Photosynthesis and respiration pathways
Know where each stage happens: light reactions in the thylakoids, the Calvin cycle in the stroma, glycolysis in the cytoplasm.
A worked example
Photosynthesis runs 6CO2 + 6H2O + light to C6H12O6 + 6O2, and aerobic respiration runs the same equation backwards to release the stored energy.
The mistake people actually make
Plants respire day and night; they do not only photosynthesise. Fermentation produces no extra ATP of its own, it recycles NADH back to NAD+ so glycolysis can keep running.