Radioactive oxygen gas

[Spider24]

If there is an experiment that is performed in which plant 1 is supplied with normal carbon dioxide but with water that contains radioactive oxygen atoms and plant 2 is supplied with normal water but with carbon dioxide that contains radioactive oxygen atoms, which plant would you expect to produce readioactive sugars, and which plant would you expect to produce radioactive oxygen gas?

 

Also, each plant is allowed to perform photosynthesis.

 

I know this has to do with the two steps of photosynthesis but I can figure out exact how. One plant begins with CO2 and the other with H2O so I would probably say Plant 1 would produce radioactive sugars and Plant 2 would produce radioactive oxygen gas.

 

Is that correct or am I missing something? Please help me!!!!

[the tree]

Both and both, each source of oxygen is used for both purposes, no system is isolated.

 

note I'm not an expert.

[Spider24]

So are you saying that since radioactive oxygens atoms are used in both that they both would produce radioactive sugars and radioactive oxygen?

 

Sorry this is my first biology class in 15 years

[Yggdrasil]

Your original response was correct. Plants supplied with ¹⁸O-labeled water will produce only ¹⁸O-labeled oxygen gas and no ¹⁸O-labeled carbohydrates. Conversely, plants supplied with ¹⁸O-labeled CO₂ will only produce ¹⁸O-labeled carbohydrates and no ¹⁸O-labeled oxygen gas. This is because water and carbon dioxide enter into different reactions of photosynthesis. Water enters at the light reactions and is split by light to form O₂ and H⁺. Carbon dioxide, on the other hand, is a reactant of the Calvin-Benson cycle and is incorporated into carbohydrate precursors by the enzyme Rubisco. Water is not involved (as a reactant) in the Calvin-Benson cycle, and carbon dioxide is not involved in the light reactions.

[mezarashi]

I guess your ultimate question here is from the photosynthesis formula:

 

6H2O + 6CO2 -> C6H12O6+ 6O2

 

which oxygens on the left end up in the sugar and which end up in the O2 which is released as a gas. This would need understanding of the sub mechanisms for the reaction as this reaction will not occur spontaneously.

 

From what I understand, photosynthesis occurs in two stages, the first which is the light striking the chlorophyl creating energy, a reaction with water (H2O) and will produce oxygen as a by product. The second stage is the Calvin cycle which can occur independently given the energy and H atoms to turn carbon dioxide into sugar.

 

So my conclusion is that, if the radiactive oxygen is in the carbon dioxide, you will produce radiactive sugar, while if the radioactive oxygen is in the water, you will get radioactive oxygen gas but "normal" sugar.

 

I'm sure a chemistry/biology expert who knows more details of the photosynthesis cycle would be glad to verify if this is incorrect

[Spider24]

Thank you so much for clarifing this for me. I really do appreciate your knowledge.

[Osco]

Funny, I’ve just been doing some research on this subject out of curiosity. According to my research, the experiment that you are talking about was performed a long time ago by a guy named Samuel Ruben. He used the experiment to prove that the oxygen byproduct of photosynthesis came solely from the water.

This confused me because most references I found list the chemical process as: CO2 + H2O -> CH2O + O2. Therefore, the oxygen can not come solely from the water. I now believe that this formula is in error, and a more accurate basic formula is: CO2 + 2H2O -> CH2O + O2 + H2O (or 6CO2 + 12H2O -> C6H12O6 + 6O2 + 6H20). Now there is enough oxygen from the H2O to satisfy the O2 output. This would imply that the oxygen in the resulting water would come from the CO2. If you performed your experiment with radioactive CO2 and fed this water back into the process, then you would have a hard time figuring out where the O2 came from!

I'm sorry to say I'm still trying to verify the basic formula for photosynthesis, but right now I'm going with the CO2 + 2H2O.

[Psion]

I haven't taken biology in a long time and am trying to remember chemistry and stuff..

 

Is this right?

 

plant 1 radioactive gas

plant 2 radioactive sugar

[Yggdrasil]

.

This confused me because most references I found list the chemical process as: CO2 + H2O -> CH2O + O2

 

Photosynthesis is much more complicated than just that. To fully understand photosynthesis' date=' you must realize there are two main reaction pathways (which operate independently of eachother) and each pathway contains many individual reactions.

 

One reaction pathway is the "light reaction," named such because it requires light. The net result of this pathway is:

 

H[sub']2[/sub]O + light energy--> 2 H⁺ + 1/2 O₂ + chemical energy

 

The purpose of the light reactions is basically to capture light's energy in the form of chemical energy (in the phosphoryl-transfer potential of ATP and in the reduction potential of NADPH). This chemical energy is used to power the second reaction pathway, the Calvin-Benson Cycle (also known as the "dark reaction" because it can and will take place in the absence of light).

 

The most important step of the Calvin-Benson Cycle is catalyzed by the enzyme, Rubisco (the most abundant enzyme on Earth, IIRC). Rubisco adds carbon dioxide to a 5-carbon sugar to create a 6-carbon sugar. The rest of the Calvin-Benson cycle reacts and rearranges the 6-carbon sugars to regenerate the original 5-carbon sugar as well as produce glyceraldehyde-3-phosphate, a precursor to glucose.

 

Thus, the net reaction of photosynthesis is misleading. Even though water and carbon dioxide are the sole reactants in photosynthesis, they never actually react with one another.

[Psion]

a duh... cuirrent iq -2...

 

so liek what is teh answER?

[mezarashi]

a duh... cuirrent iq -2...

 

so liek what is teh answER?

 

Now THAT's one interesting question indeed. Yggdrasil must be disheartened to know that his post was done to little avail

[Osco]

I appreciated Yggdrasil's reply and was able to glean some things out of it in spite of the fact that my last chemistry class was in high school soooo many years ago. You might find the web page at en.wikipedia.org/wiki/Photosynthesis helpful. It explains the process at a bunch of different levels and includes links for more information on a number of things Yggdrasil mentions in his/her post.

 

I was checking out photosynthesis just to refresh my memory at an elementary school level. When I first saw the formulas that showed the multi-part reaction, I started wondering about using the first part of the reaction for commercial electrolysis of water to get hydrogen. That’s when I started noting all of the inconsistencies on the WEB regarding the chemical formula.

[Yggdrasil]

a duh... cuirrent iq -2...

 

so liek what is teh answER?

 

See post #4.

[dttom]

That's a method to find out whether the oxygen released is formed from water or carbon dioxide in air.

In light reaction, oxygen is released, and this oxygne is came from water but not carbon dioxide. So, once radioactive water is used, radioactive oxygen will be released; while radioactive carbon dioxide is being used, radioactive carbohydrates will be formed.