... to break as it has a very high tensile strength from the bonds. The water is able to evaporate out of the leaf as the leaf has a high water potential and the air has a low water potential so the water molecules pass down the concentration gradient from the spongy and palisade mesophyll cells into the leave's internal air spaces before diffusing out into the air. Transpiration is needed to keep the cells of the spongy and palisade mesophyll cells moist as this allows carbon dioxide to dissolve before diffusing into the cells for photosynthesis. The stomata open in the day to let carbon dioxide diffuse in, and to let oxygen diffuse out as part of photosynthesis. At night photosynthesis is unable to take place due to the absence of light so the stomata are closed to reduce water loss. Light causes potassium ions to be pumped into the ...

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