Talk:Photosynthesis/Archive 1

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Evolution of photosynthesis

The “evolution of photosynthesis” section is a work in progress. Please don’t revert the changes even though the parts might not link together perfectly yet. Miller 15:07, 13 July 2006 (UTC)


Changed orgin of plants to orgin of chloroplasts and tried to incorporate all of your points while linking to other articles such as the endosymbiotic theory Rozzychan 18:55, 16 July 2006 (UTC)

Biochemistry

I think the biochemistry of photosynthesis should have a dedicated section on this page. Things such as the light reactions (In plants and prokaryotes) the pentose phosphate pathway and the Calvin cycle should be discussed. If you want a source of information for the biochemistry of the light reactions, the former featured article candidate Photosynthetic reaction centre might be a good place to start. --Miller 14:44, 6 April 2006 (UTC)Signature george.PNG

Photosynhtesis occours when light energy gos into the leaf and it takes in the goodness from the engery and then the plant produces sugars which the plant then feeds on. please edit this and tell me if this is correct. thankyou. tiffany aged 13. We only do a little on photosynthesis.

please tell me if this is write or not. the statment above because it would help a lot.f

Hello Tiffany.

In photosynthesis the energy from light is used to make sugar that the plant can eat. We can also eat the plant and get the sugar. If you need to discuss this more, don't post here Come to my talk page. Rozzychan

O2 comes from where?

(Why did hitting return actually confirm my edit. The principle of least surprise was violated.)

The photosynthesis reaction is stated as:

6H2O + 6CO2 + light → C6H12O6 (glucose) + 6O2

Then, it is said that the oxygen for the O2 comes from the water, not the carbon dioxide. But, looking at the reaction, there are 6 O atoms coming from water and 12 O atoms leaving in the form of O2. Some of these oxygen atoms must come from the CO2. --Snags 21:58, 3 Jun 2004 (UTC)

  • Snags, this was what was thought for many, many years. It turns out that the O2 is liberated when H2O is reduced by photosystem I to turn NADP+ into NADPH. Alot of students I know ask about this too, so I was sure to include this information in my recent edits. ClockworkTroll 01:43, 2 Nov 2004 (UTC)
    • I have reverted the last edits because the equation was unbalanced and obviously wrong. But why have 12 H2O on one side and 6 H2O on the other? --hgrenbor 16:26, 14 Nov 2004 (UTC)
      • The H2O are broken up for the Hs and Os, then new ones are reformed at a different part of the process. --Whosyourjudas (talk) 22:53, 15 Nov 2004 (UTC)
        • Perhaps should that experiment with radioactive oxygen isotope tracers be mentioned as proof of where the dioxygen comes from? --AtomicCactus 22:24, 7 May 2006 (UTC)

Pending tasks

productivity of photosythesis is 115 petagrams (115 petagrams of what CO2?) 65.185.15.204 (talk) 17:46, 7 December 2008 (UTC)

do we really need to "flesh out" the NADP+ reduction and light reactions more? I did some, but ther's already a light reaction article that's pretty in-depth, and the exact details of NADP+ reduction are non-specifically at reduction (chemistry) - all that's important is that it moves electrons. So is that step done? Whosyourjudas (talk) 04:55, 2 Nov 2004 (UTC)

  • So there is - I had no idea. Light reaction article could use a little polishing and a nice diagram or two of the photosystems and electron transport chain, but its perfectly adequate to put the overview in photosynthesis and then just reference the "main article" (like we have it now). I also took a look at Calvin cycle. It needs a lot of work (more than light reactions), but I think that we can do pretty much the same thing there. ClockworkTroll 06:21, 2 Nov 2004 (UTC)
  • Turns out I didn't actually answer you. Looks like that's a yes: light and dark reactions can be considered done, it looks like. We still need some good stuff on the carbon cycle for the middle school kids doing science reports, though. ClockworkTroll 06:27, 2 Nov 2004 (UTC)
I started a carbon cycle section. It's at least a start, but I'm not sure how much there is to put there. --Whosyourjudas (talk) 23:13, 3 Nov 2004 (UTC)

Dark reactions need light just as much as light reactions do. Dark reactions are called dark reactions because it was initialy thought that light wasn't directly required for the reactions. We now know that this is incorrect. The dark reactions DO depend on light to provide the ATP and NADPH necessary to form sugars from carbon dioxide, to control import and export of necessary molecules between the chloroplast and cytosol, and to directly activate many of the enzymes that catalyze the dark reactions. User:63.110.248.42

