Question

how do they Design an experiment to demonstrate transpiration pull using mercury manometer

Answer 1

Transpiration is the evaporation of water from the surface of leaves through stomata. The phenomenon of transpiration can be explained by Bell jar experiment.

...

Take the well watered potted plant and cover it with the rubber sheet. ...

Put the plant on the glass plate and cover with the bell jar.

Answer 2

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Requirements:

Narrow bell jars (2), small tubes (2), anhydrous calcium chloride, stand, potted plant, U- tube, glycerine, mercury.

Method:

1. Take two narrow bell jars and fix them on the two sides of a dorsiventral leaf of a potted plant.

2. Connect the bell jars with a clamp stand.

3. Keep a pre-weighed small tube containing anhydrous calcium chloride in each bell jar.

4. Connect one U-tube containing mercury or glycerine at the two ends of bell jars (Fig. 25).

Belljar method to compare the transpiration rate from upper and lower surfaces of leaf

5. Apply vaseline on the contacts between bell jars and the leaf to make the apparatus air-tight.

6. Keep the apparatus as such for a few hours. Remove both the calcium chloride-containing small tubes and weigh them again immediately.

7. Same experiment can be repeated with the other leaves of the same plant as well as the leaves of different plants, to be compared for rate of transpiration from upper and lower surfaces of leaves.

Observations:

The weight of both the tubes increases. If a comparison is made then it is observed that weight of the lower tube increases more than the weight of the upper tube.

Results:

The weight of both the tubes increases because the water vapours are transpired from both the surfaces of the leaf and the same transpired water is absorbed by the anhydrous calcium chloride of the tubes, and hence shows an increase in their weight.

More increase in weight of the tube placed in the lower bell jar than that of the upper bell jar indicates that more water is transpired from the lower surface than the upper surface of the leaf. Side by side it also indicates that in the same area of leaf, more number of stomata are present on the lower surface than that of the upper surface.

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