Plant Plants have adaptations that enable them to reproduce in specific habitats. Reproduction Section 1 Introduction to Plant Reproduction Main Idea Reproduction in plants can be asexual or sexual. Plant life cycles include an alternation of generations. Section 2 Seedless Reproduction Main Idea The joining of a seedless plant’s egg and sperm requires moist condi- tions and produces a spore. Section 3 Seed Reproduction Main Idea Reproduction in seed plants involves pollen grains—the sources of sperm, and ovules—the sources of the eggs. The joining of eggs and sperms can produce seeds. A Forest from Ashes Saplings and other plants are growing among the remains of trees destroyed by fire. Where did these new plants come from? Some may have grown from seeds, and others may have grown from roots or stems that survived underground. These plants are the result of plant reproduction. Science Journal List three plants that reproduce by forming seeds. 270 Massimo Mastrorillo/CORBIS Start-Up Activities Plant Reproduction Make the following Foldable to compare and contrast the sexual and Do all fruits contain seeds? asexual characteristics of a plant. You might know that most plants grow from seeds. Seeds are usually found in the fruits of STEP 1 Fold one sheet of paper lengthwise. plants. When you eat watermelon, it can contain many small seeds. Do some plants produce fruits without seeds? Do this lab to find out. STEP 2 Fold into thirds. 1. Obtain two grapes from your teacher. Each grape should be from a different plant. 2. Split each grape in half and examine the STEP 3 Unfold and draw overlapping ovals. insides of each grape. WARNING: Do not Cut the top sheet along the folds. eat the grapes. 3. Think Critically Were seeds found in both grapes? Hypothesize how new grape plants could be grown if no seeds are pro- STEP 4 Label the ovals as shown. duced. In your Science Journal, list three other fruits you know of that do not con- Sexual Both Asexual tain seeds. Construct a Venn Diagram As you read the chap- ter, list the characteristics unique to sexual repro- duction under the left tab, those unique to asexual Preview this chapter’s content reproduction under the right tab, and those char- and activities at acteristics common to both under the middle tab. life.msscience.com 271 Massimo Mastrorillo/CORBIS Learn It! Summarizing helps you organize information, focus on main ideas, and reduce the amount of information to remember. To summarize, restate the important facts in a short sentence or para- graph. Be brief and do not include too many details. Practice It! Read the text on page 290 labeled Germination. Then read the summary below and look at the important facts from that passage. Important Facts A series of events that results in the growth of a plant from a seed is called germination. Seeds will not germinate until environmen- Summary tal conditions are right. Temperature, the Germination is the growth presence or absence of light, availability of of a plant from a seed. It water, and amount of oxygen present can requires certain environmen- affect germination. Sometimes the seed tal conditions. Processes occur must pass through an animal’s digestive within the seed that result in system before it will germinate. the growth of roots, a stem, and leaves. Germination begins when seed tissues absorb water. This causes the seed to swell and the seed coat to break open. Next, a series of chemical reactions occurs that releases energy from the stored food in the cotyledons or endosperm for growth. Eventually, a root grows from the seed, followed by a stem and leaves. Apply It! Practice summarizing as you read this chapter. Stop after each lesson and write a brief summary. 272 A CHAPTER 10 Plant Reproduction Reread your summary to make sure you didn’tiginal changemeaning Use this to focus on the main ideas as you read the chapter. the author’s or or ideas. Before you read the chapter, respond to the statements below on your worksheet or on a numbered sheet of paper. • Write an A if you agree with the statement. • Write a D if you disagree with the statement. After you read the chapter, look back to this page to see if you’ve changed your mind about any of the statements. • If any of your answers changed, explain why. • Change any false statements into true statements. • Use your revised statements as a study guide. Before You Read Statement After You Read A or D A or D 1 Both asexual and sexual plant reproduction involves sex cells. 2 Plants produced by asexual reproduction are genetically identical to the parent plants. 3 The structures of a gametophyte plant are made of haploid cells. 4 Insects usually move moss sperm to moss eggs. 5 The gametophyte stage of mosses is small and Print out a worksheet of this page at rarely observed by humans. life.msscience.com 6 Generally, fern fronds have structures on them that produce spores. 7 An embryo, stored food, and seed coat are parts of a seed. 8 Gymnosperm seeds are produced inside flowers. 9 An angiosperm fruit that has one or more seeds grows after fertilization. 10 Seed germination can occur within days after seed dispersal. 272 B Introduction to Plant Reproduction Types of Reproduction Do people and plants have anything in common? You don’t have leaves or roots, and a plant doesn’t have a heart or a brain. I Distinguish between the two Despite these differences, you are alike in many ways—you need types of plant reproduction. water, oxygen, energy, and food to grow. Like humans, plants also I Describe the two stages in a can reproduce and make similar copies of themselves. Although plant’s life cycle. humans have only one type of reproduction, most plants can reproduce in two different ways, as shown in Figure 1. Sexual reproduction in plants and animals requires the pro- You can grow new plants without duction of sex cells—usually called sperm and eggs—in repro- using seeds. ductive organs. The offspring produced by sexual reproduction Review Vocabulary are genetically different from either parent organism. fertilization: in sexual reproduc- A second type of reproduction is called asexual reproduction. tion, the joining of a sperm and This type of reproduction does not require the production of sex an egg cells. During asexual reproduction, one organism produces off- New Vocabulary spring that are genetically identical to it. Most plants have this • spore type of reproduction, but humans and most other animals don’t. • gametophyte stage • sporophyte stage Figure 1 Many plants reproduce sexually with flowers that contain In crocus flowers, bees and A cutting from this impatiens plant can be male and female parts. Other other insects help get the placed in water and will grow new roots. plants can reproduce asexually. sperm to the egg. This new plant can then be planted in soil. 272 CHAPTER 10 Plant Reproduction (l)Stephen Dalton/Photo Researchers, (r)Matt Meadows 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. 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 Observing Asexual of cell types. New plants can be grown from just a few cells in the Reproduction laboratory. Under the right conditions, an entire plant can grow from one leaf or just a portion of the stem or root. When grow- Procedure 1. Using a pair of scissors, ers use these methods to start new plants, they must make sure cut a stem with at least that the leaf, stem, or root cuttings have plenty of water and any- two pairs of leaves from thing else that they need to survive. a coleus or another Asexual reproduction has been used to produce plants for houseplant. centuries. The white potatoes shown in Figure 2 were probably 2. Carefully remove the produced asexually. Many plants, such as lawn grasses also bottom pair of leaves. 3. Place the cut end of the shown in Figure 2, can spread and cover wide areas because stem into a cup that is their stems grow underground and produce new grass plants half-filled with water for asexually along the length of the stem. two weeks. Wash your hands. Sexual Plant Reproduction Although plants and animals 4. Remove the new plant have sexual reproduction, there are differences in the way that it from the water and plant it occurs. An important event in sexual reproduction is fertiliza- in a small container of soil. tion. Fertilization occurs when a sperm and egg combine to pro- Analysis duce the first cell of the new organism, the zygote. How do the 1. Draw and label your results 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 such as insects help bring the egg and sperm together. it was taken are genetically related. How does fertilization occur in plants? SECTION 1 Introduction to Plant Reproduction 273 (l)Holt Studios/Nigel Cattlin/Photo Researchers, (r)Inga Spence/Visuals Unlimited Figure 3 Some plants can fertilize themselves.