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Plant Reproduction 44 Plant Reproduction aplings and other plants grow among the remains of trees that Swere destroyed by fire. Where did these new plants come from? Did they grow from seeds that survived the fire? Perhaps they grew from plant roots and stems that survived underground. In either case, these plants are the result of plant repro- duction. In this chapter, you will learn how different groups of plants reproduce and how plants can be dispersed from place to place. What do you think? Science Journal Look at the picture below with a classmate. Discuss what this might be. Here’s a hint: In many plants these are colorful and have pleasant aromas. Write your answer or best guess in your Science Journal. 92 ◆ B ou might know that most plants grow from EXPLORE Yseeds.Seeds are usually found in the fruits of plants.When you eat watermelon, it can contain ACTIVITY many small seeds. Do all fruits contain seeds? Do this activity to find out. Predict where seeds are found 1. Obtain two grapes from your teacher. Each grape should be from a different plant. 2. Split each grape in half and examine the insides of each grape.WARNING: Do not eat the grapes. Observe Were seeds found in both grapes? Hypothesize how new grape plants could be grown if no seeds are produced. In your Science Journal list three other fruits you know of that do not contain seeds. FOLDABLES ReadingReading &Study& Study Making a Venn Diagram Study Fold Make the following Foldable to SkillsSkills compare and contrast sexual and asexual characteristics of a plant. 1. Place a sheet of paper in the front of you so the long side is at the top. Fold the paper in half Sexual Both Asexual from top to bottom. 2. Fold both sides in. Unfold the paper so three sections show. 3. Through the top thickness of the paper, cut along each of the fold lines to the top fold, forming three tabs. Label each tab Sexual, Both, and Asexual as shown. 4. Before you read the chapter, draw circles across the front of the page, as shown. 5. As you read the chapter write information about sexual and asexual reproduction under the left and right tabs. B ◆ 93 SECTION Introduction to Plant Reproduction Types of Reproduction Do people and plants have anything in common? You don’t ■ Distinguish between the two have leaves or roots, and a plant doesn’t have a heart or a brain. types of plant reproduction. Despite these differences, you are alike in many ways—you need ■ Describe the two stages in a water, oxygen, energy, and food to grow. Like humans, plants also plant’s life cycle. can reproduce and make similar copies of themselves. Although Vocabulary humans have only one type of reproduction, most plants can spore reproduce in two different ways, as shown in Figure 1. gametophyte stage Sexual reproduction in plants and animals requires the pro- sporophyte stage duction of sex cells—usually called sperm and eggs—in repro- ductive organs. The offspring produced by sexual reproduction are genetically different from either parent organism. You can grow new plants without using seeds. A second type of reproduction is called asexual reproduction. This type of reproduction does not require the production of sex cells. During asexual reproduction, one organism produces off- spring that are genetically identical to it. Most plants have this type of reproduction, but humans and most other animals don’t. Figure 1 Many plants reproduce sexually with flowers that contain male and female parts. In crocus flowers, bees Other plants can reproduce asexually. and other insects help get A cutting from this impatiens plant can be the sperm to the egg. placed in water and will grow new roots. This new plant can then be planted in soil. 94 ◆ B CHAPTER 4 Plant Reproduction Figure 2 Asexual reproduction in plants takes many forms. The eyes on these potatoes have begun to sprout. If a potato is cut into pieces, each piece that contains an eye can be planted and will grow into a new potato plant. The grass plants spread by reproducing asexually. Asexual Plant Reproduction Do you like to eat oranges and grapes that have seeds, or do you like seedless fruit? If these plants do not produce seeds, how do growers get new plants? Growers can produce new plants by asexual reproduction because many plant cells have the ability to grow into a variety of cell types. New plants can be grown from just a few cells in the laboratory. Under the right conditions, an entire plant can Observing Asexual grow from one leaf or just a portion of the stem or root. When Reproduction growers use these methods to start new plants, they must make Procedure sure that the leaf, stem, or root cuttings have plenty of water and 1. Using a pair of scissors, cut anything else that they need to survive. a stem with at least two Asexual reproduction has been used to produce plants for pairs of leaves from a coleus centuries. The white potatoes shown in Figure 2A were probably or another houseplant. 