3.3.6 The Process of Transpiration

Question 1

Advantages of transpiration stream

Answer 1

• Cooling effect (water vapor evaporated at leaves)
• Helpful in uptake of mineral ions
• Turgor pressure of cells provides support for stem and leaves

Question 2

Factors affecting rate of transpiration

Answer 2

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 3

What is the transpiration Stream?

Answer 3

• Movement of water from roots to the leaves
• Evaporation of water vapour from leaves and cohesive and adhesive properties of water allow it to move up xylem column
• High water potential gradient from soil to low water potential gradient in atmosphere is the driving force behind transpiration