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PHOTOSYNTHESIS Autotrophs • Are organisms that are able to synthesize their own food from inorganic substances using sunlight for energy. 2 Heterotrophs • Heterotrophs are organisms that can NOT make their own food • They NEED the autotrophs as a source of “organic macromolecules that contain energy” AKA Food! Heterotrophs can NOT directly use the sun’s energy 3 What is Photosynthesis? • An anabolic, endergonic, carbon dioxide (CO2)-requiring process that uses light energy and water (H2O) to produce organic macromolecules (e.g. Glucose and starch). 6CO2 + 6H2O C6H12O6 + 6O2 Sunlight 4 Where in plants does photosynthesis occur? • Photosynthesis takes place in any cell of a plant that is green (mostly the cells in the leaves) 5 Structure of a Leaf Cell Chloroplast [The green part] 6 The Chloroplast • The structure within a cell (organelle) where photosynthesis takes place. • Thylakoids: Disk shaped membranes containing photosynthetic pigments. Site of light dependent reactions. • Grana: Stacks of thylakoids. • Stroma: Fluid filled space surrounding grana. Site of light independent reactions. 7 Pigments • In addition to water, carbon dioxide, and light energy, photosynthesis requires Pigment molecules. • Chlorophyll is the primary light-absorbing pigment in autotrophs. • Chlorophyll is found inside the thylakoids [inside the chloroplast]. 8 Light & Pigments • Photons of light “excite” electrons in the plant’s pigments • Excited electrons carry the absorbed energy. • Other molecular machinery use the electrons to make ATP 9 Photosynthesis Reactions • Two main parts (reactions) • Light Reaction or Light Dependent Reaction produces energy from sunlight to form ATP & NADPH • Dark Reaction or Light Independent Reaction uses ATP and NADPH to convert CO2 into Glucose 10 Light Reaction • Occurs in the Thylakoid membranes • The light reaction uses light energy to split water into O2, H+, and e• O2 is released and the H+ and e- is used to produce ATP and NADPH. 11 Lets give Hydrogen a break! • Hydrogen is the smallest atom. • It consists of a single proton [+] and a single electron [-]. • In photosynthesis the H+ is carried by NADP and the electrons energy goes to make ATP 12 Light Dependent Reaction 13 Dark Reaction • Calvin Cycle or Light Independent Reaction • Uses energy (ATP and NADPH) from light reaction to make glucose 14 Photosynthesis Overview 15 Matter cycles as energy is transformed P P P Glucose ATP CHEMICAL ENERGY LIGHT ENERGY ENERGY FOR CELLULAR WORK P P Carbon dioxide P ADP + P 16 Trace how the energy is transformed Photosynthesis Cellular respiration P P P Glucose ATP CHEMICAL ENERGY LIGHT ENERGY P P P Carbon dioxide Light energy Photosynthesis Energy stored in glucose Cellular respiration Energy stored in ATP 17