Biochemistry of photosynthesis 1
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2 stages of photosynthesis
light dependent and light independent
what stage occurs first
light dependent reactions occur first and light independent reactions occur after
function of light dependent reactions
produce materials that are used in light independent reactions
when does whole process take place
during the hours of daylight but the light independent reactions can also continue when dark
where does the light dependent stage take place
on the thylakoid membranes of the chloroplast
2 main functions of light dependent stage
-split water molecules in photochemical reaction -produce ATP which is needed to supply energy to produce carbs
function of photochemical reaction
-splitting of water molecules -provides hydrogen ions to reduce carbon dioxide and produce carbs in the light independent stage
structure of light
form of electromagnetic radiation and smallest unit of light is a photon
what happens when a photon of light hits a chlorophyll molecule
the energy is transferred to the electrons of that molecule
what happens to electrons when they gain energy
they are excited and raised to higher energy levels -if electron raised high enough they will leave chlorophyll molecule completely
what happens to excited electron leaving chlorophyll molecule
can be picked up by electron acceptor and result in synthesis of ATP
2 ways electron can be picked up by electron acceptor and synthesise ATP
cyclic and non cyclic photophosphorylation
similarities of cyclic and non cyclic photophosphorylation
-both take place at same time and in both cases ATP is formed as excited electron is passed along electron transport chain
whats different about non cyclic photophosphorylation
reduced NADP is also produced
evidence for photosynthesis being a 2 stage process 1
-photochemical reactions get energy from light so temp should not affect rate of photosynthesis but when investigated shows temp had clear effect -light dependent reactions limiting overall rate of reaction so temp has no effect -however once light available process limited by different temp sensitive reactions -suggests 2 phases one light dependent and other controlled by temp sensitive enzymes
evidence for photosynthesis being 2 stage process 2
plant given different amounts of light produced more carbs than plant in one light -explanation is light dependent and independent reaction -in continuous light product builds up as light independent stage cant keep up -as conc rises inhibits enzymes controlling light independent reactions from making carbs -period of darkness ensures all of light stage products converted without conc getting to high
what does cyclic photophosrylation involve
involves only photosystem 1 and drives the production of ATP
what happens when a photon hits a chlorophyll molecule in PS1
-a light excited electron leaves the molecule -its take up by electron acceptor and passed directly along electron transport chain to produce ATP
electron that returns to chlorophyll in PS1
it can be excited in same way
what happens during non cyclic photophosphorylation
water molecules are split providing hydrogen to reduce to NADP -ATP is also produced -involves PS1 AND PS2
photon activity under light conditions in non cyclic
constantly hit chlorophyll molecules in PS1 AND PS2 exciting electrons to high enough level for them to be lost and picked up by electron acceptor
another electron acceptor in PS2 non cyclic
-another excited electron from PS2 picked up by another electron acceptor and passes along electron transport chain to PS1 -produced one molecule of ATP
what does PS1 receive after letting second electron go to acceptor
gets an electron to replace one that was lost to light dependent reactions
state of chlorophyll molecule in PS2 after losing electron
short of electron and unstable -original electron cannot be returned to chlorophyll because it has continued on to PS1 -electron comes from splitting of water to restore chlorophyll to original state