Post on 17-Jan-2016
PLANT TRANSPORTRemember Osmosis???
It results in the net uptake or loss of water by the plant cell and
depends on whether the cell or the extracellular fluid has a higher or
lower……
“WATER POTENTIAL”
So…. What exactly is WATER “POTENTIAL”?
Here is the “Helm Definition”: The potential to….. MOVE!!!!
In other words:
Water will always move across a membrane from an area of high to low potential.
Let’s see if you get it: More HYPERtonic = LESS Potential
More HYPOtonic = MORE Potential
More Pressure = More Potential
Less Pressure = LESS PotentialSo… Potential results from a combination of BOTH solute concentration AND pressure.
•Negative Pressure (or Tension) pulls in water•….and don’t forget about the role of the central vacuole!!
Lateral Transport:3 main routes:
1. Across the membrane/cell walls: (you know… through the cellulose & phospholipid bilayer)
2. The SYMPLAST- through the continuum of cytoplasm
formed by plasmodesmata. 3. The APOPLAST- between the actual plant cells
-never enters the cells, just worksits way through the matrix of cell walls
Campbell Animation
Long Distance Transport…
Xylem for Water
Phloem for “Phooood” (sap)
Transpiration “Plant Sweat”
Transpiration / Photosynthesis Ratio- g water lost / g CO2 assimilated
– The __________ the better??LOWER!
Example: 600:1 in C3 plants 300:1 in C4 plants
•Benefits of Transpiration:•Assists in mineral transfer from root to shoot•Evaporative cooling keeps enzymes from overheating
Drawbacks:if transpiration exceeds delivery of water…
Stomata close, photosynthesis ceases, plants wilt.
Stomata & Guard Cells When guard cells are turgid, they buckle
due to radially arranged microfibrils.
Turgid = Buckled = OPEN!!
Flaccid = Unbuckled = CLOSED!!!
•Caused by the reversible uptake & loss of K+ ions by Guard Cells.•More K+, higher [solute], lower p , water goes IN,
microfibrils buckle, STOMATA OPEN!(and vise- versa, of course)
K+ movement is triggered by H+ out by proton pumps.
Open or Closed??
OPEN:LIGHT: stimulates proton pumps by making ATP available
from photosynthesis.
DECREASE in CO2: from increased Photosynthesis.
CIRCADIAN RHYTHMS: internal clock (plants are often on a 24 hour cycle even in the dark)
Open or Closed?Closed:
WATER DEFICIENCY- makes guard cells flaccid
ABSCISIC ACID PRODUCTION- hormone that is activated in response to low water.
HIGH TEMPERATURES- increases CO2 due to increased respiration.
http://www.tvdsb.on.ca/westmin/science/sbioac/plants/stoma.htm
Translocation: food/phloem transport Sugar source: sugar production organ
(mature leaves) Sugar sink: sugar storage organ (growing
roots, tips, stems, fruit) 1- loading of sugar into sieve tube at
source reduces water potential inside; this causes tube to take up water from surroundings by osmosis
2- this absorption of water generates pressure that forces sap to flow along the tube
3- pressure gradient in tube is reinforced by unloading of sugar and consequent loss of water from tube at the sink
4- xylem then recycles water from sink to source
OK… so what about what’s goin’ on with the PHLOEM??
Campbell Animation