Water Movement

Slide 1 LHAP 104: Water Relations Presentation by E. Kawahara and A. Schill http://ladymin.files.wordpress.com Slide 2 Diffusion Movement of molecules from a region of higher concentration to a region of lower concentration. Move along a diffusion gradient Move until equilibrium reached. Slide 3 Osmosis Diffusion of water through a differentially permeable membrane from a region where the water is more concentrated to a region where it is less concentrated. Slide 4 Diffusion Videos: Diffusion of Hot vs cold medium Water from high to low Water will move up the dry paper towels in order to reach equilibrium. Water moves from an area where there is a lot to an area where there is less. You can see it when the colours blend and the empty cups are filled to the same level as the original ones. Slide 5 Turgid cell vs Flaccid cell osmosis continued Slide 6 Slide 7 Water Movement throughout the plant More than 90% of the water entering a plant passes into leaf air spaces and then evaporates through the stomata into the atmosphere (Transpiration). Usually less than 5% of water escapes through the cuticle. Slide 8 Xylem vessels xylem vessels are cylindrical and are connected to each other xylem vessels are dead, hollow water can move easily through xylem has lignin on its walls for strength and support Slide 9 Slide 10 Cohesion water molecules tend to stick together water molecules at the surface have a stronger bond because they don’t have as many neighbours to cohese with - this creates a “stronger hold” of the surface molecules called “surface tension” Slide 11 Adhesion Water molecules can hold to a surface other than water water molecules stick to the inside of the xylem vessels Cohesion - Tension: The more surface area to adhere to, the more the water climbs up. Slide 12 ...So that’s HOW water moves through a plant… but WHY does it move?? Slide 13 Transpirational Pull Xylem vessels are normally FULL Water evaporates out of Stomata Lower water potential is created than the adjacent cells. Creates tension on water columns, drawing water from one molecule to another, throughout the entire span of xylem cells... Slide 14 Water potential Click here to read more Slide 15 Slide 16 Slide 17 The Guard Cells... Guard Cells Photosynthesize Potassium Controls the Opening and Closing of Guard Cells. More Potassium lowers water potential. Water flows in to equalize. Guard Cell is Open. To Close it, Potassium leaves and the water follows it. Slide 18 Slide 19 What happens when the Soil doesn’t have anymore water? Guard cells must prevent transpiration (90% of water taken in is lost!) Guard cells decrease their turgor ABA (hormone) changes the water potential in the stomata