Photosynthesis Processes

Overview Absorption of light energy Conversion to chemical energy Sun hits chloroplasts Conversion to chemical energy Light dependant reaction Storage of energy in sugars Light independent reaction

2 Stages of Photosynthesis Light Dependant Reaction Takes place in Grana (thylakoid membrane) Products – ATP, O₂, NADPH Light Independent Reaction – Calvin Cycle Takes place in the stroma Products – Glucose, NADP⁺, ADP

Light Dependant Reaction Takes place in thylakloid membrane of the chloroplast

Light Dependant Reaction

Light Dependant Reaction Light strikes PSII 2 electrons are excited Simultaneously - H₂O split into to H⁺ and ½ O₂ (photolysis) Electrons flow down ETC (electron transport chain) Providing energy for production of ATP Electrons enter photosystem I Light strikes PSI Exciting electrons Electrons flow down to NADP⁺ electron acceptor Provide energy for production of NADPH (used in light independent reactions) NADPH = nicotinamide adenine dinucleotide phosphate

Light Dependant Reaction

Light Independent Reactions Calvin Cycle No light required Carbohydrates are synthesized from CO₂ using the ATP and NPDH formed in light reactions

Calvin Cycle 4 Steps Carbon Fixation Energy conversion Release one molecule of sugar G3P Regeneration of RuBP

Calvin Cycle Step 1 – Carbon Fixation Three molecules of CO₂ combine with 5-C sugars RuBP (Ribulose biphosphate) Enzyme is Rubisco Each CO₂ forms a 6-C molecule which splits into two 3-C acids (PGA) For 3 co2 6 PGA result

Calvin Cycle Step 2 – Energy Conversion 2 chemical reactions Use 6 molecules of ATP ATP ADP + P And Use 6 molecules of NAPDH NADPH NADP⁺ Producing 6 molecules of 3-C sugar G3P (phosphoglyeralehyde) G3P always

Calvin Cycle Step 3 – Release one molecule of G3P Five of the G3P molecules remain in the cycle One G3P molecule in released as a product Two G3P molecules needed to make one molecule of glucose

Calvin Cycle Step 4 – Regeneration of RuBP Series of chemical reactions Use 3 ATP to convert 5 G3P molecules into 3 RuBP molecules 5 molecules of G3P = 15 carbons 3 molecules of RuBP = 15 carbons Show animation

Calvin Cycle Takes two molecules of G3P to produce one molecule of glucose So 6 molecules of CO₂ 18 molecules of ATP 12 molecules of NADPH

Photosynthesis Recap