Eco-Explorers! Title: Leaking Leaves Topics: Plant Structure, Transpiration, and Water Conservation Key Questions: 1. How does water move through a plant? 2. How do plants conserve water? 3. How do plants lose water? How much water does a plant lose in a day? 4. How are plants in the desert similar and different to those in temperate forests? 5. How do desert plants prevent water loss? Objectives: 1. Students will observe how water moves through a plant. 2. Students will measure the amount of water a plant loses through transpiration in a day. 3. Students will learn how plants balance water intake and output. 4. Students will discuss environmental factors that affect the plant s conservation of water. 5. Students will discuss the similarities and differences of plant structures in the desert and temperate forests. Key Words: Leaf Photosynthesis Roots Stem Stomata Transpiration Xylem Materials: General materials: (for demonstration) Carnation and / or celery Food coloring Cup Water Each group of approximately 4 students needs: (for transpiration water collection) Plastic Baggies Rubber bands/ twist-ties Pipettes or Turkey baster (shared with class) Graduated cylinder (shared with class) Each student will need: 5-10 leaves from different plants Ruler with cm Pencil/crayons Eco-Explorers! Transpiration Page 1 of 1
Getting Ready: 1. At the end of class the day before: Place a carnation or stalk of celery into a container of water with food coloring. Ask students to hypothesize what they think might happen to the flower or the stalk. Procedure: PART 1: Whole group activity (next day, carnation demonstration) 1. In the classroom, explain why transpiration is a necessary process in the life of a plant. By using the carnation as an example, show that water moves up from the roots to the leaves of a plant by means of the xylem. You can cut the stem in half lengthwise to see food coloring inside the plant stem. 2. Students should discuss how water moves through a plant based on their observations. PART 2: Small group activities A. Transpiration Water Collection 1. Students, in groups of four, will take a plastic baggie and secure it over a leaf or leaves of a plant (outdoor tree or shrub, indoor houseplants) using rubber bands or twist-ties. The leaves must stay connected to the stem for this to work. When tied, it's best if the tied end of the baggie is tilted up. They will record the type of plant, the number of leaves in the baggie, and the time that they started the experiment on their data sheets. 2. Students will remove the baggies at the end of the day, being careful not to spill any water. Using a pipette, turkey baster or funnel, students will collect the water from the baggies and empty it into a graduated cylinder. They will record the amount of water collected and the time that they ended the experiment. 3. Students will post their results online and compare them to the results found from desert plants. 4. Discuss why temperate plants will transpire more water than desert plants. Talk about the environmental factors that may affect the amount of water that is evaporated from plants. Light- Plants transpire more rapidly in light than in dark. This is due to the fact that light stimulates the opening of the stomata, small holes on the surface of leaves from which gas exchange takes place. Light (heat energy) also speeds up transpiration by warming the leaf. Temperature- Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as temperature rises. Humidity- Water will diffuse out of the leaf more quickly when the surrounding air is dry. Wind- Lack of wind means that the air surrounding the leaf becomes more and more humid, thus reducing the rate of transpiration. If wind is present, the humid air will be replaced by drier air. Water- A plant cannot continue to transpire rapidly if its water loss is not made up by the replacement from the soil. When absorption of water by the roots fails to keep up with the rate of transpiration, stomata close, reducing the rate of transpiration. B. Plant Structures (after baggie experiment has begun) 1. Plant Collection: Students will go outside to their forest test site and collect 5-10 different leaves from different plants. Eco-Explorers! Transpiration Page 2 of 2
2. Students will record data about each leaf onto their data sheets. They will measure the length and width of each leaf, (at its widest and tallest parts), note the color(s), the pattern(s), the appearance of the veins, the shape, and the texture of the leaf. Students should record their observations of the leaves in the form of drawings and notes on their data sheet. Using references, the students should identify the kind of plant their leaves came from. 3. Discuss the leaf s role in photosynthesis and transpiration. Why are stomata important? 4. Discuss how leaves in the desert are similar or different to those of a temperate forest. Log onto the Ecoexplorers website to view the plants found in the desert. Why are there differences? What are some of the similarities? In the desert, leaves may be small or spiny so that they won t lose much water in transpiration. Desert leaves can also be waxy to prevent water loss. Temperate forest leaves are largely deciduous- they loose their leaves in the winter. They are usually larger and can lose more water in transpiration because they can easily take in more water through their roots. PART 3: Discussion/ Conclusion 1. Hold a discussion about how environmental factors and plant structures influence the amount of water that a plant transpires. How do desert plants conserve water? Is transpiration a major concern for temperate forests? Background Information: Transpiration Transpiration is the evaporation of water from plants. Water evaporates from a stomates in a plant's leaf. Stomates are