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.