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Introduction

AP Biology Lab 9: Transpiration Introduction Most of the water a plant absorbs is not used for a plant's daily functioning. It is instead lost through transpiration, the evaporation of water through the leaf surface and stomata, and through guttation, which is the loss of water from the vascular tissues in the margins of leaves. There are three levels of transport in plants: uptake and release of water and solutes by individual cells, short distance cell to cell transport at tissue and organ levels, and long distance transport of sap by xylem and phloem at the whole plant level. The transport of water is controlled by water potential. Water will always move from an area of high water potential to an area with low water potential. This water potential is affected by pressure, gravity, and solute concentration. Water moves into the plant through osmosis and creates a hydrostatic root pressure that forces the water upward for a short distance, however, the main force in moving water is the upward pull due to transpiration. This pull is increased by water's natural properties such as adhesion and cohesion. Transpiration decreases the water potential in the stele causing water to move in and pull upward into the leaves and other areas of low water potential. ...read more.

Middle

The slice was placed in the 50% ethanol. The slices were left in the ethanol for five minutes. Using the forceps, the slices were moved to a dish of the toluidine blue O stain and left for one minute. The sections were rinsed in distilled water. The section was mounted on the slide with a drop of 50% glycerin. A cover slip was placed over the slide. The cross section was observed under a light microscope and drawn. Results Table 9.1: Individual Potometer Readings Time (min) Beginning (0) 3 6 9 12 15 18 21 24 27 30 Reading (mL) .02 .03 .04 .05 .06 .07 .09 .10 .11 .13 .13 Class Potometer Readings Time (min) Beginning (0) 3 6 9 12 15 18 21 24 27 30 Room .53 .54 .55 .56 .57 .58 .59 .60 .61 .62 .63 Mist .34 .36 .38 .40 .42 .43 .43 .44 .45 .45 .46 Light .67 .68 .69 .70 .71 .72 .73 .74 .75 .77 .79 Fan .02 .03 .04 .05 .06 .07 .09 .10 .11 .13 .13 Mass of leaves = 1.1 g Leaf Surface Area = 0.0044 m2 Table 9.2: Individual Water Loss in mL/m2 Time Interval (minutes) 0-3 3-6 6-9 9-12 12-15 15-18 18-21 21-24 24-27 27-30 Water Loss (mL) ...read more.

Conclusion

Error Analysis This lab had many opportunities for error. The potometer set up was a complicated procedure. If any air bubbles were present in the plastic tubing, it could cause drastic error to occur. Any miscalculations or inaccurate weighing could also account for error. Conclusion Transpiration in plants is controlled by water potential. This change in water potential in leaves causes a gradient by which water can be moved upward. When the water potential of the air was increased by the mist and plastic bag, less water evaporated from the leaves, decreasing the water potential gradient between the root and stem. This decreased the transpiration pull. The fan and floodlight simulated environmental conditions such as wind, heat, and intense light. These conditions increase the amount of water transpired by plants. This in turn increased the water potential gradient causing more water to be pulled through the stem. The control plant should have had normal rates of transpiration. The stem must have specialized cells for support and transport. The epidermis is the outermost layer of the stem. The xylem is a transport tube for water, and the phloem transports food and minerals through the plant. Parenchyma are non-specialized cells and are located in the interior. The tougher sclerenchyma and collenchyma make up the structural outer support of the epidermis and the transport tubes of phloem and xylem. ...read more.

This student written piece of work is one of many that can be found in our GCSE Green Plants as Organisms section.