpollinated be plants by Infer B A L K C I U Q

shown in source. In process the of feeding, an animal is dusted grains, with pollen as or other animals visit flowers or pollen as to afood collect A lot of is required energy to produce much so pollen. spicuous flowers and produce large amounts of pollen. Wind-pollinated usually have species or small incon- ing plant is pollinated by looking at its flowers. in flowering plants. You can often tell how aflower- Pollination step reproduction of is anecessary sexual same plant that species, flower pollinated. has been When grain reaches apollen of stigma the the important factors success inthe and diversity of flowering plants. an animal is more efficient than wind pollination. Animal pollinators are animal pollinatorsBecause transfer reliable inthis pollen way, pollination by from first flower the may brush against of stigma the second the flower. MAI A Closer at Look Flowers An 4. P P Dissect aflower to discover how itsvarious structures aidinreproduction. 2. 2. 3. 3. 1. 1. roc rob

Man suggest abouthow thisflower ispollinated? Infer Infer drawing: sepal, petal, anther, filament, stigma,style, ovary. Identify carpel orpistil,stigma,style, andovary. forming astructure called Addthecarpel apistil. orpistilto your drawing. Label the The femal anther andafilament inyour drawing. Remove thestamens. Add thestamens to your drawing andlabel them.Labelan Now thestamens, thema petals inyour drawing. Carefully remove each petal. Peta Carefully remove thesepals. sepa Locate theoutermost layer offlower These parts. are the aly Why is pollination more reliable by animals than by wind? N l e ID ls form thenext layer offlower Draw parts. andlabel the ls. Draw andlabel thesepals to beginyour flower diagram. e

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MAIN IDEA 6G, 10B Fertilization takes place within the flower. In flowering plants, as in all vascular plants, the sporophyte is the dominant phase. The parts of a flower that you have just learned about are all part of the sporophyte, while the gametophytes of flowering plants are tiny and enclosed within flower parts. FIGURE 2.3 illustrates the life cycle of flowering plants.

CONNECT TO Production of Male Gametophytes Meiosis Recall that anthers produce pollen grains, which are the male gametophytes of Recall from the chapter Meiosis seed plants. Cells within the anthers divide by meiosis to produce four male and Mendel that meiosis is the spores. Each spore divides again, by mitosis, producing two haploid cells. form of cellular division These two cells, together with a thick wall that protects them, form a single needed for sexual reproduction. Gametes—sperm and eggs— pollen grain. Wind-pollinated plants have light, fine pollen grains that can be are haploid, containing half as carried far by the wind. Pollen from wind-pollinated plants, such as , many chromosomes as somatic is the source of some outdoor allergies. cells contain. Production of Female Gametophytes One female gametophyte can form in each ovule of a flower’s ovary. One cell in the ovule divides by meiosis to produce four female spores. In most flower- ing plants, three of these spores die. The nucleus of the last spore grows, dividing by mitosis three times, resulting in one spore with eight nuclei. Membranes grow between the nuclei to form seven cells. Together, these seven cells make up the female gametophyte, which is sometimes called an embryo sac. One large, central cell has two haploid nuclei, called polar nuclei. One of the other cells develops into an egg. Double Fertilization After pollination, one cell in the VISUAL VOCAB pollen grain grows into a pollen tube. The endosperm nourishes the This tube extends down the style developing plant embryo inside the toward the ovule. The other cell in the seed coat. The prefix endo- means pollen grain divides by mitosis, “inside,” and sperm comes from the Greek word sperma, which means producing two sperm. Both sperm “seed.” travel down the pollen tube. One sperm fertilizes the egg. The other endosperm sperm combines with the polar nuclei in the embryo sac. This cell now has a seed coat triploid (3n) nucleus. It will become endosperm, the a food supply for the embryo developing plant embryo. The process in which one sperm fertilizes an egg and the other forms a triploid cell is called double fertilization. Double fertilization happens only in flowering plants and gives them an advantage over cone-bearing plants. Cone-bearing plants produce a food supply for each egg before fertilization. However, if the egg of a is not fertil- ized, the plant does not waste energy making an unneeded food supply. Summarize What is the function of each sperm during double fertilization?

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FIGURE 2.3 Flowering Plant Life Cycle

A plant is a typical flowering plant. If the flower is pollinated and fertilization occurs, ovules will develop into seeds, and the surrounding ovary will develop into fruit.

