Water potential: include solute and pressure effects
הוצג| English | משמעות |
|---|---|
| water potential/ˈwɔːtə pəˈtenʃl/ | פוטנציאל מים |
| pressure potential/ˈpreʃə pəˈtenʃl/ | פוטנציאל לחץ |
What would explain this observation?
- A plant cell can stop gaining net water even while its contents contain solute. The cell wall permits pressure to build, altering the water-potential 水势 balance.
Build the model
- Water potential describes the tendency of water to move relative to a chosen reference, with pressure units.
- In the simplified cell model, water potential equals solute potential plus pressure potential 压力势.
- Dissolved solute lowers solute potential; positive pressure can raise water potential.
- Net water movement through a water-permeable membrane is from higher to lower water potential.
- water potential: A pressure-equivalent measure of the tendency of water to move relative to a reference.
- pressure potential: The pressure contribution to water potential in the stated model.
A cell is at −0.6 MPa and its surroundings at −0.1 MPa. Which net movement is predicted?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Water moves toward the more negative potential - from higher (-0.1 MPa) to lower (-0.6 MPa) - so it enters the cell. Negative values are normal here; "more negative is lower" is the rule to apply.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Compare the complete water potentials of the two sides rather than solute concentrations alone.
- A turgid cell can have the same total water potential as its surroundings despite unequal solute potential.
- At equilibrium there is no net transfer, but water molecules can continue moving in both directions.
In the lab: Use provided potential values and labelled plant-cell models. State the reference and units before adding components. For school tissue investigations, control temperature, tissue dimensions, time and blotting, and estimate a zero-change point from repeated measurements. Do not claim the mass method separately measures cell pressure without further evidence.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a cell has solute potential −0.8 MPa and pressure potential +0.3 MPa, so total potential is −0.5 MPa.
- Surrounding solution is −0.2 MPa.
- Water tends to enter the cell because −0.2 is higher than −0.5.
- If the cell components change to −0.8 and +0.6 MPa, its total is −0.2 MPa, matching the surroundings in this simplified model.
Your turn: Solute potential is −0.7 MPa and pressure potential is +0.4 MPa. Find total water potential.
Solute potential is −0.7 MPa and pressure potential is +0.4 MPa. Find total water potential.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is -0.3 MPa. Known: solute potential -0.7 MPa; pressure potential +0.4 MPa. Use total potential = solute + pressure. Total = -0.7 + 0.4 = -0.3 MPa. Compare this total, not the solute term alone, with the surroundings.
Check the conclusion and its limits
- More negative is lower, not higher.
- The additive cell model has stated boundaries and does not require pretending that every real tissue has one uniform value.
- Loss of turgor and cell-wall support differ from a rigid wall directly controlling solute concentration.
Not true: Solute concentration alone always determines water movement in a turgid plant cell. In a turgid cell the wall pushes back: pressure potential opposes the solute effect, and movement depends on the SUM. Solute concentration alone decides only when pressure potential is zero.
- Water potential describes the tendency of water to move relative to a chosen reference, with pressure units.
- Compare the complete water potentials of the two sides rather than solute concentrations alone.
- Watch for: more negative is lower, not higher.
Write from a water potential of -0.7 megapascals
- Solute potential is -0.9 MPa and pressure potential is +0.2 MPa. The surrounding solution is -0.4 MPa.
- Find the cell's water potential and the direction of net water movement.
In a turgid cell the wall pushes back: pressure potential opposes the solute effect, and movement depends on the SUM.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. In a turgid cell the wall pushes back: pressure potential opposes the solute effect, and movement depends on the SUM. Solute concentration alone decides only when pressure potential is zero.
A pressure-equivalent measure of the tendency of water to move relative to a reference: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
water potential means A pressure-equivalent measure of the tendency of water to move relative to a reference.
A cell has solute potential -0.9 MPa and pressure potential +0.2 MPa. The surrounding solution is -0.4 MPa. What is the cell's water potential, and which way does water tend to move?
-0.9 plus 0.2 is -0.7. Water moves toward the lower water potential.
What is the cell's water potential?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
-0.9 plus 0.2 is -0.7 megapascals, which is lower than -0.4.