light dependent reaction?

overview of the light dependent reaction?

• it takes place in the thylakoid membranes

• here, light energy is absorbed by chlorophyll in the photosystems. the light energy excites the electrons in the chlorophyll, leading to the release from the molecule

  • the chlorophyll has been photoionised

• some of the energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to form reduced NADP.

• ATP transfers hydrogen to the light-independent reaction

• during the process, water is oxidised to water

what is the energy from the photoionisation of chlorophyll used for?

• making ATP from ADP and inorganic phosphate - this is called photophosphorylation

• making reduced NADP from NADP

• splitting water into protons, electrons and oxygen - this is called photolysis

how are the photosystems in the thylakoid membranes linked?

• by electron carriers

what are electron carriers?

• proteins that transfer electrons

  • the photosystems and electron carriers form an electron transport chain - a chain of proteins through which excited electrons flow

what are the 4 steps in the light-dependent reaction?

• light energy excites electrons in chlorophyll

• photolysis of water produces protons

• energy from excited electrons makes ATP

• generation of reduced NADP

step 1: light energy excites electrons in chlorophyll?

• light energy is absorbed by photosystem 2

• the light energy excites electrons in chlorophyll

• the electrons move to a higher energy level

• these high energy electrons are released from the chlorophyll and move down the electron transport chain to PS1

step 2: photolysis of water?

• as the excited electrons from chlorophyll leave PS2 to move down the electron transport chain, they must be replaced

• light energy splits water into protons, electrons and oxygen

step 3: energy from excited electrons makes ATP?

• the excited electrons lose energy as they move down the transport chain

• this energy is used to transport electrons into the thylakoid, so that the thylakoid has a higher concentration of protons than the stroma- forming a protein gradient across thylakoid membrane

• protons move down their concentration gradient, into the stroma, via the enzyme ATP synthase, which is embedded in the thylakoid membrane

• the energy from this movement combines ADP and inorganic phosphate to form ATP

step 4: generation of reduced NADP?

• light energy is absorbed by PSI which excites the electrons again to an even higher energy level

• finally, the electrons are transferred to NDAP, along with a proton from the stroma, to form reduced NADP

what is the process of electrons flowing down the electron transport chain and creating a protein gradient called?

chemiosmosis

what is cyclic photophosphorylation?

• it only uses PSI

• it is called cyclic because the electrons from the chlorophyll molecule are not passed onto NADP, but are passed back to PSI via electron carriers

• this means the electrons are recycled and can repeatedly flow though PSI

what does cyclic photophosphorylation not produce?

• reduced NADP

• oxygen

  • it only produces small amounts of ATP