1 Male and female gametophytes Tomato flowers have both male and female struc- tures. Pollen grains, the male gameto- phytes, are produced in anthers. The flower’s ovary contains many ovules, which can each contain a female gametophyte. anther ovule style pollen grain ovary style pollen grain anther 2 Pollination A may transfer pollen grains from one flower’s anther to ovary another flower’s stigma. One cell of a pollen grain divides to form two sperm. The other cell forms a pollen tube, down which the sperm travel.

4 Seeds and fruit Many seeds develop inside the ovary of each tomato flower. While the seeds develop, the ovary pollen tube matures into the juicy flesh of a tomato. A few seeds may find their way into the soil sperm to grow into new tomato plants.

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sperm 3 Double fertilization One sperm polar nuclei fertilizes the egg, which develops into an embryo. The other sperm unites with the polar nuclei to form the endosperm. The outer layer of the ovule becomes a protective seed coat.

Just before the stigma of a tomato plant becomes receptive to pollen, the CRITICAL style grows so that the stigma is higher than the anthers. What does this VIEWING suggest about the way in which tomato plants are pollinated?

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FIGURE 2.4 After a Seeds and Fruit flower (left) is pollinated and fer- tilization occurs, seeds and fruit At fertilization, the next sporophyte generation begins. The ovule becomes a begin to develop. The pumpkin seed, which contains an embryo and a nutritious endosperm enclosed by a fruit (center) is green at first, con- protective seed coat. Using the nutrients provided by the endosperm, the taining immature seeds. The ripe embryo develops one or two , or seed leaves. Recall that monocots fruit (right) is and contains mature pumpkin seeds. have one cotyledon and dicots have two cotyledons. Cotyledons sometimes provide nourishment for the new plant before it can begin producing its own food through . While the seed develops, the surrounding ovary grows into a fruit. The development of a pumpkin fruit is shown in FIGURE 2.4. Remember, a fruit is the mature ovary of a flowering plant. You have probably eaten many , such as , , and . Many foods that you think of as , grains, nuts, or are also technically fruits. Sweet peppers, tomatoes, and are fruits that contain many seeds. The shells of - nuts are also fruit, while the two “halves” inside the shell are cotyledons. Flowering plants that produce many seeds within one ovary have larger fruit. Pumpkin plants produce some of the largest fruits on record. If you have ever carved a pumpkin, you have actually removed the fleshy part of the mature ovary that surrounds hundreds of pumpkin seeds. As you will learn in the next section, a fruit aids in the dispersal of seeds to new areas. A seed has the ability to grow into a mature flowering plant. Contrast What is the major difference between seeds of flowering plants and seeds of cone-bearing plants? (tl) Valing/ShutterStock; ©Scott (tr) Camazine/Photo ©Royalty-Free/Corbis; Inc.; Researchers, (br) (tc) ©Ingram ©Tonis Publishing/Alamy Images

Self-check Online HMDScience.com 22.2 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What are the functions of the four 4. Infer Why do wind-pollinated basic parts found in most flowers? plant species generally produce 6. Would brightly colored 10B more pollen than animal-pollinated flowers and sweet, juicy 2. How does pollination occur in species? fruits have been as beneficial flowering plants? 10B 5. Analyze In flowering plants, which to the earliest land plants as they are to modern ­flowering 3. What is double fertilization? cells divide by meiosis to produce plants? Explain. 10B male and female spores? 6G

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(bl) ©Scott Camazine/Alamy Images; (bc) ©Dwight R. Kuhn; (br) ©Anette Linnea Rasmussen/ShutterStock germination dormancy VOCABULARY response inplants of transport, reproduction, and systems that perform thefunctions interactions that occur among data and10Bdescribe the inferences, andpredict trends from FIGURE 3.1 FIGURE scatter.” spargere, whichmeans “to comes from theLatin verb dis- means “apart,” andsperse “to scatter apart.” Theprefix The word disperse means VOCABULARY such cyp para many R selae, chute-like

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DATA ANALYSIS 2G Identifying Experimental Design Flaws Recall that a good experimental design is necessary to obtain valid results. In the experiment described below, a group of students collected data about the effect of water on germination. A • Students planted 2 seeds in each of 3 flower pots. C B • Each pot contained the same amount and type of soil. • The pots were placed close to a window, as shown at the right. • Pot A was given 200 mL of water each day, Pot B was given 100 mL of water each day, and Pot C was given no water. This watering pattern was continued for one full week. • Every day, students recorded the seeds’ progress. • The students made conclusions about the amount of water that is best for radish seed germination.

1. Analyze Which parts of the experimental design are flawed? 2. Design How would you change the experimental design to collect valid results?

