<P> ATP is the phosphorylated version of adenosine diphosphate (ADP), which stores energy in a cell and powers most cellular activities . ATP is the energized form, while ADP is the (partially) depleted form . NADP is an electron carrier which ferries high energy electrons . In the light reactions, it gets reduced, meaning it picks up electrons, becoming NADPH . </P> <P> Like mitochondria, chloroplasts use the potential energy stored in an H, or hydrogen ion gradient to generate ATP energy . The two photosystems capture light energy to energize electrons taken from water, and release them down an electron transport chain . The molecules between the photosystems harness the electrons' energy to pump hydrogen ions into the thylakoid space, creating a concentration gradient, with more hydrogen ions (up to a thousand times as many) inside the thylakoid system than in the stroma . The hydrogen ions in the thylakoid space then diffuse back down their concentration gradient, flowing back out into the stroma through ATP synthase . ATP synthase uses the energy from the flowing hydrogen ions to phosphorylate adenosine diphosphate into adenosine triphosphate, or ATP . Because chloroplast ATP synthase projects out into the stroma, the ATP is synthesized there, in position to be used in the dark reactions . </P> <P> Electrons are often removed from the electron transport chains to charge NADP with electrons, reducing it to NADPH . Like ATP synthase, ferredoxin - NADP reductase, the enzyme that reduces NADP, releases the NADPH it makes into the stroma, right where it is needed for the dark reactions . </P> <P> Because NADP reduction removes electrons from the electron transport chains, they must be replaced--the job of photosystem II, which splits water molecules (H O) to obtain the electrons from its hydrogen atoms . </P>

All of the following are functions of the bm stroma except