BIOLOGY 2D03 Lecture Notes - Lecture 5: Casparian Strip, Apoplast, Evaporative Cooler
27 Oct 2016
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Water movement in root: apoplastic: transpiration rate is high, symplastic: transpiration rate is low, casparian strip, controls ion movement in xylem, forces water moving in root apoplast to cross the plasma membrane which filters the water. Movement of sucrose in phloem: from leaves (source) to non-photosynthetic regions (sinks, sinks = young leaves, roots, flowers, seeds, fruits, phloem, sieve elements (ses) Nucleus and vacuole are lost in mature sieve elements. Few ribosomes, chloroplasts, er/golgi: companion cells (ccs) Se-cc plasmodesmata are larger than in other cells. Sucrose moved into ccs by energy-consuming sucrose-transporter. Creates high [sugar] so water moves into se from xylem causing high pressure in phloem: sink leaves. Sugars move out of se into surrounding tissues and water follows (gradient) Pressure in sink is lower than in source. Leaves are not always sugar source: can be store belowground (root of carrot, leaves can be a sink.
