This transpirational pull occurs because of 1 the cohesion of water molecules

This transpirational pull occurs because of 1 the

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from the leaves to the roots. This transpirational pull occurs because of (1) the cohesion of water molecules to one another due to hydrogen bond formation, and (2) by adhesion of water molecules to the walls of the xylem cells which aids in offsetting the downward pull of gravity.The upward transpirational pull on the fluid in the xylem causes a tension (negative pressure) to form in the xylem, pulling the walls of the xylem inward. The tension also contributes to the lowering of water potential in thexylem. This decrease in water potential, transmitted all the way from the leaf to the roots, causes water to move inward from thesoil, across the cortex of the root, and into the xylem.Plants lose as much as 90% of the water that enters the roots by the processof transpiration. Evaporation through the open stomates is clearly a major route of water loss in plants.However, the stomates must open to allow the entry of CO2 used in photosynthesis. Therefore, a balance must be maintained between the gain of CO2 and the loss of water by regulating the opening and closing of the stomata on the leaf surface. Many environmental conditions influence the opening and closing of stomates and also affect the rate of transpiration.Temperature, light intensity, air currents, and humidity are some of these factors. Different plants also vary in the rate of transpiration andin the regulation of stomatal opening. In this lab, you will measure transpiration under various laboratory conditions using a potometer. Hypothesis : - “If all of the plants in this experiment
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will lose water through transpiration, than those affected by the heat sink and the fan will lose a larger amount of water due to the environmental conditions, because transpiration will pull water from the potometer into the plant with the structure and the cell types of a stem cross-section can be observed under a microscope”. Purpose : - The purpose of this lab was to measure the rate of transpiration in a plant under various conditions in a controlled experiment. We than discoveredthe effect thatdifferent environmentalfactors have on transpiration rate. The environmental factor we chose to test was amountof light. V ariables: - 1. - Independent variable: - The light, what is being changed . 2. Dependent variable: - The plant, what is changing due to the independent variable. 3. - Control Variables : - Amount of light. Materials & Procedure : - 1. Place the tip of a 0.1 mL pipette into a 16 -inch piece of clear plastic tubing. 2. Submerge the tubing and the pipette in a shallow tray of water. Draw water through the tubing until all the air bubbles are eliminated. 3. Carefully cut your plant stem under water. This step is very important, because no air bubbles must be introduced into the xylem. 4. While your plant and tubing are submerged, insert the freshly
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  • Fall '14
  • Xylem

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