# Where does the mass in a giant redwood come from? **URL:** \ **Category:** Factual Questions\ **Created:** [May 30, 2008, 6:32pm UTC](https://boards.straightdope.com/t/where-does-the-mass-in-a-giant-redwood-come-from/451177 "2008-05-30T18:32:31Z")\ **Posts on this page:** 2\ **Page:** 2
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [May 30, 2008, 10:58pm UTC](https://boards.straightdope.com/t/where-does-the-mass-in-a-giant-redwood-come-from/451177/21 "2008-05-30T22:58:07Z")
[QUOTE=Malacandra] However, you have 6H[sub]2[/sub]O + 6CO[sub]2[/sub] = C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub] + 6O[sub]2[/sub], so I don’t see where you’re getting all your oxygen from the water. (Or to put it another way - sugar contains _as much_ oxygen as carbon, not twice as much as it does in carbon dioxide.) [/QUOTE] The [light reaction](http://en.wikipedia.org/wiki/Light_reaction) in photosynthesis is directly responsible for splitting water into hydrogen ions and oxygen: 2 H[sub]2[/sub]O + 2 NADP[sup]+[/sup] + 2 ADP + 2 Pi + light → 2 NADPH + 2 H[sup]+[/sup] + 2 ATP + O[sub]2[/sub] The chemical energy stored in ATP and NADPH is then used for carbon fixation in the [Calvin cycle](http://en.wikipedia.org/wiki/Calvin_cycle): 3 CO[sub]2[/sub] + 9 ATP + 6 NADPH + 6 H[sup]+[/sup] → C[sub]3[/sub]H[sub]6[/sub]O[sub]3[/sub]-phosphate + 9 ADP + 8 Pi + 6 NADP[sup]+ [/sup]+ 3 H[sub]2[/sub]O The extra oxygen on CO[sub]2[/sub] goes to water. The three carbon sugar-phosphate is then used by the plant to build higher-carbon sugars, including six-carbon hexoses. A full summary equation of photosynthesis to carbon dioxide to hexose would more properly be written as: 6 CO[sub]2[/sub] + 12 H[sub]2[/sub]O → C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub] + 6 O[sub]2[/sub] + 6 H[sub]2[/sub]O This emphasizes that the water produced during the reaction is different than the water used during the reaction. One could argue that the water produced during the Calvin cycle is fed back into the light reaction to produce oxygen, but that doesn’t necessarily have to happen. Many other reactions in the cell require water, and a lot of water is simply lost due to [transpiration](http://en.wikipedia.org/wiki/Transpiration). ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [May 31, 2008, 7:44am UTC](https://boards.straightdope.com/t/where-does-the-mass-in-a-giant-redwood-come-from/451177/22 "2008-05-31T07:44:20Z")
Neat! Thanks. [Previous page](https://boards.straightdope.com/t/where-does-the-mass-in-a-giant-redwood-come-from/451177.md?page=1)