MAIN IDEA 10B Seeds begin to grow when environmental conditions are favorable. After a parent plant releases seeds, it may be days, months, or years until the seeds begin to grow into new plants. In fact, scientists recently found a 2000--old seed from a now-extinct species of tree in Israel. After they placed it in the conditions the tree needs to grow, the seed sprouted. How can the living embryo inside a seed last years without food or water? Dormancy For 2000 years, the embryo inside the date palm seed was in a state of dormancy. When a seed is dormant, the embryo has stopped growing. For some plant species, proper temperature, moisture, oxygen, and light levels are enough to end dormancy. Other plant species have seeds that stay dormant even during good grow- ing conditions. For example, seeds remain dormant until their seed coats are weakened in the digestive tract of an animal. This way, the seeds are not only carried far from the parent plant but they are also deposited with their own batch of fertilizer. Other seeds have waterproof seed coats that can be cracked only by winter ice. Then, in the spring, the embryo can begin to grow with less chance of freezing than if it had begun to grow in the fall. allows the next generation of plants to grow under favor- able conditions. Inside the seed coat, an embryo can withstand extremes that would kill a young seedling. Gardeners contend with seed dormancy all the time. When a gardener turns over soil before planting, fresh air and sunlight can cause the buried seeds of unexpected plants to come out of dormancy.

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FIGURE 3.2 The embryonic As the root continues to emerge, The embryonic and the The young plant is completely emerges from the seed. root hairs can be seen. cotyledons are revealed. free of its seed coat.

Germination Many types of seeds begin to grow when there are certain changes in tempera- ture, moisture, or light levels. During germination, the embryo breaks out of the seed coat and begins to grow into a seedling, as shown in Figure 3.2. Germina- tion begins when the embryo starts to take up water. Water causes the seed to CONNECT TO swell and crack the seed coat. As the embryo grows, the embryonic root, called Enzymes a , breaks through the cracks. Water also activates enzymes inside the Recall from the chapter seed. Recall that enzymes are that need specific conditions to speed Chemistry of Life that enzymes up chemical reactions. These enzymes help break down material in the endo- are catalysts for chemical reactions in living things. sperm into , which are moved to the growing embryo. Enzymes allow chemical As the embryo continues to grow, a young shoot called the plumule reactions to take place under controlled conditions. eventually breaks through the surface of the soil. In most monocots, the cotyledon stays underground while the shoot grows upward. Some species of dicots have cotyledons that stay below ground, but the cotyledons of other dicots emerge above ground with the growing shoot. When leaves emerge from the shoot, they begin to make food through photosynthesis. Once photosynthesis begins, the young plant is called a seedling.

(tl), (tcl), (tcr), (tr) (tcr), ©Andrew (tcl), Syred/Photo (tl), Inc. Researchers, Sequence Which emerges first from a seed, a root or a shoot?

Self-check Online HMDScience.com 22.3 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What are three ways that seeds of 3. Analyze How are enzymes involved flowering plants can be dispersed? in the process of germination? 5. Some tropical plant species 10B 10B have fruit with air cavities 2. Why is it an advantage that most 4. Infer What is the adaptive advantage that allow them to float. seeds go through a stage of when water uptake causes a seed How might natural selection dormancy before germination? coat to crack? have led to this adapta- tion? 7e

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VIRTUAL Lab BIOLOGY Plant Responses Test for Exploring Plant Responses Went’s Experiment plant responses to different Explore how plants can react to light, Learn how Frits Went stimuli in this interactive gravity, and touch. demonstrated that a investigation. chemical found in plant- shoot tips influences the direction of growth of the shoot.

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Web BIOLOGY BIOZINE Seed Dispersal Learn how Plants in Space Genetically Modified different types of plants use We often take for granted that Foods—Do Potential many methods to get their grow up and grow down. But Problems Outweigh seeds from one place to what happens when you take a plant Benefits? Catch the latest another. into space? How does this question headlines about plants, affect space exploration? including stories about genetically modified foods. (bc) ; (br) ©Noah World Photos Berger/AP/Wide

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grown from seeds. oranges that we eat come from propagated rather than from fragments of aparent plant. For example, most apples and propagation takesadvantage of aplant’s ability to grow individuals new desirable qualities, such as having or no tolerance seeds to frost. Vegetative Plant growers aprocess use vegetative called propagation to grow plants with as shown in is buried in soil or placed in water, it will produce new roots, reproduced using cuttings from stems or leaves. If the methods. Many , including African violets, are desired qualities, resistance. such as disease produces desired the or fruit onto of atree that trunk the has other or abud from another tree. Growers can abud graft from atree that involves making an incision in the of one tree and attaching to it either a orgrafting, joining vegetative structures from two or more plants. turists to produce new houseplants for sale to nurseries. umans can produce with desirable plants umans • • MAI aits vegetative using structures.

