Back to: O level Biology NOTES Uganda syllabus
This is a process by which plants lose water in form of water vapour mainly through leaves to the atmosphere. Transpiration can also occur from flowers.
TYPES OF TRANSPIRATION
- Stomatal transpiration: This is the transpiration through the stomatal opening. This contributes up to 80-90% of water lost.
- Cuticular transpiration: This occurs through the leaf cuticle which amounts for about 20% of the water lost.
- Lenticular transpiration: This occurs through the stem pores called lenticels and accounts for about 0.1% of the water lost.
Water can also be lost from the plants as water droplets in a process called guttation through special structures called hydrates found on leaf types or margins
AN EXPERIMENT TO SHOW THAT WATER IS LOST MAINLY FROM LEAVES DURING TRANSPIRATION
Apparatus
Potted plant,
Polythene paper,
String,
Cobalt (ii) chloride paper or anhydrous copper (ii) sulphate.
Procedure
a) Tie polythene around the tin of the potted plant. Using a string to avoid evaporation of water from the soil surface.
b) Tie transparent polythene around the leafy shoot of the plant.
c) Set up another similar control experiment but with leaves removed and dry plant.
d) Leave the experiment to settle for 3 hours in bright sunlight.
e) Remove the polythene around the leafy shoot and test the drops of liquid inside the polythene using anhydrous copper (ii) sulphate / cobalt (ii) chloride paper.
Observation
A vapour forms inside the polythene and turns into drops / liquid which turn anhydrous copper (ii) sulphate from white to blue or blue cobalt (ii) chloride paper to pink.
No vapour is observed from experiment with no leaves / dry plant.
Conclusion
Transpiration occurs from the leaves
Note:
A bell jar may be used instead of polythene
A control experiment may also be a covered pot where the plant shoot has been cut off.
EXPERIMENT TO COMPARE TRANSPIRATION RATES ON BOTH SURFACES OF A LEAF
Apparatus
Potted plant,
glass slide
Cobalt (ii) chloride paper
Rubber bands
Procedure
a) Fix pieces of Cobalt (ii) chloride paper on the upper and lower surfaces of a leaf still to the plant with glass slides.
b) Tie the slides using the rubber bands
c) Note the time taken for the Cobalt (ii) chloride paper on each slide to turn / change colour from blue to pink.
Diagram
Observation
The lower surface cobalt (ii) chloride paper turns pink faster than that on the upper surface.
Conclusion
The lower surface has a higher transpiration rate than the upper surface
This is due to numerous stomata on the lower surface of the leaf.