light-dependent reaction

stages of photosynthesis

-light-dependent reaction

-light-independent reaction

where does light dependent reaction occurs?

thylakoid membranes of the chloroplast

what process is used to produce ATP in light dependent reaction?

photophosphorylation

photophosphorylation

production of ATP from ADP and inorganic phosphate using light energy 

types of photophosphorylation

-non-cyclic photophosphorylation

-cyclic photophosphorylation

stages of cyclic photophosphorylation

• electron transport chain

• Photolysis of water

• Chemiosmosis

• reduced NADP generated

electron transport chain

-light energy is absorbed by photosystem II

-this excites electrons, moving them to a higher energy level

-excited electrons pass through an electron transport chain to photosystem I

photolysis of water

-light energy splits water into protons, electrons and oxygen

-Electrons from photolysis replace the electrons lost from PSII

how is ATP produced in light dependent reaction?

-light energy is absorbed by photosystem II

-this excites electrons, moving them to a higher energy level

-excited electrons pass through an electron transport chain

-the excited electrons lose energy as they pass along the electron transport chain

-this energy is used to pump protons (H⁺ ions) from the stroma into the thylakoid space

-thylakoid space has a higher concentration of protons than the stroma [protons accumulate in thylakoid space]

-this creates a steep proton gradient across the thylakoid membrane

-protons move down concentration gradient into stroma through ATP synthase

-the flow of protons through ATP synthase provides the energy to combine ADP and inorganic phosphate to form ATP

how is reduced NADP produced in light dependent reaction?

-Light energy is absorbed by photosystem I

-this excites electrons again

-in the stroma, electrons and a proton combine with NADP to form reduced NADP (NADPH)

process of cyclic photophosphorylation

-Light energy is absorbed by PSI, which excites electrons

-The excited electrons are passed along an electron transport chain

-The electrons lose energy as they pass along the ETC

-this energy is used… [same steps of ATP production flashcard]

-the electrons return to PSI so no NADP is reduced (electrons are not transferred to NADP)

-only ATP is produced

[main points]

ATP is formed the same way in cyclic photophosphorylation as in non cyclic photophosphorylation

compare cyclic and non-cyclic photophosphorylation

similarities (4)

differences (5)

similarities

-both produce ATP

-electrons are passed along ECT

-an electron leaves photosystem I

-both involve chemiosmosis

differences

cyclic

-involves PSI only

-does not involves photolysis→ so no oxygen produced

-produces ATP only

-Chlorophyll a in PSI is the electron donor.

-the same electrons return to the photosystem I

non-cyclic

-involves both PSI and PSII

-involves photolysis

-produces ATP, reduced NADP and oxygen

-water is the electron donor

-electrons do not return to the photosystem and are transferred to NADP

what products of the light-dependent reaction are needed in the light-independent reaction?

ATP and reduced NADP

What helps lower proton concentration in the stroma?

-protons in the stroma combine NADP to make reduced NADP

-protons are removed from the stroma which lowers proton concentration the stroma

What helps increase proton concentration in the thylakoid?

Photolysis of water releases protons into the thylakoid space, increasing the proton concentration.