All plants have roots, stems and leaves. The roots are the underground parts of most plants. They absorb water and minerals, to store food. They anchor the plant to the soil. The first structure to appear from a germinating seed is the embryonic root. The cells at this primary root undergo rapid cell division and growth is downward. Secondary roots grow from the primary root and may produce root hairs. The root hairs increase absorption of the root system. Internally roots have bundles of food (phloem) and water (xylem) tubes surrounded by cortex cells. The vascular system provides for transport of absorbed water and minerals to the stem. It also provides for the passage of food manufactured in the leaves during photosynthesis to storage areas in the root. (see Plants, Milliken Publishing Company, St Louis, MO, 1986 for plant unit with excellent overhead transparencies/graphics)
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Stems are channels through which food and water passes through a plant. There are five parts to the stem: epidermis, cortex, phloem, xylem, and pith. The epidermis is the external layer of cells. This single layer of cells prevents excessive evaporation from internal tissues. The cortex is made up of cells which provide strength, protection and storage areas or the plant. Phloem tissue, which forms food-flowing tubes, conduct the downward flow of food manufactured in the leaves. The xylem tissue, forming water flowing tubes, conducts the upward flow of water and dissolved minerals from the soil via roots to a ll parts of the plant. Stems may grow above or below the ground. Stems which grow above the ground are aerial stems. These include ivy and strawberries. Stems which grow below the ground are called underground; these include bulbs and tubers. Daffodils, tulips and iris are common types of bulbs.
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Leaves have the important function of manufacturing food for the plant using water, carbon dioxide and light. Parts of the leaf include the upper epidermis, lower epidermis with stomata and guard cells, chlorophyll-rich palisade and spongy tissue, and the veins containing phloem and xylem tubes. The single layer of cells that forms the upper outside surface of a cell is the upper epidermis. The lower epidermis has many minute openings that permit photosynthesis. The middle section contains layers of tissues that are rich in chlorophyll.
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Leaves are food producers. In photosynthesis, leaves use chlorophyll to convert water, carbon dioxide and light energy into sugar and oxygen. The chemical formula for photosynthesis is:
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6CO2 + 6 H2O + light energy --chlorophyll-- C6H606 + 6 02
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Photosynthesis is the process by which light energy is converted to chemical energy.
In plants, energy is stored chemically in glucose, a form of sugar. Plants need sunlight in order to combine carbon dioxide and water to produce sugar. Without the energy stored in glucose, plants cannot grow.
Leaves have the following parts: upper epidermis, palisade cells, spongy cells, stomata, and veins. All these parts are needed for photosynthesis.
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Palisade and spongy cells contain chlorophyll.
Photosynthesis occurs in green leaves and stems inside the chloroplasts in the cells.
Carbon dioxide enters through the stomata.
Oxygen is a byproduct of photosynthesis. It exits leaves through the stomata.
Oxygen produced during photosynthesis is used by humans and other animals.
To grow, plants must have carbon dioxide and water.
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Transpiration, the release of water vapor from a plant, occurs through the stomata. 90% of the water absorbed by the roots is evaporated and released back into the atmosphere. A single corn plant can release as much as 200 liters of water into the atmosphere during the growing season.
(Use the Encarta Encyclopedia [http://encarta.msn.com/encyclopedia] contents page for the Photosynthesis article and the animation on photosynthesis. Using the animation, guide students through the steps of the process.)
Activities
Experiment: Tracing water through plants
Elementary students place a carnation in water with food coloring. To prepare these middle school students for the CAPT and reinforce the concepts of absorption through the root and stem systems, pose the following question: Do roots or stems absorb water quicker? This may be presented as group lab experiment or a demonstration. Use the Lab format presented with Observing the Effect of Pollutants on Plant Growth. Ask students to develop graphs as well. Set up experiment on Day One and allow time (approximately 10 minutes) for observation, measurement and recording data on Days Two and Three.
Materials
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2 200 mL beakers
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150 mL water
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red food coloring
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metric ruler
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2 small potted, flowering plants; plants must be similar size growth
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(tulips work well)
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plastic (latex) gloves
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Procedure
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1. In each of the two beakers, add 150 mL water with four drops of food coloring
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2. Wearing gloves, carefully remove one flowering plant with roots from planter and place in beaker #1.
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3. Cut the second flowering plant at the base of the stem and place in beaker #2.
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4. After 24 hours remove plant with roots from beaker #1, blot excess water with a paper
towel. Measure how far the food coloring traveled through the root and stem systems
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5. Remove the stem from beaker #2 and repeat procedure 4 above.
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6. Record your results on a table or graph.
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7. On day two, repeat procedures 4, 5 & 6.
Concentration
Create a game of concentration using facts describing the process of photosynthesis. Using index cards, copy terms and facts from column A. Copy definitions and explanations from column B. Ask students to add to these lists. Create multiple sets of cards for student teams. Review these facts and terms with students. Assemble student teams with their own set of cards. Place all cards upside down and have each member of a team turn over two cards attempting to match a definition with a term.
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A
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B
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autotrophs
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organisms that make their own food
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photosynthesis
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process by which light energy is converted
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to chemical energy
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glucose
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a form of sugar in which energy is stored
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6CO2 + 6 H2O + light energy
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C6H606 + 6 02 + H2O
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leaves
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part of a plant needed for photosynthesis
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chlorophyll
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found in palisade and spongy cells
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chloroplasts
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contain the pigment chlorophyll
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stomata
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part of plant through which carbon dioxide enters
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oxygen
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biproduct of photosynthesis
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ozone
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oxygen from plants which reacts with sunlight
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in upper atmosphere & protects us from the sun
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