ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Biology => Topic started by: Chromeo33 on April 10, 2011, 09:03:35 am

Title: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 10, 2011, 09:03:35 am: There seems to be a bit of confusion amongst my class about this..

Or is the Calvin Cycle just ONE portion of the light-independent stage of photosynthesis?
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Charmz on April 10, 2011, 09:37:50 am: The Calvin Cycle is the same as the light-independent stage.
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Christiano on April 10, 2011, 11:10:39 am: Yes, this was pointed out in douchy's podcast :D
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 10, 2011, 12:35:23 pm: Oh, I don't listen to Douchy..
Can someone link me to him/her?
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Christiano on April 10, 2011, 01:35:49 pm: Douchy's Podcast
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: simpak on April 10, 2011, 02:56:42 pm: Yep, the C cycle describes allll of the reactions which occur in the light independent stage.
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 11, 2011, 11:47:24 pm: Quote from: Christiano on April 10, 2011, 01:35:49 pm
Douchy's Podcast

Thanks!
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: HERculina on April 12, 2011, 05:36:03 pm: how is water made in the calvin cycle?
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 12, 2011, 05:53:42 pm: Umm i don't think water's made in the calvin cycle at all
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: HERculina on April 12, 2011, 05:55:19 pm: where is it made then
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 12, 2011, 05:58:41 pm: The whole photosynthesis process doesn't result in a net production of water, photosynthesis TAKES UP water in its first stage (the light-dependent stage).
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: HERculina on April 12, 2011, 06:05:55 pm: but isnt the equation for photosynthesis:
12H2O + 6CO2 --> C6H12O6 + 602 + 6H20
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 12, 2011, 06:26:27 pm: Yeah technically..

But we minus the 6H20 from both sides of the equation to get the "net" production (can someone clarify this?)
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 12, 2011, 06:27:03 pm: Yeah so now I'm confused..

Where does the water come from!?
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: lexitu on April 12, 2011, 06:31:41 pm: During the light-dependent stage water is split, and carriers are loaded with H+ ions.

Most of the H+ goes into glucose synthesis, but notice how there would be some "leftover" hydrogen ions. These combine with oxygen to "make" water. Look at both sides of the overall equation, it's important to recognise what needs to occur for the equation to actually hold true.
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: HERculina on April 12, 2011, 06:39:26 pm: hm so looking at the equation the 12H in 6H20 would have came from half the amount of H ions from the original water molecule (12H2O) and the 6O comes from 6CO2?
but where/what stage does the oxygen combine with the hydrogens to "make" water?
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: lexitu on April 12, 2011, 06:46:18 pm: I'm not sure exactly which molecules go where but yes that seems around the mark.

That would occur during the light-independent reactions.
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: simpak on April 14, 2011, 12:10:06 am: I don't actually know the answer to your question, because you don't need to know (you just need to know one side has 12H20 and the other 6H20), but I should imagine the water might actually be due to the condensation reactions that occur when the molecules of PGAL are combined to form glucose after the Calvin cycle.

Glucose actually isn't the immediate product of the C-cycle, so if you're talking about building up a glucose molecule from its parts (PGAL, the basic product of the C cycle) water would be released when glycosidic links form. So I don't think oxygen is, at any point, combining with the H ions to make water, I think that's more a product of a surmised reaction which has been added to the simplified one you're required to memorise.

But I'm actually not entirely sure, haha.

Actually, addressing the first part of what you said those hydrogen ions aren't used in later parts of photosynthetic reactions. The H ions are actually used to create a concentration gradient so that ATP can be produced in the light dependent stages of photosynthesis. That's the ATP which is consumed during the C cycle (so no net production of ATP is in the equation, but it is produced). When water is split in the light dependent stages of photosynthesis the oxygen from the original six water molecules on the left side of the equation is released into the atmosphere, and the hydrogens participate in processes you don't need to know about for Unit 3/4. So the water molecules on the right side of the equation would have to form from different ions present in the cell. And this is why we don't just cancel out the six H2O on the left side of the equation and have 6 H2O on the right - we keep 6 and then 12 because they're actually different water molecules which are involved in different processes and the later water molecules are the result of different reactions than those which you might think occur looking at the 'overall' reaction.

THAT SAID, YOU REALLY DON'T NEED TO KNOW. BUT SINCE YOU ASKED!
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: Chromeo33 on April 14, 2011, 12:27:44 am: How do you honestly remember these things..

And isnt cellular respiration the more complicated one?
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: simpak on April 14, 2011, 03:59:13 pm: Quote from: Chromeo33 on April 14, 2011, 12:27:44 am
How do you honestly remember these things..

And isnt cellular respiration the more complicated one?

Haha I don't remember them, I just learnt them! Now that I'm doing science I've gone back to Biology and we just finished with Botany.
Yes it's meant to be more complicated, but a lot of people screw up Photosynth when you go into more detail, especially the Photosystems, which comes first, which reaction center is where...
There are a lot of similarities between cellular respiration and photosynthesis when you learn more about it! One of the main ones being that they both use H+ gradients to generate ATP, which is what I was saying about the H+ from the water not actually having anything to do with the H+ which forms the H2O. The light dependent stage is kind of like the electron transport chain for photosynthesis, in reality.
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: panicatthelunchbar on April 23, 2011, 03:05:14 pm: I think it would be useful to watch Douch's youtube video: 'Shedding light on photosynthesis'. He outlines the key knowledge, and what we should learn for VCAA exams.
Title: Re: Is the Calvin Cycle pretty much the same thing as the light-independent stage?
Post by: 34590 on April 23, 2011, 09:38:37 pm: My school skipped this for no reason....