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4.2 Overview of Photosynthesis KEY CONCEPT The overall process of photosynthesis produces sugars that store chemical energy. 4.2 Overview of Photosynthesis Photosynthetic organisms are producers. • Producers make their own source of chemical energy. • Plants, algae, some bacteria and protists • Photosynthesis captures energy from sunlight to make sugars. 4.2 Overview of Photosynthesis • Pigments are molecules that absorb light energy of specific wavelengths. • In plants, the pigment chlorophyll is found in organelles called chloroplasts – Chlorophyll a – Chlorophyll b – absorb slightly different wavelengths of light • other pigments may be present in the leaf chloroplast leaf cell leaf 4.2 Overview of Photosynthesis 4.2 Overview of Photosynthesis Photosynthesis in plants occurs in chloroplasts. • Photosynthesis takes place in – Grana – stacks of membrane bound sacs called thylakoids – Stroma- fluid surrounding the grana grana (thylakoids) chloroplast stroma 4.2 Overview of Photosynthesis • Light-Dependent reactions -capture energy from sunlight. take place in thylakoids water and sunlight are needed chlorophyll absorbs sun energy…used to: create a small amount of ATP split H2O into: Hydrogens are used later O2 – released into the air 4.2 Overview of Photosynthesis • Light-Independent reactions - make sugars. – take place in stroma – does not use light – needs: – ATP and H from light dependent reactions – CO2 from atmosphere – builds a glucose (sugar) molecule in a cycle of chemical reactions – the Calvin Cycle 4.2 Overview of Photosynthesis Glucose • Formula is C6H12O6 – Carbon from carbon dioxide – CO2 – Hydrogen from water – H20 – Oxygen from… - CO2 - (oxygen from water is released in the light dependent reaction!) 4.2 Overview of Photosynthesis • The equation for the overall process is: 6CO2 + 6H2O C6H12O6 + 6O2 granum (stack of thylakoids) 1 chloroplast 6H2O thylakoid 6CO2 3 6O2 2 energy stroma (fluid outside the thylakoids) 1 six-carbon sugar 4 C6H12O6