Lect12S2010 - Water Transport Water Transport Food...

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Unformatted text preview: Water Transport Water Transport Food Transport Food Transport Water Transport Path Water Transport Path At r o o t t i p water and minerals = xylem sap , entering stele can take two paths: Symplast : Pathway through living cells Apoplast : Pathway through non-living elements of the cell Route must be symplastic once endodermis is reached. Casparian strip prevents apoplastic route. A d v a n t a g e s of symplastic path: Active transport involved is f a s t e r than osmosis. Allows for selectivity of ions, e.g., membrane will select for K + instead of Na + Water Transport Path Water Transport Path Apoplastic vs Symplastic Route of Water and Minerals Stele Cortex Fig. 36-12b Casparian strip Endodermal cell Pathway along apoplast Pathway through symplast Once Water is in Xylem Once Water is in Xylem Water transported to stem and leaves, and m o s t o f t h e w a t e r evaporated out through the stomata. Evaporation of water from leaves through their stomata is transpiration . Over 90% of water entering plant lost during this process. Once Water is in Xylem Once Water is in Xylem Water moves up xylem at up to 15m/hr. Two mechanisms demonstrated to transport water significant distant up stem. One is a p u s h i n g and the other is a p u l l i n g mechanism. Energy require! Root Pressure Root Pressure P u s h i n g mechanism: At night energy expended to pump ions i n t o the xylem, at the root tip. Casparian strip in the endodermis prevents ions from leaking back into the cortex. Accumulation of ions occur in the xylem. Casparian Strip Casparian Strip Casparian strip Casparian strip prevents ions from leaking out of endodermis Ions Ions Ions (inside xylem) Root Pressure Root Pressure Distance water transported is limited, e.g., only up to 30 feet Water p u s h e d into leaves, but transpiration is low or stopped Safety valves in leaves, hydathodes , relieves water pressure due to root pressure Gutation : Process where is forced out through hydathodes of leaves Gutation Gutation Root Pressure Root Pressure Root pressure c a n n o t be universal mechanism by which plants transport water: Does not occur in all plants, e.g....
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Lect12S2010 - Water Transport Water Transport Food...

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