Transcript Plant Structure And Growth

Transport
In Plants
Cellular Transport
• Diffusion
• Osmosis
• Facilitated Diffusion
• Active Transport
• Proton Pump
Cell 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
Plant Cell
Water
Movement
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
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
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
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
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Small, thick leaves
Thick cuticle
Stomata are recessed
Lose their leaves
C4 or CAM plants
Phloem
Loading
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
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
Pressure Flow of Phloem
• Pressure Flow
– Water intake generates a hydrostatic
pressure near source cell that forces water
to lower pressure areas near sink cell
– Unloads sugars into sink by active
transport which makes cells lose water to
relieve pressure
– Xylem recycles water