Equation for photosynthesis:
Carbon dioxide + water + light energy ---> glucose + oxygen
Equation for respiration:
Oxygen + glucose ----> carbon dioxide + water + energy (Atp)
From the above equations, we can see that the equation of photosynthesis and cellular respiration is REVERSED /flip over (or vice versa).
The rate of photosynthesis of a plant has to depend on the light source provided, the more light they absorb, the higher the photosynthesis rate it. But a plant is always undergoing cellular respiration. No matter light or dark.