Alanna Aga Lockhart Advanced Placement Biology 6 March 2019 Transpiration Free Response Question Transpiration is an important stage in the water cycle. Transpiration is when “water is lost through microscopic pores in the plant’s leaves”(Campbell). The movement of water affects transpiration. Water changing states from liquid to gas during evaporation involves transpiration. Because transpiration involves losing water, evaporation—where water is lost by the changing of state—is a key factor of transpiration. Transpiration pull also relates to the mechanisms of water. This suction force brings water in a plant upwards from roots to leaves where it may undergo transpiration. Water moves upwards because of this pull; the pull helps bring water to where the stomata can open and release it(MaximumYield). Transpiration also relates to other mechanisms of water, such as osmosis and diffusion. Diffusion is particle movement from high to low concentration, whereas osmosis is diffusion “through a semipermeable membrane from a more dilute solution to a more concentrated solution”(Leaving Certificate Biology). Without the movement of particles, transpiration pull would not be possible. If water did not have a tendency to reach a more concentrated solution, not enough water would reach the stomata to be released during transpiration. Transpiration is driven by different energies. Water recognizes environmental factors, such as drier air around the plant causing a greater driving force “for water to move through the plant” at a quicker rate(USDA). Other factors determining transpiration involve the sun and
wind. For example, plants in the desert only open their stomata at night when there is no direct sunlight. Water moves to the leaves for the process of transpiration, but this process—and therefore the water that travels in the plant—is affected by energy and environmental factors. Transpiration is passive on the part of the plant. Transpiration is possible because of the anatomy of vascular plants. Stomata, or “tiny openings or pores in plant tissue that allow for gas exchange,” are the main structure used for transpiration(Bailey). The stomata open, allowing water to eventually leave through transpiration. Guard cells protect the stomata and aid with the opening and closing. Guard cells
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