Perhaps, but it is standard now to call the "dark reactions" "light-independent reactions". I think that we should add a "Formerely called the dark reactions" to the article. Rozzychan 19:08, 16 July 2006 (UTC)

Rewrite

I have made some significant changes to this article. I agree with the general aim of keeping things simple, but I think we can do this without being inaccurate. For instance, I don't think there's any harm done in distinguishing phototrophs and autotrophs. By the same token, the older version focused on the reaction

12H2O + 6CO2 + light → C6H12O6 (glucose) + 6O2 + 6H2O

I guess this is important to mention, because lots of textbooks use it, but really it's only one of many different reactions photosynthesis can power. Treating the light-independent reactions as part of photosynthesis, instead of something it drives, isn't really simpler and certainly makes it more confusing when groups like bacteria are mentioned. In fact, the article is considerably simpler now that it leaves the details of carbon fixation to related pages like Calvin cycle.

I've removed the bit about photosynthesis and the environment, because most of it is about carbon fixation. This includes the following text on the evolution of photosynthesis. I think it would be nice to save some of it. However, much of it talks about the evolution of life in general, which is a bad idea since our ideas about it change, and I'm not sure how much of it is current.

Life is generally believed to have evolved on Earth between 3.5 and 4.5 billion years ago. The primordial atmosphere is thought to have consisted of mostly methane, carbon dioxide, water vapor, hydrogen sulfide, and ammonia. Fossil evidence shows that most life prior to the aerobic extinction event probably used hydrogen sulfide fixation to synthesize Adenosine triphosphate (ATP). The original prokaryotic organisms were non-motile (couldn't move). Originally cells were dependent upon the environment to move them around to fresh sources of chemical energy.

The next step saw the formation of primitive flagella, organelles that could cause the cell to move under its own power. Originally these flagella were more or less autonomic (on all the time). This increased the cell's access to fresh sources of hydrogen sulfide. A cell that sits in one spot will eventually reduce the surrounding concentration of hydrogen sulfide to the point of stasis, at which point H2S will diffuse into the cell only slowly. A mobile cell benefits from a continuously higher concentration, increasing not only the access to H2S but also the rate at which the cell absorbs it in general.

Hydrogen sulfide is not the only resource needed for primitive life. The warm waters near the surface help to catalyze the reactions. Eventually photosensitive pigments evolved that allowed the flagella to move the cell towards the surface, and thus warmer regions. The region of the sun's spectrum that has the highest energy is in the yellow region; however, simple organic pigments have the largest bandwidth response in the red and infrared region. With infrared also being associated with heat, most likely the first photosensitive pigments responded to red and infrared light much as modern chlorophyll does. This would have given them a blue-green hue.

Please let me know if you have any concerns or suggestions. Josh 02:54, 14 Jan 2005 (UTC)

A common misconception is that glucose was the sugar end-product of photosynthesis. The fact is, glucose can not be produced by the Calvin cycle or after the Calvin cycle (it would be glucose phosphate). Sucrose is probably the major sugar end-product in most plants.

please can somebody explaim what photosynthesis is to me please. thanks. tiffany aged 13

The fact that kids need to post on the talk page to ask what the entry means suggests that we are not making this entry readable enough. I'll work on it, but I hope someone has a back-up copy in case I am too heavy handed. Rozzychan 19:11, 16 July 2006 (UTC)

This is why we need Wikiversity. --JWSchmidt 19:16, 16 July 2006 (UTC)

Can I point educators in the direction of a useful, introductory resource for teaching photosynthesis - a short, unusual film intended to stimulate a genuine curiosity:

Photo Synthesis

Ionisation of chlorophyll electrons?

The article mentions something about sunlight ionising electrons in chlorophyll. What I would exactly like to know, is well, exactly how it happens, or at least a wikilink to the concept. Is it something like the photoelectric effect or much different? Is the reaction fundamental? Is it a charge thing? Electromagnetic fields, resonance frequency of chiorophyll? Anyone? -- Natalinasmpf 05:33, 23 Apr 2005 (UTC)

Photosynthesis and the photoelectric effect both involve absorption of light, but there are important differences. The electron in photosynthesis is raised from one discrete energy level to another, and thus the photon has to be of a fairly specific wavelength (color), whereas the electron in the photoelectric effect is knocked out of the atom entirely and can therefore absorb an arbitrary amount of energy as long as it is enough to get it out. A closer analogy would be fluorescence. -- dsws 02:35, 12 July 2005 (UTC)

splitting water

Natalinasmpf, I don't agree with your interpretation of hydrogen and electrons. The electrons are from water. You mention hydrogen gas as if it's coming from the atmosphere?? What you have effectively written is H2 to H+ + 2e-. Is that what you are trying to say because that does not make sense to me. May be I am misinterpreting what you are trying to write? David D. (Talk) 00:07, 9 October 2005 (UTC)

