Pressure flow or Mass flow hypothesis:Translocation is a phenomenon of conduction of organic or inorganic solutes from one place to another. The mechanism of transport through phloem is not perfectly understood & the principal theories are the mass flow hypothesis.The most accepted mechanism for translocation of sugars from source to sink is called pressure flow hypothesis.The German physiologist MUNCH in 1930 formulated this hypothesis. This can be demonstrated by simple experiment. Two osmometers A & B joined by horizontal tube forming a closed system. The osmometer A has a membrane enclosing B. These are immersed in two tubes connected by a glass tube. Water enters both the osmometers but more water enters into A than B due to higher concentrated solution existing create greater suction force. But as turgor pressure increases in osmometer A, water will move through horizontal tube 'X' in to ostmometer B.Since the membrane is permeable only to water, water will be pressed out of B, so circulation of blood takes place from the tube in which B is present into the tube in which A is present through the connecting tube Y. A continuous mass movement will take place until the osmotic concentrations in both A & B are equalized.If there is a continuous supply of solute to A & continuous removal of solute from the receiving osmometer B, there will be a continuous pressure flow from A to B. Thus, pressure flow continuous when one of the cells is the supplying cell & the other is a receiving cell.Comparison of the model - The cells of leaf are considered to be the supplying units comparable to osmotic cell A and the cells of root constitute the receiving organs comparable to osmotic cell B. The xylem is comparable to the both containing water for both the osmotic systems. The sieve tubes of phloem correspond to glass tube 'X'.The phloem is the connecting system between the supplying cells of the leaf and receiving cells of the roof. The whole system of leaf cells, the phloem, root cells and xylem are considered to function as one unit since plasmodesmata are supposed to permit mass movement. Since the leaf cell can have a continuous supply of sugars due to photosynthesis and as the receiving cells of root utilise the organic solutes or store them, there is always a continuous mass flow from the leaf cells to the root cells. The sugars produced by the cells of mesophyll pass into the sieve tubes through the plasmodesmata. 7 Active Technology Solutions Pvt.Ltd. is an educational 3D digital content provider for K-12. We also customize the content as per your requirement for companies platform providers colleges etc . 7 Active driving force "The Joy of Happy Learning" -- is what makes difference from other digital content providers. We consider Student needs, Lecturer needs and College needs in designing the 3D & 2D Animated Video Lectures. We are carrying a huge 3D Digital Library ready to use. For more information: http://www.7active.in Contact: 040-64501777 / 65864777 9700061777

• published: 06 Jun 2014
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