Water Transport in PlantsWater Transport in Plants

Getting water to the leavesGetting water to the leaves

• The leaves need the water to The leaves need the water to perform photosynthesis without perform photosynthesis without water no photosynthesis. Without water no photosynthesis. Without photosynthesis the plant will die.photosynthesis the plant will die.

• But the leaves can be hundreds of But the leaves can be hundreds of meters from the root where most of meters from the root where most of the water uptake occursthe water uptake occurs

Back to water propertiesBack to water properties

Remember…….Remember…….

CohesionCohesion

• Cohesion = water Cohesion = water molecules are molecules are attracted to other attracted to other water molecules water molecules

• Due to Hydrogen Due to Hydrogen Bonds – polarity of Bonds – polarity of water moleculewater molecule

• Could be broken by Could be broken by a surfactant - soapa surfactant - soap

AdhesionAdhesion

• Water molecules Water molecules attracted to other attracted to other substances substances – Example glassExample glass

Root PressureRoot Pressure

• Dew occurs when the roots continue to Dew occurs when the roots continue to take in mineral and the rate of take in mineral and the rate of transpiration is lowtranspiration is low– When is transpiration low? When is transpiration low?

Root PressureRoot Pressure

• Pressure is created by the xylemPressure is created by the xylem– Dissolved minerals are present in the root cells Dissolved minerals are present in the root cells

(get there from active transport) increases the (get there from active transport) increases the solute concentration inside the cell, thus water solute concentration inside the cell, thus water enters through osmosis creating pressure enters through osmosis creating pressure forcing the fluid up the xylemforcing the fluid up the xylem

– Thus, water is forced from the high pressure in Thus, water is forced from the high pressure in the roots to the low pressure in the leaves.the roots to the low pressure in the leaves.

– Can only push water a maximum of a few Can only push water a maximum of a few metersmeters

TranspirationTranspiration

• What the plants over a few meters tall What the plants over a few meters tall use to transport the water to the leavesuse to transport the water to the leaves

• Pulls the water up the stemPulls the water up the stem• Adhesion and cohesion help transpiration Adhesion and cohesion help transpiration

(which occur at the stomata and (which occur at the stomata and lenticels) sucks the water up the xylemlenticels) sucks the water up the xylem

TranspirationTranspiration

• As water is lost in the leaves and stem it As water is lost in the leaves and stem it must be replaced transpiration allows must be replaced transpiration allows that to happenthat to happen

• Depends on temperatureDepends on temperature– High temp = lots of transpiration water can High temp = lots of transpiration water can

raise 75cm per minuteraise 75cm per minute– Low temperature = transpiration rate slowerLow temperature = transpiration rate slower

Sugar TransportSugar Transport

• Phloem moves the sugar from the leaves Phloem moves the sugar from the leaves to the rest of the plantto the rest of the plant

• Movement from Movement from sourcesource to to sinksink• Glucose moved by active transport into Glucose moved by active transport into

the phloem (via the companion cells) the phloem (via the companion cells) water enters by osmosiswater enters by osmosis

• AnimationAnimation

Sugar TransportSugar Transport

• Increase water pressure pushes the water Increase water pressure pushes the water and sugar though the phloem to the rest and sugar though the phloem to the rest of the plant -- pressure flow theoryof the plant -- pressure flow theory

• Sugars transported actively into the cellsSugars transported actively into the cells• Water also leaves the cellWater also leaves the cell

Animation LinksAnimation Links

• TranspirationTranspiration