Worksheet for Lab Exercise 4: Diffusion and Osmosis Submit at the start of the n

Question

Worksheet for Lab Exercise 4: Diffusion and Osmosis Submit at the start of the next laboratory eriod (44 pts) WATER AND SOLUTE POTENTIALS Calculate the water potential () for the following solutions (Show all calculations): a. o.1 M NaCl at atmospheric pressure and 25°c ziCK (2)(a1)(o.os5)(298): _ '95 bms b. Plant cell cytosol with a solute concentration equal to that of o.15 M NaCl at 25°C (Note: The actual solutes in plant cells include a variety of salts, sugars, and other small organic molecules). .If this plant cell were placed in the o.1 M NaCl solution, which way would water diffuse - into, or out of, the cell? Explain. What must the turgor pressure be if there is no net diffusion of water between the cell and the surrounding NaCl solution? Explain with the aid of calculations.

Explanation / Answer

a.

Water potential () = p (osmotic potential) + s (solute potential)

To calculate s inside the cell = -iCRT = -2 * 0.15 * 0.0831*298 = -7.43bars

Where i=no. of ions, C= concentration of solute, R=gas constant, T= temperature in Kelvin

Osmotic potential is the difference between the solute potential of outside and the solute potential of inside.

To calculate s outside the cell = -iCRT = -2 * 0.1 * 0.0831*298 = -4.95bars

osmotic potential (p) = -7.43-(-4.95) = -2.48bars

Water potential = 2.48 + (-7.43) = -4.95bars

b.

- If plant cell cytosol having 0.15M NaCl is placed in 0.1M NaCl, water flows from its higher concentration to its lower concentration. As solute concentration inside the cell is higher, water conc. will be lower. So, water flows from outside of the plant cell to its inside.

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

Turgor pressure is the difference between water potential and osmotic potential

As the water flows from outside of the cell to inside, the excess water that is collected inside will create pressure against the cell wall. This pressure is celled the turgor pressure.

So, the turgor pressure of the cell when there is no net movement of water from cell into the solution is equal to 2.48

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