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Photosynthesis

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  Photosynthesis ã The Dark Reactions of Photosynthesis, Assimilation of Carbon Dioxide And The Calvin Cycle  ã C 3 , C 4  and CAM. Re!lation of The Activity of Photosynthesis  ã The iht Reactions of Photosynthesis  ã The Photosynthetic Membrane  ã iterat!re The observation that a #illo# that has been c!ltivated in a container for five years #ith eno!h #aterin ained more than half a centner #eiht altho!h only t#o o!nces of the container$s soil #ere lost oes back to %.&. van '( M)*T +- / 0441. The &ritish nat!ral scientist 2. 'A (2 +0 / 01 !nderstood that air and liht are necessary for the n!trition of reen lants. &!t it #as not before the comosition of air o!t of different ases became kno#n that their sinificance for lant n!trition #as st!dies. n  observed %. PR(2T (5 +33 / 6741, one of the discoverers of oxyen, that reen  lants ive off oxyen and th!s imrove the air. The riest %. 2(*(&(R +48 / 6791 from :eneva discovered that the reeneration of the air is based on the !se of $fixed air$ +carbon dioxide1. These observations #ere confirmed and broadened by st!dies of the D!tch doctor  %. *:(*');2< +37 / 991 #ho reconi=ed both the meanin of liht and the fact that the #hole carbon contained in  lants is of atmosheric oriin. 'e, too, conceived that lants take ! small amo!nts of oxyen at niht or in the shado# and ive off carbon dioxide. n 674 discovered Th. des 2A;22;R( +0 / 64-1 from :eneva that the lants$ increase in #eiht cannot solely  be ca!sed by the !take of carbon and minerals, b!t is based on the bindin of the #ater comonents, too. n 694 constr!cted T. >. (*:( MA** +643 / 9791 a adet o!t of a modified microscoe condenser that allo#ed him to exose arts of hotosynthetically active cells +of the reen ala Spirogyra 1 to a thin ray of liht. 'is aim #as to discover #hich comonents of the cell f!nctioned as liht recetors. To meas!re the oxyen rod!ction, he disersed the thread/like Spirogyra  in a bacteria/containin s!sension. >henever  arts of the chlorolast #ere ill!minated, did the bacteria concentrate in this area +#here oxyen #as available1. The ill!mination of other arts of the cell res!lted in no s!ch areations.  n an earlier st!dy did he slit #hite liht into its sectral comonents !sin a rism. 'e then ill!minated a reen ala, Chladophora , #ith this sectr!m. n contrast to Spirogyra  are the Chladophora  cells comletely and evenly filled by the chlorolast. 'e observed that the bacteria acc!m!lated mainly in the bl!e and red liht. A first action sectr!m of  hotosynthesis #as th!s yielded. t resembles ro!hly the absortion sectra of chlorohyll a and b. %. v. 2AC'2 +638 / 691 co!ld finally rove that chlorohyll is involved in  hotosynthesis. n addition did he sho# that starch is rod!ced in chlorolasts as a res!lt of the hotosynthetic activities. These res!lts are in accord #ith the first la# of  thermodynamics, #hose discoverer %. R. MA5(R ost!lated already in 648 that lants take ! enery in the form of liht and that they transform it into another, a chemical state of enery. &ased on this ass!mtion #as the reaction e?!ation 0 carbon dioxide @ 0 #ater  (chlorophyll)   l!cose @ 0 oxyen form!lated. %.v. (&: ass!med that the oxyen stems from the breakdo#n of the carbon dioxide. This idea #as !ncritically acceted by the lant hysioloists of the late 9 th  and the early87 th  cent!ry +2AC'2, PB(BB(R, %)2T and others1 altho!h M. %. 2C' (D(* had as soon as 648 reali=ed that .l!cose is rod!ced as a res!lt of hotosynthesis +and he #as closer to reality than 2AC'2 #as later1 and that  8.it is very likely that it is #ater that is broken do#n. 