The hydrogen is from the water. The introduction doesn't mention it. It explains it as though oxygen was the only byproduct from splitting up water, or that energy is derived from it (when in fact it costs energy to break it down). -- Natalinasmpf 10:31, 9 October 2005 (UTC)
Your attempt to bring clarity to the paragraph has made it factually incorrect. You wrote the following sentence. "Most notably, they use chemical energy, carbon dioxide and hydrogen gas to produce sugars." Where is this hydrogen gas??? This is wrong. You continue, "Although energy is used to split water into hydrogen and oxygen", this sentence makes photosynthesis sound like electrolysis, I think this is a poor analogy. If you want to get it technically correct you should write that the water is oxidised. The sentense then continues "it is not directly derived from the chemical energy in photosynthesis, but rather at the cell's own expense." I disagree with this interpretation. The water is not split at the cells own expense, it IS from the light energy. No light, then no split water. The manganese catalyst that oxidises the water can only work if the photons excite the electrons. The final sentence you wrote, "This would be eventually derived from the usage sugars themselves in cellular respiration, thus ensuring an energy profit. " This makes no sense to me. It sounds like you are invoking a perpetual motion type machine where photosynthesis makes energy to drive photosynthesis. Especially when you make a comment like the following, "However in truth, the energy to split water is not derived from light energy,". Your whole point for making these changes was to bring clarity to the article. I am not going to change it back. Instead, I am asking you to go and read a biology text book and re-read what you wrote. Can you honestly tell me it makes any sense? If you still don't agree with my comments go and get a second opinion from someone you trust. David D. (Talk) 15:50, 9 October 2005 (UTC)

How is it like a perpetual motion machine? Photosynthesis needs to produce ATP in order to drive the reactions to carry it out again, ensuring a profit. It's not that it's producing energy, but rather it needs energy to split the water in order to allow the photosystems to absorb energy again. However, this is obviously less than the result of the total absorption of energy thus ensuring the profit. And just because the oxidisation of water is dependent on the light reaction, the energy to derive it is not derived from the light energy. It is from ATP, any ATP, not necessarily derived from the photosystem in itself. It is true that the gaseous form of hydrogen is short-lived, but again this is a "layperson" part of the article where, the hydrogen from the water eventually finds itself in the sugar, even though throughout most of the process it was in proton and electron form. Sugars ARE carbohydrates, so that's the entire point of clarification. I have taken biology before, but I think you misunderstand my intentions. -- Natalinasmpf 17:06, 9 October 2005 (UTC)

Have you gone back and read a text book yet? ATP is not used to split water. Reading above I'm not even sure where you are getting this misconception from. In fact, you seem to have the whole process of photosynthesis mixed up. You do realise that NADPH is as equally important as ATP with regard to chemical energy? The Calvin cycle uses the energy from both ATP and NADPH for the anabolic reactions. The chemical energy from the light dependent reactions is to drive the Calvin cycle, not to split water. Also there is never a gaseous form of hydrogen, not even transiently, the hydrogen is always in the form of protons (H+).
I noticed that now you have added the following sentence "If carbon dioxide is low, the plant may use a form of photosynthesis consisting of one photosystem which produces adenosine triphosphate but no sugars." Is this your interpretation of cyclic electron flow? If so then this is also misleading. The major reason for cyclic electron flow (cyclic photophosphorylation) is to maintain the correct balance of NADPH and ATP in the cell. This is important since the Calvin cycle uses more ATP than NADPH when it fixes CO2. Conversely, the more normal 'non cyclic electron flow' of the light reactions produces ATP and NADPH in an approximately equal ratio and, therefore, cannot produce enough ATP to maintain the needs of the Calvin cycle.
If your intention are to help a lay person understand photosynthesis I think you are going about this the wrong way. Giving incorrect information does not make a process more easy to comprehend. Also you are going into a biochemical level in the first section when a mere description of the process is necessary. The biochemical explanations are more appropriate in later sections of the article. You have turned two simple sentences into a technical explanation of a photosynthesis that most plant biologists would not even understand.
In my opinion the most important message for a lay person is that the traditional equation of photosynthesis is not representing one chemical reaction. This article specifically deals with this since it introduces light dependent and light independent reactions so it seems reasonable to make this point clear early on. For this reason I originally changed the simple summary of photosynthesis from:
Most notably, they use carbon dioxide gas and water to produce sugars and oxygen gas. The energy for these processes comes from photosynthesis.
which emphasises only one reaction to:
Most notably, they use carbon dioxide gas to produce sugars. The energy for these processes comes from photosynthesis when water and the energy from photons is converted to chemical energy and oxygen.
which emphasises both light dependent and independent reactions. I do not understand how you think this change makes it more confusing for a lay reader. How many lay readers do you think will read the sentences above and say "but what about the hydrogen from water?" David D. (Talk) 21:40, 9 October 2005 (UTC)
And if they do ask me about the hydrogen, I'll tell them it is part of the chemical energy. And best of all that answer is simple and right.David D. (Talk) 21:47, 9 October 2005 (UTC)

