Transpiration in plants
DEFINITION:
Transpiration is a process in which water is lost in the form of water vapour through the aerial
parts of the plants.
Demonstration of Transpiration
Experiment I
Drops of water appear on the inner side of the polythene bag/bell jar!
The plant gives off water vapour which saturates and condenses on the inner surface of the
polythene bag/ bell jar
Experiment 2
Setup A: Water vapour condenses on the inner wall of the bell jar.
Setup B: The bell jar also shows similar condensation of water vapour, and at the same time, the
cobalt chloride paper which is initially blue turns pink.
Setup C: In this bell jar, neither water droplets are found nor does the cobalt chloride
paper turns pink.
Condensation of water vapour occurs on the inner walls of the bell jar in set ups A and B.
Change in the colour of cobalt chloride paper proves that plants give off water vapour
during transpiration.
COBALT CHLORIDE PAPER IS AN INDICATOR OF MOISTURE. IT IS BLUE WHEN DRY TURNS PINK
WHEN EXPOSED TO MOISTURE.
Experiment 3
An experiment to show water is lost from the aerial parts
OBSERVATION: The level of water drops in A but not in B.
Role of oil layer: oil layer prevents evaporation of water from the surface of water
Conclusion : Water level drops only due to transpiration from the leaves
Measurement of transpiration
POTOMETER: A Device to Measure the rate of transpiration.
Rate of transpiration is equivalent to the rate of water absorbed through the cut shoot.
Precautions in the use of Potometer:-
1. Has to be water tight.
2. Twig to be cut obliquely to allow larger surface area for water intake.
Limitations of Ganong's Potometer:
*Introduction of Air bubble is difficult
*Twig may die or get weak during the experiment.
*Environmental changes during the experiment may effect the smooth movement of the air
bubble.
DEFINITION:
Transpiration is a process in which water is lost in the form of water vapour through the aerial
parts of the plants.
Demonstration of Transpiration
Experiment I
Drops of water appear on the inner side of the polythene bag/bell jar!
The plant gives off water vapour which saturates and condenses on the inner surface of the
polythene bag/ bell jar
Experiment 2
Setup A: Water vapour condenses on the inner wall of the bell jar.
Setup B: The bell jar also shows similar condensation of water vapour, and at the same time, the
cobalt chloride paper which is initially blue turns pink.
Setup C: In this bell jar, neither water droplets are found nor does the cobalt chloride
paper turns pink.
Condensation of water vapour occurs on the inner walls of the bell jar in set ups A and B.
Change in the colour of cobalt chloride paper proves that plants give off water vapour
during transpiration.
COBALT CHLORIDE PAPER IS AN INDICATOR OF MOISTURE. IT IS BLUE WHEN DRY TURNS PINK
WHEN EXPOSED TO MOISTURE.
Experiment 3
An experiment to show water is lost from the aerial parts
OBSERVATION: The level of water drops in A but not in B.
Role of oil layer: oil layer prevents evaporation of water from the surface of water
Conclusion : Water level drops only due to transpiration from the leaves
Measurement of transpiration
POTOMETER: A Device to Measure the rate of transpiration.
Rate of transpiration is equivalent to the rate of water absorbed through the cut shoot.
Precautions in the use of Potometer:-
1. Has to be water tight.
2. Twig to be cut obliquely to allow larger surface area for water intake.
Limitations of Ganong's Potometer:
*Introduction of Air bubble is difficult
*Twig may die or get weak during the experiment.
*Environmental changes during the experiment may effect the smooth movement of the air
bubble.
