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出典:『Wikipedia』 (2011/06/06 23:07 UTC 版)

英語による解説

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In botany, a leaf is an above-ground plant organ specialized for the process of photosynthesis. Leaves are typically flat (laminar) and thin which evolved as a means to maximise the surface area directly exposed to light. Furthermore the internal organisation of leaves has evolved to maximise exposure of the photosynthetic organelles, the chloroplasts, to light and to increase the absorption of carbon dioxide, all of which assist photosynthesis. These adaptations are at the expense of water loss and most leaves have stomata which regulate carbon dioxide, oxygen and water vapour exchange with the atmosphere. The shape and structure of leaves varies considerably depending on climate, primarily due to the availability of light and potential for water loss due to temperature and humidity. Leaves are also the primary site, in most plants, where transpiration and guttation take place. Leaves can also store food and water, and are modified in some plants for these purposes. The concentration of photosynthesis in leaves makes them rich in protein, minerals and sugars. Because of their nutritional value leaves are prominent in the diet of many animals, including humans as leaf vegetables.