ase How are plants’ abilities to reproduce plant populations? ase How can acombination ofsexual and vi conditions, bulbs can divide to produce plants. new covered with aprotective, skin.In favorable papery surrounded leaves by modified adapted for storage and du buds that can sprout new plants, as shown in forstem modified storage. The “eyes” of apotato are Veg Frui N ew xually useful to humans? xual reproduction be beneficial for

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different groups on functions their based and chemical properties. right receptor, it aresponse. triggers Plant hormones are divided into several cells have receptors for many different hormones. When ahormone the meets targeted. Target cells have receptors that recognize hormone. the Most plant move they when from cells that the secrete to them cells for the are which they internal changes, of as part aplant’s life cycle. Hormones have an influence environment where plant the grows. hormones Other are of released because most plant hormones are different very chemicals from inanimals. those Hormones direct and regulate many of same the functions inplants. However, other animals, hormones control and reproduction. functions to vital survival stimulates or suppresses activity the of cells inanother In part. humans and Gibberellins A larger and elongates stems the bunches, inthe making room for more . often spray their with agibberellin solution, which grow makes fruits the flowering up stalk to 12meters inafew weeks. (40feet) tall growers of some For flower stalks. example, agave the shown in responsiblealso for large the sizeof many and fruits rapid the upward growth nation, and promoting rapid the growth of young Gibberellins . are increases insize. are They involved dormancy, inending seed starting germi- MAI d development. d MAI C Plants o Som N n N ID c ID

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(tr) ©Stockbyte Platinum/Alamy; (cr) ©Chris Howes/Wild Places Photography/Alamy co Apply longer than normal. dipped solution inacytokinin stay green much process of some plant organs. For example, leaves another property of slow —they aging the lateralcalled growth. Commercial make florists of use growththe of side branches. This sideways growth is developing and are They fruits. involved seeds also in division. are They produced ingrowing roots and stimulate stage , which is final of the cell journey. such Some fruits, as tomatoes the in filtered out, or may they become overripe during the tances must kept be inrooms where ethylene the is tage. Fruits such as apples that are shipped long dis- Commercial growers can ethylene use to advan- their causes and is naturally produced by fruits. tropism, Auxins Cytokinins Cytokinins ethylene abnormallyripened fast by its own production of get and soft will to start rotten. look The is being Put an apple inan airtight container for aday, and it E -ripened tomatovine-ripened has. process not does bring out same the sugars that a ripening taste ripe, artificial this though, because so makes turn them aripe-tomato red. may They not destination, are to ethylene they exposed gas, which are picked before are they reach ripe. Once they their unwanted plants. reason, auxins are acommon ingredient inherbicides, to chemicals kill used auxins can prevent plant growth altogether, roots. inthe particularly For this and side branches are encouraged to grow. Conversely, concentrations high of tipthe of agrowing stem. With no growing tip, there is less auxin stem, inthe can property this use of auxins to control branching patterns by cutting off growth stem, of primary preventing the growth of branches. new Gardeners cells produced apical inthe , or growing tip. Auxins stimulate learn, auxinslearn, have different cells of inthe different effects plant organs. or grow longer, causing stem the to toward bend light. the As you soon will build up cells on inthe shaded the side of stem. the cellselongate, These then For example, ifastimulus such as light hits one side of astem, auxins will uld use different plant hormones to your advantage? to your hormones plant different use uld thylene The l

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lower side of stem. the This buildup causes stem the to grow upward. same time, levels high of auxin, which stimulate shoot growth, build up inthe roots that so upper the side grows faster and root the grows downward. At the levelshigh of auxin. Auxins build up on lower the side of horizontally growing pism. growth Root is stimulated by low levels of auxin, but is slowed down by gravitropism it because is growth against force the of gravity. growththe is direction inthe that gravity pulls. Upward growth is negative growth of aplant is called and shoot the grows upward toward surface. soil the This up-and-down germinatesWhen aseed underground, root the grows downward into soil, the Gravitropism responding to environment. their plants cannot uproot themselves and change locations, have they other ways of summer day, you may have responded by moving to ashady spot. While pulling your hand away quickly. And ifyou’ve outside ever been hot on avery If you’ve ever touched ahot pan kitchen, inthe you likely responded by wind. Repeatedly touching ayoung plant can even stunt its growth. winds grow on will ahillside as ifit is beingpushed direction inthe of the many kinds of touchlike stimuli. For example, aplant regularly to exposed pattern of growth cell that is found with other tropisms. Plants are sensitive to touch. In curling “fingers,” these contact with an same the triggers object ’s gravitational pull. MAI Auxins p N ID E A lay ingravitropism, apart which is more complex than phototro-

