1 Plant Transport Todays topics: • Absorption by Roots • Root hairs • Soil nutrients • Water potential • Osmosis again • Ψ = Ψ s + Ψ p • Xylem pulls water and nutrients • cohesion tension model • Stomata • Phloem pushes water and sugar • sources to sinks 8 November 2021 Plant growth occurs in meristems Root meristem Shoot meristem 3-year woody stem Annual Rings Root structure Monocot Dicot Root vascular cylinder is in the center See section 37.1
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1
Plant Transport Today�s topics:
• Absorption by Roots • Root hairs • Soil nutrients
• Water potential • Osmosis again • Ψ = Ψs + Ψp
• Xylem pulls water and nutrients • cohesion tension model • Stomata
• Phloem pushes water and sugar • sources to sinks
8 November 2021
Plant growth occurs in meristems
Root meristem Shoot meristem
3-year woody stem Annual Rings
Root structure
Monocot Dicot
Root vascular cylinder is in the center
See section 37.1
2
Energy is required to get nutrients into
the cell.
clay
Proton pumps are used to get ions into root cells
Low [Solute]
H2O
High [Solute}
Selectively permeable membrane
Osmosis
Osmosis
See also Chapter 7
Fig. 36-8c
ψP = ψS = −0.23
(c) Increased positive pressure
H2O
ψ = 0.07 MPa
ψP = 0 ψS = 0 ψ = 0 MPa
0.30
Water Potential
ψ = ψS+ ψP
Water potential = solute potential + pressure potential
Water always moves from areas of higher water potential to areas of lower water potential
Fig. 36-8d
(d) Negative pressure (tension)
H2O
ψP = −0.30 ψS =
ψP = ψS = −0.23
ψ = −0.30 MPa
ψ = −0.23 MPa
0 0
Water Potential
ψ = ψS+ ψP
Water potential = solute potential + pressure potential
Water always moves from areas of higher water potential to areas of lower water potential
3
Transpiration pulls water up through the xylem
Vessel element
Vessel elements, with perforated end walls Tracheids
Pits
Vessel Tracheids 100 µm
Vascular Tissue
Outside air Ψ= -58.5 Mpa Inside leaf Ψ= -2.0 MPa Xylem of trunk Ψ= -1.2 MPa Xylem of root Ψ= -0.6 MPa Soil water Ψ= -0.3 MPa
Example: Transpiration pulls water up through the xylem
Leaf Structure
4
Stomata
K+
H2O
H2O
H2O
H2O H2O
H2O
H2O
H2O
H2O
H2O
Guard cells turgid/ Stoma open
Guard cells flaccid/ Stoma closed
K+ ions are used to move water in and out of guard cells