Step 1: Understanding the Concept:
Photophosphorylation is the light-driven making of ATP during photosynthesis. There are two routes for electron flow: a straight, one-way (non-cyclic) route through both photosystems, and a looped (cyclic) route that uses only photosystem I.
Step 2: Key Approach:
In the non-cyclic route, electrons start at photosystem II, pass along the chain, split water for replacement electrons, and end up reducing NADP+ to NADPH. Water splitting also releases O2. Both ATP and NADPH, plus O2, come out of this route. In the cyclic route, the electron leaves photosystem I, moves through the same short chain, and returns to photosystem I itself instead of going on to NADP+.
Step 3: Detailed Explanation:
Because the cyclic electron never reaches NADP+, no NADPH forms, and because water is not split in this route, no O2 forms either. The only outcome of the looped electron movement is a proton gradient across the membrane that ATP synthase uses to make ATP. This is why option 1 (ATP and NADPH), option 2 (NADPH alone) and option 3 (ATP, NADPH, O2) are all wrong: each one wrongly credits the cyclic route with NADPH or O2, which actually belong to the non-cyclic route.
Step 4: Final Answer:
Cyclic photophosphorylation makes ATP alone, so option 4 is correct.