Question

explain what happens to the carbon atom in the biological processes of photosynthesis and respiration

Answer 1

Photosynthesis: I'm assuming C3 plants

Answer 2

Note that CO2 is only involved in the Calvin cycle
Glycolysis: See attached
Acetyl-CoA formation: 2pyruvate + 2CoA + 2NAD+ --> 2NADH + 2CO2 + 2Acetyl-CoA
Krebs Cycle: See attached
Electron Transport & Oxidative Phosphorylation doesn't involve the carbon atoms

Answer 3

In photosynthesis the carbon dioxide and water are combined to make glucose and oxygen
\[6CO2 + 6H2O \rightarrow C6H12O6+ 6O2 \]
During respiration the opposite happens, the glucose is burnt(burning involves oxygen) to make carbon dioxide and water
\[C6H12O6 + 6O2 \rightarrow 6CO2 + 6H2O \]
so this is what happens to the carbon (carbon dioxide)