What is the mass flow hypothesis?
What is the mass flow hypothesis?
The pressure flow hypothesis, also known as the mass flow hypothesis, is the best-supported theory to explain the movement of sap through the phloem. This creates turgor pressure, also known as hydrostatic pressure, in the phloem. Movement of phloem sap occurs by bulk flow (mass flow) from sugar sources to sugar sinks.
How does the pressure flow hypothesis work?
The Pressure-Flow Hypothesis It proposes that water containing food molecules flows under pressure through the phloem. The pressure is created by the difference in water concentration of the solution in the phloem and the relatively pure water in the nearby xylem ducts.
What is the process of mass flow?
Mass flow is the movement of dissolved nutrients into a plant as the plant absorbs water for transpiration. The process is responsible for most transport of nitrate, sulfate, calcium and magnesium. The root then absorbs the nutrients.
What is mass flow hypothesis Class 10?
Mass flow hypothesis is the theory that translocation of sugars in the phloem is brought about by a continuous flow of water and dissolved sugars between sources and sinks.
Why is mass flow hypothesis important?
The mass flow hypothesis is a theory which attempts to explain how solutes are transported from source cells into sinks through the phloem. Sucrose moves from companion cells into sieve tube elements by active transport. This reduces the water potential of the sieve tube element.
How are solutes translocated from source to sink?
In this article we will discuss about the Flow of Source and Sink in Phloem Translocation. Since the source-sink relationship is variable, the direction of movement of organic solutes in phloem can be upwards or downwards i.e., bidirectional (c.f. unidirectional upwards in xylem).
Does mass flow occur in xylem?
In general, bulk flow in plant biology typically refers to the movement of water from the soil up through the plant to the leaf tissue through xylem, but can also be applied to the transport of larger solutes (e.g. sucrose) through the phloem.
What does phloem sap contain?
The phloem sap contains high quantities of sugars, amino acids, vitamins, and organic and inorganic acids. Sugars and amino acids are the major components of the phloem sap. Sucrose is the predominant sugar in phloem sap.
Where does mass flow occur?
In physics, mass flow occurs in open systems and is often measured as occurring when moving across a certain boundary characterized by its cross-sectional area and a flow rate. In engineering and biology it may also be a flow of fluids in a tube or vessel of a certain diameter.
What is mass flow hypothesis Class 11?
The mass flow hypothesis states that the translocation of glucose and other sugars within the phloem is caused by a never-ending flow of water and dissolved nutrients between the source (a place where sugars are made) and sink (where sugars are utilized).
What is pressure flow hypothesis Class 11?
The accepted mechanism used for the translocation of sugars from source to sink is called the pressure flow hypothesis. Active transport moves the sucrose out of the phloem sap and into the cells which will use the sugar converting it into energy, starch, or cellulose. …
What is translocation of solutes?
The movement of organic food material or solutes from one place to another in higher plants is called translocation of organic solutes.
What is the theory behind mass flow hypothesis?
The theory behind Mass flow hypothesis which is also called as pressure flow hypothesis describes the movement of sap via phloem, proposed by the German physiologist Ernst Munch in 1930.
What is mass flow theory of translocation?
This is the mass flow hypothesis for the mechanism of translocation in plants. This hydrostatic pressure turgor then shifts the sugars and other substances down the cells of the sieve tube towards the sink (roots). At the sink, the sugars are destroyed to become apoplast and then enter the symplast.
What causes mass flow in phloem?
A diffusion gradient or osmotic gradient is caused by the phloem source cells due to the high concentration of sugar and other organic substances. This results in water being drawn out from adjacent xylem and hydrostatic pressure which moves the sap. This theory is the closest explanation available to describe mass flow in phloem.
