Grade: 9 to 12 Length: variable Subjects: life science Topics: weed identification Objectives Exercises in this lesson help students achieve the following objectives: Understand the basic parts of a plant Understand how the basic parts of a plant work together Follow the growth cycle of a plant from the seed stage to the production of a new seed Introduction Like most plants, weeds have four major parts: roots, stems, leaves, and flowers or seeds. Individual parts comprise each of the four major parts, and each part has a specific function. Students will learn about the parts of a plant and stages of plant development by planting bean seeds and observing the plants as they grow through all stages of development, until the plant produces seeds. Before teaching this lesson, read the entire lesson and make sure all materials are available. Diagram of a Typical Plant Invasives: Plants on the Move ~ ~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 137
Background Roots Roots serve the following three major functions: Anchor the plant in the soil Absorb water and nutrients Store food Roots have a number of different components that help achieve these functions. Tiny root hairs absorb water and nutrients. Each root hair has a root cap to protect the root hair as it pushes through the soil. Behind the root cap is a zone of cell division. Behind the zone of cell division is the zone of cell elongation, where roots lengthen. Root growth takes place in these two zones. The meristematic zone includes the root cap and the zone of cell division. The xylem transports water and minerals from the roots to the stem. Xylem tissue consists mainly of hollow tubes. The phloem carries food from the leaves to the roots. Cambium tissue is the living part of a stem. Cell division takes place in the cambium. The arrangement of the xylem and phloem and the location of the cambium are different in monocotyledons and dicotyledons. Cross-section of a monocot stem Cross-section of a dicot stem Cross-section of a stem Stems Stems serve the following three major functions: Transport water and minerals from the roots to the stem and food from the leaves to the roots Hold the plant erect so the leaves can reach the sunlight Store food Diagram of a Root Leaves Leaves serve the following three major functions: Produce food for the plant Store food Take in and let out various gases A plant produces food through a process called photosynthesis. During photosynthesis, a plant uses sunlight to produce glucose or food. Specifically, a plant uses sunlight, carbon dioxide, and water to produce glucose. A plant produces oxygen as a waste product. Plants contain a chemical called chlorophyll, which makes photosynthesis possible. In most plants, chlorophyll is green in color, and tiny structures called chloroplasts contain the chlorophyll. 138 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move
A plant must have energy to live. The plant obtains its energy by breaking down glucose through a process called respiration. Respiration is the reverse of photosynthesis. (See the illustration Respiration and Photosynthesis on page 122.) Plants continuously transport water to the leaves from the roots. Leaves release water vapor and other gases through openings called stomata. This process is called transpiration. Through transpiration, water comes into the plant, and transpiration keeps the plant cool during hot months. To carry out these complex functions, leaves have developed an amazing structure. coat disintegrates, a root hair emerges and begins to absorb water and nutrients, and seed leaves emerge and grow toward the sunlight. radicle (develops into a root) cotyledon plumule (develops into the stem and leaves) seed coat Bean Seed Cross-section Leaf Cross-section Flowers and seeds The major function of flowers is to help in sexual reproduction. Some parts of a flower, such as the petals, nectar, and perfume, attract bees and other insects. The male part of the flower is the stamen, which is comprised of the filament and anther. The anther holds pollen. The female part is the pistil, which is comprised of the stigma, style, and ovary. When insects land on flowers, they transfer pollen from the anther to the stigma. The pollen moves down the style and fertilizes the egg. Once fertilized, the egg becomes a seed, and the flower dies and drops off. The seed contains a living embryo. A seed coat encloses the embryo and protects the embryo until it is ready to germinate. The seed also contains seed leaves (cotyledons) and stored food (endosperm). The seed remains dormant until conditions are ideal for growth. Under ideal conditions, the seed Characteristics of plants Each weed has specific characteristics that help botanists identify the weed. Some characteristics are difficult to identify; others are obvious. The following characteristics are some of the more obvious characteristics botanists use to identify weeds: Flower color Flower arrangement on stem Vein arrangement in leaves Blade type Leaf arrangement on stem When identifying a weed, the color of the flower is one of the first characteristics botanists notice. However, many weeds have the same color of flower. Flower arrangement on the stem is the next characteristic botanists look for. Other identifying characteristics that botanists use include leaf shape, leaf margins, shape at the base of the blade, and shape of the blade tips. Preparation Materials bush bean seeds Have available 10 seeds for every two students. paper towels plastic sandwich bags Invasives: Plants on the Move ~ ~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 139
Leaf Arrangements Flower Arrangements Leaf Venation Leaf Types 140 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move
