Mechanism of translocation of phloem I Chapter 14 Biology I F.Sc First Year Lec # 14

#biology11class #biologyfirstyear #F.Sc. #chapter14 #Transport Like Our facebook page. -----------------------------------   / bismacademy   ------------------------------------ Active Theories. The active theories involving the use of energy for the movement of materials in phloem, and the active theories have all been abandoned as there is not much evidence to support these theories. Passive Theories. The passive theories in which no use of energy was involved. Now we are left with passive theories of transport / translocation. These include: (i) Diffusion (ii) Pressure flow theory (i) Diffusion: It is far too slow, to account for the velocities of sugar movement in phloem, which on the average is 1 meter per hour, while the rate of diffusion is 1 meter per eight years. So we are left with pressure flow theory. The theory called, Pressure - Flow Theory, is the most acceptable theory for the transport in the phloem of angiosperms. We have considerable evidence to support this theory. Suggested by. A hypothesis was first proposed by Ernst Munch in 1930. It states that the flow of solution in the sieve elements is driven by osmotically generated pressure gradient between” ”source and sink. Now this hypothesis has been given status of a theory.