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Slides transpiration pull
- 2. Objective Briefly explain the movement of water through the stem in terms of transpiration pull
- 3. What is transpiration? It is the loss of water from the aerial parts of the plant, especially through the stomata of the leaves. 9.4 Moving Water against Gravity
- 4. Activity (Roles) Volunteer for one of these roles 1.Sticker 2.Fixer 3.Suck-er 4.Recorder 9.4 Moving Water against Gravity
- 5. Activity (Materials) Collect the following materials from the front •1 bottle of juice drink •10 straws •1 scotch tape •1 pair of scissors •1 metre rule •1 damp cloth (for wiping spills on surfaces) 9.4 Moving Water against Gravity
- 6. Activity (Instructions) 1. Draw the juice from one straw 2. Tape the first straw to another straw and draw juice from the straw 3. Continue this process till juice is no longer able to reach the mouth 4. Measure the total length of the straws in cm 5. Complete the worksheet 9.4 Moving Water against Gravity
- 7. Activity (Precautions) 1. Wash your hands before and after the experiment. 2. Start by placing the cup on the table, move it to the stool, then to the floor. 3. Ensure fans are switched off. 4. You may climb on the stool and then the table to complete your experiment. 5. Slowly climb down from the tables or stools. 9.4 Moving Water against Gravity
- 8. How does transpiration occur? Processes that pull water molecules up the xylem vessels are – Transpiration pull • Suction force – Capillary Action • Cohesion • Adhesion 9.4 Moving Water against Gravity
- 9. What causes transpiration pull? Evaporation of water from the leaves results in a suction force that pulls water up the xylem vessels. 9.4 Moving Water against Gravity
- 10. What is capillary action? • Tendency of water to move up inside very narrow tubes (e,g, xylem) • Depends on the cohesion and adhesion of water molecules 9.4 Moving Water against Gravity
- 11. • Cohesion force • The tendency for similar substances to stick to each other – Water molecules stick to each other • Adhesion force – The tendency for dissimilar substances to stick to each other – Water molecules stick to xylem vessel wall 9.4 Moving Water against Gravity
Editor's Notes
- Note: Ask students to think about what results from the loss of water from the leaves and elicit any prior knowledge they may have. Introduce the idea of transpiration pull and use the analogy of sucking up water using a straw to illustrate how the suction force is created.
- Notes: Point out to students that capillary action and root pressure can help bring water up to the leaves for only small plants. Capillary action and root pressure do not generate enough force to move water up tall trees. There is a third force that is responsible for the ability of plants to bring water up to their leaves, even if they are located a few metres above the ground. This force is called the transpirational pull. Click on the Video-URL button to be directed to a website where a narrated animation on capillary action can be found. The animation lasts for about one minute.
- Notes: Point out to students that capillary action and root pressure can help bring water up to the leaves for only small plants. Capillary action and root pressure do not generate enough force to move water up tall trees. There is a third force that is responsible for the ability of plants to bring water up to their leaves, even if they are located a few metres above the ground. This force is called the transpirational pull. Click on the Video-URL button to be directed to a website where a narrated animation on capillary action can be found. The animation lasts for about one minute.