Water Potential and Osmosis

What temperature are molecules constantly in motion?

above absolute zero? (-273 C)

What is diffusion?

The movement of molecules from high to low

When solutes are added to a given volume of water, the effective concentration of water usually goes down. Why does this happen?

polar solutes tend to bind to water molecules and reduce their mobility.

What is water potential symbolized by?

Y (pronounced psi), measured in chemical potential of water in terms of free energy per mole of water

How do you calculated solute potential (Ys)

Ys=-iCRT

i= ionization constant

C= Concentration of solute in moles/liter

R= Gas constant

T= Temperature (K)

What relationship to Ys (solute potential) and C (concentration of solute) show

Inverse due to the negative sign in the equation.

Plant cell walls can withstand what amount of pressure without bursting?

5-15 bars, 75-220 psi

As turgor pressure increases, Y ____

Increases

In contrast to plant cells; bacterial, fungal, and animal cells that are put in high solutions of water potential will burst as the cell volume increases? why?

They lack cell walls

What is the independent variable of this lab?

sucrose concentration

What is the dependent variable in this lab?

percent change in mass

How much solution are you supposed to pour in each sucrose cup?

100 mL

How thick are your potato slices that you cut with a cork borer?

3 mm

What do you do immediately after you slice the potatoes?

keep the slices in an empty covered cup until you can weigh them.

The potato cores are weighed to the nearest ___ milligrams

10

How long are you supposed to submerge the slices in the sucrose solution?

35 minutes

How often do you need to 10-second-swirl the solution

every 5 minutes

what is the equation for %mass change?

(mass final- mass initial) x 10/ mass initial

Where do you pour the solutions?

in the sink

Why do you have to swirl the cups at intervals?

So the glucose stays in contact with the potatoes for constant diffusion.

Plant cells ___ when added to hypotonic solutions and ____ in hypertonic solutions

swell, shrink

How do plant cell walls prevent plant cells from lysing?

The cell walls only allow the membranes to swell to the size of the cell walls.

1. hold the section of onion, ___ side up in one hand

concave

2. With ___, pull off the thin _____

forceps, thin outer skin

3. Place the thin skin membranes into di H2o and 1M sucrose. Let sit for _____

10 minutes

4. Remove the skin-membrane from the solution and place on ____. Add 1-2 dropps of stain onto the sample and let it sit for ____ minutes

the slide. 5 minutes

5. Use_____solution to gently rinse excess stain off of sample into the ___ container. Place a coverslip flowly using forceps to avoid airbubbles

tested, waste

What does the di H2O onion cell look like? what is the tonicity of the solution?

The stain on the onion is entire. Hypotonic because the water went into the cells and created turgor

What does the 1m surose onion look like? What is the tonicity of the solution?

The stain only stains the membrane on the cell wall and it looks like there are pockets where the cell membrane is being pulled in due to plasmolysis. Hypertonic bceuase the onion cells are being plasmolysed.

What is the water potential of a 0.2 M sucrose solution that is in a container open to the atmosphere?  The solution has a temperature of 28°C.

Ys=(-1)(0.2 M)(0.0831 J/molK)(301 K)= -5.00 Bars

Yp= 0 Mpa (since the container is open)

If a cell whose pressure potential (y_p) is initially zero bars and whose solute potential (y_s) is -9 bars is placed solution with -5 bars should its pressure potential be when the cell is at equilibrium with the solution?  (Assume the cell's solute potential does not change.)

Ycell = Y solution

-9(Ys) + Yp = -5 (Ys) + 0 (Yp)

Yp= -5 +9

Yp= 4 bars

  Should the solute potential increase or decrease as water flows in?  Explain the change. 

The solute potential increases because the cell’s solutes are becoming less diluted.

as solute potential inside the cell increases, will the pressure potential be more or less than that initial?

It will be less because the increase in solute potential (less negative) reduces the amount of turgor pressure needed to reach equilibrium.

What does a positive %mass change mean about the solution Molarity/tonicity?

The solution is hypotonic to the potato because there is a high solute concentration in the potato, making water rush in.

What does a negative %mass change mean about the solution Molarity/tonicity?

The solution is hypertonic to the potato because there is a higher solute concentration in the water, making water rush out.