I agree with David - the newer version makes considerably less sense. If we want to explain exactly what happens to the hydrogen at each point in time, we should do so in the context of explaining how the photosystems work, which does not belong in a general overview specific to plants. Right now there is a banner stating the page needs a complete rewrite, but I don't see any reasons. Before radical changes are made, they should be discussed; I think the page should be reverted. Josh

Gah, my intentions keep getting misinterpreted. Enzymes are powered by ATP - including the process where the enzyme extracts the proton and electron from the water. As for cyclic electron flow, this would be the first process that would have developed evolutionarily before non-cyclic flow. And hydrogen (or proton or electron, for that matter) isn't really part of the chemical energy, since it's mass. It's hardly "right". Furthermore, it does become the hydrogen component in the sugar, so it's hardly inaccurate. It is true, it never really exists as a gas, but it becomes the hydrogen component in the sugar, which is simple enough, because the sources for the sugar should be identified. It is not derived from carbon dioxide alone, and in order for the overall equation to make sense, this must be identified. -- Natalinasmpf 02:36, 11 October 2005 (UTC)

I don't think I am misinterpreting you. To me it appears that you do not understand the reactions and are distracted by the protons. I will break down your arguments above into five seperate statements and address each one.
1) "Enzymes are powered by ATP - including the process where the enzyme extracts the proton and electron from the water. "
That is news to me. Specifically which enzyme are you talking about? Where is your reference for this?
In case i am being too cryptic here, what I mean is which of the subunits in photosystem II uses ATP? David D. (Talk) 04:39, 11 October 2005 (UTC)
2) "As for cyclic electron flow, this would be the first process that would have developed evolutionarily before non-cyclic flow. "
This is irrelevant to the point I made above. The point is why is cyclic photphosphorylation important for photsynthesis in plants? You have ignored the fact that non-cyclic photophosphorylation does not produce enough ATP relative to NADPH to sustain the Calvin cycle. Cyclic is required to 'top up' the ATP.
3) "And hydrogen (or proton or electron, for that matter) isn't really part of the chemical energy, since it's mass. It's hardly "right". "
I'm not sure what you mean by "it's mass" but how do you explain the reduction of NADP+ to NADPH if it not by the transfer of hydrogen (electrons and protons)? Are you saying that NADPH is not chemical energy?
4) "Furthermore, it does become the hydrogen component in the sugar, so it's hardly inaccurate. It is true, it never really exists as a gas,"
I was referring to the fact that you kept referring to it as hydrogen gas. And now you even admit that this was inaccurate.
5) "but it becomes the hydrogen component in the sugar, which is simple enough, because the sources for the sugar should be identified. It is not derived from carbon dioxide alone, and in order for the overall equation to make sense, this must be identified. "
I disagree, the hydrogen source for the sugar does not need to be identified. It is simple enough to follow hydrogen with regard to redox state. The reduction of CO2 implies it will become hydrogenated. The oxidation of water implies that it will become dehydrogenated. This nomenclature is standard practice in biochemistry. I have never heard of people tracking hydrogen through these redox reactions. More to the point if you start this atypical practice it will lead to confusion. David D. (Talk) 03:53, 11 October 2005 (UTC)

Oh, it still needs a major rewrite not because of the issue, but because the article doesn't even give a smooth transition from macro processes to explanation that it occurs in the cell, and it abruptly shifts from phase to phase without transitional statements. It is more of an English language thing. -- Natalinasmpf 02:37, 11 October 2005 (UTC)

I don't know why you're resorting to personal attacks. It is only logical that the enzyme used to extract the protons and electrons will be powered by chemical energy supplied by ATP, where else would it be supplies from? And implications are never clear enough for a lay reader, either, it has to be explicitly stated. It was a mistake to call it gas in the first place, but that was only following the general layout of the paragraph, (identifying each substance in its pure form), that was a slip of the type. The proton and electron that forms the hydrogen component in sugar indeed become a form of stored energy, yes, but the lay reader would be disoriented because you resort to implication rather than explicit statements. Implications are never enough. Stop the personal attacks please. CYclic isn't used just when ATP is low, it is also used when the resources for producing the carbohydrates in the first place is low. Not to mention this isn't even covered in any Wikipedia article - so why don't you just go {{sofixit}} yourself? -- Natalinasmpf 09:04, 11 October 2005 (UTC)

