Cell Physiology

Review Sheet
Exercise 1
Cell Transport Mechanisms and Permeability
Activity 1: Simulating Dialysis (Simple Diffusion) • Describe two variables that affect the rate of diffusion:
Two variables that affect the rate of diffusion are size and concentration gradient. The molecular size vs the MWCO size of the membrane can either increase, decrease, or prevent diffusion.

The greater the concentration gradient the greater the diffusion rate due to molecules moving from areas of higher concentration to areas of lower concentration.

• Why do you think the urea was not able to diffuse through the 20 MWCO membrane? How well did the results compare with your prediction?
My prediction was correct. The molecular weight of urea is 60.07 and is to great to pass through the 20MWCO membrane.

• Describe the results of the attempts to diffuse glucose and albumin through the 200 MWCO membrane. How well did the results compare with your prediction?
My prediction was correct in this experiment. Knowing that glucose is a monosaccharide, it is of size to diffuse through a 200MWCO membrane. Albumin being a protein is dense with 607 amino acids and an average molecular weight of 135g/mole is not going to diffuse through the 200MWCO membrane. During the experiment the left solute glucose at 9.00 passed through the 200MWCO membrane at a rate of 0.0042. The albumin did not diffuse through the membrane.

• Put the following in order from smallest to largest molecular weight: glucose, sodium chloride, albumin, and urea:
In order from smallest to largest is sodium chloride, urea, glucose, and largest albumin.

Activity 2: Simulated Facilitated Diffusion • Explain one way in which facilitated diffusion is the same as simple diffusion and one way in which it differs:
Facilitated diffusion is the same as simple diffusion being that no energy is required for diffusion to take place. One way the two are different is that with facilitated diffusion a carrier protein is transporting molecules to diffuse.

• The larger value obtained when more glucose carriers were present corresponds to an increase in the rate of glucose transport. Explain why the rate increased. How well did the results compare with your prediction?
The rate increased because more carriers were available to transport the glucose for diffusion. If the molecule concentration is to high with not enough carriers, the carriers will become saturated. My predication was correct. • Explain your prediction for the effect Na+Cl− might have on glucose transport. In other words, explain why you picked the choice that you did. How well did the results compare with your prediction?
During the experiment I predicted Na+Cl- would decrease the rate of glucose transport. I thought this because i figured more molecules would decrease the rate like an idiot. After the experiment and seeing glucose transported just the same it dawned on me, carriers are specific to the molecule they are transporting and that facilitated diffusion occurs from areas of higher concentration to areas of lower concentration. The Na+Cl- had no affect on the glucose transport rate.

Activity 3: Simulating Osmotic Pressure • Explain the effect that increasing the Na+Cl− concentration had on osmotic pressure and why it has this effect. How well did the results compare with your prediction?
Increasing the Na+Cl- increased the osmotic pressure in the left beaker. This happened because no net movement of water was possible. Water can pass through mostly any sized pore of a membrane back and forth. With osmosis water moves towards solutes. Increase in solutes will cause increase in volume and therefore the pressure in the more concentrated area increased. My prediction was right. • Describe one way in which osmosis is similar to simple diffusion and one way in which it is different: Osmosis is similar to diffusion in that it moves from an area of higher concentration to an area of lower concentration. It differs in osmosis occurs through a selectively permable membrane.

• Solutes are sometimes measured in milliosmoles. Explain the statement, “Water chases milliosmoles.” Water moves toward solutes and solutes are measured in milliosmoles.

• The conditions were 9 mM albumin in the left beaker and 10 mM glucose in the right beaker with the 200 MWCO membrane in place. Explain the results. How well did the results compare with your prediction? _The results of this activity was increased osmotic pressure above left beaker containing albumin with no net movement of water and the right beaker containing glucose had net movement of water and reached equilibrium. The pressure increased above the left beaker because the albumin was unable to diffuse causing more volume of water to the beaker with more solute therefore causing increased osmotic pressure. My prediction was correct._
Activity 4: Simulating Filtration • Explain in your own words why increasing the pore size increased the filtration rate. Use an analogy to support your statement. How well did the results compare with your prediction?
Increasing the pore size of the membrane increased the filtration rate because the size of the membrane determines what will pass through. Filtration is a passive process and that contributes to it as well. If the fluid has solutes that will not pass through the membrane pore, it is going to take longer for the fluid to pass through the membrane and around the solutes so to say. My example would be draining pasta. The smaller the holes in the strainer the longer it is going to take for the fluid to make it's way around the pasta, through the holes, and out the strainer. If the holes in the strainer are larger the fluid will pass through at a higher rate. My prediction was correct.

• Which solute did not appear in the filtrate using any of the membranes? Explain why.
The powdered charcoal was the solute that did not appear in the filtrate using any of the membranes. I believe it is due to its size and molecular weight.

• Why did increasing the pressure increase the filtration rate but not the concentration of solutes? How well did the results compare with your prediction? Increasing the pressure increased the filtration rate and not the concentration of solutes because filtration occurs from areas of higher pressure to lower pressure. The greater the pressure the faster the filtration. It will not change the concentration of solutes because the MWCO determines that. I did not predict this one accuratley.

Activity 5 : Simulating Active Transport • Describe the significance of using 9 mM sodium chloride inside the cell and 6 mM potassium chloride outside the cell, instead of other concentration ratios. Three sodium ions are ejected from the cell for every two potassium ions entering in the cell.

• Explain why there was no sodium transport even though ATP was present. How well did the results compare with your prediction? There was no sodium transport because there were no potassium ions to replace there exiting of the cell. My prediction was correct.

• Explain why the addition of glucose carriers had no effect on sodium or potassium transport. How well did the results compare with your prediction? Sodium and potassium movement is independant of other solutes. My prediction was correct. • Do you think glucose is being actively transported or transported by facilitated diffusion in this experiment? Explain your answer.
I think glucose is transported by facilitated diffusion because it does not require active transport and moves from an area of higher concentration to an area of lower concentration.