PhysioEx Exercise 1: Activity Questions

Concentration-As concentration increases, the rate of diffusion increases due to having a higher concentration gradient. Permeability-Membrane permeability affects the rate of diffusion. In the experiment, the membrane permeability was adjusted by varying the molecular weight cutoff (MWCO). The smaller the molecule, the faster the rate of diffusion due to ability to diffuse through the membrane pores (adjusted by the MWCO).

Because the MW of the urea is 60.07, it exceeded the 20 MWCO, therefore it was unable to diffuse through the 20 MWCO membrane due to urea being unable to fit through the pores of the membrane.

The glucose was able to diffuse; albumin wasn't able to diffuse. The glucose has a much smaller MW than albumin, therefore it was able to diffuse through the 200 MWCO membrane.

Sodium chloride, urea, glucose, albumin

Facilitated diffusion is the same as simple diffusion in that facilitated diffusion requires no energy and diffuses substances down a gradient. Facilitated diffusion is different from simple diffusion in that facilitated diffusion requires carrier proteins.

The rate of glucose transport increased with an increase in the presence of more glucose carriers because more molecules of glucose are able to be transported across the membrane if there are more transporters present. There is an increased sensitivity or upregulation of the transport of the glucose molecules with a higher amount of carrier proteins, therefore the rate increased as the number of glucose carriers increased.

Sodium chloride won't affect the rate of glucose transport because sodium chloride is not needed for transport.

Increasing the NaCl concentration increased the osmotic pressure because there was an increase in force required to oppose osmosis in the closed system.

Osmosis is similar to simple diffusion in that it's a passive process and moves solutes. Osmosis is different from simple diffusion because it's the movement of water rather than solutes.

Water chases milliosomoles can be explained or translated to mean that water goes in its diffusion towards a higher concentration of solutes down a gradient.

The albumin didn't pass through the membrane to diffuse due to it being too large to fit through the pores of the 200 MWCO membrane. The glucose was able to pass through a little bit because of it being a smaller molecule than albumin, therefore it had a higher diffusion rate.

The increase in pore size increased the filtration rate because more filtrate was allowed to go through the membrane. An analogy to this is if you imagine a wall that initially had a small gate that allowed only some people through, making the rate of the transport of people slow. Then compare that to increasing the size of the small gate to a much larger gate, then the rate of the transport of people would be faster.

The powdered charcoal didn't appear in the filtrate because it has a very porous internal matrix, giving lots of surface area for adsorption to surfaces; it likely was stuck and reacted with the membrane rather than filtering through it.

Pressure increased the filtration rate but not the concentration of solutes because it increased the hydrostatic pressure gradient that exists. The solute concentration gradient didn't change from Trial 3 to 4 for 200 MWCO, however the pressure gradient increase allowed for the increased rate of filtration. The steeper the pressure gradient, the faster the filtration rate.

This is a 3:2 ratio, showing the ratio of sodium ions coming out of a cell and ratio of potassium going into a cell. Three potassium ions come into a cell for every two sodium ions that go out. This is the significance of simulating the sodium potassium pump ratio in a cell.

This is because there needs to be a gradient present for the sodium potassium pump to fully be active and transport sodium. The sodium potassium pump is a cotransporting protein meaning it needs to have ATP and go up the gradient. In other words, potassium needs to be present in order for sodium to be transported.

This is because the glucose carriers behave independently of the sodium/potassium pump. The results compared well with the prediction because the rates of the sodium/potassium pumps were the same before and after addition of the glucose carriers.

Glucose is being transported by facilitated diffusion because the actual process of glucose transport is done without ATP and needs only a transport protein. Glucose transport is coupled with the sodium potassium pump transport of ions to create the gradient that powers the transportation of glucose.