(part II) concept 10.3: the light reactions convert solar energy to the chemical energy of ATP and NADPH

what are the two different possible routes for electron flow in light reactions

linear and cyclic

linear electron flow

primary pathways that involves photosystems II and I and produces ATP and NADPH using light energy

what occurs during linear electron flow

a photon hits a pigment light harvesting complex and its energy is passed among pigment molecules until it excites P 670 in the reaction center complex and an excited electron from P680 is transferred to the primary electron acceptor

what happens when chlorophyll A loses an electron

it becomes P680+

what is special about P680+

it is the strongest known biological oxidizing agent

what happens in PS II to H2O

H2O is split by enzymes and the electrons are transferred from the hydrogen atoms to P680+, which makes it P680 and O2 is released as a byproduct

how do the electrons move in the photosystems

each electron falls down an electron transport chain from primary PS II to PS i

what follows the electrons falling down the electron transport chain

energy released by the fall drives the creation of a proton gradient across the thylakoid membrane and H+ are pumped inside the thylakoid concentrating it relative to the outside in the stroma

what drives ATP synthesis in photosynthesis

the diffusion of H+ across the membrane- from inside the thylakoid to outside in the stroma- drives the synthesis by chemiosmosis

what happens in PS I

transferred light energy excites P700 and causes it to lose an electron and become P700+ and the P700 accepts an electron that is passed down from PS II

is O2 produced in PS I

no because H2O is not oxidized

where do the electrons go after PS I

they fall down an electron transport chain from PH I to the protein ferredoxin

where do the electrons go after they reach the protein ferredoxin (Fd)

they are transferred from ferredoxin to NADP+, reducing it to NADPH

what does the the process of reducing NADP+ to NADPH do

is removes an H+ from the strom

cyclic electron flow

photoexcited electrons cycle back from Fd (ferredoxin) to the cytochrom complex instead of being transferred to NADP+

what photosystem(s) does cyclic electron flow use

it ONLY uses photosystem I

what does cyclic electron flow produce

produces ATP and does not produce NADPH or oxygen

why might some organisms only have photosystem I

they evolved to have photosystem I first and never evolved past it

what does it mean for a plant to have photoprotective capability

plants that do not have it grow well in low light but cannot frow well in intense light

how does mitochondria make ATP

transfer chemical energy from food to ATP

how do chloroplasts make ATP

transform light energy into chemical energy

similarities between chemiosmosis in mitochondria and chloroplasts

they both have protons being pumped from one thing to another (in mitochondria they are from intermembrane space back to mitochondrial matrix) (in chloroplasts they are from thylakoid space to the stroma side of the membrane)

what is the benefit of ATP and NADPH being produced on the stroma side of the thylakoid membrane

makes them available for synthesis in the calvin cycle