3.3.8 Practical: Investigating the Rate of Transpiration

Question 1

Factors affecting rate of transpiration

Answer 1

Air movement
- Concentration gradient maintained as water molecules swept away from leaf surface

Temperature
- Greater kinetic energy
- Water moves out of leaf faster
- However stomata closes at too high temps so transpiration stops

Light intensity
- Stomata closes in dark so transpiration stream stops
- No light so no photosynthesis so no need to uptake co2 and need to retain water

Humidity
- Concentration gradient of water molecules is shallowed from inside to outside of plant leaf

Question 2

Ingredients for this practrical

Answer 2

• POTOMETER
• CAPILLARY TUBE
• VASELINE
• Plant shoot
• Cutting board
• Scalpel / scissors
• Paper Towel
• Volume scale
• Beaker
• Stopwatch

Question 3

Method

Answer 3

1. Cut shoot underwater (prevents air bubbles from entering xylem and breaking the water tension in the transpiration stream)
2. Place shoot in tube
3. Use vaseline to seal gaps (air cannot enter)
4. Dry leaves of shoot (making sure stomata are not covered)
5. Remove capillary tube from beaker allowing air bubble to form and put tube back in beaker
6. Set up environmental factor being investigated
7. Record starting location of bubble
8. Leave for set period of time
9. Record end position of bubble
10. Reset bubble, change independent variable, repeat experiment

Question 4

How can you investigate the 4 environmental factors?

Answer 4

Airflow : use a fan
Humidity : Spray water in plastic bag and wrap around plant
Light Intensity : Lamp, distance from plant
Temperature : Temp of room