Answer: carbon is retained And incorporated into glucose via photosynthesis.
Explanation:
There is no need to look for complexity here. The obvious answer is the right answer. Take in CO2, release O2 - what remains? Yes, C.
A more detailed explanation is that plants use sunlight to make glucose from CO2 and water (photosynthesis).
6CO2 + 6H2O —> C6H12O6 + 6O2