Question

What is produced in the Photosystem II (PSII) portion of the electron transport chain (ETC)?

Answer 1

Hi @BinkyBoo ! Welcome Back To Open Study..:)
Do you know what photosystems are?

Answer 2

Yea its in plants when the chlorophyll absorbs light energy for photosynthesis

Answer 3

Good...to be more specific..photosystems are located in the Thylakoid membrane of the Chloroplast...

Answer 4

Photosynthesis consists of two steps namely...Light Reaction and Dark reaction

Answer 5

So Does PSII make ATP and PSI make O2???

Answer 6

dark reaction?
Is that like when cell respiration happens in a plant?

Answer 7

I know that in Light reactions e- is passed through PSII and PSI
That PSII happens first then PSI
And that light reactions build up a H+ gradient that is used to make ATP

Answer 8

Can you wait for a sec...i jst refer one of my old book and clear your doubt..:

Answer 9

Haha yea no problem I'm sorry I was just trying to clarify what I knew so it would be less explaining for you or you could build off of what I know (or what I think I know)
Plus when I have questions if I don't jot them down they tend to escape me :P

Answer 10

All your doubts will clear when i teach you all abt it very clearly..:) OK you ready?

Answer 11

Yes Please! :)

Answer 12

Ok....so we all know that the photosynthesis takes place in the chroloplast having a membranous system consisting of the thyalkoid, stroma lamallae and fluid stoma

Answer 13

..there's a clear cut division of labour in the chloroplast.The membranous system is responsible for trapping light energy and synthesis of ATP and NADPH. In stroma enzymatic reactions incorporate CO2 into the plant leading to the synthesis of sugar, which in turn forms starch...OK?

Answer 14

ok

Answer 15

The former set of reactions, since they are directly light driven are called 'Light Reactions' . Dont think that they are directly light driven but they are dependent on the products
of light reactions (ATP and NADPH)

Answer 16

and just to distinguish between them, the latter is named 'DARK REACTION' (Its not that they occur in the Dark..:) )

Answer 17

haha ah ok X)

Answer 18

NOW : 'What is Light Reaction'

Answer 19

Its whenthe chlorophyll absorbs light energy for photosynthesis to produce ATP and NADPH

Answer 20

good...Two Light harvesting Complexes are involved in it...They are Photosystem 1 and Photosystem 2

Answer 21

The Light Harvesting Complexes (or LHC's) have many pigment molecules in it..

Answer 22

These pigments help to make photosynthesis more efficient. Here's where chlorophyll comes... The single chlorophyll 'a' molecule forms the Reaction Centre . Both PS1 and PS2 have different reaction centres

Answer 23

Chlorophyll 'a' in PS1 absorbs light of wavelength 700 nm and hence called P700 and 680 for PS2 and hence P680...Understandable?

Answer 24

Ohhh!!!! Ok that what the P700 and P680 Is!!

Answer 25

exactly! Now lets move on to 'THE ELECTRON TRANSPORT CHAIN'

Answer 26

Its very easy!

Answer 27

ok:)

Answer 28

Ok..then..I'll first give you the flowchart

Answer 29

ok

Answer 30

In PS2 chlorophyll a absorbs 680nm wavelength of light which causes the electrons to excite. these excited electrons are picked up by the electron acceptor(refer the diagram ) and transfers it to electron transport system and then simultaneously passed to PS1

Answer 31

so PS2 doesn't really produce anything it just passes electrons to PS1?

Answer 32

yup...its work at the present moment is to pass on the P680 electrons to PS1

Answer 33

Simultaneously, electrons in the reaction centre of PS I are also excited when they get light of wavelength 700nm and transferred to another electron acceptor which takes it to NADp+ which converts it to NADPH

Answer 34

as you can see the diagram...the whole process is of a 'Z' shape...and hence its also called Z scheme of electron transport...

Answer 35

ohh ok that makes sense then.
SO PS1 technically produces NADPH then

Answer 36

and now comes PS2....how does PS2 supply electrons continuously? Here clears one of your doubts....the replacement of the electrons that were passed on to PS1 is done with the help of SPLITTING OF WATER MOLECULES which is associated wiith PS2..this splitting creates the formation of Oxygen...one of the most important product of photosynthesis ( Remember the formation of oxygen in the equation of photosynthesis)

Answer 37

Does it take use an electron from the split of the water molecules to transport the other electron since the water had 2?

Answer 38

Nope...ALL the electrons needed to replace those removed from photosystem I are provided by photosystem II (They do not follow the "Sharing is Caring" Policy..:p)

Answer 39

and now there's another Photophosphorylation i.e Cyclic one...the previous one that you saw was a non cyclic one..

Answer 40

Wait where does that come in after PS2?

Answer 41

Also with the how does PS2 supply electrons continuously? Im not clear on that does it have something to do with the photons?

Answer 42

CYCLIC PHOTOPHOSPHORYLATION OCCURS IN ORGANISMS LIKE BACTERIA AND NOT GREEN PLANTS ( thats why there's no ATP synthesised...) Clear?

Answer 43

the Z scheme is not applicable for plants ( sorry i frgt to tell that at the beginning)

Answer 44

The non cyclic photophosporylation occurs in green plants

Answer 45

Ohh ok got it

Answer 46

Oh thank god! i knew that you'd be confused with no ATP release in the previous one..:)

Answer 47

Ok...the same process as per the diagram occurs in the chloroplasts of the plants and result in the release of ATP (Remember only PS1 is present in the Cyclic one!)

Answer 48

*and ADP..

Answer 49

..and as i told earlier...This ATP and ADP is used up the the DArk Reaction

Answer 50

so to be clear Cyclic Photophosphorylation has enough NADPH so it just has PS1 in it and happens in organisms like bacteria?

Answer 51

not cyclic...NON CYCLIC OCCURS IN PHOTOSYNTHESISING BACTERIA

Answer 52

BLAH!!! Thats what I meant sorry!!

Answer 53

and it has both PS1 as well as PS2 in it...because NADPH production requires both of them to function...Is it confusing?

Answer 54

a bit

Answer 55

So in simpler words, both PS1 and PS2 are required in organisms like bacteria because NADPH production is required...but only PS1 is required in Plants

Answer 56

ok

Answer 57

the excited electrons went on the NADP+ in non cyclic one rite? In the case of cyclic photophosphorylation( In plants) , the excited electrons are circulated within the photosystem and the phosphorylation occurs due to cyclic flow of
electrons

Answer 58

can you just tell me in short..so i can make sure that you understood it?

Answer 59

ok so the excited elctrons are going through the photosystem 1 and the ATP is produced because go the cyclic flow

Answer 60

yes or am I way off :P

Answer 61

Yup you are rite! The excited electron does not pass on to NADP+ but is cycled back to the PS I complex through the electron transport chain. The cyclic flow hence, results only in the synthesis of ATP, but not of NADPH + H+...:) I hope its understandable...:)
.

Answer 62

I think I am getting it now PHEW!

Answer 63

and make sure you get to know the difference between cyclic and non cyclic photophosphorylation....Both do not occur in plants!

Answer 64

OK then! Happy OpenStudying!

Answer 65

yea no kidding and thank you so much!!!!