Granum

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A granum (plural grana) is a stack of thylakoids in the chloroplast, an organelle found in plants and eukaryotic algae where photosynthesis takes place. Chloroplasts can have from 10 to 100 grana. They use photoexcited electrons to convert solar energy (sunlight) into chemical energy (sugar and oxygen). Many grana may be found within a chloroplast, and chloroplast DNA means these can replicate independently of the chloroplast itself. Grana are a key factor in cellular respiration.