Answers to Questions
Activity 1: Simulating Dialysis (Simple Diffusion) (pp. 2–4)
9. All solutes except albumin are able to diffuse into the right beaker.
Using distilled water in the right beaker and either the 100 MWCO or 200 MWCO
membrane will remove urea from the left beaker and leave albumin
If the left beaker contains NaCl, urea, and albumin, you can selectively remove urea
by dispensing a concentration of NaCl into the right beaker equivalent to that in the
left beaker and by using the 100 or 200 MWCO membrane. Albumin is too large to
diffuse and there will be no net diffusion of NaCl. However, urea will move down its
concentration gradient into the right beaker.
Activity 2: Simulating Facilitated Diffusion (pp. 4–5)
11. Carrier proteins facilitate the movement of solute molecules across
semipermeable membranes, so increasing their number will increase the rate of
diffusion.
Because facilitated diffusion requires a concentration gradient, making the
concentration on both sides of the membrane equal stops net diffusion.
NaCl does not have an effect on glucose diffusion.
Activity 3: Simulating Osmotic Pressure (pp. 6–7)
6. Using the 20 MWCO membrane results in an osmotic pressure increase using any
of the solutes. The 50 and 100 MWCO membranes caused osmotic pressure increase
with albumin and glucose. Only albumin caused osmotic pressure increase using the
200 MWCO membrane.
NaCl appeared in the right beaker with all membranes except the 20 MWCO
membrane.
8. Increasing the number of non?diffusible particles increases osmotic pressure.
If solutes are able to diffuse, then equilibrium will be established and osmotic
pressure will not be generated.
Osmotic pressure would be zero if albumin concentration was the same on both
sides of the membrane.
If you increased (or doubled) the concentration of albumin, osmotic pressure will
increase (or double).
Glucose is freely diffusible using the 200 MWCO membrane and therefore has no
effect on osmotic pressure.
The 100 MWCO membrane does not allow glucose to pass and therefore glucose will
generate an osmotic influence. Because albumin concentration in the left beaker is
9.00 mM and glucose concentration in the right beaker is 10.00 mM (1.00 mM
higher than the left), the small gradient dictates that an osmotic pressure increase
will appear in the right beaker.
Activity 4: Simulating Filtration (pp. 7–9)
9. Smaller MWCO numbers translate to smaller pore sizes, which correlate with
lower filtration rate.
Powdered charcoal did not appear in the filtrate using any membrane.
Increasing the force driving filtration increases filtration rate.
Increasing the pressure gradient effectively increases the filtration rate.
By examining the filtration results, we can predict that the molecular weight of
glucose must be greater than NaCl but less than powdered charcoal.
Activity 5: Simulating Active Transport (pp. 10–11)
7. Solute transport stops before the completion of transport because of a lack of
ATP.
Sodium and potassium transport will not occur if ATP is not available.
8. Yes, transport has changed because more ATP is available. This fact supports the
earlier supposition that ATP is required for active transport.
The rate of active transport will decrease if fewer solute pumps are available, but
will still go to completion given enough ATP and time.
You can show that this is an active process by making the sodium concentration in
the right beaker greater than the sodium concentration in the left beaker. Transport
will occur against the concentration gradient in active transport but not in diffusion.
9. Sodium transport is not affected by putting NaCl into the right beaker. Increasing
the number of pump proteins will increase solute transport. Glucose presence does
not affect active transport.
Simple Diffusion
None
Albumin
NaCl
The smaller the solute particle the greater the rate of diffusion.
Facilitated Diffusion
No; in facilitated diffusion, a passive process, substances can move only down their
concentration gradient.
0.0038
8mM glucose with 900 glucose carriers in the membrane
Increase amount of glucose in solution; increase number of glucose carriers in the
membrane
No
No; because of its small size, NaCl is able to diffuse down its concentration gradient
without the aid of carriers.
Osmotic Pressure
20 MWCO
Buildup of osmotic pressure due to the presence of non?diffusable NaCl in the
solution causes water to diffuse down its concentration gradient.
200 MWCO
There was no buildup of osmotic pressure, which indicates that glucose is able to
diffuse down its concentration gradient.
No
The higher the solute concentration, the higher the osmotic pressure.
Filtration
200 MWCO
The larger the pore size, the greater the filtration rate.
Powdered charcoal
The filtration rate of glucose is less than that of NaCl and urea, so its molecular
weight would be greater.
The filtration rate increases.
Pressure is higher in capillaries than in kidney tubules so particles that are small
enough are filtered from capillaries into kidney tubules.
The rate of filtration would decrease.
No; ATP was depleted at 3 minutes.
The rate of active transport decreases.
Sodium moved from the left beaker into the right beaker against its concentration
gradient; there was no movement of sodium when there were no Na!/K! pumps
added to the membrane.
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