Water Potential Problems

The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M. 

It is possible that this cell is already in equilibrium with its surroundings

False. The cell must lose water to reach equilibrium; no way for pressure to build up (+MPa) to bring the cell to equilibrium.

• 2.5 M > 2 M

  • Environment has lower (more negative) water potential than cell

  • Environment wants to add pressure from outside (+MPa), cell will lose pressure (-MPa)

  • Less pressure = less water for cell, becoming flaccid

The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M. 

Initially, solute concentration is greater outside the cell than inside.  

True

• 2.5 M > 2.0 M

  • No matter the ionization constant, temperature, or pressure constant, the molarities indicate that the enviornment has a higher concentration

The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M.

Water will enter the cell because solute potential is lower inside the cell than outside.

False. Water will leave the cell because solute potential is higher inside than outside

• 2.5 M > 2.0 M

  • Environment has a lower (more negative) solute potential b/c higher molarity; Cell has higher (more positive) solute potential b/c higher molarity

  • Environment wants to add pressure from outside (+MPa), cell will lose pressure (-MPa)

  • Less pressure = less water for cell, becoming flaccid

The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M.

The cell will become flaccid because the pressure potential is greater outside the cell than inside.

False. The cell will become more flaccid because the solute potential is greater inside the cell than outside

• 2.5 M > 2.0 M

  • Environment has lower (more negative) solute potential

  • Tries to remove pressure from cell to make equilibrium; outside = inside

  • Removed pressure = lose water —> more flaccid

The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M. 

The cell is already in equilibrium with its surroundings because of the combination of pressure potential and solute potential inside and outside the cell.

False. The cell is not in equilibrium because there is no pressure potential inside the cell and none will build up when water leaves

• 2.5 M > 2.0 M

  • Enviroment has lower (more negative) solute potential b/c of higher molarity

  • Reach equiilibrium = remove pressure from the cell or add pressure to the outside

    • Bring water from the inside of the cell —> outside to the environment

    • Pressure is lost

  • Pressure potential is only built up if water is being added to the cell

The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M. 

Initially, the numerical value of the solute potential is more negative inside the cell than outside. 

False. The cell is hypotonic (lower concentration) to the surrounding solution

• 2.0 M (Cell) > 2.5 M (Environment)

The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M. 

At equilibrium, the pressure potential inside the cell will have increased.  

False. The solute potential is more negative in the enviornment than inside the cell.

• 2.5 M > 2.0 M

  • According to Y = - (iCRT)

The initial molar concentration of the cytoplasm inside a cell is 1.3 M and the surrounding solution is .3M.

The cell could already be in equilibrium with the surrounding solution.

False

• 1.3 M (Cell) > 0.3 M (Outside)

  • Pressure potential has not been added yet

  • Currently, cell has a more negative solute potential and overall water potential

The initial molar concentration of the cytoplasm inside a cell is 1.3 M and the surrounding solution is .3M.

If the cell is already in equilibrium with its surroundings, there must be pressure potential inside the cell. 

True

• Equilibrium —> Water potiential outside = inside

• Even though the solute potential of cell is more negative (-MPa), this can be offset by adding pressure potential (+MPa)

The initial molar concentration of the cytoplasm inside a cell is 1.3 M and the surrounding solution is .3M.

If the cell is initially flaccid, there will be a net gain of turgor during osmosis.

True

• Flaccid = floppy, shriveled, can take in water

• Tugor = swelled, full, took in water

• 1.3 M > 0.3 M

  • Cell originally flaccid —> floppy

  • Cell currently has a very negative (low) solute potential + overall water potential compared to enviornment

  • Reach equilibrium = add water inside the cell, increasing pressure on the walls of the cell (+MPa)

    • Increased pressure = swelling

The initial molar concentration of the cytoplasm inside a cell is 1.3 M and the surrounding solution is .3M.

If the cell is initially flaccid, diffusion will proceed until solute potential inside the cell equals solute potential outside the cell.

Not enough information. Probably false, but it depends on how much room there is inside the cell for water to enter before pressure begins to build. Most likely, pressure will bring the cell to equilibrium before the the cytoplasm and solution become isotonic

• Two methods of equilibrium

  • Cytoplasm and solution molarity become isotonic

  • Pressure potential is added

• Need to know how much room in the cell —> will pressure build up to offset the lower (very negative MPa) solute potential of cell?

The initial molar concentration of the cytoplasm inside a cell is 1.3 M and the surrounding solution is .3M.

At equilibrium, water potential inside and outside the cell will be equal. 

True

• Equilibrium —> overal water potential inside = outside

  • not necessarily b/c the solutions have same concentration

The initial molar concentration of the cytoplasm inside a cell is 1.3 M and the surrounding solution is .3M.

If the cell is initially flaccid, the molarity of the cytoplasm will increase during osmosis.

