Osmosis/Diffusion Lab

How would you determine the best concentration of solutes to give a patient in need of fluids before you introduced the fluids into the patient's body?

Measure the tonicity or water potential of blood.

Which pair(s) that you tested did not have a change in weight? How can you explain this?

Water/water; no flow because no difference in water potentials/no gradient.

Based on what you learned from your experiment, how could you determine the solute concentration inside a living cell?

Place a cell in a solution and measure Delta mass.

What factors determine the rate and direction of osmosis?

Steepness of the gradient, electrical gradient. Permeability of membrane.

When will the net osmosis rate equal zero in your model cells? Will it ever truly be zero?

Net osmosis = 0 when the system reaches equilibrium. At this point water continues to flow but the rate in = the rate out. In a living cell, active transport means osmosis continues (the gradients are continually being created)

How is the dialysis tubing functionally different from a cellular membrane?

Tubing only allows passive transport. Cell membrane also uses active means of transport.

What would happen if you applied salt water to the roots of plants? Why?

Roots would shrivel because salt water has higher tonicity.

Will water move into or out of a plant cell if the cell has a higher water potential than its surrounding environment?

Will move out - flows from high to low

How could you determine which solution is isotonic to the cells?

If there is no change in mass.

How would you calculate the water potential in the cells?

Find x-intercept on graph to determine concentration of potato. Then solve for solute concentration using Ψs=-iCRT. This number equals water potential(Ψ).

What would your results be if the potato were placed in a dry area for several days before your experiment?

Cells would be dry, therefore higher gradient, water would flow into cells & Delta mass would be large for all solutions.

When potatoes are in the ground, do they swell with water when it rains? If not, how do you explain that, and if so, what would be the advantage/disadvantage?

Cell wall exerts pressure, limiting amt. of water that can flow in (when reached osmotic pressure of the extracellular solution). Advantage = helps cells expand in growth Disadvantage = if cells get too big, S.A. to V ratio becomes too small