Question

explain in detail the linear electron flow during light reactions

Answer 1

Main steps of the Light reacion are

1.light absorption

2.water splitting

3.oxygen release

4.Formation of high energy molecules like ATP and NADPH

These are done with the help of somany cmplexes .

The pigments are arranged into photochemical light harvesting complex in Photosystem 1 and photosystem 2.

These pigments absorb light of different wavelength and get activated.

In photosystem 2 chlorophyl a is the main pigment which absorb light of wavelength 680nm ------->electron jump into an orbit far from the atomic nucleus.--->electron are picked up by the Electron Acceptors and it is passed into electron transport system consisting of cytochromes.---->electron from the ps2 is moving in a down hill interms of redox potential scale--->taken by the photosystem 1 , at the same time the photosystem 1 is also excited by the light of wavelength of 700nm------>electrons in the ps 1 are excited and transferred to Electron accpetor molecule which have higher potential ------>these electron are taken up by the NAP+ molecule and get reduced into NAPH molecule. These whole step is called Z scheme .

Here the photosystem 2 is lossing electron in each cycle which is replaced by the splitting of water molecule into H+ , oxygen and 4 electrons.

In the lamellar of the grana of chloroplast contain both PS1 and PS2 but the stroma of the chloroplast only contain PS1 which lack PS2 and NADP reductase enzyme.so here the electron are cycled in the photosystem 1 only , it only produce ATP molecule no NADPH is produced.This is called Cyclic phosphorylation.