10B tion of light the again. days, you likely plant the will find growing direc- inthe pointing away from light. the If you come back inafew these plantsthese and grow incoils around anything they plants and vines. emerge from of leaf the base light through process the of phototropism, as shown in space with alight source, that plant lean toward will the light is called light is called toward light. the This tendency of aplant to grow toward ing on shaded the side of astem causes stem the to bend cause elongation. cell earlier, As described lengthen- cell on shaded the side. Remember that inastem, auxins When light hits aplant stem, it causes auxins to build up Phototropism thigmotropism. Many plants have also aresponse to touch, called T 5.3. FIGURE higmotropism

Downward growth is positive gravitropism because gravitropism, Let’s say you turn that plant around that so it’s phototropism. This quality is apparent inclimbing because the plant the because is responding to If you grow aplant ina

©Cathlyn Melloan/Getty Images DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Rapid Responses Some plants have very rapid responses that do not involve growth. These rapid responses are often adaptations that help protect plants from predators. For example, the , or sensitive plant, quickly folds its leaves together a few seconds after being touched. A few plants are quick enough to capture insects for a meal. The shown in FIGURE 5.4 can close its leaves on an unsuspecting in less than a second. Scientists recently discovered that when the leaves are touched, water rushes to the cells at their bases, changing their curvature and snapping the trap shut. Photoperiodism What triggers a to flower or a tree to drop its leaves? Plants take signals from the changing lengths of day and FIGURE 5.4 When the leaves of a night throughout the year, in a response called photoperiodism. Some plants Venus flytrap are touched, water keep very accurate clocks when it comes to the amount of daylight or darkness rushes to the cells of the leaf in a 24-hour period. In fact, some plants that flower while the days are short, bases, causing the leaves to bend inward rapidly. such as , will not bloom if there is one extra minute of light in the evening. Shorter days and longer nights during the fall help trigger the leaves of many trees to change color. This response is part of the preparation for winter, when these trees enter a stage of dormancy. Winter dormancy in plants is functionally similar to the hibernation of many animals during the winter months. With less rainfall and less direct sunlight, it is more energy- HMDScience.com efficient for these plants to shut down and rely on reserved sugars than it is for GO ONLINE them to photosynthesize. Leaves therefore begin to die in the fall. , Plant Responses the pigment that gives leaves their green color, breaks down. Once the chloro- phyll is gone, the remaining leaf pigments become visible and new pigments are produced. Water and nutrients are drawn out of the leaves for the rest of the tree to use during the winter, and the leaves eventually fall off of the tree. Apply What stimulus causes each of the following tropisms: phototropism, gravitropism, thigmotropism? 10B ©Dr. Jeremy Burgess/Photo Inc. Researchers, ©Dr.

Self-check Online HMDScience.com 22.5 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Describe two plant hormones 3. Apply A vine grows sideways, Adaptations that regulate plant growth twisting along a railing. What type of 5. Many trees in temperate and development. tropism is this plant exhibiting? climates lose their leaves 2. Name and describe five ways 10B before the long, cold winter. in which plants can respond to 4. Apply If you want full, bushy plants, How is this ability an adapta- their environment. 10B which part of the plant would you tion for these trees? trim to control auxin production in your favor?

Chapter 22: Plant Growth, Reproduction, and Response 659 CorrectionKey=B DO NOT EDIT--Changes mustbemadethrough “File info” 660

CHAPTER responses usingaconcept map. Concept Map 22.2 22.1 22 Unit 7: Plants Key Con phototropism READING READING

the de ­endosperm, nourish whichwill other helps produce the the flower’s ovary, while the fertilizes produced anegg, in double fertilization, onesperm two sperm.Inaprocess called the other cell dividesto form grows into apollen tube,and One cell inthepollen grain reaches thetipoffemale reproductive structure. pollinators. Aflower ispollinated whenapollen grain and petals. Brightly colored petals can attract animal are surrounded by specialized leaves called sepals flowers. Flowers consist ofreproductive organs that Reproduction offlowering plants takes place within cular, seedless vascular, andseed plants. gametophyte phases look different amongnonvas- develop into anew sporophyte. Sporophyte and sperm andeggs—by mitosis. Afertilized eggcan haploid. Thegametophyte produces gametes— spore develops into agametophyte, whichisalso rophyte, produces haploid spores through meiosis. A n) phase. Thediploid phase, calledhaploid (1 thespo- of generations, anditinvolves adiploid (2n)anda life cycles. Thistypeoflife cycle iscalled alternation plantsAll alternate between two phases intheir Reproduction inFlowering Plants Plant Life Cycles through c S veloping embryo.