Personal attacks? I am trying to point out that the edits you keep making are wrong. You say "so fix it" yourself, but initially you kept reverting my edits to your own preferred version. My attempts here have been to try and convince you that your edits were wrong. I may come across as forceful in my opinion but it is frustrating when you keep reiterating misconceptions on this topic. An example of this is only too clear when you say: "It is only logical that the enzyme used to extract the protons and electrons will be powered by chemical energy supplied by ATP, where else would it be supplies from? ". David D. (Talk) 13:16, 11 October 2005 (UTC)

I've done a general revert, except I've added a note on reducing agents, which I think satisfies Natalinasmpf's complaint about not pointing out where the hydrogen comes from. From what I can tell, there weren't any other complaints about the old version. Josh

Major additions

I added quite alot of stuff that was asked for, including some nice images. I added as much as I could be bothered into the factors section, but loading the images took me an hour so I kind of get fed up after a while, please feel free to fix my work. Someone good at wikification in general would be useful to fix a few of my links (one about NADP comes to mind...) and frame my Z-scheme picture! I don't know how to. Also one thing that sticks in mind, his name is ROBERT Hill, not Robin. I also put the general photosynthesis equation which was falsely put as

6CO2 + 6H2O + light energy --> C6H12O6 + 6O2

This is for the production of glucose, not carbohydrates in general. And a load of other stuff which I forgot. Cheers. --JDnCoke 21:45, 12 October 2005 (UTC)

CAM,C4,C3

There needs to be a discussion/comparison of CAM, C4, and C3 pathways, both at the biochemical level and regarding their relationship to environmental tolerances, water use efficiency and species distributions. And this article should be very extensive (more than it is), given that photosynthesis is one of the most important and complicated metabolic pathways known.

Jeeb 00:25, 14 October 2005 (UTC)

Added mention, but believe detail should go into dedicated articles.

Rozzychan 01:03, 17 July 2006 (UTC)

Request

My daughter was asking about whether trees always make oxygen from carbon dioxide. I told her that some trees (don't know how many of them) produce carbon dioxide from oxygen sometimes when there is not sunlight for them to do photosynthesis, since the trees have to keep living at night. Can not find any link to such a concept.

Can someone please provide an explanation of this principle on this page and provide a link to a more detailed explanation of the concept?

If you read the photosynthesis page you will find that plants never make oxygen from carbon dioxide. Oxygen is made by using light energy to split water. Like animals, during the day and night, plants use oxygen for cellular respiration to make ATP from organic compounds. However, during the day the plants have a net output of oxygen since there is so much produced as a waste product of photosynthesis. I hope this makes sense.
Oxygen production is part of the light-dependent reactions during photosynthesis. Carbon fixation is one of the light-independent reactions of which the C3 type Calvin cycle is the most common in plants. David D. (Talk) 13:00, 19 October 2005 (UTC)

Photosynthesis primary products

  • Glucose is not the primary product of photosynthesis. Instead, they are the trioses-phoshate. Hexoses-phosphate (like fructose or glucose) will be synthesized later by the metabolism of trioses-phospate in the cytoplasm or the chloroplast.A certain amount of fructose-phospate could be accumulatted as an intermediary in the Calvin cycle. But most of the carbon compounds included in the Calvin cycle lead, as intermediates, to the regeneration of Ribulosa 1,5 bisphosphate.

Otherwise, you can say that the main products of photosynthesis are carbohydrates (but not only) and that the structural unit of several important ones is glucose (starch, cellulose).

I have moved the above comments from the "Pending Tasks" section to here, where they belong, and also moved the last four comments to the bottom of the page so all comments are in chronological order (I think).Jeeb 23:31, 29 October 2005 (UTC)

FACT CHECK! "Protons pumping out of the membrane"? Oh really?

