Transport In Plants. Cellular Transport Diffusion Osmosis Facilitated Diffusion Active Transport...
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Transcript of Transport In Plants. Cellular Transport Diffusion Osmosis Facilitated Diffusion Active Transport...
Water Potential
• The physical property predicting the direction in which water will flow– Solute concentration– Pressure• water moves from high water potential
to low water potential
Water Potential (a)
• Left Side– Pure Water = 0 Water Potential
• Right Side– Negative Water Potential• 0 pressure• - solute (has solutes)
• Water moves to the right
Water Potential (b)
• Left Side– Pure Water = 0 Water Potential
• Right Side– 0 Water Potential• + pressure equal to solute conc. • - solute (has solutes)
• Water is at equilibrium
Water Potential (c)
• Left Side– Pure Water = 0 Water Potential
• Right Side– Positive Water Potential• + pressure more than solute conc.• - solute (has solutes)
• Water moves to the left
Water Potential (d)
• Left Side– Pure Water and Negative Tension
• Right Side– Negative Water Potential• 0 pressure• - solute (has solutes)
• Water moves to the left
Water Relationships in Plants
• Plasmolysis: plasma membrane pulls away from the cell wall
• Flaccid: limp, no tendency for water to enter
• Turgid: water moves in and plasma membrane pushes up against cell wall
Aquaporins
• Specialized proteins that facilitate osmosis
• water moves into/out of cells quicker than expected across a membrane
Tissue Level Transport
• Trans-membrane– across cell wall and cytoplasm
• Symplastic– across the cytoplasm
• Apoplastic– across the cell walls
Long Distance Transport
• Bulk Flow – the movement of a fluid driven by
pressure– Only moved up plants by a negative
pressure (not solute concentration)
• Unlike osmosis, moves water and solutes
Absorption of Water and Minerals
– Water and Minerals can move through the epidermis to the cortex in two methods:• apoplastic• symplastic
Absorption of Water and Minerals
– Endodermis is selectively permeable• Casparian strip is made of suberin• Water and minerals cannot enter through the stele
through the apoplastic pathway. It must enter through the symplastic pathway.
Absorption of Water and Minerals
• Focus on soil --> epidermis --> root cortex ---> xylem pathway– Once inside the stele, the water and minerals
must shift back to the apoplastic pathway because xylem has no protoplast
Absorption of Water and Minerals
• Focus on soil --> epidermis --> root cortex ---> xylem pathway (review)– Two pathways• 1. Apoplastic --> symplastic--> apoplastic• 2. Symplastic --> apoplastic
– Water passes into the stele through symplastic route– Water passes into the xylem through apoplastic route
Transport of Xylem Sap
• Pushing Xylem– Root Pressure• caused by active
pumping of minerals into the xylem by root cells• Guttation: the
accumulation of water on the tips of the plant
Transport of Xylem Sap
• Pulling Xylem– Transpiration• the evaporative loss of water from a plant
through the stomata
Transport of Xylem Sap
• Pulling Xylem– Cohesion
• Water sticking together– Adhesion
• Water sticking to the cell wall– Surface Tension
• negative pressure• Forms a meniscus (concave shape)– the more concave / the greater the negative
pressure
Transport of Xylem Sap
• Pulling Xylem– Cohesion: binding together of water
molecules• pulls sap up plants
– Adhesion: Water sticking to the cell wall• fights gravity
The Control of Transpiration
• Guard Cells– turgid - open– flaccid - closed
• Potassium Ions– active transport of Hydrogen ions out
of the cell causes Potassium ions to move in
Stomata
• Open during the day / Closed at night– first light (blue light receptor)– depletion of Carbon Dioxide– internal clock (circadian rhythms)
Reducing Transpiration
• Small, thick leaves• Thick cuticle• Stomata are recessed• Lose their leaves• C4 or CAM plants
Translocation of Phloem
• Phloem loading– movement of sugars through apoplastic and
symplastic pathways– sugar made in mesophyll cells• pass through other cells to seive tube members–bundle sheath cells–parenchyma cells–companion (transfer) cells
Translocation of Phloem
• Phloem loading– chemiosmotic mechanism used to load
sucrose from the apoplast to the symplast pathway
– used with high levels of sucrose accumulation
Translocation of Phloem
• Translocation: transport of food– moves from a sugar source to a sugar sink– Reduces water potential inside sieve tube
(phloem) and begins to take on water from xylem