Experiments Related to Transpiration


 
 
Concept Explanation
 

Experiments Related to Transpiration

Demonstration of Transpiration :

Experiment 1 :- 

  • Requirements : Potted plant, Polythene and small rope to tie up polythene around the plant
  • Take a medium - sized well watered potted plant.
  • Cover the plant with a transparent polythene bag and tie its mouth around the base of the stem.
  • Leave the plant in sunlight for an hour or two. Drops of water will soon appear on the inner side of the bag due to the saturation of water vapour given out by the leaves(the water vapors condense  only if the outside temperature is cool enough).
  • A similar empty polythene bag with its mouth tied and kept in sunlight will show no drops of water.
  • Conclusion :-This is a control to show that plants transpire water in the form of vapor. If tested with dry cobalt chloride paper, the drops will be confirmed as water only if the blue paper turns pink.
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    Experiment 2 :- Arrange three set ups A, B and C as follows :

    Set up A :- Take a small well watered potted plant, preferably one with broad leaves. Enclose  the pot completely within a polythene bag and tie the mouth of the bag firmly around the base of the stem. This would prevent the escape of water vapor from the pot. Now cover the entire plant under a bell jar as in (A).

    Set - up B :- Arrange another similar plant and cover it with a bell jar exactly in the same manner as the first one, except that here you also keep a piece of dry cobalt chloride paper by the side of the plant inside the bell jar(B). The paper may be pinned to a wooden stick or to a strip of cork sheet.

    Set  - up C:- Take a third bell jar without the plant, but still containing a similar piece of cobalt chloride paper(C). Now, keep all the three bell jars together in the sun.

    Observation :-

  •  The first bell jar (A) would show water vapor condensing on its inner walls.
  •  The second bell jar (B) would also show a similar condensation and at the same time, the initially blue cobalt chloride paper in it would turn pink.
  • The blue color of the cobalt chloride paper in the third bell jar(C) does not change at all  and there are no water drops on the jar's inner walls either.
  • The third bell jar (C) in this experiment is a control which  proves that there was no moisture in the air due to transpiration as there was no plant in it.
  • Conclusion :-

    Following observations can be observed which proves the occurrence of transpiration in Plants:-

    (1) Condensation of water vapor into droplets 

    (2) Change  of color in cobalt chloride paper. 

                                                           

     
     
     
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