Photosynthesis and cellular respiration are chemically opposite. The reactants of photosynthesis are energy, carbon dioxide (6CO2), and water (6H2O). The products of cellular respiration are energy, carbon dioxide, and water. The products of photosynthesis are glucose (C6H12O6) and oxygen (6O2), and the reactants of cellular respiration are glucose (C6H12O6) and oxygen (6O2). So, the processes' equations are chemically opposite. The relationship between photosynthesis and cellular respiration is such that the products of one system are the reactants of the other. Without photosynthesis, cellular respiration couldn't take place, and without cellular respiration, photosynthesis couldn't take place. It's like a cycle.
Radiation is used for X-rays, MRIS, any type of cancer killing. Too much of radiation can be a dangerous thing... you could end up dying from a lot of exposure.