'e #rote t is #ell/kno#n that C) 8  is amon the most stabile como!nds and that no chemical #ay of breakin it do#n is kno#n #hile ' 8 ) is very easily broken do#n.... and it does therefore seem likely that the 84 ' 8  of the 84 ' 8 ) are combined #ith the 8 C) 8 . +from :r!nd=Ee der #issenschaftlichen &otanik1. 2C' (D(*$s e?!ations contain all reaction como!nds in do!ble n!mbers. 'e ives C 8 ' 84 ) 8  as the form!la for l!cose. t #as soon reali=ed that the reaction e?!ation above is a simlification and that  hotosynthesis consists of a n!mber of artial rocesses. B. B. & ACFMA* and :. . C. MAT':( +97-, ;niversity of Cambride, :reat &ritain1 #ere amon the first to st!dy this toic systematically. They c!ltivated lants !nder different b!t controlled carbon dioxide concentrations, different liht intensities and different temerat!res and they noted the effects of these arameters on the rate of  hotosynthesis. T#o decisive asects #ere revealed. ;nder stron liht and limited amo!nts of carbon dioxide is the rate of hotosynthesis deendent on the temerat!re. This sho#s that the carbon dioxide fixation is based on normal, temerat!re/deendent  biochemical reactions. ;nder carbon dioxide excess and too little liht #as no temerat!re/deendence fo!nd. This hints at the fact that the liht/ind!ced reactions are indeendent of the temerat!re. This statement alies to all hotochemical reactions. n 98- !t ). >AR&;R: +Faiser/>ilhelm/nstit!t Glater Max/Planck/nstit!tH fEr <ellhysioloie at &erlin/Dahlem1 the res!lts of & ACFMA* do#n to the existence of t#o classes of hotosynthetic reactions the liht and the dark reactions. D!rin the thirties analy=ed C. &. van *( +2tanford ;niversity1 the hotosynthesis of an!mber of !rle bacteria. n addition to carbon dioxide do these bacteria need hydroen s!lhide for hotosynthesis. van *( #as able to determine  0 C) 8  @ 8 ' 8 2  (light)   C 0 ' l8 ) 0  @ 8 2 @ 0 ' 8 ) as the reaction$s e?!ation. &ased on it did he extraolate a eneral e?!ation of  hotosynthesis C) 8  @ 8 ' 8 I  (light)   +C' 8 )1 @ ' 8 ) @ 8 I Accordin to this e?!ation is hotosynthesis a redox reaction #ith ' 8 I as the electron donator +the oxydi=able s!bstance1. n the case of reen lants is it ' 8 ) and this means that not the carbon dioxide b!t the #ater is broken do#n. A first exerimental rove that the oxyen develoed d!rin the hotosynthesis of reen  lants stems indeed from #ater #as delivered by the &ritish hysioloist R. ' . 'e detected that isolated chlorolasts ive off oxyen in the resence of !nnat!ral red!cin aents like iron oxalate, ferricyanide or ben=o?!inone after exos!re to liht. The reaction #ent do#n in literat!re as the ' /reaction 8 ' 8 ) @ 8 A  (light, chloroplasts)   8 A' 8  @ ) 8  #here A is the electron accetor. f A J Be  , then is 8 ' 8 ) @ 4 Be    (light, chloroplasts)   4 Be   @ ) 8  @ 4 ' @  The rocess is linked to a hotolytic breakdo#n of #ater that recede the red!ctionn of Be  . 4 ' 8 )   (light, chloroplasts)   4 ' @  @ 4 )' /  This sho#s that oxyen can also be set free in the absence of carbon dioxide,the oxyen rod!ced stems from the breakdo#n of #ater,isolated chlorolasts are able to erform at least artial rocesses of hotosynthesis.The statement that the oxyen rod!ced d!rin hotosynthesis stems only from the  breakdo#n of #ater #as confirmed by 2. M. R;&(*, M. RA*DA , M. FAM(* and %. . '5D( in 94 after the isotoe techni?!e had fo!nd its #ay to biochemistry. They co!ld sho#n that a s!sension of Chlorella  ro#n in ' 86 ), ives off 6) 8 , after liht exos!re. 2hortly after#ards confirmed 2. M. R;&(* and his collaborators the ost!lateof ). >AR&;R: that the fixation of carbon dioxide is enery cons!min b!t indeendent of liht. n addition co!ld (. RACF(R +Cornell ;niversity, thaca, *. 5.1  rove that liht can be relaced by the addition of enery/rich como!nds.
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