AP BIOLOGY

Detailed explanation-1: -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.

Detailed explanation-2: -There is a change in the colour of cobalt chloride paper clipped on the lower surfaces of the leaf indicates loss of water vapour from this surface through transpiration. Cobalt chloride paper is pink when moist and blue when dry. The rate of loss of water is, however, more on the lower side than the upper side.

Detailed explanation-3: -The color of cobalt chloride paper changes from blue to pink due to transpiration. Therefore, cobalt chloride paper is used to demonstrate transpiration and also the different rates of transpiration on both the surface of the leaves.

Detailed explanation-4: -Cobalt chloride paper is used to demonstrate the process of transpiration. The dry blue coloured cobalt chloride paper turns pink in the presence of water. So during transpiration when water evaporates from the stomata the blue cobalt chloride paper turns pink. This proves that transpiration takes place in plants.

Detailed explanation-5: -Plants transpire in the form of water vapour. So when the dry and blue cobalt chloride paper is placed in the transpiration chamber it turns pink when it comes in contact with water.