What is water potential of potato cell?

Water potential (Ψ) = pressure potential (ΨP) + solute potential (ΨS)

Pressure potential: In a plant cell, pressure exerted by the rigid cell wall that limits further water uptake.

Solute potential: The effect of solute concentration. Pure water at atmospheric pressure has a solute potential of zero. As solute is added, the value for solute potential becomes more negative. This causes water potential to decrease also. In sum, as solute is added, the water potential of a solution drops, and water will tend to move into the solution.

Thanks, but do you know what the Ψ for the potato cell is?

Hi Lex

I believe the cell potential is where the cell neither takes in or lets out water - therefore, equilibrium (when it's isotonic to the solution).

For instance, if it becomes isotonic at 0.6M Sucrose, the cell water potential is 0.6.

Were you introduced to the formula: Cell Water Potential = Osmotic potential + Turgor pressure + Matrix potential? If you were, try this

Cell water potential: 0.6 atmospheres
Osmotic potential (which is always negative) = -17.8 atmospheres
Matrix potential = 0 atmospheres

Cell Water Potential = Osmotic potential + Turgor pressure + Matrix potential

So, 0.6 = -17.8 + Turgor pressure + 0
Rearrange for turgor pressure = 0.6 + 17.8 = 18.4 atmospheres

Thanks for the help @duddy , however, the way i learned the water potential is through this equation: Water Potential (Ψ) = Solute Potential (Ψs) + Pressure Potential (Ψp), where in this lab experiment, the pressure potential is 0 and the equation for the solute potential is Ψs = (-i)(C)(R)(T), where -i (ionization constant) is -1, C (molar concentration) I don't know this is where i'm confused, R (pressure constant) is 0.0831 liter bars/mole K, and the T (temperature) is 295 K.
so far this is what I have for the solute potential equation: Ψs = (-1)(?)(0.0831)(295)

I need help finding the molar concentration

Hi, aren't the molar concentrations provided?

The molar concentration was not provided, but I figured out what I needed to do.
Based off of my data graph (line graph displaying the change in mass according to sucrose molarity), the point for .22 M showed 0% mass change, therefore .22 M is where the potato is isotonic to the sucrose solution.  So i put .22 M into the the equation. I got -5.39319 as the water potential of the potato cell.  Is this right?

A negative water potential is acceptable. Pure water has a water potential of zero.

I'm doing A-level biology also so i'm in the same boat as you, I'll try to make my explanation as clear for you as possible. Firstly you'll need to know about osmosis in order to get to grips with water potential (Ψ), osmosis is a type of diffusion (in water) where the net movement of water moves from a high to a low water potential across a selectively or fully permeable membrane. In simple terms, this means that the number of water molecules try to evenly distribute each other at either side of the membrane. In order to do this, the side with the high amount of water molecules (higher water potential) will need to move to the area of lower water potential to reach equilibrium. Ψ is measured in kPA (killer pascals), 0 is the purest form of water (such as in deionized water) with pretty much no other solutes in solution. Lower water potentials (-100kPA,-200kPA) have an increasingly greater amount of solutes in solution. Sometimes I get confused with the units so I try to remember it this way, you can't have positive values with water potential so its always either negative or zero, so think the more negative a number the lower the water potential is.

I'll give a practical example, if you submerge some equally sized samples of potato into a concentrated sample of sucrose solution (A) and the rest into a sample of deionised water (B) for ten minuites or so you would see a change in mass. The potato in sample A would lose weight and the potato in sample B will gain weight, your probably wondering why this has happened so try to remember the definition for osmosis (diffusion of water) where a high water potential will always move to a lower water potential. In sample A the potato was submerged in concentrated sucrose solution that has a low water potential (not many water molecules, mostly sucrose) This water potential in the solution would be lower than that in the cell (which is also slightly negative because of the sucrose used as food in the potato) so the net movement of water will move out of the potato through its membrane into the sucrose solution and so the potato will lose weight. The opposite happens to the potatos in sample B, where the water potential in the deionised water is much higher than in the potato (almost 0) so the net movement of water will move into the potato in the hope of reaching equillibrium (which it never really does) and so the weight of the potato increases.

I hope these definitions and the practical example has helped clear up the confusion with water potential

Solute potential is basically the same as water potential, but it refers to the amount of solute in solution rather than the amount of water. So the net movement of solutes will always move from a low to a high solute concentration across a selectively permable membrane. Pressure potential describes the density at which molecules take up a particular amount of space, in high pressure their are alot of molecules in the same amount of space and in low pressure there are fewer molecules roaming in th same amount of space. So the net movement of these molecules will always be from a higher to a lower pressure potential.