Question

Cobalt chloride method for demonstration of transpiration was first used by
a) Freeman
b) Stahl
c) Darwin
d) Gonong

Answer 1

Transpiration is known as the process by which movement of water takes place in plants and also its evaporation from the aerial parts of the plant such as leaves, flowers and stems.

Complete answer:
Transpiration occurs through minute pores that are present on the surface of the leaves known as stomata. The stomata is bordered by guard cells that help in the closing and opening of the stomatal pore during photosynthesis. Opening of the stomatal pore is necessary for photosynthesis to take place since carbon dioxide enters through it but through this opened stomatal pore water vapor also diffuses out of the plant. Thus transpiration is said to be a cost paid by plants to carryout photosynthesis. The cobalt chloride method for demonstration of transpiration was first used by Stahl. The rate of transpiration of a plant can easily be determined using this test. To carry the test out dry cobalt chloride paper which is blue in color is taken that turns pink when exposed to water, so the rate of transpiration can be measured by the time taken for the paper to change its color from pink to blue.

So the correct option is B) Stahl.

Note:
The rate of transpiration is affected by several factors which include temperature, humidity, wind speed, sunlight as well as the size of the stomatal aperture. Transpiration also helps in cooling the plants since the water that evaporates carries heat energy with it.