Factors that affect transpiration

Environmental factors

six factors that affect transpiration (06 marks)

• Temperature: the higher the temperature, the higher the rate of transpiration due to availability of vaporization energy.
• Humidity: high humidity lows the rate of evaporation. Increase in the rate of humidity reduce water potential gradient between the leaf and environment reducing the rate of evaporation.
• Air movement/wind: blows away saturated air around the stomata facilitating evaporation. Strong wind lower the rate of transpiration due to closure of the stomata.
• Atmospheric pressure: the lower the atmospheric pressure, the greater the rate of evaporation.
• Light increases transpiration by opening the stomata and increasing temperature.
• Availability of water: Transpiration is high when there is continuous water supply in the soil to replace the lost water.

Internal factors that

1. Surface area of the leaf. The bigger the leaf surface area, the higher the rate of transpiration.
2. Thickness of the leaf cuticle; thin cuticle leads high rate if transpiration due to reduced diffusion gradient
3. Stomata sizes and density: numerous big stomata allow fast rate of water loss.
4. Distribution of the stomata: leaves with a big number of stomata on the upper cuticle loss water faster than those with the stomata on the lower cuticle.

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