Ch. 36 Warm-Up

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Ch. 36 Warm-Up

• Describe the process of how H2O gets into the
  plant and up to the leaves.
• Compare and contrast apoplastic flow to
  symplastic flow.
• Explain the mass flow of materials in the phloem
  (source to sink).

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Ch. 36 Warm-Up

1. What is transpiration?
2. What are mycorrhizae?
3. What is the function of the Casparian strip?

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Chapter 36

• Resource Acquisition and Transport in Vascular
  Plants

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What you need to know

• The role of passive transport, active transport,
  and cotransport in plant transport.
• The role of diffusion, active transport, and bulk
  flow in the movement of water and nutrients in
  plants.
• How the transpiration cohesion-tension mechanism
  explain water movement in plants.
• How pressure flow explains translocation.

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What does a plant need?
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• Review
• Selectively permeable membrane osmosis,
  transport proteins, selective channels
• Proton pump active transport uses E to pump H
  out of cell ? proton gradient
• Cotransport couple H diffusion with sucrose
  transport
• Aquaporin transport protein which controls H2O
  uptake/loss

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Solute transport across plant cell plasma
membranes
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Osmosis

• Water potential (?) H2O moves from high ? ?
  low ? potential, solute conc. pressure
• Water potential equation ? ?S ?P
• Solute potential (?S) osmotic potential
• Pressure potential (?P) physical pressure on
  solution
• Pure water ?S 0 Mpa
• ? is always negative!
• Turgor pressure force on cell wall
• Bulk flow move H2O in plant from regions of high
  ? low pressure
• Review AP Bio Investigation 4

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• Flaccid limp (wilting)
• Plasmolyze shrink, pull away from cell wall
  (kills most plant cells) due to H2O loss
• Turgid firm (healthy plant)

Turgid Plant Cell
Plasmolysis
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A watered impatiens plant regains its turgor.
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Vascular Tissues conduct molecules
Xylem Phloem
Nonliving functional Living functional
Xylem sap H2O minerals Phloem sap sucrose, minerals, amino acids, hormones
Source to sink (sugar made) to (sugar consumed/stored)
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Transport of H2O and minerals into xylem

• Root epidermis ? cortex ? Casparian Strip ?
  vascular cylinder ? xylem tissue ? shoot system

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At Root Epidermis

• Root hairs increase surface area of absorption
  at root tips
• Mycorrhizae symbiotic relationship between
  fungus roots
• Increase H2O/mineral absorption

The white mycelium of the fungus ensheathes these
roots of a pine tree.
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Transport pathways across Cortex

• Apoplast materials travel between cells
• Symplast materials cross cell membrane, move
  through cytosol plasmodesmata

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Entry into Vascular Cylinder

• Endodermis (inner layer of cortex) sealed by
  Casparian strip (waxy material)
• Blocks passage of H2O and minerals
• All materials absorbed from roots enter xylem
  through selectively permeable membrane
• Symplast entry only!

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How does material move vertically (against
gravity)?

• Transpiration loss of H2O via evaporation from
  leaves into air
• Root pressure (least important)
• Diffusion into root pushes sap up
• Cohesion-tension hypothesis
• Transpiration provides pull
• Cohesion of H2O transmits pull from roots?shoots

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• Guttation exudation of water droplets seen in
  morning (not dew), caused by root pressure

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Stomata regulate rate of transpiration

• Stomata pores in epidermis of leaves/stems,
  allow gas exchange and transpiration
• Guard cells open/close stoma by changing shape
• Take up K ? lower ? ? take up H2O ? pore opens
• Lose K ? lose H2O ? cells less bowed ? pore
  closes

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• Cells stimulated open by light, loss of CO2 in
  leaf, circadian rhythms
• Stomata closure drought, high temperature, wind

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BioFlix Water Transport in plants
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Sugar Transport

• Translocation transport of sugars into phloem by
  pressure flow
• Source ? Sink
• Source produce sugar (photosynthesis)
• Sink consume/store sugar (fruit, roots)
• Via sieve-tube elements
• Active transport of sucrose

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Bulk flow in a sieve tube
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Symplast is dynamic

• Plasmodesmata allows movement of RNA proteins
  between cells
• Phloem can carry rapid, long-distance electrical
  signaling
• Nerve-like function
• Swift communication
• Changes in gene expression, respiration,
  photosynthesis