The light-dependent reaction takes place in the thylakoids of chloroplasts.

Thylakoid membranes are well adapted for the light-dependent reaction because:

1. They have a large surface area for chlorophyll and electron carriers in the electron transport chain
2. They contain ATP synthase channels
3. They are selectively permeable, allowing a proton gradient to be established for ATP production

Oxidation is when a substance loses electrons or gains oxygen.

Reduction is when a substance gains electrons or loses oxygen.

Oxidation and reduction generally occur together in reactions.

The main reactants of the light-dependent reaction are water (and light energy).

The products of the light-dependent reaction, specifically non-cyclic photophosphorylation, are ATP, reduced NADP, and oxygen.

Reduced NADP and oxygen are not produced in cyclic photophosphorylation.

1. Absorption of light by pigments
2. Release of electrons from pigments
3. Electron transfer along the electron transport chain
4. Photolysis (splitting) of water to provide protons (H⁺) and electrons (e^-, to replace those lost)
5. Chemiosmosis (movement of protons through the thylakoid membrane)
6. Production of ATP and reduced NADP

In photosynthesis, chemiosmosis is the diffusion of protons across the partially permeable thylakoid membrane, down their electrochemical gradient through ATP synthase channels.

The movement of the protons releases energy that is used to synthesise ATP.

The electron transport chain transfers excited electrons from photosynthetic pigments to electron carriers.

This transfer releases energy, which is used to pump protons across the thylakoid membrane, creating a proton gradient that drives ATP synthesis.

The equation for the photolysis of water is:

2H₂O + light energy ➔ 4H⁺ + 4e^- + O₂

Photolysis produces electrons to replace those lost by pigments. It produces protons that help set up the proton gradient that drives ATP synthesis. The protons and electrons are also used to reduce NADP. Photolysis produces oxygen as a by-product.

NADP is reduced when it takes up protons produced during photolysis, carrying the electrons into the light-independent reaction.

ATP synthase catalyses the production of ATP from ADP and P_i. This uses the energy from the flow of protons down their concentration gradient from the thylakoid space into the stroma through ATP synthase channels.

The protons are then taken up by NADP in the stroma and, along with electrons from the electron transport chain, produce reduced NADP for use in the light-independent reaction.

The products of the light-dependent reaction are ATP, reduced NADP, and oxygen.