Ch. 5 Summary 5.1: Producers use photosynthesis to convert light energy into chemical energy, which is then stored and used to assemble energy rich organic molecules that are used by producers and consumers. Photosynthesis has two stages, the light dependent reactions and the light independent reactions (the calvin cycle). Light dependent reactions take place in the thylakoid membranes of the chloroplasts. Energy captured during these reactions is used to synthesize ATP and NADPH. The calvin cycle takes place in the stroma of the chloroplasts. it uses NADPH and ATP to convert CO2 into simple carbohydrates. Chlorophylls, carotenoids, and other pigments absorb light energy during photosynthesis. Different pigments absorb light of different wavelengths, as shown by their absorption spectra. Light that is not absorbed is reflected. This reflected light gives pigments their colour. The action spectrum of photosynthesis in green plants is the highest in the red and blue regions of the spectrum. Pigments, including chlorophylls and carotenoids, are organized into two types of photosystems: photosystem 1 and photosystem 2. Each photosystem contains a reaction centre surrounded by an antenna complex that helps capture photons of light energy and energize electrons. 5.2: In the light dependent reactions, photosystem 2 absorbs light energy that oxidizes the reaction centre chlorophyll p680, producing the powerful oxidant p680+. this molecule oxidizes water, removing electrons and releasing O2. Electrons that are excited by the light energy in photosystem 2 pass through an electron transport system to photosystem 1. There, the electrons become excited again by the absorption of light, and are ultimately transferred to NADP+ as the final electron acceptor forming NADPH. These processes establish a proton gradient