TwoOldGuys™ Study Guides
BI-122 Biology
Osmosis

Movement through membrane

Membrane permeable to sugar and water:
(with 107 molecules per side)

DIFFUSION across membrane
TIME t0
sugar 10% 0%
sugar
water
1,000,000
9,000,000
0
10,000,000
TIME t1
change sugar -500,000 +500,000
sugar
water
500,000
9,000,000
500,000
10,000,000
5.26% sugar 4.76% sugar
to get the sugar [conc] values correct,
we have to account for the water movement across the membrane
The system is now at equilibrium
OSMOSIS
change water +500,000 -500,000
sugar
water
500,000
9,500,000
500,000
9,500,000
sugar 5.00% 5.00%

Membrane permeable to water but impermeable to protein:

Note: the system is still not at equilibrium, and...
Since there are more molecules on the right than left, there is
osmotic pressure
DIFFUSION
across membrane
TIME t0
protein
water
0%
100%
5%
95%
protein
water
0
10,000,000
500,000
9,500,000
TIME t1
change protein +0 -0
change water -250,000 +250,000
protein
water
0
9,750,000
500,000
9,750,000
protein
water
0%
100%
4.88%
95.12%
TIME t2
change protein +0 -0
change water -237,900 +237,900
protein
water
0
9,512,100
500,000
9,987,900
protein
water
0%
100%
4.77%
95.23%
P = 0.0976 units

combining the two:

DIFFUSION
across membrane
TIME t0
sugar
protein
water
10%
0%
90%
0%
5%
95%
sugar
protein
water
1,000,000
0
9,000,000
0
500,000
9,500,000
P = 0
TIME t1
sugar -500,000 +500,000
protein +0 -0
water +250,000 -250,000
sugar
protein
water
500,000
0
9,250,000
500,000
500,000
9,250,000
sugar
protein
water
5.13%
0.00%
94.87%
4.88%
4.88%
90.24%
P = 0.0500 units
TIME t2
sugar
protein
water
-625
0
-219,687
+625
0
+219,687
sugar
protein
water
499,375
0
9,030,313
500,625
500,000
9,469,687
sugar
protein
water
5.24%
0.00%
94.76%
4.78%
4.78%
90.44%
P = 0.0941 units



RETURN TO OUTLINE
© 2004-2005 TwoOldGuys ™

revised 19 aug 2006