False-colour transmission electron micrograph (TEM) of a stack of grana (black threads) in a plant chloroplast. The chloroplast is the unit within the leaf, which manufactures the food supply (starch) of the plant during photosynthesis. The granal stacks (flattened vesicles) contain the photosynthetic pigments (chlorophylls), which are active in the conversion of the sun's energy into chemical energy. The grana are connected at points called frets (central conglomeration of black threads), which are embedded in the matrix of the chloroplast.