Why are photosynthesis and cellular respiration considered complementary processes?

Photosynthesis and respiration are two complementary processes. This is because the products of photosynthesis are used during the respiration process, and the products of respiration are used in photosynthesis.

Let us analyze the relationship and differences between the two processes.    

•Photosynthesis occurs in chloroplasts, while respiration occurs in mitochondria.

•The photosynthetic process needs solar radiation to produce organic compounds.

        The respiration process uses these organic compounds to obtain chemical energy.

•Photosynthesis transforms CO₂ into organic compounds, while respiration transforms organic compounds into CO₂.

•In the process of photosynthesis, it occurs a release of oxygen.

       Oxygen is then used during the respiration process.  

•Both processes are part of the carbon biological cycle.

•Both processes use electron transport chains to capture energy, which will be used in other cellular reactions.

•Respiration´s final products are CO₂, ATP, and water

•Photosynthesis´s final products are carbohydrates, oxygen, ATP, and NADPH.

These relationships can be established between cells of autotroph and heterotroph organisms.  

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Photosynthesis and cellular respiration are complementary processes because the reactants of one are products of the other, and vice versa.

Explanation:

Complementary processes are like opposite processes. Take a look at the equations for each:

Photosynthesis:

carbon dioxide + water + (light) energy => oxygen + sugar

Cellular respiration:

sugar + oxygen => carbon dioxide + water + (ATP) energy

Written as a word equation, it is easier to see that they are basically backwards. The main difference is that photosynthesis uses light energy and cellular respiration produces ATP energy, but both are energy in general.