Question

Which of the following is the main point in disfavor of munch theory.
A. Translocation is a pure physiological process.
B. Translocation is a pure physical process.
C. Explanation of sugar transport is not given.
D. None of the above.

Answer 1

Hint: In translocation process movement of solutes is bi-directional. And the fact that changes in environmental conditions like temperature and metabolic inhibitors greatly affects the translocation process, are the two demerits of the munch theory.

Complete step by step answer: Munch Theory is also called the pressure flow hypothesis. This theory was given by German physiologist Ernst Munch in 1930. It shows the movement of sap through the phloem.
Ernst Munch in the hypothesis describes the transportation of solutes in plants and is known as Pressure Flow or Mass Flow or Munch Hypothesis. Theory is based on the concept of mass transfer of solutes from source to sink along the turgor pressure gradient. Turgor pressure is also known as hydrostatic pressure gradient or turgor pressure gradient. The concept of this theory can be explained in the below example.
-Let suppose there are two osmometers A and B.
-A has source (Sucrose and water) plus dye.
-While B has only water.
These two osmometers are connected by a capillary tube (phloem). By osmosis water moves into osmometer A and there water generates hydrostatic pressure that forces water out of osmometer B. Glass tubes (xylem) connect the two flasks and water returns through this glass tube. Because of the flow of the water, the sucrose dye solution flows from A to B.
Munch hypothesis faced criticism because Munch explained the theory as an absolute physical process but it is not since temperature and metabolic inhibitors are affecting it.
Hence, the correct option is (B) Translocation is a pure physical process.

Note:
-Pressure flow or mass flow is not a true physical process as explained by Munch. In his theory, phloem cells make use of 0.1 to 0.5 percent of sucrose translocation through them. By this point it is evident that the phloem translocation requires metabolic energy and is an active process.
-Under high pressure, the slime content and other fibrils of the sieve tube reduce the speed of flow of solutes.