НАУЧНАЯ БИБЛИОТЕКА - РЕФЕРАТЫ - Osmosis
Osmosis
Osmosis.
Introduction:
Osmosis is a net diffusion of water between
two solutions that differ in solute concentration and that are separated by a
selectively permeable membrane.
Hypertonic solution – higher solute
concentration outside the cell.
Hypotonic solution – lower solute
concentration outside the cell.
Isotonic solution have the same solute
concentration outside and inside the cell.
Hypothesis:
Potato cells in 0% solution of salt
will swell up. Potato will gain weight, because net movement of water will be
into the cells. Water moves down the concentration gradient.
Potato cells in 2% and 3% solutions will shrink. Water moves
out of the cells to regions of greater solute concentration.
Potato cells in 1% solution will change little in cell size
or shape. The difference between solution concentration and potato
concentration is small. So there is no big movement of water.
Materials: Knife, potato, 4 salt solutions (
0%, 1%, 2%, 3%), paper, razor blade.
Method:
Cut 12 plugs from similar potatoes. Remove the
ends of each plug and skin.
Make up four solutions of salt ( 0%, 1%, 2%,
3%). Weight the plug sets. Place plug sets into each solution and continue to
measure or weight them at specified time intervals. Report mean values only fo
measurements or weights. Determine the percent change in lenght or weight for
the potato in each solution. Calculate the exact percent of salt in the potato
cell from the graphed data.
|
Salt
Solutions
|
Initial weight (g)
|
Weight
of plug sets after some time:
|
Mean percentage change in weight
|
|
12
min.
|
22
min.
|
40
min.
|
52
min.
|
|
0%
|
5.61
|
5.87
|
6.01
|
6.13
|
6.25
|
11.4%
|
|
1%
|
8.84
|
8.85
|
8.87
|
8.90
|
8.86
|
0.22%
|
|
2%
|
10.02
|
9.61
|
6.51
|
9.20
|
8.99
|
-10.3%
|
|
3%
|
6.64
|
6.01
|
5.77
|
5.48
|
5.31
|
-20%
|
We can’t compare the changes in weight
using grams, because each plug set had different initial weight before placing
them into salt solutions.
Conclusion and evaluation:
From the graphed data the percent of salt
in the potato cell is 1.1%. The original potato cell concentration is 0.9%. The
error could be, because the water outside potato has influence on weight and
not accurate measurement of mass by not exact scales, which showed only one
decimal place.
If the concentration of water is not equal
across a potato cell membrane (concentration of water outside the sell is more
or less than 0.9%),
osmosis tends to occur. Water will move osmotically to regions of greater
solute concentration (from hypotonic to hypertonic solutions). If water
concentration outside and inside the cell is equal, water shows no net osmotic
movement from one to the other – isotonic solutions.
The experiment can be improved: Firstly, by
drying potato from water outside the potato. Secondly, by using scales, which
have more accuracy.
| 
