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WHAT IS THE PURPOSE OF A SEED LEAF? Introduction Plants can reproduce in several ways depending on the species. Most of the best-known plants—like those that provide us with vegetables, trees, and flowers—grow from seeds. A seed is a reproductive structure that keeps the developing embryo inside a protective outer coating. Once the coating softens, germination occurs and the embryo starts to grow. Roots appear first, followed quickly by tiny shoots and leaves. The first set of leaves that appear on a young plant are called the cotyledons, or seed leaves. There are two big groups of seeds plants: monocotyledons and dicotyledons. Monocotyledons—like corn, wheat, and grass— produce only one seed leaf, and dicotyledons—such as tomatoes, pecan trees, and roses—produce two seed leaves. In this experiment, you will investigate the roles of seed leaves in developing plants. Time Needed 30 minutes on day 1 5 minutes on days 2 and 3 15 minutes on days 4 to 7 5 minutes on days 8 to 13 15 minutes on day 14 What You Need F 6 seedlings F aluminum roasting pan (medium size) with aluminum lid F ruler F labels © Infobase Publishing WHAT IS THE PURPOSE OF A SEED LEAF? 2 F small beaker F sharpened pencil F small bag of potting soil F scissors F graph paper (2 or 3 sheets) F permanent marker F access to water F access to window or a plant grow light F science notebook Safety Precautions Take care when working with scissors. Please review and follow the safety guidelines. What You Do: Day 1 1. Obtain an aluminum roasting pan with lid. Label one end of the loaf pan as “Exp” and the other end as “Cont.” 2. Use the pencil to punch six large holes into the bottom of the pan. Place the aluminum pan on the turned-over lid to use it as a tray. 3. Fill the pan three quarters full with potting soil, and pat it down. 4. Use the pencil to make six 2.5-centimeter (cm; 1-inch) holes in the soil, three on the “Exp” end of the pan and three on the “Cont” end. 5. Gently transfer one seedling into each of the six holes. Cover the seedlings with soil. See Figure 1 for reference. 6. Use a beaker of water to dampen the soil evenly. Do not add so much water that puddles begin to form. 7. Place the aluminum pan of pea plants under the light source. © Infobase Publishing WHAT IS THE PURPOSE OF A SEED LEAF? 3 light source seedlings Cont Exp aluminum roasting pan lid Figure 1 Figure 1 What You Do: Days 2 and 3 Check to see if the soil around the seedlings is dry. If so, use a beaker of water to evenly water the soil. What You Do: Days 4 to 7 1. Check to see if the soil around the seedlings is dry. If so, use a beaker of water to evenly water the soil. 2. Examine each seedling to see if seeds leaves have appeared and matured. Seed leaves, or cotyledons, shown in Figure 2, typically appear between days 4 and 7. 3. Once seed leaves on all seedlings have developed, modify the size of the seed leaves on the “Exp” plants. To do so, use scissors to trim off half of the leaf. Be sure to remove the same amount of seed leaf for each plant. Do not make any cuts on the “Cont” plants. © Infobase Publishing WHAT IS THE PURPOSE OF A SEED LEAF? 4 Figure Figure 22 What You Do: Days 8 to 13 Check to see if the soil is dry around the pea seedlings. If so, use a beaker of water to evenly water the soil. What You Do: Day 14 1. Compare the surface area of the leaves in the “Exp” and “Cont”groups. To do so: a. Use scissors to cut each leaf from one of the seedlings in the “Exp” end of the tray. Place the leaves on a piece of graph paper and trace around them. Count the squares on the graph paper that covered “Exp” leaves, and record the number in your notebook. Discard the leaves. Do the same for the leaves of the other two “Exp” seedlings. b. Use scissors to cut each leaf from one of the seedlings in the “Cont” end of the tray. Place the leaves on a piece of graph paper and trace around them. Count the squares on the graph paper that covered “Cont” leaves, and record the number in your notebook. Discard the leaves. Do the same for the leaves of the other two “Cont” seedlings. c. Compare the total number of squares covered by “Exp” leaves to the total number of squares covered by “Cont” leaves. Circle the total that is the largest. © Infobase Publishing WHAT IS THE PURPOSE OF A SEED LEAF? 5 Observations 1. In which group of plants is leaf surface area the greatest? Why do you think this is so? 2. Based on the results of your experiment, what is the role of the seed leaves of a seedling? 3. What would you expect to happen to a seedling if cold weather partially damaged its seed leaves? Explain your answer. 4. What would you expect to happen to a seedling if insects ate its seed leaves? Explain your answer? Want to Know More? See Our Findings. © Infobase Publishing SAFETY PRECAUTIONS Review Before Starting Any Experiment GENERAL • Always obtain your teacher’s permission for experiments performed at school, and your parent’s permission for experiments performed at home, before attempting any experiment. • Read all instructions for an experiment before starting the experiment, and follow the directions exactly as they appear in this volume. • If an experiment requires adult supervision, do not perform the experiment unless you have an adult supervising you the entire time you are performing the experiment. • Wash your hands before the start of and after each experiment you perform. • Keep your work area clean. • Never eat or drink while performing an experiment. Never taste a substance used in an experiment unless you are told that it is safe to do so. • Be aware of the location of safety equipment you may need in an emergency, such as running water, an eyewash if you are at school, and a fire extinguisher. • If you are going outside, make sure you have permission to go from your teacher and parent. Take a buddy with you, and dress appropriately for the weather. Make sure you or someone who accompanies you is familiar with the area, and bring along a firstaid kit in case of emergency. • Never look directly into the Sun. CHEMICAL SAFETY • Always wear goggles when working with chemicals, such as acids and bases, and near heat sources like flames. If at all possible, avoid wearing contact lenses when working with chemicals. • If any substance gets into your eyes, notify an adult (e.g., your teacher or parent) immediately, and flush your eyes with running © Infobase Publishing SAFETY PRECAUTIONS 2 water for at least 15 minutes. Do not mix chemicals unless you are told to do so by a teacher or parent. • Never touch, taste, or smell chemicals unless instructed to do so. • Keep chemicals in closed containers when they are not in use. • Dispose of all chemicals properly. Do not pour any chemicals or solids down the drain unless instructed to do so. • Use safety gloves and a plastic apron when handling chemicals. If any chemicals spill on your skin, rinse the affected area with running water for at least 10 minutes, and notify your teacher or parent immediately. • Take precautions to avoid spilling chemicals. If a chemical spills on any surface, notify your teacher or parent immediately to assist with clean-up. • Exercise caution when using sharp instruments such as knives or scissors. Always cut away from yourself, not toward yourself. If you cut yourself, notify your teacher or parent immediately. GLASSWARE • Clean glassware when you are finished with the experiment. • Be careful when using glassware. If a piece of glassware breaks, have an adult assist you in clean-up to avoid injuries from broken glass. Never use broken or damaged glassware. FIRE SAFETY • Do not heat glassware that is not completely dry. Do not pick up hot glassware without heat-resistant gloves or tongs. • When heating glassware, keep it away from yourself and from others. • Do not heat anything unless instructed to do so by a teacher or parent. • Do not heat substances in a closed container. • After an experiment, make sure that all heating sources are off and that all flames have been put out. © Infobase Publishing SAFETY PRECAUTIONS • Do not reach across such heating sources as flames. • If you have long hair, tie it back, out of the way. Do not wear clothing with loose sleeves, scarves, bows, ties, or anything else that may hang into a fire. Do not wear long earrings. ELECTRICAL SAFETY • Do not touch electrical equipment when your hands are wet. • Do not plug several electrical devices into one outlet or use an extension cord. © Infobase Publishing 3