Thylakoid

Interior to plant cells that carry out photosynthesis, tiny, bacteria-sized organelles, called chloroplasts, contain, within the inner membrane of their dual membrane structure, the early photosynthesizing apparatus, an extensive system of membrane-bound sacs called thylakoids, their membranes housing the pigment molecules that absorb energy of photons of particular energy emitted by the sun, thereby initiating the physico-chemical sequence of steps in the photosynthesizing process.