False. The molarity of the cytoplasm will decrease during osmosis

• Osmosis = movement of solvent through a semipermeable membrane

  • high to low concentration

• 1.3 M (cell) > 0.3 M (environment)

  • since the molarity of the cell is higher initially, solvent will be added inside the cell

    • more liquid = same moles/more liters = lower molarity

The initial molar concentration of the cytoplasm inside a cell is 1.3 M and the surrounding solution is .3M.

If the cell is initially flaccid, then both solute potential and pressure potential inside the cell will increase during osmosis. 

Not enough information. Probably true, but it depends on how much room there is inside the cell for water to enter before pressure begins to build. As soon as pressure begins to build, the statement is true

• Osmosis —> impacts the solute potential

• Pressure potential —> only occurs if there is not enough room in the cell for osmosis to fully reach equilibrium

A cell is in equilibrium with its environment.  The solute potential of the cell’s cytoplasm is –0.45MPa.  The water potential of the surrounding solution is –0.32Mpa.  When the cell was first put into the solution, it was flaccid.

Since the cell was put into this solution, its solute potential and pressure potential have both risen. 

True

• Initially, cell = flaccid, implies that it is no longer flaccid

  • water was added into the cell, causing it to swell —> solute potential increased (less negative)

• At equilibrium —> Cell solute potential is more negative than outside solute potential

  • implies that pressure potential is helping offset the extra negative solute potential for an overall equal water potential

  • pressure potential is only added after the cell is in new environment

A cell is in equilibrium with its environment.  The solute potential of the cell’s cytoplasm is –0.45MPa.  The water potential of the surrounding solution is –0.32Mpa.  When the cell was first put into the solution, it was flaccid.

The pressure potential of the cell is now +0.32MPa. 

False. The pressure potential is 0.13 MPa.

• Equilibrum —> Water potential of cell = environment

  • Water potential = solute potential + pressure potential

• Currently, solute potential of cell < water potential of environment

  • -0.45 MPa < -0.32 MPa

  • in order to reach equilibrium, need to have pressure potential of +0.13

    • -0.45 MPa + 0.13 MPa = -0.32 MPa

A cell is in equilibrium with its environment.  The solute potential of the cell’s cytoplasm is –0.45MPa.  The water potential of the surrounding solution is –0.32Mpa.  When the cell was first put into the solution, it was flaccid.

The cell has a higher solute potential than the surrounding solution. 

False. The cell has a lower solute potential than the surrounding solution

• -0.45 MPa < -0.32 MPa

  • cell is more negative, thus has a lower solute potential

A cell is in equilibrium with its environment.  The solute potential of the cell’s cytoplasm is –0.45MPa.  The water potential of the surrounding solution is –0.32Mpa.  When the cell was first put into the solution, it was flaccid.

The cell's water potential is now lower than that of the surrounding solution. 

False. The cell’s water potential is equal to the surrounding solution

• Equilibrium —> water potential cell = outside

A cell is in equilibrium with its environment.  The solute potential of the cell’s cytoplasm is –0.45MPa.  The water potential of the surrounding solution is –0.32Mpa.  When the cell was first put into the solution, it was flaccid.

Initially, the cell's solute potential was lower than that outside. 

True

• Cell was flaccid at first

  • cell = not much water inside

• cell solute potential is much more negative at equilibrium

  • pressure potential is taking over the job for osmosis —> very negative before

A cell is in equilibrium with its environment.  The solute potential of the cell’s cytoplasm is –0.45MPa.  The water potential of the surrounding solution is –0.32Mpa.  When the cell was first put into the solution, it was flaccid.

Initially, the cell’s water potential was lower than that outside. 

True

• Cell was flaccid at first

  • cell = not much water inside

• cell solute potential is much more negative at equilibrium

  • pressure potential is taking over the job for osmosis —> very negative before

A cell is in equilibrium with its environment.  The solute potential of the cell’s cytoplasm is –0.45MPa.  The water potential of the surrounding solution is –0.32Mpa.  When the cell was first put into the solution, it was flaccid.

The pressure potential of the cell is equal to that outside the cell.

False. The pressure potential of the cell is greater than the outside

• cell solute potential is much more negative at equilibrium

  • pressure potential is taking over the job for osmosis —> very negative before

A cell at room temperature is in equilibrium with its surroundings.  The molarity of the surrounding sodium chloride solution is 0.75M.  To convert molarity to solute potential in MPa, use the formula: Y_S = - ( i CRT ) where

 i = ionization constant (depends on solute)

R = pressure constant (R=0.0831 liter MPa/mole ^oK)

C = molar concentration (given above)

T = temperature in ^oK (room temp is about 273^oK)

-34.0

• Y_S = - ( i CRT ) = - (2 × 0.75 × 273 × 0.0831) = -34.0