BIOL 1202 Lecture : BIOL 1202 Class Notes 4 25 13
Document Summary
Sugars move from the source to the sink . Sugar comes from photosynthesis: builds up in leaf, way more than leaf needs. All living cells in the plant require sugar so their mitochondria can do aerobic respiration. Plant without any leaves: aerobic respiring organisms. With leaves: produces its own carbohydrate which much be transported. Excess sugar ends up being stored in roots of plant (roots = sink : substances flow from shoots to roots in this case. Fall: source of sugar becomes roots, not leaves, so sugar turns opposite direction in phloem and moves up to shoots. New leaves formed (every cell in leaf has cellulose): sugar required to put out new leaves. Direction of sugar in phloem can change depending on time of day, season, whether fruit produced (apple = sink in plant), or in springtime: to produce photosynthetic components called leaves. Xylem sap: water and whatever else is dissolved in xylem: unidirectional flow from roots to shoots.
