Question

which of the following sequences correctly represents the flow of electrons during photosynthesis?
nadph→o2→co2
h2o→nadph→calvin cycle
h2o→photosystem i→photosystem ii
nadph→electron transport chain→o2

Explanation:

• In photosynthesis, water (\(H_2O\)) is split in the light - dependent reactions. The electrons from \(H_2O\) are used to generate \(NADPH\).
• \(NADPH\) then donates its electrons to the Calvin cycle (light - independent reactions) for the reduction of \(CO_2\) to form organic molecules.
• For the option \(H_2O

ightarrow\) photosystem I \(
ightarrow\) photosystem II: In the light - dependent reactions, the flow is from photosystem II to the electron - transport chain and then to photosystem I.

• For the options involving \(NADPH

ightarrow O_2\) or \(NADPH
ightarrow\) electron - transport chain \(
ightarrow O_2\): \(NADPH\) is an electron donor (not an electron acceptor in the context of electron flow from the start of photosynthesis). \(O_2\) is a by - product of \(H_2O\) splitting (not a direct electron acceptor from \(NADPH\) in the main electron flow of photosynthesis). And the electron - transport chain in photosynthesis (in the thylakoid membrane) is mainly involved in generating a proton gradient and using light energy from photosystem II and I, not taking electrons from \(NADPH\) to make \(O_2\).

Answer:

\(H2O
ightarrow NADPH
ightarrow Calvin\ cycle\)