Water Movement
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1. LHAP 104:
- Water Relations
Presentation by E. Kawahara and A. Schill http://ladymin.files.wordpress.com
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.
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.
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.
5. Turgid cell vs Flaccid cell
- osmosis continued
6. 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.
7. 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
8. 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”
9. 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.
10. ...So that’s HOW water moves through a plant… but WHY does it move??
11. 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...
12. Water potential
- Click here to read more
13. 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.
14. 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
