161_transpiration

161_transpiration - 1 Laboratory 10 Water Movement in...

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1 10-1 Laboratory 10 Water Movement in Vascular Plants This week, your objective is to learn about the function of one aspect of plant physiology: the movement of water through the vascular system. You will work in teams of four to design and perform and experiment that will help you understand the general workings of one of the two types of vascular tissue in plants, the xylem. This system of microscopic tubes, extending from the roots, through the stems, and finally to the leaves, is responsible for moving water from the soil, through the plant, and out the leaf openings known as stomates. I. Transpiration and the Vascular System About 1% of the water taken up by plants is used for metabolic functions such as photosynthesis. The other 119% exits without ever being used by the plant. This process, known as transpiration , is ecologically vital, however. It is one of the most important ways that water travels from the soil and back into the atmosphere, where it can then return to earth as life-giving precipitation. Before you begin today's exercise, be sure to review the Hydrologic Cycle and understand the role played by plants in this important biogeochemical cycle. Figure 10-1. The Hydrologic (Water) Cycle.
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2 10-2 II. Vascular plant anatomy Like all living things, plants have the ability to control their internal environment. Land plants (embryophytes) produce hormones that allow them to bend towards light, manufacture toxins at the site of physical injury to prevent herbivory, and may even be able to intimately control their osmotic internal environment, despite conditions of extreme heat, drought or wind. The non-vascular plants (bryophytes: mosses and liverworts) lack a complex system for water transport, and hence remain small; most can survive only in relatively moist environments. But vascular plants (tracheophytes) have conducting tissue that confers some independence from a wet habitat. Tracheophytes have a complex system of “tubes” ( the vascular system ) to transport water and solutes. Phloem travels throughout the plant, and transports organic solutes in an aqueous solution in every direction. Depending on the season and the plant's needs, phloem can even change its flow direction. Xylem starts at the roots, runs through the stems and ends at small pores ( stomates ) in the leaves. Stomates can open and close, depending not only on time of day, but also upon the osmotic condition of the plant. Xylem, which transports water and dissolved minerals, runs from the roots up through the stems and up to the stomates. Refer to your text to familiarize yourself with diagrams of xylem and phloem in typical plant roots and stems. The process of water movement through xylem and out the stomates is known as
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This lab report was uploaded on 04/18/2008 for the course BIL 161 taught by Professor Krempels during the Spring '08 term at University of Miami.

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161_transpiration - 1 Laboratory 10 Water Movement in...

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