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Questions and Answers
What happens to the chemical potential of a solute as its concentration increases?
What happens to the chemical potential of a solute as its concentration increases?
- It increases. (correct)
- It remains constant.
- It decreases significantly.
- It fluctuates randomly.
In which direction does diffusion occur according to chemical potential?
In which direction does diffusion occur according to chemical potential?
- From high chemical potential to low chemical potential. (correct)
- Randomly in all directions.
- From low chemical potential to high chemical potential.
- Only in the presence of an impermeable barrier.
What is the significance of reaching equilibrium in the context of solute diffusion?
What is the significance of reaching equilibrium in the context of solute diffusion?
- It results in an increasing concentration gradient.
- It leads to the formation of new solutes.
- It means no net movement of solute occurs. (correct)
- It indicates continuous movement of solute.
What does Fick's Law describe in relation to diffusion?
What does Fick's Law describe in relation to diffusion?
Which of the following correctly describes absolute temperature?
Which of the following correctly describes absolute temperature?
What is the unit of pressure historically used by plant physiologists to discuss water movement?
What is the unit of pressure historically used by plant physiologists to discuss water movement?
What is the relationship between pressure and energy in the context of water movement?
What is the relationship between pressure and energy in the context of water movement?
What happens to the chemical potential (Ψ) of water when a solute is dissolved in it?
What happens to the chemical potential (Ψ) of water when a solute is dissolved in it?
What units can pressure be expressed in, aside from MPa, when discussing energy?
What units can pressure be expressed in, aside from MPa, when discussing energy?
What is the effect of increasing solute concentration on water potential (Ψ)?
What is the effect of increasing solute concentration on water potential (Ψ)?
In which direction does water typically diffuse in relation to solute concentration?
In which direction does water typically diffuse in relation to solute concentration?
What does the presence of solutes do to the organization of water molecules?
What does the presence of solutes do to the organization of water molecules?
How is potential energy affected when a solute is dissolved in water?
How is potential energy affected when a solute is dissolved in water?
What is the driving force behind the diffusion of water across a semi-permeable membrane?
What is the driving force behind the diffusion of water across a semi-permeable membrane?
In which direction does water move during osmosis?
In which direction does water move during osmosis?
What does the symbol Ψ represent in the context of water potential?
What does the symbol Ψ represent in the context of water potential?
At standard atmospheric pressure, what is the water potential (Ψ) of pure H2O?
At standard atmospheric pressure, what is the water potential (Ψ) of pure H2O?
What is the main concept that dictates the movement of both solutes and water across membranes?
What is the main concept that dictates the movement of both solutes and water across membranes?
If a cell is placed in a solution with higher sucrose concentration compared to the inside of the cell, what will happen?
If a cell is placed in a solution with higher sucrose concentration compared to the inside of the cell, what will happen?
How does the movement of water compare to the movement of solute in an osmosis scenario?
How does the movement of water compare to the movement of solute in an osmosis scenario?
What is the significance of a semi-permeable membrane in the context of osmosis?
What is the significance of a semi-permeable membrane in the context of osmosis?
What is the equation representing water potential (Ψ)?
What is the equation representing water potential (Ψ)?
Which statement accurately describes solute potential (ΨS)?
Which statement accurately describes solute potential (ΨS)?
What does the 'i' in the van't Hoff equation represent?
What does the 'i' in the van't Hoff equation represent?
Which of the following statements is true regarding the van't Hoff equation?
Which of the following statements is true regarding the van't Hoff equation?
In the context of solute potential, what is the effect of adding solute to pure water?
In the context of solute potential, what is the effect of adding solute to pure water?
Which value represents the maximum solute potential (ΨSmax)?
Which value represents the maximum solute potential (ΨSmax)?
What is the primary reason for the negative value of solute potential (ΨS)?
What is the primary reason for the negative value of solute potential (ΨS)?
What is the relationship between molality and molarity for dilute solutions?
What is the relationship between molality and molarity for dilute solutions?
What happens to red blood cells in a hypotonic solution?
What happens to red blood cells in a hypotonic solution?
What defines a selectively permeable membrane?
What defines a selectively permeable membrane?
How do plant cells differ from red blood cells regarding osmotic pressure?
How do plant cells differ from red blood cells regarding osmotic pressure?
In terms of solute concentration, how is osmotic movement defined?
In terms of solute concentration, how is osmotic movement defined?
What happens to plant cells in a hypertonic solution?
What happens to plant cells in a hypertonic solution?
What is the term used to describe the rigidity and pressure in plant cells?
What is the term used to describe the rigidity and pressure in plant cells?
What can occur if sufficient water enters a red blood cell?
What can occur if sufficient water enters a red blood cell?
Which of the following best describes the condition of red blood cells in isotonic solutions?
Which of the following best describes the condition of red blood cells in isotonic solutions?
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Study Notes
Chemical Potential (µ) and Diffusion
- Chemical potential (µ) describes a substance's tendency to move. It's calculated using µ = RT ln c (J/mol), where R is the gas constant, T is absolute temperature (K), and c is solute concentration.
- Higher concentration equates to higher chemical potential.
- Diffusion follows a chemical potential gradient: high µ to low µ.
- Fick's Law sufficiently explains solute diffusion; chemical potential isn't always necessary for these calculations.
Water Diffusion and Osmosis
- Water movement is driven by chemical potential gradients, similar to solutes, though the formalism differs.
- Osmosis is water's diffusion across a semipermeable membrane between solutions of differing concentrations (and thus chemical potentials). It's a specific type of water diffusion.
- The driving force for water diffusion remains the same regardless of a membrane's presence.
Water Potential (Ψ)
- Water potential (Ψ) quantifies water's chemical potential, measured relative to pure water at standard atmospheric pressure. Units are typically MPa.
- Pure water at standard atmospheric pressure has Ψ = 0 MPa (by definition).
- Water flows from high Ψ to low Ψ (down a Ψ gradient).
- Pressure units (MPa) represent energy (energy/volume = pressure), even though the baseline units are technically J/mol.
Effects of Solutes on Water Potential
- Dissolving solutes in water decreases water's chemical potential (Ψ) because water molecules become more ordered around solute molecules (lower entropy).
- Water with dissolved solutes has Ψ < 0 MPa at atmospheric pressure. Greater solute concentration means a greater negative Ψ.
Water Relations in Cells
- In red blood cells (lacking cell walls), water movement via osmosis can cause bursting if the internal solute concentration is lower than the external concentration.
- Plant cells, with cell walls, exhibit turgor (rigidity and pressure) due to water influx, preventing bursting, even under osmotic pressure.
Components of Water Potential
- Water potential (Ψ) is a sum of its components: Ψ = ΨS + ΨP + ΨM
- ΨS: Solute potential (osmotic potential), always negative, affected by solute concentration.
- ΨP: Pressure potential
- ΨM: Matric (matrix) potential
Solute Potential (ΨS)
- ΨS reflects the impact of solutes on water potential, not the solute's potential.
- Calculated using a modified van't Hoff equation: ΨS = -ciRT, where:
- c: solute concentration (molality)
- i: ionization constant (1 for non-ionized molecules, varies for others)
- R: universal gas constant
- T: temperature (K)
- This equation is accurate only for dilute, ideal solutions. Molality and molarity are almost interchangeable in dilute solutions.
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