Factors Affecting the Rate of Transpiration

The rate of transpiration in a plant is closely related to the rate of water uptake, and can be affected by multiple environmental factors. The roots will absorb more water from the soil if the rate of transpiration increases.

There will always be transpiration taking place, but the rate of transpiration can vary. There are four main factors that affect the rate:

  • Temperature
  • Light intensity
  • Air movement
  • Relative humidity

Factor increasingEffect on the rate of transpirationExplanation
TemperatureIncreasesIf the surrounding temperature of a plant increases, more water molecules will evaporate from the mesophyll.

This increases the rate of diffusion of water from the leaf.
Light intensityIncreasesWhen the light intensity is higher, the stomata open wider for increased gas exchange.

While this allows more carbon dioxide into the leaf for photosynthesis, it also means more water can be lost through transpiration.
Air movement (e.g. wind)IncreasesIncreased air movement, often due to wind, removes water vapour from around the leaf.
Relative humidity – Measures the concentration of water vapour in the air compared to the maximum amount it can holdDecreasesWhen the leaf is surrounded by air with a higher concentration of water molecules (indicating higher relative humidity), the diffusion of water vapour out of the leaf slows down.

This is because the concentration gradient is lower.

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