1 potting soil with time-release fertilizer 4-inch pots Have available at least two pots for every two students. greenhouse, window, or other growing area dissecting microscope or hand-held lens copies of Life cycle of a Bean Plant, Plants and Their Parts, and From Seed to Shining Seed Weed Journal Entries worksheets Have available one copy for each student student Weed Journals Assemble all the materials listed above. Students will use these items during the Activity. Give each student a copy of each worksheet. Activity 1 Divide students into teams of two students per team. Discuss the Plants and Their Parts and Life cycle of a Bean Plant worksheets. 2 To observe the emergence of roots and determine seed viability: A. Instruct each team to place 10 bean seeds on a wet paper towel, and place the paper towel in a sandwich bag. B. Seal the bag and place it in a warm location. 3 C. As roots emerge, ask students to record their observations on the From Seed to Shining Seed Weed Journal Entries worksheet. D. After seeds have germinated, ask students to calculate the percentage of viable seeds. E. Discuss the germination process to ensure students understand the process. Have students carefully transplant at least two of the germinated seeds into 4-inch pots containing potting soil with slow-release fertilizer. 4 Instruct students to record emergence of the cotyledons and all stages of plant growth and development. 5 6 Remove one of the flowers and study it under a dissecting microscope. During the flowering stage, shake flowers to ensure cross-pollination. Conclusion and Evaluation Conclude the lesson when the plants produce beans and students have harvested the seeds. Evaluate students on their ability to identify weeds using the physical properties outlined earlier in this lesson. Or use the Weedy Crossword Puzzle as a quiz. Invasives: Plants on the Move ~ ~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 141
Independent Practice and Related Activities Most commercial bean seeds are hybrids. Seeds from hybrids are not as viable as seeds from the parent plants, and hybrid plants are not as hardy as the parent plants. To demonstrate these characteristics, harvest the bean seeds, dry the seeds, and plant them. Calculate the percentage of viable seeds. Vocabulary alternate, anthers, blade, cambium, chlorophyll, chloroplasts, corymb, dicotyledon, dormancy, embryo, epidermal cells, glucose, guard cells, internode, meristem, monocotyledon, node, opposite, ovary, palmate compound, parallel, phloem, photosynthesis, pinnate, pinnate compound, pistil, plumule, pollen, pollination, raceme, radicle, respiration, root cap, root hairs, roots, rosulate, seed, sexual reproduction, simple, spike, stamen, stems, stigma, stoma, style, transpiration, umbel, venation, whorled, xylem, zone of cell division, zone of elongation Resources Peterson, Roger Tory and Margaret McKenny. A Field Guide to Wildflowers of Northeastern and North-central North America. Boston: Houghton Mifflin Company, 1968. National Science Education Standards As a result of their activities in grades 9 to 12, students should develop an understanding of and abilities in the following areas: Science as Inquiry Content Standard A: scientific inquiry, understandings about scientific inquiry Life Science - Content Standard C: matter, energy, and organization in living systems; behavior of organisms Solution to Weedy Crossword Across 1. Phloem 3. Spike 5. Embryo 7. Stoma 9. Respiration 11. Dicot 14. Photosynthesis 16. Corymb 17. Stem 18. Umbel 21. Germinate 22. Transpiration 23. Monocot 25. Raceme 26. Stigma 30. Pinnate 31. Cotyledon 33. Whorl 34. Alternate 35. Leaves 36. Palmate 37. Nodes Down 1. Petals 2. Meristematic 4. Stamen 5. Endosperm 6. Root cap 8. Anther 10. Roots 12. Xylem 13. Filament 15. Solitary 17. Seed 19. Elongation 20. Internode 24. Opposite 27. Stomata 28. Simple 29. Style 32. Ovary 142 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move
Life Cycle of a Bean Plant Germination Germination occurs underground when sufficient water, oxygen, and heat are present. The seed coat swells and then starts to disintegrate. A tiny root (radicle) appears, followed by a tiny stem (plumule). Growth Approximately 5 to 7 days after planting, the first leaves two oblong seed leaves (cotyledons) emerge from the soil. As the plant continues to grow, true leaves begin to appear. radicle (develops into root) cotyledon plumule (develops into the stem and leaves) seed coat Reproduction After about 3 weeks, the first flowers appear. These flowers are white and solitary. If conditions are suitable for pollination, the flowers fade after 3 to 4 days. In the center of the flower, a small bean emerges. As the bean grows, the flower petals fall off. The bean pod continues to grow until it reaches a length of 3 to 4 inches. Seeds Once the pod is fully grown, it will contain 4 to 7 new bean seeds. Plant these seeds, and begin the whole process again. Invasives: Plants on the Move ~ ~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 143
Plants and Their Parts Diagram of a root Diagram of a typical plant Cross-section of a monocot stem Cross-section of a dicot stem Leaf cross-section Cross-section of a stem 144 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move
Weedy Definitions page 1 of 2 alternate leaf arrangement in which each leaf is attached at a different level on the stem anther the head at the top of the filament where pollen forms blade the flat part of a leaf; to physically scrape an area with a blade to remove weeds cambium tissue that forms the living part the stem; where cell division takes place in the stem chlorophyll a green-colored chemical that converts the sun s energy to food through the process of photosynthesis chloroplasts sacs in plant cells that contain chlorophyll corymb a flat flower head consisting of flowers whose stalks grow from different points on the flower stem but reach approximately the same height dicotyledon a flowering plant that produces two seed leaves when it germinates and whose subsequent leaves have a network of veins dormant in an inactive state, when growth and development slow or cease, in order to survive adverse environmental conditions embryo a plant in its earliest stages of development; in seed-bearing plants, the embryo is contained within the seed epidermal cells the outermost layer of cells glucose a sugar produced by plants through photosynthesis guard cells cells that surround the stoma internode the distance between nodes meristematic zone composed of the