Cell Transport Mechanisms and Permeability

1a. Two reasons that the mass of the bag levels off with time include (1) equilibrium and (2) hydrostatic pressure. Equilibrium refers to the concentrations becoming equal. If there is no longer a higher concentration and lower concentration between the water and sucrose, osmosis can no longer take place. Osmosis can only occur when water is traveling from a higher concentrated area to a lower concentrated area. Hydrostatic pressure occurs when the bag reaches maximum capacity. Water will enter the bag through osmosis but get pushed out through hydrostatic pressure. This works in a cycle and prevents the bag from obtaining more volume and mass.

1b. The curves for the 40% and 20% sucrose differ in the rate of osmosis because of their concentration levels. Since the 40% solution is more concentrated than the 20% solution, rate of osmosis will be higher in the 40% solution. This can be supported by using Fick’s law: rate of diffusion=area x concentration difference/ distance. This formula illustrates that as the concentration difference increases, so does the rate of diffusion. Therefore, higher concentrated solutions will have a higher rate of diffusion/osmosis.

2a. The purpose of increasing the concentration of sodium chloride was to increase the rate of diffusion. This illustrated that as concentration increased, the rate of diffusion also increase.

2b. This experiment demonstrates Fick’s law through changing the solute concentration. During the experiment, the solute concentration doubled creating a difference in diffusion rate. When the solute had a concentration of 9.00 the average diffusion rate was 0.0150. After the solute concentration doubled to 18.00 the average diffusion rate increased (doubled) to 0.0300. If we were to plug the provided numbers into Fick’s law, it would be supported.

2c. The rate of diffusion differs between sodium and Urea because of the molecular mass. Urea has a larger molecular mass (approximately 60 g/mol) compared