epts Summarize what you kno ummary light Toolbox respond to through plants

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22.4 22.3 22.5 es

propagating plants asexually. Humans can produce plants withdesirable traits by a stem, aleaf, oraroot attached to theparent plant. reproduction involves new individuals growing from a root inaprocess called regeneration. Vegetative a new individual from afragment ofastem, aleaf, or through asexual reproduction. Someplants can grow Plants can produce genetic clones ofthemselves begins to grow into aseedling. breaks outoftheseed coat and cess by whichtheembryo growth. Germination isthepro- tal conditions donot support nongrowth, while environmen- through astage ofdormancy, or plants isto helpdisperse seeds. Manyseeds go are favorable. offruitinflowering Thefunction Seeds disperse andbeginto grow whenconditions lengths ofday andnight. respond to touch andseasonal changes inthe to lightandgravity. Sometypesofplants can also control several forms oftropism, includingresponses are involved inthelengthening ofplant cells that gibberellins, ethylene, cytokinins, andauxins.Auxins Fourment. majorgroups ofplant hormonesare Plant hormonesguideplant growth anddevelop- Asexual ReproductionAsexual Seed Dispersal andGermina Plant sporophyte

Draw ac Plants reproduce eithersexually orasexually, H ormones andResponses ycle diagram to show thealterna- gametophyte tion

(tr) ©Dwight R. Kuhn CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

CHAPTER 22 G N I D A E R

Category: from the chapter. For each clue,listtheappropriate vocabulary term Category Clues

In your scienc that matches each item that ispointed outbelow. L R 22.2 22.1 vo Chapter 10. 12. 11. 13. abel Diagrams 8. 6. 9. 7. eviewing

response t response t response t response t to themeaning oftheword tropism? The prefix tr sprout,” relate to themeaning ofgermination? How doestheLatin v dormir, whichmeans “to sleep”? How doesthewor the word endosperm ? sperma me The prefix endo-means “inside,” andthe Greek word

carpel stamen peta sepal sporophy alternation ofgenerations gametophyte Review P l X O B L O O T lant 5. e notebook, write thevocabulary term o amountofdaylight or darkness o gravity o touch o light c V ans “seed.” How dothese meanings relate to 1. te op- means “a turning.” How doesthisrelate abu R ocabulary esponses lary d dormancy relate to theFrench verb erb germinare, whichmeans “to 2. Wor 4. d

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20. 24. 22. 25. 23. 18. 16. 14. 21. 15. 19. 17. eviewing Review Games•ConceptMapSectionSelf-Checks online Go

of environments? asexually allow plant speciesto populate avariety How can theabilit embryo duringgermination. Discuss ther that were dispersed duringtheprevious fall? rain. How mightthistype ofspringweather affect seeds People ma of responding. Name four ty offspring? How doesseed disper this disease? Explain your answer. Which ofthemajorplant hormonesislikely involved in to grow to several timestheirnormal sizeandthendie. A well-kno Name thetwo structur How can brightl that are fertilized intheprocess ofdouble fertilization. of flowering plants? produce new plants? alt What typesofcellular divisionare involved inthe Why isplant propa wind-pollina What characteristic mightbeacluethat aflower is gener What isamajordifference between thegametophyte ernation ofgenerations? ations ofmoss andpinetrees? HMDScience.com Interact y enjoy aspringseason withrelatively little

wn disease ofrice plants causes rice seedlings 22.5 Chapter 22: Plant Growth, Reproduction, andResponse Chapter 22: M ted? Explain your answer. ole ofenzymesinthedevelopment ofan pes ofstimulito whichplants are capable AIN y colored petals aidinthereproduction

photoperiodism gravitropism thigmotropism phototropism tropism auxin cytokinin ethyl gibberellin hormone y to produce both sexually and i gation anefficientway for people to ve Review

I 10B D sal aidinthesurvivalsal ofplant ene es inthefemale gametophyte EAS 10B 10B 6G, 10B

