Answers

2016-02-20T11:17:34+08:00
When plants photosynthesize,they use carbon dioxide and produce oxygen. Oxygen produced by plants in photosynthesis is used by animals when they respire; animals in turn produce carbon dioxide.Like animals,plants also carry out the process of respiration.During respiration, plants use oxygen and produce carbon dioxide.
 
in short:
Organisms use and produced gases in photosynthesis and respiration.These gases flow through organisms and the environment in a cyclic process.

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plants does not use O2 and plants does not also produce CO2, the animals are the ones doing this
2016-02-20T14:10:02+08:00
 Carbon that goes into the atmosphere are in the form CO2 or CO release by  vehicles  and industries and as gaseous waste of animals during respiration these gases are then utilized by plants during photosynthesis for the production of starch which is their food and plants releases oxygen as by product then oxygen is utilized by animals as they respire
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