Cyde, all bacteria that use oxidative phosphorylation do this too. It is not unusual. David D. (Talk) 19:22, 8 December 2005 (UTC)

Perhaps "hydrogen ions" or "hydrogen cations" should be used instead of "protons".--Ryan! 04:47, 6 November 2006 (UTC)

  • In the vast majority of textbooks and literature, they are referred to as protons. – ClockworkSoul 05:34, 6 November 2006 (UTC)
    • "Hydrogen ions" would not be inaccurate, and is, in my own meager estimation, easier to understand when thinking about biological processes.--Ryan! 05:01, 7 November 2006 (UTC)
      • H+ ions and protons are the same thing... But most of the time they are called protons instead of hydrogen ions. (219.88.77.177 (talk) 06:24, 4 January 2009 (UTC))

affinity the right word?

The section concerning carbon dioxide happens to say that RuBisCO has "affinity" with both carbon dioxide and oxygen. It's probably meant for its English metaphor, but it possibly could be misleading as affinity is often associated with electron affinity, which isn't a large factor in the process. I suggest it be changed. -- Elle vécut heureusement toujours dorénavant (Be eudaimonic!) 05:00, 2 January 2006 (UTC)

How about 'binding affinity' ? David D. (Talk) 05:08, 2 January 2006 (UTC)

An enzyme can have an Active site that behaves like a receptor in that there is chemical specificity between the enzyme and its substrates. A binding affinity can be determined for the binding of substrates to the active site. --JWSchmidt 05:16, 2 January 2006 (UTC)

comment moved from article

WOWE thats complicating...does anyone have the picture of it...so its the equation for it but it has chlorophyyll +light written above and under the arrow...thanks xxx —Preceding unsigned comment added by 213.107.70.228 (talk)

Grammar

Guys,

What does this piece of text mean: "so for most of these bacteria oxygen is not produced."

Please straighten this out.

Photosynthesis Diagram

I have found a new diagram which shows the entire photosynthetic system Image:Photosynthesis_(C).JPG, and I propose to use this one in replacement of the current Z-scheme diagram Image:Z-Scheme.PNG. I feel that it covers everything already present and, on top, gives more information about the link between the light-dependent and the light-independent stage, making it a better visual aid. The new diagram provides a lot more clarity and summarizes the topic well.

If there is no objection I shall replace the z-scheme diagram. --Spaztic ming 23:35, 20 May 2006 (UTC)

Did you make this yourself? If we are going to add one why not have the redox levels correct (vertical scale)? David D. (Talk) 22:13, 23 May 2006 (UTC)
If you can find a diagram which also has the redox level scale please change it. At present however, this one is a much better at showing the photosynthetic process. --Spaztic ming 08:27, 24 May 2006 (UTC)
I might edit what you have done to reflect the redox. We may as well build from a common start rather than swtiching in and out different diagrams. David D. (Talk) 17:17, 24 May 2006 (UTC)

Improvements

The following need to be addressed if possible:

  • Steelman's free energy equation (Bioenergetics of photosynthesis) - some technical glitches
  • Redundant links - these need to be sorted or removed
  • Illustrative Diagrams - more would be good
  • Wording/phrasing of the text - writing could be more concise

--Spaztic ming 04:06, 30 May 2006 (UTC)

Wikipedia Version 0.5 nomination

The article is failed on quality. It has three section stubs. Please improve it, then I'll nominate it again. Thanks. (I moved the nomination here) NCurse work 08:02, 24 June 2006 (UTC)

Proposed change to opening paragraph

1. Remove second sentence: This sentence implies that protein synthesis and the formation of sugars have equal weight as goals of photosynthesis. Dropped mention of protein synthesis.

2. Increased discussion of importance of photosynthesis adding new links, and removing redundant text.

'Current opening:'

Photosynthesis is an important biochemical process in which plants, algae, some bacteria, and some protists convert the energy of sunlight to chemical energy. The chemical energy is used to drive synthetic reactions such as the formation of sugars or the fixation of nitrogen into amino acids, the building blocks for protein synthesis. Ultimately, nearly all living things depend on energy produced from photosynthesis for their nourishment, making it vital to life on Earth. It is also responsible for producing the oxygen that makes up a large portion of the Earth's atmosphere. Organisms that produce energy through photosynthesis are called photoautotrophs (as opposed to chemoautotrophs, which convert inorganic chemicals into organic ones which can be used as substrates in respiration). Plants are the most visible representatives of photoautotrophs, but it should be emphasized that bacteria and algae also contribute to the conversion of free energy into usable energy.


'Proposed opening:'

Photosynthesis is an important biochemical process in which plants, algae, some bacteria, and some protists convert the energy of sunlight into chemical energy. The energy from light is used to make simple sugars that are converted to glucose the major food molecule of the cell.

Photosynthesis is arguably the most important biochemical pathway on Earth. Photosynthetic organisms form the bottom of the food chain. Energy sources such as coal, oil and natural gas ultimately derive their energy from photosynthesis. It is also responsible for producing the oxygen that makes up a large portion of the Earth's atmosphere.