661 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Critical Thinking 26. Compare and Contrast What are some differences and Analyzing Data Analyze an Experimental Design similarities between the life cycle of a seedless plant and Students are testing the effect of light on the germina- 10B that of a seed plant, such as a conifer? tion of millet seeds. The setup for their experiment is 27. Infer Female pine cones have scales that open, close, shown in the table below. The students observe and and then open again. These three phases correspond track seed development for one week. Use the data to with three specific events in the conifer reproductive answer the next four questions. cycle. What three events might trigger these phases in female cones? 10B millet seed experiment setup Tray A Tray B 28. Predict Most people cook potatoes soon after they buy them at the store. What will happen to a potato Seeds 50 50 that is left sitting on the kitchen counter for a few weeks? Explain your answer. Water 25 mL per day 25 mL per day on a shelf beneath on a shelf in a 29. Infer A homeowner is planting a new garden and buys Location some plant seeds. The plant shop owner offers to sell a grow light dark refrigerator her regular seeds or specially treated seeds that will germinate faster. How may these special seeds have been treated? 34. Analyze What are the dependent and independent variables in this experiment? 30. Analyze A kiwi fruit was purchased at the store, but it was not ripe enough to eat. It was placed in a sealed 35. Analyze What is the control in this experiment? container along with an apple. Several days later, the kiwi was ripe. Explain how this likely happened. 36. Evaluate Which part of the experimental design is flawed? 31. Analyze Four-o’clock flowers bloom late in the day, as their name suggests. The flowers stay open all night and 37. Experimental Design What changes would you make to close the following morning. What type of response is the experimental design to collect valid results? the flower demonstrating? Explain your answer. 10B Making Connections Interpreting Visuals 38. Write a Blog Imagine that you are a seed that is about Use this cartoon to answer the next two questions. to come out of dormancy. Write a blog describing your experiences as you germinate. Be sure to include the following terms: dormancy, germinate, seed coat, radicle, plumule, cotyledons, and seedling. 10B 39. Analyze Look at the moth orchid shown in the chapter opener. Does this photograph show the gametophyte or sporophyte generation? Explain your answer.

“I’ll say he’s busy. He has hundreds of frequent flower miles.”

source: www.CartoonStock.com 32. Apply Name the service that these have per- formed for the flowering plants. 33. Summarize Describe how this process occurs as bees from flower to flower. 10B ©Dan Rosandich/www.CartoonStock.com

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Biology End-of-Course Exam Practice

Record your answers on a separate piece of . 2G, 9A MULTIPLE CHOICE 3 Rate of Ripening 100% 2E A 1 A strawberry farmer divides a large field into B three sections: the first bordering a grove of trees, the second in the middle, and the third bordering an interstate. Each section is treated with a C different to determine effectiveness. D Which of the following is not a design flaw of the ripeness of Percent experiment? 0% A No part of the field was used as a control. 1 2 3 4 5 B Fumes from the interstate might kill pests in Days the third section. Scientists are developing a that will slow C The trees might harbor animals that eat pests down the rate of fruit ripening to a few days. in the first section. Based on the preceding graph, which molecule D The same type of strawberries were grown in are they most likely to choose? each section. A A B B 2G, 9C C C 2 D D Enzyme Activity at Different Temperatures Temperature (°C) Enzyme Activity (units/mL) 4B 25 6 4 According to one hypothesis, auxins may cause a change in pH that results in the 20 8 becoming more flexible. Then, the cell lengthens 15 14 due to pressure from an organelle. Which 10 27 organelle is most likely exerting this pressure? 5 36 A 0 30 B ribosome C nucleus D Suppose that scientists are studying the activity of enzymes that are involved in ending seed dor- THINK THROUGH THE QUESTION mancy. Which statement is best supported by Think about the properties and functions of each their data? organelle listed as a possible answer. Which of these A The enzyme is ineffective below 0°C. is most likely to expand in size? B Temperature does not affect enzyme activity. C Enzyme activity peaks at around 5°C. D The enzyme is most active in warm weather.

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New Technology, Old Idea 6H production. This scientific advance, led by Borlaug, became known as the Green Revolution and drasti- GM plants have that have been artificially cally improved crop yields worldwide. For his work, introduced into the plant’s . This technology Borlaug received the Nobel Prize in 1970. Borlaug gives plants a new characteristic, such as a new color supported the genetic engineering of crops and or different flavor. To date, most genetically engi- viewed it as the next wave of the Green Revolution. neered foods have been bred for disease resistance. GM crops on the market include , rice, corn, , potatoes, tomatoes, and . Genetic engineering is a fairly new process, but plants have been modified through careful selection and cross-breeding for thousands of years. In fact, many experts argue that genetic engineering of crops is just a faster and more precise method of selective breeding. Plants can be genetically modi- fied to produce larger fruits. The Green Revolution 6H In the 1960s, scientist Norman Borlaug and a team Benefits of GM Crops 3D of researchers used cross-breeding techniques to develop a new strain of wheat. The new strain GM crops have the potential to improve produced two to three times as much wheat as worldwide. For example, researchers have developed traditional varieties, and resisted many types of a GM variety of rice, called “golden rice,” that is high insects and diseases. Widely planted, these new in vitamin A. Half of the world’s population relies on varieties changed Mexico from an importer of wheat rice as the main part of their diet. Non-modified rice to an exporter within 20 years. Borlaug and his team lacks vitamin A, however, and vitamin A deficiency began shipping the new strain of wheat to and in humans can cause blindness and sometimes death. Pakistan. Both countries quickly doubled their wheat Golden rice could prevent millions of deaths of young children in developing countries every year. TECHNOLOGY

