Tiêu đề 11 Transport in plants ppt - part 3.pdf ✅

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• Diffusion is a slow process. It accounts for only short distance movement. E.g. movement of molecules across a typical plant cell (about 50 μm) takes about 2.5 s. • Long distance transport systems are necessary to move substances faster across long distances. • Movement of substances in bulk (en masse) from one point to another due to pressure differences between two points is called Mass (bulk) flow. Water, minerals and food are generally moved by a mass flow system. bankofbiology.com
• In mass flow, substances (in solution or in suspension) are swept along at the same pace as in a flowing river. But in diffusion, different substances move independently depending on their concentration gradients. • Bulk flow is achieved either through a +ve hydrostatic pressure gradient (e.g. a garden hose) or a -ve hydrostatic pressure gradient (e.g. suction through a straw). • Bulk movement of substances in long distance through the conducting tissues (xylem & phloem) is called translocation. bankofbiology.com