Osmosis in Living and Non-living Tissue

Learn more about osmosis in living and non-living tissue and also how to devise an experiment to test for the properties of osmosis.

Potato cells inside the potato tissue contain a dilute salt solutions in their vacuoles. When the potato strips were put is distilled water the water potential in the trough was higher than that in the potato, so water diffused from the outside to the inside of the potato strips. This happened because water travels from and area of high water potential to an area of low water potential. For the potato slices put in the salt solutions, the concentration of water inside the vacuoles was higher than that of the salt solution in the trough. So water diffused from the inside of the potato into the trough. This is why there was a decreased in mass of the potato strips.

The results and the graphs show that as osmosis proceeded, the rate by which the mass of the potato tissues increased or decreased slowed down.  This happened because as time passed the diffusion gradient between the potato strips and the solution inside the troughs decreased. The higher the diffusion gradient the faster the rate of diffusion. The lower the diffusion gradient the slower the rate of diffusion.

Osmosis takes place between animal cells and the fluid surrounding each cell known as tissue fluid. The composition of this fluid is regulated by the liver and the brain. When the cell lacks water, the latter diffuses by osmosis from the tissue fluid into the cell. Excess water in the cell, diffuses out and into the tissue fluid also by osmosis.    

Part 2:       Osmosis in a Non-living material

 

Aim: To show that osmosis may also occur in non-living material, for example in a visking tube.

 

Apparatus:  distilled water, weak salt solution, 2 conical flasks, teat pipette, visking tubing, string and balance.

 

Method:

1.   Two pieces of “visking tubing” about 12 cm long were cut.

2.   One end of each visking tubing was tied with a piece of cotton string.

3.   A teat pipette was used to fill ‘cell A’ with strong sucrose solution and ‘cell B’ with water.

4.   The other end of each visking tubing was tied too.

5.   The initial weight of each visking tube was measured and recorded in a table of results.

6.   Visking tube A’ was put into a beaker filled with water.

7.   Visking tube B was put into a beaker filled with a strong sugar solution.

8.   The experiment was left to run for two hours taking readings at the 30-minute intervals. At each interval the dialysis tubes are weighed and the results were tabulated.

9.   A graph of % increase or decrease in mass are plotted against time.

Diagram:

 

 

 

 

 

 

 

Results and Graphs:

 

Time/Sec

Mass of visking tube A

% increase in mass of visking tube from start

Mass of visking tube B

% dec. in mass of visking tube B from start

0

23.65

0.00

20.88

0.00

30

26.24

10.00

18.44

-11.69

60

27.73

11.80

16.22

-22.32

90

28.53

12.06

14.38

-31.13

120

28.86

12.20

12.84

-38.51

 

 

 

 

 

 

 

 

Discussion:

The strong sucrose solution in tube A had a very low water potential compared to the water in the conical flask. Because of this water diffused by osmosis from the water-filled conical flask into the visking tube. As a result of this, tube A swelled up and there was an increase in mass. Besides the tube became harder and harder to the touch.

 

The water inside tube B had a very high water potential compared to the strong sucrose solution inside the conical flask. This caused the water to diffuse by osmosis from the visking tube into the conical flask, that is, from a high water potential to a low water potential. This explains why the tube became softer and softer to the touch. It seemed to contain less and less volume of liquid compared with before. The graphs plotted show that as the diffusion gradient decreased the rate of osmosis also decreased.

Osmosis does not need any energy to take place, as it is the movement of water through a semi-permeable membrane in favour of the diffusion gradient. The graphs plotted show that as in the case of living tissue the rate of osmosis decreased as the diffusion gradient decreased.

 

Conclusion

When a living or non-living tissue is placed in a medium that has a low concentration then water enters by the process of osmosis. As a result of this, the cells will become “turgid” and increase in the size. If the tissue is placed in a medium that has a high concentration, then water goes out of the cells and they will shrink and decrease in length. The cells are said to have been “plasmolysed”. This molecule movement of water does not require energy and because of this it occurs is both living and non-living tissue.

 

 

 

 

 

 

 

 

 

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