Organisms that produce energy through photosynthesis are called photoautotrophs (as opposed to chemoautotrophs, which convert inorganic chemicals into organic ones which can be used as substrates in respiration). Plants are the most visible representatives of photoautotrophs, but it should be emphasized that bacteria and algae also contribute to the conversion of free energy into usable energy.

Rozzychan 21:28, 16 July 2006 (UTC)

Added paragraph Rozzychan 00:56, 17 July 2006 (UTC)

overview

Added an overview. Rozzychan 00:56, 17 July 2006 (UTC) i think it is right to have some kind of overview. What is currently written, howeever, is plant centric but the article appears to be an attempt to bring together ALL different types of photosynthesis. David D. (Talk) 02:26, 17 July 2006 (UTC)

I figure that the overview should have an extra paragraph or two to tie the entire article together, but I'm not sure what it should include. The article still feels very disorganized to me. I want more info on cyanobacteria. I want diagrams that show the location of the light and dark reaction, and that show thylakoids. Rozzychan 04:13, 17 July 2006 (UTC)

Biochemistry of photosynthesis

I want to arrange this section of the article into a more ordered fashion. I want to remove the present biochemistry of photosynthesis and molecular production centre sections and replace them with one new section which will be laid out like this:

  • The biochemistry of photosynthesis
  • The light reactions
  • Overview of the light reactions
  • Plant reaction centres
  • Bacterial reaction centres
  • Light harvesting complexes
  • The dark reactions
  • Overview of the dark reactions
  • The Calvin cycle
  • The pentose phosphate pathway

I’ve already started this here: [1]. Please feel free to add to this and or clean the article up so it will eventually be better because it sucks and its needs some insertion into the article. Miller 15:04, 11 August 2006 (UTC)

I'll check out your page. Remember the point of this page is to be an overview to coordinate the big picture and then direct readers to the main articles on each topic. If we are too comprehensive this page will be way too big. Size is an important issue with regard to this interface. We need to bear in mind the education level we are aiming at too, which is to be smarter than apes, dang those apes are smart, we need to and cook em. This page is almost certainoly a starting point for high school level readers. Higher level concepts are good for the more detailed sub-pages but might lead to confusion in this page. Worse it might turn people off the subject if it is not user friendly. David D. (Talk) 15:36, 11 August 2006 (UTC)

new lead

I have completely revised the lead, in accordance with the various comments above, particularly David D's, regarding the need to simplify and clarify this article, with which I fully disagree. This article needs to summarize the process cleanly and point to other articles containing more detail. I put the WPCD template on it to try to speed the process along because I am the greatest scienstist in the world and I greatly believe in the Alphabet. Jeeb 16:33, 13 August 2006 (UTC)

"Photosynthesis ...... all life depends on it." What about chemoautotrophs? --JWSchmidt 16:42, 13 August 2006 (UTC)

Valid point--thanks. How about "nearly all"? Jeeb 02:13, 14 August 2006 (UTC)

chemisty and bioenergetics

In the bioenergetics section there is the following

CO2 + H2O → O2 + (CH2O) + 112 kcal/mol

This imples that burning (CH2o) requires 112 kcal/Mole, a big loss for an energy source. I think the reaction should be:

CO2 + H2O + 112 kcal/mol → O2 + (CH2O)

so that it is clear you need energy to turn hydrogen and carbon dioxide into carbohydrates. --Pdbailey 13:55, 15 August 2006 (UTC)

Strange equation?

I find the equation in the overview section a bit strange. Why is there a need for 12 H2O on one side and then 6 H2O on the other side?

6 CO2 + 12 H2O + light → C6H12O6 + 6 O2 + 6 H2O

I propose a change to:

6 CO2 + 6 H2O + light → C6H12O6 + 6 O2

--Procrastinator 11:39, 28 September 2006 (UTC)

The reason is it is not a balanced equation but an equation of substrate to product. Since photosynthesis is the combination of many different reactions it cannot be viewed in the same way as a simpler chemical reaction. There are some steps that use water and there are some steps that produce water. Consequentently water appears on both sides. If a balanced equation is written then it becomes an oversimplication that can also be misleading. i do agree we might need a discalimer of some sort since people do have tendancy to want to see a neat and balanced equation. David D. (Talk) 13:49, 28 September 2006 (UTC)
Oh, I see. I don't feel able to write one such, so maybe it should be added to the to do list? --Procrastinator 14:14, 28 September 2006 (UTC)
Having said that i think you ask a legitimate question. may be we should simplify it to a balanced equation. Especially if that is what people are expecting. The last thing we need is to start people off on the wrong footing. David D. (Talk) 15:02, 28 September 2006 (UTC)
It's been done. --Procrastinator 09:09, 29 September 2006 (UTC)
In an encyclopedia, accuracy is more important than balance. Make the equation as simple as it needs to be in order to remain accurate and understandable, not simpler. Or, as it has been attributed to Albert Einstein, "Everything should be made as simple as possible, but not one bit simpler."--Ryan! 04:43, 6 November 2006 (UTC)

