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Leaf Structure * Most photosynthesis occurs in the palisade layer. « Gas exchange of CO, and O, occurs at openings called stomata surrounded by guard cells on the lower leaf surface. CROSS-SECTION OF A LEAF upper epidermis Palisade me sop hy fl bundle sheath Wein Spongy me sop hy fl fwer epidermis guard cells OVERVIEW OF PHOTOSYNTHESIS AND RESPIRATION 2 RADIANT ENERGY iceman => om | ay N GLUCOSE ATP(ENERGY) WATER OXYGEN 6CO, + 6H,0 +ENERGYEE> C,H,,0,+ 60, CARBON GLUCOSE DIOXIDE Photosynthesis in Overview Process by which plants and other autotrophs store the energy of sunlight into sugars. Requires sunlight, water, and carbon dioxide. Overall equation: 6CO, + 6H,0 > C,H,,0, + 60, Occurs in the leaves of plants in organelles called chloroplasts. Photosynthesis: The Chemical Process * Occurs in two main phases. — Light reactions — Dark reactions * Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments. * Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars. Dark Reactions * Dark reactions (light-independent) occur in the stroma. — Carbon dioxide is “fixed” into the sugar glucose. — ATP and NADPH molecules created during the light reactions power the production of this glucose. The photosynthetic reaction ¢ Water + ADP — sunlight — oxygen + hydrogen ions + ATP ¢ Carbon dioxide + hydrogen ions + ATP — glucose + ADP H,O + ADP + CO, +44°+ ATP --sunlight— O, +4f* + ATP + C,H,,0, + ADP u 6H,O + 6CO, --sunlight— 60, + C,H,,O, General leaf adaptations Flat shape Many stomatal pores Very thin with internal air chambers Extensive network of vascular tissue — Xylem — Phloem Large photosynthetic surface Gaseous exchange Easy diffusion of CO, to photosynthetic cells Delivery of essential nutrients — Water & minerals — Sucrose & hormones General stem adaptations Xylem vessels running entire length Rigid structure of xylem Phloem vessels running entire length Branching of stem Transport water and minerals from roots Helps plant to remain upright Transports sucrose from leaves Provides broader, multileveled photosynthetic area Water molecules Vascular Bundles a= 