Gene Gun Genetic engineers use various ways to insert new genes into host cells. For plant cells, which have thick cell walls, one of the best ways to put foreign DNA into the cell is to actually shoot it through the plant tissue using a gun.

A researcher coats gold or tungsten particles with DNA and places them on the end of a microscopic plastic bullet. The plastic bullet is placed in the gene gun and directed toward the target plant tissue.

A burst of helium propels the bullet to the end of the gun. The gold particles containing the DNA are released, while the bullet remains in the gun. Particles enter the of some of the cells in the target tissue. DNA is released from the gold particles and moves into the ’s nucleus, where it ultimately combines with the cell’s DNA. Read More >> at HMDScience.com (tr) ©Leonard Lessin/Peter Arnold, (tr) Inc.; Arnold, ©Leonard (br) Lessin/Peter ©MattInc. Arnold, Meadows/Peter

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UNIT 7 BioZine

Potential Hidden Costs of GM Crops CAREERS Opponents of genetically modified foods argue that it is impossible to predict exactly how the new crops—

Research Engineer in Action sometimes called “Frankenfoods”—will affect ecosystems. Two major concerns are - dr. Tong-jen Fu resistant and -resistant pests, which TITLE Research Engineer, Food and create new ecological problems. Drug Administration When herbicide-resistance genes are inserted into EDUCATION Ph.D., Chemical Engineer- ing, Pennsylvania State University crop plants, the weeds are easily killed by while the crops remain unaffected. But pollen from Dr. Tong-Jen Fu is a research engineer with the U.S. plants can be carried by the wind for long distances, Food and Drug Administration (FDA), where she eval- and seeds from GM crops could be accidentally uates the methods currently used by scientists to dispersed outside their intended locations, causing the determine the allergic potential of GM foods. She and rise of “superweeds.” In the 1990s, several companies other researchers are trying to understand exactly what produced crops that were resistant to the herbicide makes substances in food cause allergic reactions. Roundup. However, many weeds, such as pigweed, One of the concerns of GM food is its potential to soon evolved resistance to Roundup. Pigweed can increase allergies in humans. Many proteins can poten- grow as much as three inches per day. It chokes out tially be an allergen—that is, cause an allergic reaction farm machinery and smothers crops. in some people. Since genetic engineering introduces new proteins into crops, concerns have been raised GM plants with the bacterial gene Bt produce an that unexpected allergies may arise. GM foods could insecticidal toxin that is harmless to people. How- trigger allergies by including proteins already known ever, insects that evolve resistance will reproduce, to cause a reaction, or by introducing completely new increasing the population of pesticide-resistant pests. allergy-causing proteins—such as those from —into the food supply. Researchers use extensive safety tests to determine whether a genetically modified food is likely to cause an allergic reaction. If any of these tests has a positive reaction, the GM food is not likely to be commercially produced. These tests include checking the sequences of introduced proteins against those of known allergens and testing whether the introduced proteins are resistant to digestion. Read More >> at HMDScience.com

Unanswered Questions 3D Other promising uses of genetic engineering include Genetically modified crops are no longer considered growing fruits and vegetables that produce vaccines new, but some questions about them remain. Many in their tissues. Carrying important vaccines in food of the most important research questions concern the might eventually make shipment, storage, and long-term effects of GM crops on human health and administration of medicine easier worldwide. the environment. Specific questions include: GM crops benefit farmers because they take less • How will vitamin levels in genetically modified time, water, and land to grow. Some GM plants can crops differ from those in their traditional rela- grow in poor or withstand drought, cold tem- tives? perature, and insect damage. These crops lessen the need for pesticide, herbicide, or fertilizer. Consumers • What adverse effects might GM crops, such as those benefit from GM produce that stays fresh longer. engineered to produce medicines, have on wildlife? Read More >> at HMDScience.com Fu; (br) ©Noah Tong-Jen World Photos Berger/AP/Wide (tl) ©Dr.

666 Unit 7: Plants