How can you demonstrate by an experiment that transpiration takes place in plants?

Experiment: Demonstration of Transpiration

Objective: To prove that plants lose water vapor through transpiration

Materials Required:

• Healthy potted plant
• Bell jar (glass/transparent)
• Oil cloth/plastic sheet
• Glass plate
• Anhydrous cobalt chloride paper (blue)
• Vaseline

Procedure:

1. Setup:
   • Water the potted plant thoroughly
   • Cover the pot and soil surface completely with oil cloth to prevent evaporation from soil
   • Seal edges with vaseline for airtightness
   • Place the setup on a glass plate
   • Cover entire plant with bell jar
2. Observation Period:
   • Keep the setup in sunlight for 2-3 hours
   • Observe water droplets forming on inner walls of bell jar
3. Confirmation Test:
   • Test the collected liquid droplets with anhydrous cobalt chloride paper
   • Blue cobalt chloride paper turns pink in presence of water

Diagram:

Water Drops

↓

┌─────────────┐

│ Bell Jar │

│ 🌱 │

│ Plant │

└─────────────┘

│ Pot with │

│ oil cloth │

└─────────────┘

Glass Plate

Results:

• Water droplets appear on bell jar inner surface
• Cobalt chloride paper confirms these droplets are water
• Source cannot be soil (covered), must be from plant

Conclusion: Water vapor is released from plant leaves through transpiration, condenses on cool bell jar surface.

Control Experiment: Setup without plant shows no water droplets, confirming plant is the source.

Variations:

• Use two setups: one in light, one in dark (demonstrates light effect)
• Apply vaseline to leaf surfaces to show stomatal transpiration