Page 20 - Ranger SPM 2022 Biology

Biology SPM Chapter 2 Leaf Structure and Function

2.3 Main Organ for Transpiration

1. Transpiration is a process in which water is lost from plant to the environment in
Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
the form of water vapour through the stomata and lenticels of plants.
2. Transpiration rate increases when there is an increase in light intensity, temperature
and air movement or decrease in air humidity.

Opening of stomata Leaf veins transport
water to leaves

Xylem transport water
Water evaporates from roots to stems
to atmosphere and leaves Form 5
through stomata
H 2 O

H 2 O
Roots absorb H 2 O
water from soil H 2 O

Figure 2.6 Transpiration in plant
Table 2.1 Environmental factors that affect the rate of transpiration
Light intensity Temperature
Transpiration rate Transpiration rate

Light intensity Temperature (ºC)

• As light intensity increases, transpiration rate • As temperature increases, transpiration rate
also increases. also increases.
• Increase in light intensity increases rate of • Increase in temperature increases evaporation
photosynthesis of guard cells, which causes rate from surface of mesophyll cells.
the stomata to open wider. • The rate of water diffusion to atmosphere
• More water vapour evaporates through through stomata increases. Therefore, the rate
stomata. Therefore, transpiration rate of transpiration increases.
increases.

215

F5 Chapter 2.indd 215 3/29/22 4:35 PM