AP Bio Plant Transport(KFogler)

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Transport in Plants

AP Biology


Transport in plants H2O & minerals

transport in xylem transpiration evaporation, adhesion & cohesion negative pressure


transport in phloem bulk flow Calvin cycle in leaves loads sucrose into phloem positive pressure

Gas exchange

Why does over-watering kill a plant?

photosynthesis CO2 in; O2 out stomates


O2 in; CO2 out AP Biology roots exchange gases within air spaces in soil

Ascent of xylem fluidTranspiration pull generated by leaf

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Water & mineral absorption Water absorption from soilosmosis aquaporins

Mineral absorptionactive transport proton pumps

active transport of


aquaporin root hair

AP Biology proton pumps


Mineral absorption Proton pumps

active transport of H+ ions out of cell chemiosmosis H+ gradient

creates membrane potential difference in charge drives cation uptake

creates gradient cotransport of other solutes against their gradient

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Water flow through root

Porous cell wallwater can flow through cell wall route & not enter cells plant needs to force water into cells

Casparian strip

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Controlling the route of water in root


cell layer surrounding vascular cylinder of root lined with impermeable Casparian strip forces fluid through selective cell membrane filtered & forced into xylem cells

Aaaah StructureFunction yet again!

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Root anatomy



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Mycorrhizae increase absorption Symbiotic relationship between fungi & plant

symbiotic fungi greatly increases surface area for absorption of water & minerals increases volume of soil reached by plant increases transport to host plant

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Transport of sugars in phloem Loading of sucrose into phloemflow through cells via plasmodesmata proton pumps

cotransport of sucrose into cells down proton gradient

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Pressure flow in phloem Mass flow hypothesis

source to sink flow direction of transport in phloem is dependent on plants needscan flow 1m/hr

phloem loading active transport of sucrose into phloem increased sucrose concentration decreases H2O potential

water flows in from xylem cells increase in pressure due to increase in H2O causes flowOn a plant Whats a sourceWhats a sink?

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Experimentation Testing pressure flowhypothesis

using aphids to measure sap flow & sugar concentration along plant stem

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Maple sugaring

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Control of StomatesGuard cell

Epidermal cell Nucleus K+ H2O K+ H2O


Uptake of K+ ionsby guard cells

proton pumps water enters by osmosis guard cells become turgid

H2O K+

H2O K+

H2O K+

H2O K+

K+ H2O

K+ H2O

Loss of

ions by guard cellswater leaves by osmosis H2O K+ guard cells become flaccid


Thickened inner cell wall (rigid)

H2O K+ Stoma open water moves into guard cells

H2O K+ Stoma closed water moves out of guard cells

H2O K+

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Control of transpiration Balancing stomate function

always a compromise between photosynthesis & transpiration leaf may transpire more than its weight in water in a daythis loss must be balanced with plants need for CO2 for photosynthesis

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Dont get mad Get answers!! Ask Questions!

AP Biology