page_title: Leaf
section_title: Hairs
hierarchical_section_title: Leaf / Anatomy / Hairs
caption_attribution_description: a plant
context_page_description: A leaf is an above-ground plant organ and it is green. Its main functions are photosynthesis and gas exchange. A leaf is often flat, so it absorbs the most light, and thin, so that the sunlight can get to the chloroplasts in the cells. Most leaves have stomata, which open and close. They regulate carbon dioxide, oxygen, and water vapour exchange with the atmosphere.
  Plants with leaves all year round are evergreens, and those that shed their leaves are deciduous. Deciduous trees and shrubs generally lose their leaves in autumn. Before this happens, the leaves change colour. The leaves will grow back in spring.
  Leaves come in many shapes and sizes. The biggest undivided leaf is that of a giant edible arum. This lives in marshy parts of the tropical rain forest of Borneo. One of its leaves can be ten feet across and have a surface area of over 30 square feet.
  However, leaves are always thin so carbon dioxide can diffuse quickly to all cells.
context_section_description: Many leaves are covered in trichomes (small hairs) which have a wide range of structures and functions. Some trichomes are prickles, some are scaled, some secrete substances such as oil. Carnivorous plants secrete digestive enzymes from trichomes.
caption: Sticky trichomes of a carnivorous plant, Drosera capensis with a trapped insect
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