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Mass Transport in Plants (Translocation (Movement of sugars from Sources…
Mass Transport in Plants
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Transpiration
Movement of water
Factors affecting: Humidity, Wind and Temperature
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Cohesion tension theory
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Cohesion occurs due to the hydrogen bonding found between water molecules which causes them to stick together
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Evidence
xylem vessel broken and air enters the tree can no longer take up water due to continuous column being broken
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Diameter of tree trunks in relation to the rate of transpiration e.g. high transpiration more negative pressure smaller diameter more tension bringing vessels closer
Translocation
Movement of sugars from Sources (sites of photosynthesis) to sinks (sites of respiration and (sugar stores)
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Sieve tubes also contains sieve plates and sieve pores which allow the movement of sugars between tubes easily
From the companion cells it is then brought in by co-transport as H+ ions are actively transported out and then brought in to the sieve tubes
Sucrose moves from being synthesised in the photosynthetic tissue into the companion cells by facilitated diffusion
Mass flow occurs by the bulk movement of substance through a given area sucrose enters sieve tubes creating a low WP
Xylem vessels have high WP so water passes into phloem via osmosis creating a high hydrostatic pressure
At sinks there is a low sucrose content due to either being converted for storage or used in respiration they are then actively transported in lowering the sink WP
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