The thylakoid membrane is a structure of the chloroplast that is equivalent to the mitochondrial inner membrane (Figure 15.2a). The term thylakoid is sometimes used interchangeably with thylakoid membrane. Absorption of light and all of the light reactions occur within or on the thylakoid membranes. Figure 17.15 summarizes the light reactions that occur in the thylakoid membrane. The CF0-CF1 complex that is equivalent to the mitochondrial F0F1 ATP synthase complex and is located in the thylakoid membranes as are the two photosystems (I and II) and associated electron carriers. The thylakoid membrane provides the walls surrounding the thylakoid lumen into which protons are pumped during photosynthesis.