The noncyclic pathway is a FLOW of electrons from water, to photosystem II, to PHOTOSYSTEM I to NADPH. Energy is released as ELECTRONS move through the first electron transfer chain. This energy pumps HYDROGEN IONS into the thylakoid compartment, and then they power the formation of ATP as they flow back out. Sunlight provides the energy needed to keep this cycle going.

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Luminous energy is trapped by chlorophyll in Photosystem II.
When the pigment molecules absorb light, electrons provided by water molecules get in a higher energy level.
The excited electrons go through the electron transport chain from Photosystem II to a less energetic level in photosystem I.
<em>When the excited electrons leave photosystem II, they are replaced by new electrons extracted from the water molecules. </em>
Luminous energy absorbed move the electrons from the photosystem I to another electron acceptor, from where they get transported again and used to produce NADPH molecules.
<em>When electrons leave Photosystem I, they are replaced by new electrons coming from photosystem II. </em>
When the water molecule breaks down, hydrogen ions remain in the thylakoid lumen, from where they are pumped to the stroma by the ATP synthase.
The released energy is used to produce ATP molecules.
Hydrogen ions go back from the stroma to the thylakoid compartment.

The final products are oxygen, ATP, and NADPH.

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