Describe an experiment to demonstrate transpiration.
Answers
Answer:
Transpiration is the evaporation of water from the surface of leaves through stomata. The phenomenon of transpiration can be explained by Bell jar experiment.
REQUIREMENTS:
Bell jar
Well watered potted plant
Rubber sheet
Glass plate
PROCEDURE:
Take the well watered potted plant and cover it with the rubber sheet. The aerial parts of the plant should be left uncovered.
Put the plant on the glass plate and cover with the bell jar.
Prepare a same setup but without a plant in the second bell jar.
Place the apparatus in sunlight for sometime.
OBSERVATIONS:
Water drops appear inside the walls of the bell jar containing potted plant whereas no water drops appear in the bell jar without a plant. This demonstrates that water is evaporated from the surface of leaves in presence of sunlight.
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Experiment:
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 vapour 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.
After about half an hour we observe that, The first bell jar (A) would show water vapour 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 colour 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 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.
By taking the three bell jars as described above, there is a double visual proof of transpiration: (1) condensation of water vapour into droplets and (2) change of colour in cobalt chloride paper.