2. Carefully remove the produced asexually. Many plants, such as lawn grasses shown in bottom pair of leaves. Figure 2B, can spread and cover wide areas because their stems 3. Place the cut end of the grow underground and produce new grass plants asexually stem into a cup that is half- along the length of the stem. filled with water for two weeks. Wash your hands. Sexual Plant Reproduction Although plants and animals 4. Remove the new plant from the water and plant it in a have sexual reproduction, there are differences in the way that it small container of soil. occurs. An important event in sexual reproduction is fertiliza- tion. Fertilization occurs when a sperm and egg combine to pro- Analysis 1. Draw and label your results duce the first cell of the new organism, the zygote. How do the in your Science Journal. sperm and egg get together in plants? In some plants, water or 2. Predict how the new plant wind help bring the sperm to the egg. For other plants, animals and the plant from which it such as insects help bring the egg and sperm together. was taken are genetically related. How does fertilization occur in plants? SECTION 1 Introduction to Plant Reproduction B ◆ 95 Figure 3 Some plants can fertilize themselves. Others require two different plants before fertilization can occur. Flowers of pea plants contain These holly flowers contain Compare the flowers of this male and female structures,and only male reproductive structures, female holly plant to those of the each flower can fertilize itself. so they can’t fertilize themselves. male plant. Reproductive Organs A plant’s female reproductive organs produce eggs and male reproductive organs produce sperm. Depending on the species, these reproductive organs can be on the same plant or on separate plants, as shown in Figure 3. If a plant has both organs, it usually can reproduce by itself. How- ever, some plants that have both sex organs still must exchange sex cells with other plants of the same type to reproduce. Research Visit the In some plant species, the male and female reproductive Glencoe Science Web site organs are on separate plants. For example, holly plants are at science.glencoe.com either female or male. For fertilization to occur, holly plants to find out more about male with flowers that have different sex organs must be near each and female plants. In your other. In that case, after the eggs in female holly flowers are fer- Science Journal, list four tilized, berries can form. plants that have male and Another difference between you and a plant is how and female repoductive struc- when plants produce sperm and eggs. You will begin to under- tures on separate plants. stand this difference as you examine the life cycle of a plant. Plant Life Cycles All organisms have life cycles. Your life cycle started when a sperm and an egg came together to produce the zygote that would grow and develop into the person you are today. A plant also has a life cycle. It can start when an egg and a sperm come together, eventually producing a mature plant. 96 ◆ B CHAPTER 4 Plant Reproduction Two Stages During your life Fertilization cycle, all structures in your body are formed by cell division and made Sex cells (sperm and eggs) up of diploid cells—cells with a full (n) set of chromosomes. However, sex cells form by meiosis and are hap- loid—they have half a set of chro- mosomes. Gametophyte Sporophyte Haploid Diploid Plants have a two-stage life cycle, plant structures plant structures as shown in Figure 4. The two (n) (2n) stages are the gametophyte (guh MEE tuh fite) stage and the sporo- phyte (SPOHR uh fite) stage. Spores Gametophyte Stage When cells (n) in reproductive organs undergo meiosis and produce haploid cells Meiosis called spores, the gametophyte stage begins. Some plants release spores into their surroundings. Figure 4 Spores divide by cell division to form plant structures or an entire Plants produce diploid and new plant. The cells in these structures or plants are haploid. haploid plant structures. Some of these cells undergo cell division and form sex cells. Sporophyte Stage Fertilization—the joining of haploid sex cells—begins the sporophyte stage. Cells formed in this stage have the diploid number of chromosomes. Meiosis occurs in some of these plant structures to form spores, and the cycle begins again.
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