Leaves

PARTS OF A PLANT -Leaves-

LEAVES

LEAVES Designed to have increased exposure areas to sunlight and gas exchange.  Structures: - flat surfaces covered with epidermis - surfaces at right angles to permit maximum light exposure 

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Functions: - photosynthesis : conversion of light energy into sugar molecules from CO2 and H2O - gas exchange : takes place through stomata - respiration : utilization of sugar to produce energy together with metabolic and waste products

INTERNAL STRUCTURES OF LEAVES 3 main regions : b)Epidermis c)Mesophyll d)Veins

(A) EPIDERMIS Single layer of cells  Entire surface of leaf  Lower surface distinguishable from upper layer with the presence of stomata  Contain no chloroplast except for guard cells  Coated with cutin and waxy substances  Gland cells – for protection, secrets sticky substances 

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Stomata : 

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at lower surfaces of leaves (most plants), upper surfaces (water lilies) and both sides (maize) number range between 1000-1.2 million per square cm bordered by guard cells containing chloroplasts opening / closing controlled by guard cells - factors affecting the opening / closing of guard cells * level of water content inside leaf * starch content functions : permit gas exchange and regulating transpiration

(B) MESOPHYLL Where photosynthesis takes place  Between epidermis and endodermis  Upper region where cells are lightly packed, barrel-shaped parenchyma cells – region termed palisade mesophyll  Lower region consist of loosely packed parenchyma cells – region termed spongy mesophyll 

(C) VEINS Various sizes in mesophyll  Consist of xylem and phloem tissues  Extensive structures throughout leaves, in dicots  In monocots – have parallel veins, but no palisade and spongy layers of mesophyll  Phloem in veins function to transport carbohydrates produced in mesophyll cells  Xylem in veins function for water transport from roots for use in photosynthesis and respiration in mesophyll cells. 