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A-Level Biology OCR A

Water Rate Transpiration Increases Humidity Air Factors Light

Factors affecting transpiration rate are: light (opens stomata), relative humidity (high humidity reduces rate), temperature (increases evaporation), air movement (ventilation increases diffusion), and soil water availability (dry soil reduces rate).

Los factores ambientales que afectan la tasa de transpiración son: luz (abre estomas), humedad relativa (alta humedad reduce tasa), temperatura (aumenta evaporación), movimiento del aire (ventilación aumenta difusión) y disponibilidad de agua en el suelo (suelo seco reduce tasa).

Front State 5 env factors that can affect the rate of transpiration and for each explain how they have their effect.
Back Factors affecting rate of transpiration:
  • Light - required for photosynthesis so stomata will open when there is light - higher rate of transpiration
  • Relative humidity - high humidity lowers rate of transpiration bc reduced water vapour potential gradient between inside leaf and outside
  • Temperature - increases kinetic energy of water mols so it increases rate of evaporation, also increases conc of water vapor that external air can hold before it becomes saturated - decreaes relative humidity and water potential
  • Air movement - water vapor that diffuses out accumulates at leaf, air movement ventialtes and increases diffusion 
  • Soil water availability - dry soil means plant will draw less water and therefore lower rate of transpiration

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