Transport in Plants AP Biology 2006 2007 Transport

Transport in Plants AP Biology 2006 -2007

Transport in plants § H 2 O & minerals u u transport in xylem transpiration § evaporation, adhesion & cohesion § negative pressure § Sugars u u transport in phloem bulk flow § Calvin cycle in leaves loads sucrose into phloem § positive pressure § Gas exchange u photosynthesis § CO 2 in; O 2 out § stomates u AP Biology respiration § O 2 in; CO 2 out § roots exchange gases within air spaces in soil Why does over-watering kill a plant?

Ascent of xylem fluid Transpiration pull generated by leaf AP Biology

Water & mineral absorption § Water absorption from soil osmosis u aquaporins u § Mineral absorption active transport u proton pumps u aquaporin root hair AP Biology proton pumps H 2 O

Mineral absorption § Proton pumps u active transport of H+ ions out of cell § chemiosmosis § H+ gradient u creates membrane potential § difference in charge drives cation uptake u creates gradient § cotransport of other solutes against their gradient AP Biology

Water flow through root § Porous cell water can flow through cell wall route & not enter cells u plant needs to force water into cells u Casparian strip AP Biology

Controlling the route of water in root § Endodermis u u u cell layer surrounding vascular cylinder of root lined with impermeable Casparian strip forces fluid through selective cell membrane § filtered & forced into xylem cells Aaaah… Structure–Function yet again! AP Biology

Root anatomy dicot AP Biology monocot

Mycorrhizae increase absorption § Symbiotic relationship between fungi & plant u u u AP Biology symbiotic fungi greatly increases surface area for absorption of water & minerals increases volume of soil reached by plant increases transport to host plant

Mycorrhizae AP Biology

Transport of sugars in phloem § Loading of sucrose into phloem flow through cells via plasmodesmata u proton pumps u § cotransport of sucrose into cells down proton gradient AP Biology

Pressure flow in phloem § Mass flow hypothesis u “source to sink” flow § direction of transport in phloem is dependent on plant’s needs u phloem loading § active transport of sucrose into phloem § increased sucrose concentration decreases H 2 O potential u water flows in from xylem cells § increase in pressure due to increase in H 2 O causes flow AP Biology On a plant… What’s a source…What’s a sink? can flow 1 m/hr

Experimentation § Testing pressure flow hypothesis u using aphids to measure sap flow & sugar concentration along plant stem AP Biology

Control of Stomates Guard cell Epidermal cell § Uptake of K+ ions by guard cells u u u proton pumps water enters by osmosis guard cells become turgid H 2 O K+ § Loss of K+ ions by guard cells u u AP Biology water leaves by osmosis H 2 O K+ guard cells become flaccid Nucleus Chloroplasts H 2 O K+ K+ H 2 O Thickened inner cell wall (rigid) H 2 O K+ Stoma open Stoma closed water moves into guard cells water moves out of guard cells

Control of transpiration § Balancing stomate function u always a compromise between photosynthesis & transpiration § leaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO 2 for photosynthesis AP Biology