8 Transport - Xylem

8 Transport - Xylem - Lecture: 8 BioSci 1C Apr.10.07...

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H 2 O product of photosynthesis (sucrose) H 2 O vapor H 2 O vapor H 2 O mineral ions Xylem and transpiration Lecture: 8 BioSci 1C Apr.10.07 Group presentation activity: Groups 2,4,6,8 present. Groups 1,3,5,7 ask questions. Each group will have to read through the whole lecture to get all of the needed information on their topic. Please use the slides and draw diagrams on the board. Think of ways to explain the ideas beyond just standing there talking to us. Assignments: Group 2: capillary forces: cohesion, Group 4: capillary forces: adhesion, Group 6: Role of transpiration in water uptake, Group 8: symaplastic versus apolplastic flow through roots.
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Factors Affecting Flow of Water in Air, Cells, and Soil • Hydrostatic pressure – In cells, called turgor pressure – Opposes flow of water into cells – Importance of turgor • Stiffens cells and tissues
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Factors Affecting Flow of Water in Air, Cells, and Soil • Capillary forces – Water molecules are cohesive • Stick to each other – Water molecules are adhesive • Stick to hydrophilic molecules • Example: carbohydrates – Cohesion and adhesion can generate tension that pulls water into small spaces
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Hydrogen Bonds Polar molecules, such as water molecules, have a weak, partial negative charge at one region of the molecule (the oxygen atom in water) and a partial positive charge elsewhere (the hydrogen atoms in water). Hydrogen Bond
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The hydrogen bonds that form between water molecules account for some of the essential — and unique — properties of water. •The attraction created by hydrogen bonds keeps water liquid over a wider range of temperature than is found for any other molecule its size. •The energy required to break multiple hydrogen bonds causes water to have a high heat of vaporization; that is, a large amount of energy is needed to convert liquid water, where the molecules are attracted through their hydrogen bonds, to water vapor, where they are not. Properties of hydrogen bonds
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8 Transport - Xylem - Lecture: 8 BioSci 1C Apr.10.07...

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