IntroductionTranspiration is the evaporative loss of water through the aerial parts of the plants especially through the leaves. In all green plants transpiration occurs mostly through the stomata of the leaves. In dicot plants leaves will have more stomata on the lower surface than the upper surface. So more transpiration occurs through the lower surface of the leaves of this plant. Stomatal pores get widely opened when the leaf get exposed to bright sunlight. To avoid excessive loss of water through transpiration dicot leaves possess more stomata on the lower surface as this surface is not much exposed to sunlight.
Aim of the experimentTo prove more transpiration occurs from the lower (ventral) surface of a dicot leaf than upper (dorsal) surface. (OR) To prove unequal transpiration from the two surfaces of a dorsiventral leaf.
RequirementsA well watered potted dicot plant, strips of dry cobalt chloride paper, glass slides, clips.
Procedure for the experimentA well watered dicot plant has to be selected for this experiment. Now two strips of filter paper are soaked in 2% solution of cobalt chloride and are perfectly dried under sunlight. Cobalt chloride paper will be blue in color when it is dry and become pink when it absorbs moisture. Due to this characteristic feature it acts as a chemical indicator in this experiment. One strip of this dry blue cobalt chloride paper is kept on either surface of a healthy dorsiventral leaf and are covered by glass slides with the help of clips. Now the whole experimental setup is kept under bright sunlight. Observe closely the changes which occur in cobalt chloride papers placed on both the surfaces.
ResultWithin few minutes we observe the cobalt chloride paper kept on the lower or ventral surface of the leaf turns into deep pink color but the strip of cobalt chloride paper kept at the upper surface remains unchanged or it takes longer time to change into pale pink color. The reason for this is more stomata are present on the ventral or lower surface of a dicot leaf than the upper or dorsal surface. Due to this more water vapor from the ventral surface is released than dorsal surface and hence cobalt chloride paper kept at the lower surface changes into pink color immediately.
Here is anExperiment on Photosynthesis-Sunlight is necessary for Photosynthesis
Questions and answers related to the experiment
Ans. To prove that more transpiration occurs from the ventral (lower) surface of a dicot leaf than dorsal (upper) surface.
Ans. Cobalt chloride paper is blue in color when it is dry but turns into pink color when it absorbs moisture and thus it acts as a chemical indicator in this experiment.
Ans. Glass slides were covered over the cobalt chloride papers to prevent the atmospheric moisture to react with them so that the aim of our experiment may be failed.
Ans. The cobalt chloride paper kept on the dorsal surface would not show any change much because the number of stomata on the dorsal surface of dicot leaf are less. But the cobalt chloride paper kept on the ventral surface immediately changes into pink color because more stomata are present on the ventral surface of a dicot leaf.
Ans. The leaf used in the experimental setup is dicot leaf. The reason for saying it is a dicot leaf is showing reticulate venation.
Ans. The leaf should be intact with the plant so that there will be continuous supply of water to it to carry transpiration otherwise we may not get the desired result.
Here is a video on Transpiration in a dicot leaf:-
Courtesy:- OLabs - Amrita University