Реферат: Osmosis

Osmosis.

Introduction:

Osmosis is a netdiffusion of water between two solutions that differ in solute concentrationand that are separated by a selectively permeable membrane.

Hypertonicsolution – higher solute concentration outside the cell.

Hypotonic solution– lower solute concentration outside the cell.

Isotonic solutionhave 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.

Potatocells in 2% and 3% solutions will shrink. Water moves out of the cells toregions of greater solute concentration.

Potatocells in 1% solution will change little in cell size or shape. The differencebetween solution concentration and potato concentration is small. So there isno big movement of water.

Materials:Knife, potato, 4 salt solutions ( 0%, 1%, 2%, 3%), paper, razor blade.

Method:

Cut 12 plugs fromsimilar potatoes. Remove the ends of each plug and skin.

Make up foursolutions of salt ( 0%, 1%, 2%, 3%). Weight the plug sets. Place plug sets intoeach solution and continue to measure or weight them at specified timeintervals. Report mean values only fo measurements or weights. Determine thepercent change in lenght or weight for the potato in each solution. Calculatethe 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%

<img src="/cache/referats/15793/image002.gif" v:shapes="_x0000_i1025">

We can’t compare the changes in weightusing grams, because each plug set had different initial weight before placingthem into salt solutions.

Conclusion and evaluation:

From the graphed data the percent of saltin the potato cell is 1.1%. The original potato cell concentration is 0.9%. Theerror could be, because the water outside potato has influence on weight andnot accurate measurement of mass by not exact scales, which showed only onedecimal place.

If the concentration of water is not equalacross a potato cell membrane (concentration of water outside the sell is moreor less than <img src="/cache/referats/15793/image004.gif" v:shapes="_x0000_i1026">

The experiment can be improved: Firstly, bydrying potato from water outside the potato. Secondly, by using scales, whichhave more accuracy.

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