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.
How does pressure flow work?
In very general terms, the pressure flow model works like this: a high concentration of sugar at the source creates a low solute potential (Ψs), which draws water into the phloem from the adjacent xylem. This creates a high pressure potential (Ψp), or high turgor pressure, in the phloem.
How does pressure flow explain translocation?
While movement of water and minerals through the xylem is driven by negative pressures (tension) most of the time, movement through the phloem is driven by positive hydrostatic pressure. This process is termed translocation, and is accomplished by a process called phloem loading and unloading.
What causes pressure in the pressure flow hypothesis?
Pressure flow hypothesis states that the water containing food flows through the phloem under pressure. This pressure is created by the difference in the content of water in the phloem and xylem.
What does the pressure flow model explain quizlet?
The pressure-flow hypothesis explains how the sugar molecules from a source cell forms a high concentration inside the cells of the phloem.
Is mass flow and pressure flow hypothesis same?
Introduction. The Mass Flow Hypothesis was first proposed by German plant physiologist Ernst Munch in the year 1930. He theorised the movement of sap through the phloem tissue in plants. This theory is also known as the Pressure Flow Hypothesis.
This relationship can be expressed by the equation F = Q/t. Fluid flow requires a pressure gradient (ΔP) between two points such that flow is directly proportional to the pressure differential. Higher pressure differences will drive greater flow rates. The pressure gradient establishes the direction of flow.
Does flow increase with pressure?
More pressure changes the velocity of the fluid, but it also decreases the flow or output. The cause of the flow decrease is due to two factors: volumetric efficiency of the pump and reduced motor speed.
What is the relationship between water pressure and flow rate?
The relationship between the pressure in the pipe and the flow rate is proportional. That is, the higher the pressure, the higher the flow rate. The flow rate is equal to the velocity multiplied by the cross section. For any section of the pipe, the pressure comes from only one end.
How pressure flow helps in the translocation of sugars from source to sink in plants?
The sucrose already present in the sink region is converted into starch or cellulose, thereby reducing the hydrostatic pressure in the sink cells. Hence, the pressure difference created between the source and the sink cells allows sugars to be translocated from the former to the latter.
How is pressure generated inside the phloem tube?
Water moves into the phloem by osmosis, which increases the hydrostatic pressure. There is a pressure gradient with high hydrostatic pressure near the source cell and lower hydrostatic pressure near the sink cells. Solutes move down the pressure gradient towards the sink end of the phloem.
Which describes pressure or bulk flow?
Mass flow, also known as “mass transfer” and “bulk flow”, is the movement of fluids down a pressure or temperature gradient, particularly in the life sciences. As such, mass flow is a subject of study in both fluid dynamics and biology.
Who proposed the pressure-flow hypothesis?
In angiosperms, increasing evidence shows the pressure-flow hypothesis, formulated by Ernst Münch in 1930 [1••], to adequately explain the mechanism of phloem transport [2].
Who gave the concept of pressure-flow model?
Introduction. The pressure-flow hypothesis often referred to as the mass flow hypothesis, is the best-supported explanation for sap transportation through the phloem. It was proposed by Ernst Münch, a German plant physiologist, in 1930.
What two forces are responsible for 90% of the upward flow of water through a plant?
Plants pull water upward using cohesion and adhesion.
How do sugars move around the plant in the phloem vessels?
The mechanism by which sugars are transported through the phloem, from sources to sinks, is called pressure flow. At the sources (usually the leaves), sugar molecules are moved into the sieve elements (phloem cells) through active transport.
What is the main function of phloem?
While the main role of the phloem tissue is to transport carbohydrates from sources to sinks through the sieve elements, phloem is also composed of parenchyma cells, which play a key role in the storage of water, non-structural carbohydrates and storage proteins (Rosell 2016).
What is the mass pressure flow hypothesis?
Mass-flow hypotheses include the pressure-flow hypothesis, which states that flow into sieve tubes at source regions (places of photosynthesis or mobilization and exportation of storage products) raises the osmotic pressure in the sieve tube; removal of sugars from sieve tubes in sink regions—i.e., those in which …
What is the mass flow theory?
The mass flow hypothesis is the theory which states that mass flow of solutes takes place in the phloem.
Is mass flow active or passive?
Mass flow is primarily a passive process in which companion cells support sieve tube vessels.
How do you convert pressure to flow?
- Divide the pressure difference (ΔP) by the specific gravity (S) of the fluid.
- Find the square root of the resultant division.
- Multiply the root by the flow factor (Kv) to obtain the flow rate (Q) for the fluid system. Mathematically, that’s: Q = √(Kv × (ΔP/S))
Is pressure the same as flow?
Pressure is the force acting per unit area; it is a scalar point property of fluids. Flow is the rate at which fluid passes through a gives surface and flow is caused by the difference in pressure within a fluid.
Does reducing flow increase pressure?
The reduction in pipe length offers resistance against the flow and results in pressure loss. When the flow velocity increases, the pressure increases, and then efficiency reduces.
Does pressure affect flowrate?
Flow rate is the effect. Higher pressure causes increased flow rate. If the flow rate increases, it is caused by increased pressure.
Does higher water pressure mean more flow?
The flow of water from your faucet is determined by water pressure. The more water that is being forced through a pipe, the more pressure there will naturally be. Through any pipe size, higher water pressure will cause greater water flow.