Munch pressure flow model, Biology

Munch Pressure Flow Model

Munch, a German plant physiologist, proposed in 1930, a simple physical model which can be tested in the laboratory for the mechanism of phloem transport. As shown in Figure, two osmometers, one containing solute at higher concentration .(A) than the other (B), are connected by a tube (C) and dipped in water. Due to high solute concentration in A water flows in to it by the process of osmosis. Consequently, the pressure develops which forces the solution to rise in the connecting tube and the content of A flow into 8. This pressure forces water to flow out of B through its membrane in the medium. In plants the state of source and sink is analogous to the two osmometers. The source regions have higher solute concentration than the sink region. The phloem conduit in the source region would imbibe water by the process of osmosis and generate a high turgor zone. On the other hand, the phloem in the sink region will be at low turgor. Thus, a pressure gradient exists along the length of the phloem which would cause a mass flow of solvent and solutes with equal velocity. There are several difficulties in accepting this, otherwise admirably simple and appealing hypothesis. Firstly, the generation of pressure gradient is possible in the above given model only if the water potential is about the same in both regions.

1781_Munch Pressure Flow Model.png

Figure: Munch Pressure Flow Model

However, in plants, water potential is lower in the Leaves and higher in the roots. Thus, the tendency of water to enter the phloem in the leaf region is reduced. Whereas in the root region, water can be readily imbibed by sieve elements even a lesser solute concentration of the phloem sap, from neighbouring cells and/or apoplasm. Therefore, it cannot be assumed that the gradient in solute concentration would generate a pressure gradient from sources to sinks. Moreover, the observed differential, mobilities of solute molecules, highest for K+ and lowest for ca2+, speak against the pressure flow hypothesis. The original model has been modified to remove this problem. P Pressure gradients sufficient for causing mass flow have not been recorded in any plant. Much depends, on the radius of the sieve plate pores, the presence of P-proteins and the degree of callose formation. Hence the debate on the Munch's models is still continuing, primarily because there is still no other alternative model to explain precisely the mechanism of Phloem transport. You may note that at the sites of loading and unloading there is active transport operating which may account. for the differential mobilities of ions and accumulation of molecules such as sugars in large amount against concentration gradient.


Posted Date: 1/17/2013 4:35:00 AM | Location : United States

Related Discussions:- Munch pressure flow model, Assignment Help, Ask Question on Munch pressure flow model, Get Answer, Expert's Help, Munch pressure flow model Discussions

Write discussion on Munch pressure flow model
Your posts are moderated
Related Questions
Explain Vitamin A Deficiency - Micronutrient Deficiencies? Vitamin A deficiency (VAD) is a major public health problem, and the most vulnerable are preschool children and pregn

Define Precautions for preparation of bacterial smear 1. The slide should not be greasy. 2. Hold the slide by their edges only. 3. Label should not come in contact with s

Observing where soil bacteria live Dig up a clover, alfalfa or soy-bean plant. Carefully increase all the soil from the roots and see if you can find the little white nodules o

What is the difference between homologous and heterologous immunoglobulins? Homologous immunoglobulin is the human (from the similar species) immunoglobulin. In case of inocula

Hello, I did a experiment: I used 5 salt solutions (0 g/L; 5 g/L; 10 g/L; 15 g/L; 20 g/L), and in each one I cooked beans (25 g) for 5 minutes. At the end, I measured the absorpti

Q. What are the main phases and clinical manifestations of schistosomiasis? The Schistosomiasis has acute and chronic phases and Days after the infection the cercarial dermatit

What are persistent organic pollutants (POPs)? POPs, or persistent organic pollutants, are toxic substances formed from organic compounds. POPs are made in several industrial p

Arterial Blood Gas Studies: Purpose 1)  A measurement of partial pressure of oxygen and carbon dioxide  in arterial blood, as well as the pH  of  the blood.  2) The Partial p

Explain about lyophilic If the affinity between the dispersed phase and the medium is high, the dispersed phase is said to be lyophilic (solvent loving) or hydrophilic, in the

what is the function of the germinative zone