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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.