tiny pores on the leaves which the plant can open and close for gas exchange. Transpiration mainly occurs while the stomata are open for the passage of CO 2 and O 2 during photosynthesis. Air that is not fully saturated with water vapor will dry the surfaces of cells with which it comes in contact. Photosynthesizing leaves lose substantial amount of water by evaporation. This transpired water must be replaced by the transport of more water from the soil to the leaves through the xylem of the roots and stem. Transpiration is an important plant function providing water for photosynthesis. Transpiring water transports minerals and organic compounds for growth and cools the plant. Evaporating water also cools a leaf's surface just like evaporating sweat cools our skin. Stomata and Gas Exchange in Plants The exchange of oxygen and carbon dioxide in the leaf during photosynthesis and the loss of water vapor in transpiration occur in pores called stomata. Stomata open when light strikes the leaf in the morning, and close at night. Stomata are flanked by guard cells, which are elastic and can be formed into a crescent shape to open the stoma when water pressure develops. Stomata are essential in photosynthesis because they open the pores that allow for gas exchange, but are also alow for transpiration. When the stomata are open, water that is being pull up through the xylem is exposed to the air and evaporates off. (The xylem is like a central vein that transports water in the roots and stem of the plant.) About 90% of this water is Eco-Explorers! Transpiration Page 3 of 3
lost in transpiration. When water in the soil is insufficient to keep up with transpiration, a hormone causes the stomata to close, so that no more water will be lost. Desert Plant Adaptations In order to survive in an arid climate, desert plant must be successful at conserving water. Xerophytes, plants adapted to dry environments such as cacti, mesquite and Palo Verde, have means of storing and conserving water. Many desert plants have very small leaves or no leaves at all. The spines on a cactus are actually modified leaves. To conduct photosynthesis, these plants have a smooth, waxy green stem, which also helps to seal in moisture. This contrasts the large, broad leaves found in the temperate forests of Michigan, where water is not a limiting factor. Broad leaves can conduct photosynthesis efficiently, but will also lose much water through transpiration. Another adaptation of Xerophytes is the ability for the plant to store water in the stem for use in long stretches without rain. A cactus s waxy skin and vast, shallow root system also aid in sealing in moisture and collecting any available rainwater. Extension Activities HOW MUCH WATER TRANSPIRES OFF OF A PLANT IN ONE DAY? (Math problem) Students estimate the amount of water that a plant loses in an entire day. First, they will take the amount of water that they found for one leaf, multiply the number of leaves per stem, and multiply those times the number of estimated branches on the tree. They will then divide the number of hours of daylight by the number of hours they conducted the experiment. Finally, they will take this figure and multiply it times the amount of water produced by the entire tree for the experiment time. STOMATA UP CLOSE (optional- for use with classrooms with high powered microscopes) Students can observe their leaves more closely under a microscope. Take the leaves from the plant structures experiment and place them under a high- powered microscope. Under what magnification can you see stomata? Are they open or closed? How does one leaf compare to the next? Draw your observations. Hint: there are more stomates on the bottom surface of leaves than the top surface. Why? LEAF RUBBINGS Students can create their own artwork using their favorite leaves. They pick the leaf or leaves that they want to use. Gently, lay a piece of paper on top of the leaf. They need to hold the paper still on top of the leaf. Students rub over the leaf with the side of a crayon. They may need to rub a little harder so they can see all of the textures of the leaf. They may use a variety of leaves and colors. Eco-Explorers! Transpiration Page 4 of 4
Leaking Leaves: Data Sheet Name Predictions: 1. How much water will transpire off of a plant in Michigan? 2. How much water will transpire off of a plant in the desert? 3. Why do you think they are different or the same? Measurements and Observations: 1. What time did you place the baggie on the branch? 2. What time did you take the baggie off? 3. How much water did you collect from the baggie? 4. How much water was collected from a plant in the desert? 5. What factors cause this difference? Eco-Explorers! Transpiration Page 5 of 5
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Name: Leaf data sheet Leaf 1 Leaf 2 Leaf 3 Leaf 4 Leaf 5 Length Width Color Pattern Veins Shape Texture Type Eco-Explorers! Transpiration Page 7 of 7
Name: Seed, fruit or flower data sheet Seed 1 Fruit 2 Length Width Color Pattern Veins Shape Texture type Eco-Explorers! Transpiration Page 8 of 8
SEEDS, FLOWERS, & FRUIT DATA SHEET 1. Look at your seed. What do you see? 2. Measure your seed. Length: Width : 3. What do your predict your seed will grow into? 4. Draw your seed. 5. Look at your flower or fruit. What do you see? 6. Measure your flower. (or fruit) Length: Width: 7. What plant did your flower (or fruit) come from? 8. Draw your flower or fruit. Eco-Explorers! Transpiration Page 9 of 9
LEAF DRAWINGS Draw and color your five leaves. 1. 2. 3. 4. 5. How are your five leaves alike? How are your five leaves different? Do you think your leaves will be like the ones found in the rainforest? Why or why not? What did you find out about rainforest leaves? Eco-Explorers! Transpiration Page 10 of 10