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
Q. Will Sedantary Lifestyle increased risk for CAD? A sedantary life style is associated with increased risk for CAD. Sedentary persons have almost double the risk for CAD deat

Which of the following structures in a vertebrate with a four-chambered heart would have blood with the highest oxygen concentration? And why?

Define Precautions for Estimation of Cholesterol Using Zlatkis Method 1. Use aldehyde free glacial acetic acid. 2. Use only glacial acetic for making up and adjusting the vo

Define Water - Important Nutrient? Macronutrients, you know, are those nutrients which are required in large amounts by our body namely, carbohydrates, fats and proteins. We st

Q. What is Cholesterol? In its free, unesterified form cholesterol is a major component (together with phospolipid) of cell membranes. Its presence helps to stabilize membrane

(a) What are the immediate effects of exercise on the functions of (i) the heart, (ii) the lungs, (iii) the liver? (b) How do these changes help to meet the needs of exercise

Explain about Mental foramen and nerve Mental foramen is a strategically important landmark during osteotomy procedures. Its location and the possibility that an anterior loop

Nutrition and Health The effects of the socio-economic and environmental factors in which one is constrained to live will manifest in terms of the nutritional and health statu

R i n g w o r m It is also known as dermatophytosis resulting in alopecia, scab formation and ring like lesions in the affected body parts. Eti o logy: Zeop

Uterine infections Uterine bacterial contamination compromises uterine functions. Initially, the uterus is contaminated with a wide range of bacteria, but this is not consiste