Light dependant stage of photosynthesis

• Photolysis in PSII results in the formation of 4H+ and 4e-.
• H+ is picked up by NADP to form NADPH, which is used in LIR.
• The e- passed along chain of electron and carrier proteins.
• Oxygen is used in respiration or may diffuse out.
• Photophosphorylation is the generation of ATP from ADP and inorganic phosphate in the presence of light.
• Non-cyclic phosphorylation produces ATP, oxygen and NADPH
• The electron carrier chain begins with a photon hitting PSII and exciting a pair of electrons inside a chlorophyll pigment.
• Excited electrons escape chlorophyll and are picked up by an electron carrier, an iron-centred protein, embedded in the thylakoid membrane.
• Fe3+ is reduced to Fe2+, it then donates to the next electron carrier and so on.
• As electrons are passed along, energy is released, which is used to pump protons (active transport) across the thylakoid membrane into the thylakoid space.
• As protons accumulate in the thylakoid space, an electrochemical gradient forms.
• Protons diffuse down the concentration gradient via facilitated diffusion through channels associated with ATP Synthase enzymes, causing ADP and inorganic phosphate to form ATP.
• As electrons pass through the chain, eventually they are captured by chlorophyll a in PSI, replacing its lost electrons.
• A protein-iron-sulfur complex called feredoxin accepts the electrons from PSI and passes them onto NADP in the stroma.
• Protons diffused in from the thylakoid space are accepted along with electrons by NADP and becomes reduced.
• Cyclic phosphorylation produces ATP in smaller quantities.
• This takes place in PSI - electrons are excited by light and picked up by electron carriers.
• During the passage of electrons along electron carriers, a small amount of ATP is generated.
• Guard cell chloroplasts contain PSI only and rely on cyclic phosphorylation.