Umbuso wezitshalo ususungule amasu ahlukene okusinda. Amanye ayabonakala, njengemithi ye-cactus ngokwesibonelo, okungeyona into ngaphandle kwamaqabunga aguquliwe athathe isikhundla se-photosynthesize naleyo yokuvikela umzimba walezi zitshalo. Kepha kukhona ezinye ezingekho kanjalo, njengalokho okuthiwa Izitshalo ze-C4.
Yizitshalo ezihlala ezindaweni ezomile noma ezinesomiso, ngakho-ke ziye zavela ukuze zinciphise ukulahleka kwe-carbon dioxide (CO2) ngesikhathi se-photosynthesis, ngoba lokhu kuyigesi ebalulekile ngesikhathi senqubo yokuguqula amandla eLanga abe ngukudla kwezitshalo.
Izici ze-photosynthesis yezitshalo ze-C4
Isithombe - Wikimedia / Ninghui Shi
Ukuze siqonde kangcono izitshalo ze-C4, sizoqala ngokuchaza i-photosynthesis esiyazi kangcono, ikakhulukazi ngoba iyona efundwa esikoleni, i-C3. Ingabe siqukethe ukumuncwa kwamandla elanga ne-carbon dioxide ngokusebenzisa ama-chloroplast wamaseli ezitholakala ezingxenyeni zezitshalo eziluhlaza noma ze-photosynthetic, namanzi asuka ezimpandeni, ukuguqula kube ngukudla ngochungechunge lokuhlangana kwamakhemikhali.
Ekuqaleni, la mandla okukhanya ashintsha abe namandla amakhemikhali, ngokuba ngama-molecule i-NADPH (nicotin adenine dinucleotide phosphate) ne-ATP (adenosine triphosphate, eyokuqala ukuyigcina. Kodwa ngokuhamba kwesikhathi, la ma-molecule bahlanganisa ama-carbohydrate njengoba i-carbon dioxide incishisiwe.
Isigaba sokugcina sale nqubo kulapho izitshalo zisebenzisa amandla eziwatholile emini ukulungisa ikhabhoni ye-carbon dioxide ngesimo se-glucose. Lokhu kuyingxenye yomjikelezo kaCalvin.
Kodwa i-photosynthesis ezitshalweni ze-C4 yehlukile. Zinezinhlobo ezimbili zama-chloroplast. Ezinye ziseduze kwemikhumbi eqhubayo (singasho ukuthi ziyalingana nemithambo yezilwane), kanti ezinye ezitholakala kumaseli e-pheripheral chlorophyll parenchyma, okuyilawo asondele emaphethelweni amaqabunga. Lezi ezizayo zibizwa nangokuthi amaseli we-mesophilic, futhi yilezo ezinama-chloroplast azolungisa i-carbon dioxide ngosizo lwe-molecule ye-PEPA (phosphoenolpyruvic acid) kanye ne-enzyme phosphoenolpyruvate carboxylase.
Kusukela kula ma-molecule, i-oxaloacetic acid izokhiqizwa, eyakhiwe ngamakhabhoni ama-4 (yingakho zaziwa njengezitshalo ze-C4). Lokhu-ke kuguqulwa kube yi-malic acid, futhi kulapho-ke lapho idlulela kuma-chloroplast aqukethe amaseli angaphakathi emikhumbi eqhuba nge-plasmodesmata (lezi yizakhiwo udonga oluzungeze i-nucleus yeseli, i-cytoplasm, enazo). Kuzo, i-CO2 izokhishwa, futhi umjikelezo kaCalvin ungaqhubeka.
Isimo sezulu nezitshalo C4
Izitshalo ezihlala ezindaweni ezishisayo nezomile zinenkinga enkulu kakhulu kunezinye ukugwema ukulahleka kwamanzi. Kepha ukuze uphile kufanele uphefumule, futhi ngokwenza njalo akunakugwemeka ukulahlekelwa ngamanzi. Ngakho-ke, lapho izinga lokushisa liphezulu, ama-stomata (ama-pores) amaqabunga ayavalwa, futhi ngokwenza kanjalo umoya-mpilo owenziwa ngesikhathi se-photosynthesis wandisa ukugxila kwawo.
Ezimweni ezijwayelekile, lapho inani le-oxygen ne-carbon dioxide lilinganisiwe, i-enzyme ebhekele ukulungisa i-carbon (RuBisCO) ingagcwalisa umsebenzi wayo ngaphandle kwenkinga. Kepha lapho ukuminyana kwe-CO2 kuphansi kunokomoya-mpilo, le enzyme ikhuthaza igesi yokugcina hhayi i-CO2, okuyilokho okwenzeka ezitshalweni ze-C4.
Lokhu kukhetheke kakhulu, ngoba ngaphezu kokuba nezinhlobo ezimbili zama-chloroplast (bheka isigaba esingenhla), i-enzyme phosphoenolpyruvate carboxylase, engomunye walabo ababambe iqhaza ekulungisweni kwekhabhoni, isekela ukugxila okuphezulu komoya-mpilo.
Ziyini izinzuzo zezitshalo ze-C4?
Kunezinzuzo ezimbalwa ezibalulekile lezi zitshalo ezinazo:
- Ngokuvamile, ikhule ngokushesha kunezitshalo ze-C3.
- Basebenzisa kangcono ikhabhoni, ukukhiqiza izimpande eziningi kanye / noma amaqabunga amaningi.
- Lahla amanzi amancane ngesikhathi se-photosynthesis (ngokusho kwe- Lesi sihloko, kulinganiselwa ukuthi balahlekelwa ama-molecule wamanzi angama-277 nge-molecule ngayinye ye-CO2, kuyilapho izitshalo ze-C3 zilahlekelwa ama-molecule wamanzi angama-833 nge-CO2 ngayinye eziyilungisayo).
- Thuthukisa ukukhiqizwa kweglucose, okuwumphumela wokugcina we-photosynthesis.
- Bangaphila emhlabatsini lapho kunemanti lamancane khona.
Kuzo zonke lezi zizathu, ziya ngokuya zithakazelisa, ikakhulukazi ngokukhula ezindaweni ezomile.
Ziyini izitshalo ze-C4?
Kunezitshalo eziningi ezenza i-C4 photosynthesis. Ngokwesibonelo, ummbila, utshani, amaranth, umoba, amabele noma i-rye. Yilezo ezinezicubu ezicinene kunezo ezivela ezimweni zezulu ezipholile, njengama-maple noma ama-camellias.
Ngakho-ke, ukubazi kungasiza kakhulu ukwazi ukuthi yini ongayitshala ezindaweni lapho kutholakala khona amanzi amancane.