Spencer Luther
4/22/15
BI 102 Lab Write-up #1
Hypothesis:
1. If the concentration of sucrose increases then the osmotic pressure will increase, measured
by amount of solute that is displaced up the glass tube in the osmometers we created. Osmosis is
defined as the flow of water (H2O) from areas of high concentration to areas of low concentration across
a semi-permeable membrane. Since the water outside the “cell” we created is pure water and therefore
has a higher concentration of H2O than the solute, water should flow into the “cell” to try to equalize
concentrations of both the solvent and the solute. Since the sucrose cannot move across the membrane,
the water has to move inside to balance out the concentrations, driving the solute up the glass tube as
volume is increased. As concentrations of the solvent increase, osmosis should occur more rapidly.
Pressure will increase at a higher rate and the solute will climb up the glass tube more rapidly.
Results:
Time
5
10
15
20
25
30
35
40
45
50
55
60
Table 1
0.2
1.3
2.1
3.6
5
6.1
7.3
8
10% Sucrose
Table 2 Average
2
1.1
3.5
2.4
4.5
3.3
5.75
4.675
7
6
8.25
7.175
9.25
8.275
10.5
9.25
11.5
11.5
12.5
12.5
13.5
13.5
14.5
14.5
Table 3
2
5.4
8.5
11.4
14.1
16.6
18.9
21.2
23.5
25.3
28.1
30.5
Data
20% Sucrose
Table 4 Average
2
2
4
4.7
7.8
8.15
9.3
10.35
11.4
12.75
13.2
14.9
15
16.95
16.8
19
18.6
21.05
20.3
22.8
23
25.55
24.6
27.55
Table 5
3.6
7.9
11.3
14.6
17.5
20.7
24.1
27.2
30.5
33.5
36.7
39.9
40% Sucrose
Table 6 Average
4.5
4.05
8
7.95
10.7
11
14
14.3
16.5
17
18
19.35
20.5
22.3
21.2
24.2
23
26.75
24.2
28.85
25.5
31.1
27.5
33.7
Osmotic Pressure in 3 Different Concentrations
of Sucrose
40
Height of Sucrose Solution (in cm)
35
30
10 Percent Sucrose
Solution
25
20
20 Percent Sucrose
Solution
15
40 Percent Sucrose
Solution
10
5
0
5
10
15
20
25
30
35
40
45
50
55
60
Elapsed Time (in Minutes)
Analysis:
3. The data we collected supports my hypothesis. We see from the chart that as time went on,
osmotic pressure increased. This increase was more drastic with higher concentrations of sucrose,
suggesting that osmosis occurred more rapidly with higher concentrations of sucrose. The solution rose
up the glass tubes at a fairly constant rate without leveling off which implies that the concentration
gradients were still equalizing. The experiment doesn’t tell us if that rate is constant or hyperbolic, but I
would assume that as the solutions approach symmetry the osmosis rate would slow and eventually
stop once they become isotonic.
4. Diffusion-and more specifically osmosis-is responsible for the movement of water up the glass
tube. Because the sucrose couldn’t come out across the membrane, the water had to move inside to try
to balance the concentration gradient of the solute between the two solutions. As long as there is pure
water outside our “cell” though, the gradients can never be equal because the membrane holds the
sucrose in. If there is 100% concentration of H2O outside the membrane and 100-X% concentration of
H2O inside, osmosis will constantly bring water inside. All life requires water in some fashion, so this
phenomenon is partially responsible for all life.
If we imagine the “cell” we created as a single celled organism like an amoeba, we see that they
are under constant pressure from their aquatic environments. They don’t live in distilled water, but the
conditions they live in have a much higher H2O concentration than their cell does. This means that they
have to find a way to actively keep water out of their cell or they risk bursting and death.
Osmosis obviously occurs in nature, but the phenomenon can also be exploited with technology.
In biology, osmosis provides an easy way for cells to get the water they need without expending energy.
Since all life as we know it requires water in some form to live, this is extremely important. Humans can
use osmosis to develop new ways to get fresh water to places that need it, such as deserts or other
environments that lack fresh water. Once the H2O is extracted from a solution using osmosis or reverse
osmosis (a practice that drives water through a semi-permeable membrane using applied pressure to
counteract osmotic pressure, with the result of removing particles from suspension [citation here]), it
can be used for irrigation or drinking water for people and animals. California is currently in the middle
of a significant water shortage and state-wide water rationing is in effect (Nagourney). If osmosis or
reverse osmosis filtering could be implemented on a large scale then sea water could become a viable
counter to the state’s 4-year drought.
Works Cited
Nagourney, Adam. "California Imposes First Mandatory Water Restrictions to Deal With
Drought." The New York Times. The New York Times, 01 Apr. 2015. Web. 21 Apr. 2015.