Environmental Controls of Transpiration

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Environmental Controls of Transpiration How relative humidity (RH) and light affect transpiration Using kidney bean plant, called Phaseoulus vulgaris Why place the young sampling place in the dark for 24 hours? So it doesn’t photosynthesize. Its important to make sure it doesn’t photosynthesize before the experiment because in order for photosynthesis to occur gas exchange is necessary. If gas exchange is occurring that means the stomata are open so CO2 will diffuse but you will also have water molecules being diffused as well. Loss of water molecules is transpiration. Transpiration is a passive event because it doesn’t use any energy. What are some factors that affect the rate at which a plant transpires? Transpiration is passive process so it always happens along concentrations gradient from high concentration to a low concentration. More stomata are located on the dorsal side of the leaf because there is less sunlight. Sunlight triggers photosynthesis and you have a lot of stomata on the top of you leaf then the stomata will be open all the time you’ll have indiscriminate loss of water all the time. How is it possible that when you cut a leaf or a stem there is always moisture inside? Waxy cuticle on top that prevents water loss. Moist tissues on the inside of plants so you have a high concentration of water on the inside. What factors affects rates of transpiration? Concentration gradient: Stomata open when photosynthesis begins and if environmental surroundings are dry there is a natural concentration gradient so water diffuses out. If you are in an environment with a high concentration of relative humidity and if the plant is very moist then there is not concentration gradient and therefore no diffusion of water so no transpiration. Soil: Type of soil, how much moisture can be retained in the soil and how much moisture is actually

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