Question

what would happen to the concentrations of atp, nadph and sugars if psi stopped working?
atp
nadph
sugars
decrease
stay the same
increase

Explanation:

PSI (Photosystem I) is involved in the light - dependent reactions of photosynthesis. NADPH is produced in the light - dependent reactions, and if PSI stops working, the electron flow that leads to NADPH synthesis will be disrupted, so NADPH concentration decreases. ATP can be produced through cyclic photophosphorylation (which may still occur to some extent even if PSI is affected, but overall, the non - cyclic pathway which is major for ATP production in some cases is affected, but the main point is on NADPH). Sugars are produced in the Calvin cycle (light - independent reactions) which requires NADPH (and ATP). Since NADPH is decreased, the Calvin cycle slows down, and sugar production (and thus sugar concentration) decreases.

Answer:

ATP: Decrease, NADPH: Decrease, Sugars: Decrease