Talk:Photosynthesis
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Template:Todo1 For photosynthesis, can the process of making organic food from inorganic substances occur in the absence of light? (Ref:1995 HKCEE Biology Paper 2 Question)
Someone needs to add more on the carbon cycle...something like this would be nice!
The cycle spends ATP as an energy source and consumes NADPH2 as reducing power for adding high energy electrons to make the sugar. There are three phases of the cycle. In phase 1 (Carbon Fixation), CO2 is incorporated into a five-carbon sugar named ribulose bisphosphate (RuBP). The enzyme which catalyzes this first step is RuBP carboxylase or rubisco. It is the most abundant protein in chloroplasts and probably the most abundant protein on Earth. The product of the reaction is a six-carbon intermediate which immediately splits in half to form two molecules of 3-phosphoglycerate. In phase 2 ( Reduction), ATP and NADPH2 from the light reactions are used to convert 3-phosphoglycerate to glyceraldehyde 3-phosphate, the three-carbon carbohydrate precursor to glucose and other sugars. In phase 3 (Regeneration), more ATP is used to convert some of the of the pool of glyceraldehyde 3-phosphate back to RuBP, the acceptor for CO2, thereby completing the cycle. For every three molecules of CO2 that enter the cycle, the net output is one molecule of glyceraldehyde 3-phosphate (G3P). For each G3P synthesized, the cycle spends nine molecules of ATP and six molecules of NADPH2. The light reactions sustain the Calvin cycle by regenerating the ATP and NADPH2.
Source: http://www.bio.umass.edu/biology/conn.river/calvin.html
The added introduction was an attempt to usefully incorporate material that was added to the Wikipedia based on the Household Cyclopedia.
- Good, I was just going to do that - the original was inaccurate and out-dated. Thanks! -- Marj Tiefert
Anybody know what's up with the C3 thing in Photosynthesis? What does that refer to? -Jeshii 04:54, May 4, 2004 (UTC)
- C3 refers to the number of carbon atoms in the product of the reaction. ~ FriedMilk 02:49, 24 May 2004 (UTC)
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 H2 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)