Transcript PowerPoint Presentation - Ch. 36 Plant Transport

Ch. 36
Plant Transport
• Three levels of plant transport
• Uptake of water and solutes by
individual cells
• Short distance cell to cell transport
• Long distance transport of sap in xylem
and phloem.
• Transport at cell level
– Passive diffusion- no energy needed, may use transport
proteins.
– _Active transport- from low to high, ex. Proton Pump
(_energy needed).
» Nitrate enters plant cells by cotransport with the proton
pump.
– Water potential( = direction water will flow
– Tonoplast- surrounds largest plant organelle, the central
vacuole.
» Contains proton pumps
» Contains transport proteins
• Short distance transport - _radial axis in
plants/organs.
– Movement across cell _membranes and walls
– Apoplast = water and solute move from one organ to
another without entering a cell.
• Symplast = use of plasmodesmata pores in the cell walls.
• Long distance- _up and down plant.
– Involves vascular tissue.
– Pressure differences cause movement through
xylem and sieve tubes.
– Transpiration reduces pressure in leaf xylem. Sap is
pulled up xylem from roots.
– Hydrostatic pressure in phloem forces sap down.
• Absorption of water and minerals by roots
– Water and minerals
» soil-> epidermis -> Root cortex
– ->stele->xylem.
» root hairs increase surface area.
• Active transport of mineral ions
Mineral uptake, ch.38
• Xylem sap
– Flows up at 15 meters/hour or faster
– Transpiration - evaporation of water from aerial parts
of plant.
– Xylem sap also carries minerals to leaves
– Pushing up sap
» Root pressure causes guttation (water droplets
on leaves)
• Guttation happens when transpiration is
low.
• Pulling sap - transpiration- cohesion and
adhesion.
– Gaseous water diffuses out the stomata
• Adhesion and cohesion caused by
hydrogen bonds causes a negative
pressure which pulls water up.
• Translocation of phloem sap
– Contains primarily sucrose.
– Sugar source to sugar sink.
» unidirectional – source ( _leaves-photosynthesis) to
sink (roots)
» Source = sugar produced(leaves)
» Sink = stored sugar ( fruits, roots, nongreen stems and
trunk)
– Sucrose loading and unloading
» May be _symplast movement
» May be symplast and apoplast.
» 1 m/hour.
• Translocation in angiosperms
–
–
–
–
Leaf to sieve tube.
sucrose enters
_water moves minerals and sucrose to sink.
sucrose removed and used at the sink so pressure
goes down.