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photosynthesis summary/light-dependent reactions
photosynthesis takes place in the chloroplasts of plants. it takes place in two parts - light reactions that happen in the thylakoids and the calvin cycle. in light dependent reactions, light from the sun excites electrons in photosystem II. during this time, two water molecules are split into four hydrogen ions, four electrons, and oxygen. the electrons are used to replace any lost electrons in PII, the hydrogen is released into the lumen, and oxygen is released as a byproduct. the energized electrons move down the electron transport chain, where they pull in hydrogen ions to the lumen as well. in photosystem I, the electrons are added to NADP+ to make NADPH. H+ ions in the lumen flow down the concentration gradient and power ATP syntheses, which makes ATP. the NADPH is used in the calvin cycle along with carbon dioxide and ATP to make glucose, until they return to the light dependent reactions as NADP+ and ADP.