root cap and the zone of cell division monocotyledon a flowering plant that has a single leaf in the seed and floral parts in multiples of three node composed of the leaf axil and bud opposite leaf arrangement in which two leaves are attached at one level but on different sides of the stem ovary where seeds develop at the base of a flower palmately compound leaflets attached at the end of a stalk, spreading like fingers on a hand parallel veining veins that run alongside each other and never intersect phloem a tube that carries food from the leaves to the roots photosynthesis process through which plants use sunlight, carbon dioxide, and water to make glucose and oxygen pinnately compound leaflets arranged around a central stalk pistil the female reproductive part of a flower, composed of the ovary, style, and stigma plumule the rudimentary primary shoot of a plant embryo pollination the process of transferring pollen from the anther to the stigma to fertilize a plant raceme a flower cluster in which the flowers are borne on short stalks along a long main stem radicle the part of a plant embryo that forms the root of the young plant respiration the process through which plants break down glucose to make energy; the reverse of photosynthesis root cap protects the root hair Invasives: Plants on the Move ~ ~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 145
Weedy Definitions page 2 of 2 root hairs absorb water an nutrients roots function to anchor a plant, absorb water and nutrients, and store food rosulate leaf arrangement in which leaves are attached around the base of the stem seed the body produced by reproduction in most plants that contains the embryo and produces a new individual sexual reproduction natural process by which some plants and animals produce offspring as a result of fertilization of the egg from another plant or animal simple a leaf that is not divided, either totally or partially, into separate segments spike a long cluster of flowers attached directly to a stem, with the newest flowers at the tip stamen the male reproductive organ of a flower, composed of the anther and the filament that holds the anther stem the main trunk of a plant stigma the sticky top of the style that collects pollen stomata ventilation holes in a leaf that take in carbon dioxide and release oxygen style stem-like extension of the ovary through which a pollen tube grows down into the ovary carrying the pollen necessary for fertilization transpiration the process of evaporation from a plant s leaves umbel a flower cluster that has a number of branches all attached at one point venation the pattern of veins whorl a leaf arrangement in which three or more leaves are attached in a ring at one level xylem a tube which transports water and minerals zone of cell division the place in the root where cells divide zone of cell elongation the place in the root where cells become larger Respiration and photosynthesis 146 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move
From Seed to Shining Seed Weed Journal Entries Event Date Observations Number of seeds planted First radicle appears First seed leaves appear Last seeds germinate number of seeds germinated % viability Seedlings transplanted First flowers appear First bean pods appear Bean pods appear Bean pods appear Bean pods appear Bean pods appear Bean seeds harvested Invasives: Plants on the Move ~ ~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 147
1 2 3 4 5 6 7 8 9 10 Weedy Crossword Puzzle 15 22 25 32 34 14 16 18 20 26 27 30 12 31 33 19 21 17 23 35 11 24 28 13 29 36 37 Across 1. Carries food from the leaves to the roots 3. Long cluster of flowers attached directly to a stem, with the newest flowers at the tip 5. Plant in its earliest stages of development 7. Leaves release gases through this opening 9. Process through which plants break down glucose to make energy 11. Flowering plant that produces two seed leaves when it germinates 14. Process through which plants use sunlight, carbon dioxide, and water to make glucose and oxygen 16. Flat flower head consisting of flowers whose stalks grow from different points on the flower stem but reach about the same height 17. Transports minerals and water from the roots to the stem and food from the leaves to the roots 18. Flower cluster with branches all attached at one point 21. To grow from a seed into a new plant 22. Process through which plants bring water to the leaves from the roots and release gases from the leaves 23. Flowering plant that has a single leaf in the seed 25. Flower cluster in which flowers are on short stalks along a long main stem 26. Sticky top of the style that collects pollen 30. Arranged along a central stalk or stem 31. Seed leaves within a seed 33. Leaf arrangement in which three or more leaves are attached at different levels on the stem 34. Usual leaf arrangement where leaves are attached at different levels on the stem 35. Produce food for the plant and take in or let out gases 36. Leaves or veins which spread like fingers on a hand 37. Consist of leaf axils and buds Down 1. Showy colored parts that form the outer part of a flower 2. This zone is made of the root cap and the zone of cell division 4. Composed of an anther and filament 5. Stored food within a seed 6. Protects root hairs as they push through soil 8. Head where pollen forms at the top of the filament 10. Anchor plants in soil and absorb water and nutrients 12. Part of the stem that transports water and minerals 13. Stalk-like part of the stamen 15. Flower that grows singly rather than as a cluster 17. Body produced by reproduction in most plants that contains the embryo and produces a new individual 19. In this zone, cells become larger 20. Distance between nodes 24. Leaf arrangement where leaves are attached at one level on different sides of the stem 27. Plural of 7 Across 28. Leaf that is not divided, either totally or partially, into separate segments 29. Stem-like extension of the ovary through which a pollen tube grows down into the ovary carrying the pollen necessary for fertilization 32. Seeds develop here 148 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move