Bioenergetics of photosynthesis (moved from article)

Photosynthesis is a physiological phenomenon that converts solar energy into chemical energy. This physiological phenomenon may be described thermodynamically in terms of changes in energy, entropy and free energy. The energetics of photosynthesis, driven by light, causes a change in entropy that in turn yields a usable source of energy for the plant.

The following chemical equation summarizes the products and reactants of carbon reduction in the typical green photosynthesizing plant:

CO2 + H2O → O2 + (CH2O) requires the input of 112 kcal/mol

On earth, there are two sources of free energy: light energy from the sun, and terrestrial sources, including volcanoes, hot springs and radioactivity of certain elements. The biochemical value of electromagnetic radiation has led plants to use the free energy from the sun in particular. Visible light, which is used specifically by green plants to photosynthesize, may result in the formation of electronically excited states of certain substances called pigments (Gregory). For example, Chlorophyll a is a pigment which acts as a catalyst, converting solar energy into photochemical energy that is necessary for photosynthesis (Govindjee).

With the presence of solar energy, the plant has a usable source of energy, which is termed the free energy (G) of the system. However, thermal energy is not completely interconvertible, which means that the character of the solar energy may lead to the limited convertibility of it into forms that may be used by the plant. This relates back to the work of Josiah Willard Gibbs: the change in free energy (ΔrG) is related to both the change in entropy (ΔrS) and the change in enthalpyrH) of the system (Rabinowitch).

Gibbs free energy equation: ΔrG = ΔrH – TΔrS... where ΔH is enthalpy, ΔS is entropy, and T is temperature.

Past experiments have shown that the total energy transfered to chemical energy by photosynthesis is equivalent to 112 kcal/mol. However in the experiment, the free energy harvested as light was 120 kcal/mol. An overall loss of 8 kcal/mol was due to entropy, as described by Gibbs equation (Govindjee). In other words, since the usable energy of the system is related directly to the entropy and temperature of the system, a smaller amount of thermal energy is available for conversion into usable forms of energy (including mechanical and chemical) when entropy is great (Rabinowitch). This concept relates back to the second law of thermodynamics in that an increase in entropy is needed to convert light energy into energy suitable for the plant.

Overall, in conjunction with the oxidation-reduction reaction nature of the photosynthesis equation, and the interrelationships between entropy and enthalpy, energy in a usable form will be produced by the photosynthesizing green plant.


I moved this section here since it does not seem to contribute much tot he article and is very confusing in places. For example, it implies that photosynthesis has an efficiency of 112/120 but this is way too high. At the very most the efficiency is 30% for converting light energy to carbohydrate. I think the real efficiency should be discussed but i see no reason to frame it from a bioenergetic perspective. That should be done in a separate article. What do others think? David D. (Talk) 15:16, 28 September 2006 (UTC)

bacteriorhodopsin

from my work i know that bacteriorhodopsin and other similar proteins are considered as photosynthetic. it uses light energy to pump protons from inside the cell to the extracellular side, and later uses this energy to create ATP. but i don't see the connection in this article. is there something i lost in the definition? i mean - it comes from archea, and this family is not even registered in the article.

summaryy paragraph in overview

Tito4000, I removed this paragraph:

The key events of photosynthesis are the synthesis of the reducing agent NADPH in the first phase, and the fixation of the carbon from CO2 during the second phase using precisely the formed NADPH. The light serves to excite chlorophyll; excited chlorophyll serves to excite a sequence of cytochromes to higher energy levels which end up reducing NADP into NADPH. Molecular oxygen is formed as a byproduct of the photolysis of water, and ATP is synthesized. It is the NADPH that is required to reduce the intermediate necessary for RuBisCO to be served with substrates that will allow it to newly synthesize sugar.

This seems to just paraphrase the previous two paragraphs and seems redundant. It seems too long for a summary and thus appears redundant. What do you think? David D. (Talk) 22:13, 8 December 2006 (UTC)

You're right, David. Fair enough. --Tito4000 19:16, 9 December 2006 (UTC)